CNC Programming Handbook: Practical Guide

CNC
Programming
H ndbook
Second Edition
c C
Programming
Handbook
Second Edition
A Camp
hensiv
t r
989
uid
Practical CNC
rogramming
mi
ue
York, NY lOO 18
.com
Li
of Congress Cataloging-in-Publication Data
Smid, Peter.
CNC programming handbook: comprehensive guide to practical CNC programming!
Smid.
11-3158-6
1. Machine-louls--Numerical control--Programming --Handbooks, manuals,etc ..I.
Title.
TJ1189 .S
2000
1.9'023--dc21
00-023974
Second
on
CNC Programming Handbook
Industrial Press Inc.
989
ue of
Copyright
2003.
Americas,
w York, NY 10018
in the United States
This book or parts thereof may not
America.
reproduced, stored in a retrieval
system. or transmitted in any form without tbe permission of
5678910
publishers.
Dedication
To my
who
my mother
never to give
dmila,
Acknowledgments
In this second edition of the CNC Programming Handbook, I would like to express my
thanks and appreciation to Peter Eigler for being the bottomless source of new ideas,
knowledge and inspiration - all that in more ways than one. My thanks also go to Eugene
Chishow, for his always quick thinking and his ability to point out the elusive detail or two
that I might have missed otherwise. To Ed Janzen, I thank for the many suggestions he offered and for always being able to see the bigger picture. To Greg Prentice, the President of
GLP Technologies, Inc., - and my early mentor - you will always be my very good friend.
Even after three years of improving the CNC Programming Handbook and developing the
enclosed compact disc, my wife Joan will always deserve my thanks and my gratitude. To
my son Michael and my daughter Michelle - you guys have contributed to this handbook in
more ways than you can ever imagine.
I have also made a reference to several manufacturers and software developers in the
book. It is only fair to acknowledge their names:
•
FANUC and CUSTOM MACRO or USER MACRO or MACRO B
are registered trademarks of Fujitsu-Fanuc, Japan
•
GE FANUC is a registered trademark of GE Fanuc Automation, Inc.,
Charlottesville, VA, USA
•
MASTERCAM is the registered trademark of eNC Software Inc.,
Tolland, CT, USA
•
AUTOCAD is a registered trademark of Autodesk, Inc.,
San Rafael, CA, USA
•
HP and HPGL are registered trademarks of Hewlett-Packard, Inc.,
Palo Alto, CA, USA
..
IBM is a registered trademark of International Business Machines, Inc.,
Armonk, NY, USA
..
WINDOWS is a registered trademarks of Microsoft, Inc.,
Redmond, WA, USA
About the Author
Smid is a professional consultant, educator and
with many
of practiexperience, in the industrial and ed
his career, he has
on all levels. He
an extensive experience with CNC and CAD/CAM
to manufacturing industry and educational
ns on practical use of ComNumerical Control technology, part programm
CAD/CAM, advanced machining, tooling, setup, and many other related
comprehensive industrial background in CNC programming, machining and company
training has assisted
hundred companies to benefit from his wide-rang
knowledge.
ro.-.'7iOl"'I
companies and CNC maMr.
long time association with advanced
of Community and Technical Colchinery vendors, as well as his affiliation with anum
industrial technology programs and
skills training, have enabled him to
broaden his professional and consulting
areas of CNC and CAD/CAM training
computer applications and
evaluation, system benchmarking.
programming, hardware
and operations management.
l
Over the years Mr. Smid has
tional programs to thousands of
across United States, Canada and
companies and private sector
l
hundreds of customized
at colleges and universities
as well as to a large number of manufacturing
individuals.
.rliOTtTc.'
He has actively participated in many
shows, conferences, workshops
various seminars, including
delivering presentations
a
of speaking engagements to
organizations. He is also the author
of CNC and CAD/CAM. During his
and many in-house publications on
years as a professional in the CNC
educational field, he has developed tens
of thousands of pages of high quality training materials.
The author
suggestions and other input
You can e-mail him through the publisher of this handbook
You can also e-mail him from the CNC Programming Handbook
and industria! users.
of the
CD.
at www-industriaipress.com
TABLE OF CONTENTS
1 ~ NUMERICAL CONTROL
1
DEFINITION OF NUMERICAL CONTROL
NC and CNC Technology.
CONVENTIONAL AND CNC MACHINING
2
NUMERICAL CONTROL ADVANTAGES
2
Setup Time Reduction
Lead Time Reduction.
Accuracy and RepealabiliJy
Contouring of Complex Shapes.
Simplified Tooling and Work Holding.
Cutting Time and Productivity Increase.
3
TYPES OF CNC MACHINE TOOLS
Mills and Machining Centers.
Lathes and Turning Centers
Axes and Planes
Point of Origirl
Ouadrarlts.
Right Hand Coordinate System
MACHINE GEOMETRY.
Axis Orientation - Milling .
Axis Onenlation - Turning.
Additlona! Axes.
16
16
16
17
17
17
18
18
3
3
3
3
4
4
4
5
5 - CONTROL SYSTEM
19
GENERAL DESCRIPTION
20
20
Operation Panel
Screen Display and Keyboard
Handle.
21
22
PERSONNEL FOR CNC
5
SYSTEM FEATURES
22
CNC Programmer
CNC Machine Operator
5
Parameter Settings
System Defaults
Memory Capacity.
22
23
24
SAFETY RELATED TO CNC WORK.
6
6
MANUAL PROGRAM INTERRUPTION.
2 ~ CNC MILLING
7
Single Block Operation.
Feedhold
Emergency Stop
25
25
25
25
CNC MACHINES - MILLING.
7
MANUAL DATA INPUT - MDI
26
Types of Milling Machines .
Machine Axes
Vertical Machining Centers.
Horizontal Machi ning Centers
HOrIZontal Boring Mill
Typical Specifications
7
PROGRAM DATA OVERRIDE
26
8
8
9
10
10
3 - CNC TURNING
11
CNC MACHINES - TURNING
11
11
Types of CNC Lathes.
Number of Axes
11
AXES DESIGNATION
11
Two-aXIs Lathe .
Three-axis Lathe
Four-axis Lathe.
Six-axis Lathe
FEATURES AND SPECIFICATIONS
Typical Machine Specifications.
Control Features
4 - COORDINATE GEOMETRY
12
12
13
13
Rapid Motion Override.
Spindle Speed Override
Feedrale Override.
Dry Run Operation
Z Axis Neglect .
Manual Absolute Setting
Sequence Return
Auxiliary Functions Lock
Machine Lock
Practical Applications
SYSTEM OPTIONS.
G raphlD Display.
In-Process Gauging .
Stored Stroke Limits.
Drawing Dimensions Input
Machining Cycles.
Cutting Tool Animation.
Connection \0 External DeVices
26
27
27
27
28
28
28
28
28
29
29
29
30
30
30
30
30
30
13
13
14
6 - PROGRAM PLANNING
31
15
STEPS IN PROGRAM PLANNING
31
INITIAL INFORMATION
31
MACHINE TOOLS FEATURES.
31
REAL NUMBER SYSTEM
15
RECTANGULAR COORDINATE SYSTEM.
15
Machine Type and Size.
31
ix
X
-
---------~-.-.
Control System.
31
PART COMPLEXITY
32
MANUAL PROGRAMMING
32
32
32
Disadvantages .
Advantages
CAD/CAM AND CNC
Integ ration
Future of Manual Programming
32
33
33
TYPICAL PROGRAMMING PROCEDURE
33
PART DRAWING
34
Title Block.
Dimension ing
Tolerances.
Surface Fintsh
Drawing ReVisions
Special InSHucllons
METHODS SHEET.
MATERIAL SPECIFICATIONS
Malerial Unlformit)'
Machinability Rating.
34
34
35
35
36
36
--------_.-...
Table of Contents
---
-
--
8 - PREPARATORY COMMANDS
47
DESCRIPTION AND PURPOSE.
47
47
49
50
APPLICATIONS FOR MILLING.
APPLICATIONS FOR TURNING
G CODES IN A PROGRAM BLOCK
Modality of G-commands.
Conflicting Commands in a Block
Word Order in a Block
GROUPING OF COMMANDS
50
50
51
51
Group Numbers
51
G CODE TYPES.
52
G Codes and Decimal POln! _
52
36
36
9 - MISCELLANEOUS FUNCTIONS
53
36
DESCRIPTION AND PURPOSE.
53
37
Machine Related Functions .
Program Related Functions
53
53
MACHINING SEOUENCE
37
TOOLING SELECTION
38
TYPICAL APPLICATIONS
54
38
38
Applications for Milling
Applications for Turning
Special MOl Functions.
Application Groups
54
54
54
PART SETUP
Setup Sheet
TECHNOLOGICAL DECISIONS
Cutter Path
Machine Power Rating.
Coolants and Lubricants
WORK SKETCH AND CALCULATIONS
Identification Methods.
QUALITY IN CNC PROGRAMMING
7 ~ PART PROGRAM STRUCTURE
BASIC PROGRAMMING TERMS
O-lsr3cter
l/-Jcr0
38
38
WORD ADDRESS FORMAT
FORMAT NOTATION
StarlU p of M Functions.
Duration of M Functions
56
.sf)
40
PROGRAM FUNCTIONS
56
40
40
41
41
41
41
42
42
43
System Formal
System Format·
Word Addresses'
43
43
44
45
SYMBOLS IN PROGRAMMING
45
and ivli nus Sign.
45
PROGRAM HEADER
45
46
TYPICAL PROGRAM STRUCTURE.
55
39
39
41
42
PROGRAMMING FORMATS
M FUNCTIONS IN A BLOCK
54
Program Stop
Oplional Program Stop.
Program End.
Subprogram End
!'iR
MACHINE FUNCTIONS
58
Cooiant Functions
Spindle Functions.
Gear Range Selection
Mil r. hi n e Ac:r.ess ori flS
58
59
60
56
57
58
flO
10 - SEQUENCE BLOCK
61
BLOCK STRUCTURE
61
61
8u ildlng the Block Structure
Block Structure for Milling
PROGRAM IDENTIFICATION
Program Number
ProgrClm Nome.
SEQUENCE NUMBERS
Sequence Number Command.
Sequence Block Format
Numbering Increment
Long Program:> Dnd Block Numbers.
END OF BLOCK CHARACTER.
STARTUP BLOCK OR SAfE BLOCK
61
62
62
62
63
63
63
64
64
64
65
xi
PROGRAM COMMENTS
CON
MING VALUES
66
67
ITY.
68
NG WORDS IN A BLOCK
11 - INPUT OF DIMENSIONS
69
Unit Values
69
70
AND INCREMENTAL MODES
70
AND METRIC UNITS
Commands G90 and G9l .
Absolute Oats
G90
- G91
Combinations in a
Block
PROGRAMMING
Exact
Command
Mode Command
Exact
Automatic Corner Override
Mode
Mode
Circular Morion Feedrates
MAXIMUM
89
89
89
89
90
90
90
91
Maximum Feedrate Considerations,
91
AND OVERRIDE
Feedhold SWitch
Feedrate Override Switch
Feedrate Override Functions
91
91
71
72
72
72
E
73
14 - TOOL FUNCTION
93
73
T FUNCTION FOR MACHINING
74
74
75
76
76
Tool Storage Magazine
Fixed Tool Selection,
Random Memory Tool Selection
Regist8T1flg Tool Numbers
Programming Format
Empw Tool or Dummy Tool
93
93
94
94
94
95
95
IN THREADING
92
92
MINIMUM MOTION INCREMENT.
DIMENSIONAL INPUT
FuJI Address Forma! ,
Zero
Decimal Point Programming,
Input
CALCULATOR TYPE INPUT
TOOL CHANGE FUNCTION - M06 .
12 • SPINDLE CONTROL
SPINDLE FUNCTION
77
Spindle Speed Input,
77
DIRECTION OF SPINDLE ROTATION
Direction for Milling
Direction for Turning.
Direction Specilication ,
Spindle Startup
77
78
78
79
79
ORIENTATION
80
80
SPEED - R/MIN
81
SPINDLE STOP.
81
Material
Spindle Speed Units
Spindle Speed - Metric Units
CONSTANT SURFACE
Maximum Spindle SpAAri
Part Diameter Calculation in
13 - FEEDRATE CONTROL
81
82
82
82
84
85
87
FEEDRATE FUNCTION.
87
87
Feedrate per Minute,
Feedrate per Revolution
87
88
FEEDRATE SELECTION
88
ACCELERATION
88
FEEDRATE CONTROL
<
95
Conditions for Tool
95
AUTOMATIC TOOL
96
ATC System
MaXimum Tool Diameter
Maximum Tool Length
MaXimum Tool Weight.
ATC Cycle,
MDIOperatlon
PROGRAMMING THE
Single Tool Work
Programming Several Tools.
Keeping Track of Tools,
Any Tool in Spindle - Not the First.
First Tool in the
No Tool in the
First Tool In the Spindle with Manual
No Tool In the Spindle With Manual
First Tool In the Spindle and an Oversize Tool
No Tool in the
Ie and an Oversize Tool
96
97
97
97
98
98
98
98
99
99
99
100
101
101
102
102
102
T FUNCTION FOR
103
Lathe Too! Station
Tool
103
103
104
TOOL
Offset.
104
WAil( Off<:;At
105
Wear Offset
106
The Rand T
106
15 - REFERENCE POINTS
POINT G
107
xii
Center Line Tools
POINT
Zero,
129
108
Relatlonshi p.
.
109
POINT
109
Tools
Tools
Command Point and Tool Work Offset
129
130
130
130
109
110
Centers.
112
TOOL
POINT
19 ~ TOOL LENGTH OFFSET
112
PRINCIPLES
MMANDS
16 - RE
131
131
131
113
132
Face.
COMMAND
POSITION REG
3
13
114
114
114
114
115
115
Tool Set at Machine Zero
Tool Set Away from Machine Zero.
Position
in Z )\xis .
LATHE APPLICATION.
OFFSET COMMANDS
113
Position
Definition
Proqrammlnq Format
Tool Position
MACHINING
115
116
116
116
Tool Setup .
Three-Tool Setup Groups
Center line Tools Setup.
External Tools Setup
Internal Tool Setup.
Corner Tip Detail .
Programmtr'\g Example
117
117
117
117
Distance-Ta-Go in Z AXIs.
Z AXIS
1
Pres~t Tool
"135
Tool length
Touch Off
a Master Tool
Drfference
136
135
136
137
PROGRAMMING
Tool
Offset not Available.
Tool Length Offse1 and G92
Tool
Offset and G54·G59
APPLICATION.
TOOL LENGTH
141
141
20 - RAPID POSITIONING
143
120
122
RAPID TRAVERSE MOTION
GOO Command
143
122
122
RAPID MOTION TOOL
144
119
119
120
1
WORK AREAS AVAILABLE
123
Additional Work Offsets
124
Work Offset Change
24
125
Z Axis Application
126
OFFSETS.
127
Tool Length Offset and
HORIZONTAL
Single Axis MOllon .
Multiaxis Motion.
Angular Motion.
Reverse Rapid Motion
TYPE OF MOTION &
OF RAPID MOTION
128
128
129
129
143
144
144
146
146
146
147
TOTHE PART
147
148
21 - MACHINE ZERO RETURN
149
MOTION FORMULAS,
128
1
of Offsets.
Offset
Offset
and Offset Numbers
138
140
119
HORIZONTAL MACHINE APPLICATION.
137
138
OFFSET.
DESCRIPTION.
WORK OFFSET DEFAULT AND
134
139
119
d
133
134
Tools
17 - POSITION COMPENSATION
Programming Commands
Programming Formar
Incremental Mode
Motion Length Calculation.
Position Compensation Along the Z axis
G47 and G4B.
Face Milling.
132
132
SETUP
On-Machine Tool Length Selting
Off·Machlne Tool
Setting
Tool
Offset Value Register.
CHANGING TOOL
18 WORK OFFSETS
131
MACHINE REFERENCE POSITION
Machining Centers.
lathes.
the Machine Axes
Program Commands
Command Group
149
150
150
151
151
xiii
RETURN
PRIMARY MACHINE
151
Intermediate Point .
Absolute and Incremental Mode
Return from the Z Depth Position
Return Required for the ATe,
Zero Return for CNC Lathes
151
152
POSITION CHECK COMMAND.
156
FROM MACHINE
157
RO POINT.
SECONDARY MACHI
158
- LINEAR INTERPOLATION
159
LIN
COMMAND
Starr and End of the Linear Motion
Single Axis Linear Interpolation .
Two Axes Linear Interpolation
Three Axis Linear Interpolation
Tool Motions VS, Fixed Cycles,
178
SELECTION
178
FORMAT
179
FIXED
180
181
R
LECTION .
181
Z
CALCULATIONS
182
162
163
TYPICAL APPLICATIONS,
163
BLOCK SKIP SYMBOL
1
CONTROL UNIT SETTING
163
164
1
165
166
68
69
170
170
24 - DWELL COMMAND
171
PROGRAMMING APPLICATIONS
171
171
171
171
172
172
AND DWELL
173
Time
Number of Revolutions Setting
173
173
SETTING
F
PTION OF FIXED CYCLES
183
G81 Drilling Cycle,
G82 Spot-Drilling Cycle,
G83 Hole Drilling Cycle Standard
G73
Hole Drilling
G84
Cycle - Standard
G74 - Tapping Cycle - Reverse
G85 Cycle,
G86
Cycle,
G87 Backboring Cycle ,
G8S - Boring Cycle ,
G89 Boring Cycle,
G76 P(€cision Bonng
183
183
184
184
186
186
187
187
187
188
188
189
CYCLE CANCELLATION
189
189
FIXED CYCLE REPETITION
The L or K Address.
LO or KO in a Cycle ,
26 - MACHI
190
190
HOLES
SINGLE HOLE EVALUATION.
Tooll ng Selection and Applications,
Program Data ,
DRILLING 0
Types of Drilling
Types of Drills
Progiamming ConsIderatIons,
Nominal Drill Diameter
Effective Drill D,ameter
Drill Pomt
Center
Through Hole
Blind Hole
Flat BoHom
173
MINIMUM
REVOLUTIONS
177
INITIAL LEVEL SELECTION
PROGRAMMING EXAMPLE
DWELL
177
180
161
161
Dwell Command Structure,
CYCLES
AND
Feedrate Range
Individual Axis Feedrate ,
DWELL COMMAND
176
160
160
161
for
for Accessories
AND DWELL.
FIXED
159
159
LINEAR FEEDRATE
Variable Stock Removal
Machining Pattern
Trial Cut for
Program Proving,
Barfeeder Application,
Numbe(ed Block Skip,
176
176
159
160
SKIP AND MODAL COMMANDS
Axis,
POINT-TO-POINT MACHINING
PROGRAMMING FORMAT
~ BLOCK SKIP FUNCTION
Machine
X AXIS is the
and Dwell,
153
155
155
175
175
LONG
174
174
174
191
191
19i
194
194
194
194
195
195
195
195
196
196
197
197
198
PECK DRILLING
Typical Peck
Calculating the Number of Pecks
199
199
199
xiv
Selecting the Number of Pecks _
Controlling Breakth rough Depth.
REAMING
Reamer Design
Sprndle Speeds for Reaming
Feeorates for Reamir\~
Stock Allowance
Other Reaming ConSiderations
Table of Contents
200
200
28 - FACE MILLING
227
201
CUTTER SELECTION .
227
201
Basic Selection Criteria
Face Mill Diameter _
Insert Geometry .
227
227
201
201
202
202
SINGLE POINT BORING
202
Single Point Boring Tool
Spindle Orientation_
Block Tools
202
203
203
BORING WITH A TOOL SHIFT
Precision Bormg Cycle G76
Backboring Cycle G87,
Programming Example
Precau1ions in Prog ramming and Sew p_
ENLARGING HOLES
Counters inking
Counterborlng ,
Spotfacing
MULTILEVEL DRILLING
WEB DRILLING
TAPPING
Tap Geometry
Tapping Speed and Feedra1e .
Pipe Taps.
Tapping Check List.
203
203
204
205
205
205
206
207
CUTTING CONSIDERATIONS
Angle of Entry
Milling Mode
N uJrloer of Cuttiny IIlSl:;rls
PROGRAMMING TECHNIQUES
Single Face Mill Cut
Multiple Face Mill CU1S
USING POSITION COMPENSATION.
29 ~ CIRCULAR INTERPOLATION
ELEMENTS OF A CIRCLE,
Radius and Diameter ,
Circle Area and Circumference
214
215
216
TYPICAL HOLE PATTERNS
RANDOM HOLE PATTERN
217
217
STRAIGHT ROW HOLE PATTERN
218
ANGULAR ROW HOLE PATTERN
218
218
POLAR COORDINATE SYSTEM
Plane Seleclion
Order of Machining,
235
235
235
236
237
237
238
217
Bolt Circle Formula _
Pattern Orientation ,
233
Arc Cutting Direction
Ci reular Interpolation Block.
Arc Start and End POlntS_
Arc Center and Hadius
Arc Center Vectors,
Arc
Planes
2 1
2'12
27 - PATTERN OF HOLES
BOLT HOLE CIRCLE PATTERN
232
237
Quadrant Points
RADIUS PROGRAMMING
Blend Radius
Partial Radius
FULL CIRCLE PROGRAMMING
ARC HOLE PATTERN.
231
PROGRAMMING FORMAT
213
213
214
Ang ular Grid Pattern
230
210
210
212
GRID PATTERN
229
229
230
QUADRANTS.
Tool Approach Motion
Tool Return Motion,
alld Reaming on Lathes,
Cycle - G74,
Tapp!ng on Lathes
Other Operations
CORNER PATTERN
228
207
208
209
HOLE OPERATIONS ON A LATHE
Pattern Defined by Coordinates,
Patlern Defined by Angle
228
80ss Milling
Internal Ci rcle Cutting - Linear Start
Internal Circle Cutting - Circular Start ,
Circle Cutting Cycle
ARC PROGRAMMING.
FEEDRATE FOR CIRCULAR MOTION
Feedrate for Outside Arcs
Feedrate for InSide Arcs.
236
236
238
238
239
240
240
240
240
242
243
243
244
245
245
246
246
L1~
220
220
221
222
223
224
224
225
226
226
30 - CUTTER RADIUS OFFSET
247
MANUAL CALCULATIONS
247
Tool Path Center Points
Cutter RadiUs
Center Points CAlculation
248
249
249
COMPENSATED CUTTER PATH.
250
Types of Cutter Radius Offset.
Definition and Applications.
250
250
PROGRAMMING TECHNIQUES
250
Direction of Cutting Motion
251
xv
Table of Co ntents
251
or Right - not CW or CCW
=,f(set Commands
of the Cutler
of Offset Types
Format
r\ddr8ss H or D 7,
and Wear Oifsets
APPLYING CUTIER
251
252
252
253
253
L5Ll
OFFSET
254
254
Methods,
Cffset Cancellation,
::::utter Direction
256
256
WORKS
256
257
~:lok-Ahead Offset
for Look-Ahead Cutter Radius Offset
257
276
Steel End Mills
Solid Carbide End Mills
Indexable Insen End Mills
Relief Ailgles
End Mill Size
Number of Flutes
276
276
276
276
277
277
SPEEDS
278
278
Coolants and Lubricants,
Tool Chatter
279
STOCK
279
279
279
280
Infeed .
In and OUI Ramping
Direction of Cut
Width and
of CUI
258
259
LOO
RULES
261
. MILLING
262
:JVERVIEW OF
PRACTICAL EXAM
Part Tolerances
\,leasu red Part Size,
Offsets
Amount General Selting,
Data
TOOL NOSE
Slot Example.
Closed Slot Example
2GO
265
General Principles
Pocket
US OFFSET
266
Offset
266
266
266
267
267
268
268
31 - PLANE SELECTION
269
WHAT
269
269
A
MACHINING IN PLANES
Mathematical Planes
Machine
Planes,
Program Commands for Planes Definition,
Default Control Status
STRAIG
MOTION IN
269
270
270
271
271
CIRCULAR INTERPOLATION IN
G 17-G 18-G 19 as Modal Commands
Absence of Axis Data in a Block,
Cutter Radiu:J Otr~et in Planes
PRACTICAL EXAMPLE
FI
D
32 -
RAMMING SLOTS
281
283
MILLING.
284
285
RECTANGULAR
285
Stock Amount,
",,,,,'nm!,,,r Amount
of Cut _
Semifinishing Motions
Tool Path
ular Pocket Program Example
272
272
273
273
Minimum Cutter Diameter _
Method of
Linear
Linear and Circular Approach,
ng a Circular Pocket,
CIRCULAR POCKET
286
287
287
287
288
- TURNING AN
BORING
FUNCTION - TURNING
T Address
Offset Entry
Independent Tool Offset.
Tool Offset With Motion.
Offset
Shoulder Tolerances
Diameter and Shoulder Tolerances,
OFFSET SETTING,
289
289
289
290
291
292
MULTIPLE
275
286
CIRCULAR POCKETS,
LATHE OFFSETS
IN PLANES
PHERAL MILLIN
281
28
Closed Boundary,
263
263
264
264
265
266
281
OPEN AND
262
?fi2
Nominal or Middle)
Nose
Offset Command!::
33 - SLOTS AND PO KETS
293
293
293
294
294
294
295
295
295
296
296
297
297
298
XVI
of
FUNCTIONS
RANGES
298
AUTOMATIC
299
301
301
301
Stock and Stock Allowance
A
IN CSS MODE
FORMAT.
1
G74 - PECK DRILLING CYCLE
1
G74 Cycle Format· lOT111T/15T
G74 Cycle Formal- OT/lOT/18T/20T/21
322
304
305
306
36 - GROOVING ON LATH
323
306
GROOVING OPERATIO
323
Main Grooving AP~)IICEmOflS
Grooving Crltena ,
Nominal Insert S]ze.
Insert Mool fit;i1tion
324
307
GROOVE LOCATION
324
307
GROOVE
324
307
307
- STRAIGHT CUTTING CYCLE
308
Format
Turning Example
Cutting
ht and Taper Cutting Example
308
309
309
311
312
312
MULTIPLE REPETITIVE CYCLES.
and Part Contour.
Ch,pbreaking Cycles
314
314
315
315
315
316
316
317
Direction of
317
G72 - STOCK REMOVAL IN FACING.
G72 Cycle Format - 10TI1
317
G72 Cycle Format - OT/16TI18T/20T/21
318
G70· CONTOUR FINISHING
Groove Width Selection
Method
327
327
328
Groove Tolerances
Groove Surface Finish,
329
330
Radial Clearance
33
331
/ NECK GROOVES
GROOVING CYCLES.
Applications ,
Groove with G75 .
Multiple Grooves with G75.
332
332
333
333
GROOVES
GROOVES AND SUBPROGRAMS
316
G71 for External Roughing.
G71 for Internal
G73 Cycle Form<:lt - 10T/1 H/15T
G73 Cycle Format· OT/16T/18T/20T/21T
G73 Example ot Panern
326
330
313
313
313
315
G73 - PATTERN REPEATING
325
325
325
313
Programming Type I and Type II
G7 .
Groove Position
Groove
330
TYPE I AND TYPE II CYCLES.
G71 . STOCK REMOVAL IN TURNI
G7
Format- OT/llTI15T
G71
Format - OT/16T/18T/20T/21T
324
313
CONTOUR CUTTING CYCLES
Boundary Definition
Stan Point and tile Points P and 0 .
323
323
323
GROOVE
307
Format
321
BASIC RULES FOR G74 AND
306
. FACE CUTTING CYCLE.
32
322
322
302
303
303
306
REMOVAL ON LATHES
320
BASIC RULES FOR G70-G73
G75 • GROOVE CUTTING
G75 Cycle Formal 10T/l1T/15T
G75 Cycle Format· aT /16T/18T/20T/21T
302
Fillish
G70 Cycle Format - All Controls,
317
8
.il R
319
9
- PART-OFF
PART-OFF PROCEDURE
Parting Tool Description.
Tool Approach Motion
Stock Allowance.
Tool Return IVlotion .
Part-off with a Chamfer
Preventing Damage to the Part
38 - SINGLE POINT THREADING
335
335
336
337
337
337
338
339
xvii
Table
TH
339
ON CNC LATHES
339
Form of a Thread.
Operations.
340
TERMINOLOGY OF THREADING
PROCESS
341
in
Thread Starl Position
Thread
Diameter and
Thread Cutting Motion
Retract from Thread
i1eturn to Stzlrt Position
341
342
342
343
344
344
THREADING FEED AND SPINDLE
344
345
345
Feedra1e Selection.
Ie Speed Selection.
Maximum Threading Feedrate
Lead Error
348
BLOCK-BY-BLOCK THREADING
348
349
350
THREADING
MULTIPLE REPETITIVE
G76
Format- lOT/11T/15T
G76
Format· OT/16T/18T .
Programming Example
First Thread Calculation
350
351
351
352
SUBPROGRAMS
Subprogram Benefits .
ItJtJll\iflci;ltiull (.)f
367
n::;
368
SUBPROGRAM FUNCTIONS.
368
368
369
ram Call Function .
Subprogram End FunClion. .
Block Number to Return to. .
Number of
ram Repetitions
LO
Call.
369
370
1
372
373
SU
DEVELOPMENT.
373
Pattern Recognition
Tool Motion and Subprograms .
Modal Values and Subprograms.
MULTI
374
375
NESTING
376
376
One Level Nesting
Two Level
Three Level
Four Level Nesting .
377
377
377
353
THREAD INFEED
353
Radial Infeed .
Compound Infeed
Thread Insert Angle· Parameter A
Thread Cutting Type - Parameter P
353
354
378
CHANGE SUBPROGRAM
379
100000 000 HOLE GRID.
379
40 ~ DATUM SHIFT
381
DATUM SHIFT WITH G92 OR
381
Zero Shift.
381
354
ONE-BLOCK METHOD CALCULATIONS.
355
355
355
Initial Considerations
Z Axis Start Position Calculation.
THREAD RETRACT
357
357
357
357
Thread Pullout Functions
Single AXlS Pullout
Two-Axis Pullout
HAND OF THREAD
383
COORDINATE SYSTEM
384
G52 Command
COORDINATE
THREADING TO A S
358
Insert iv'lod Ification .
Program Testing.
358
360
RMS.
360
Thread Depth .
361
TAPERED
Depth and Clearances
Taper Calculation
Block
Block
Tapered Thread
a
Tapered Thread and a MultI
MULTISTART
Threading Feedrate Calculation,
Shift Amount
THREAD
MAIN PROGRAM
346
347
REFERENCE POINT
OTHER THREAD
39 - SUBPROGRAMS
340
361
361
362
386
386
Dat<'l
Command
Coordinate Mode
386
386
WORK OFFSETS .
Slandard Work Offset
386
Additional Work Offset Input.
External Work Offset Input.
387
387
387
LENGTH OFFSETS.
Valid Input Range
388
363
CUTTER RADIUS
388
364
364
LATHE OFFSETS
388
MOl DATA SETTING
389
363
Cycle.
384
365
366
PROGRAMMABLE
Modal G10 Command.
Parameters Notation
Program Portability, .
Bit Type Parameter. ,
Effect of Block Numbers
ENTRY,
389
389
390
390
391
392
xviii
of
ATIACHMENT.
41 - MIRROR IMAGE
393
Bar
4 '14
393
394
414
4'15
415
395
Control Setting
. Manual Mirror Setting
E
Mirror
MI
395
396
PROGRAMMING EXAMPLE
415
45 - HELICAL MILLING
417
HELICAL MILLING OPERATION
417
396
Functions
Mirror Image Example
Mirror Image Example
396
397
IMAGE ON CNC
398
42 ~ COORDINATE ROTATION
398
Format,
Arc Modifiers for
and
THREAD MILLING,
Thread
Conditions tor Thread
Thread
399
Center of Rotation ,
Radius of Rotation
Coordinate Rotation Cancel
Common Applications
399
THE HELIX,
399
THREAD MILLING
401
401
Straight Thread
In itial Calculations
Starting Position
Motion Rotation and Direction
Lead'in Motions ,
Thread Rise Calculation
Milling the Thread
Lead-Out IV" 1,lIn."
401
APPLICATION
43 - SCALING FUNCTION
405
405
405
PTION.
Function Usage .
406
406
407
4'18
18
418
418
418
4'19
419
419
419
421
421
421
422
422
423
424
424
425
425
425
425
426
405
PROGRAMMING FORMAT
417
417
419
Clearance Radius
Productivity of Thread
399
COMMANDS.
414
393
394
394
395
395
395
MIRROR IMAGE BY
413
413
ADDITIONAL OPTIONS
RULES OF MIRROR IMAGE
ntenls
HELICAL RAMPING
426
427
46 - HORIZONTAL MACHINING
429
INDEXING AND ROTARY
429
INDEXING TABLE (8 AXIS)
429
THREAD MILLING SIMULATION METHOD
407
44 - CN
LATHE ACCESSORIES
409
CHUCK CONTROL
Chuck Functions
Chucking Pressure
Chuck Jaws,
409
TAILSTOCK AND
410
410
L110
410
TSllslock
Quill.
Center,
Quill Functions
Programmable Tailstock
Safety Concerns,
81-DIRECTIONAL
Programming
11
41 I
411
411
INDEXING
B
Units 01 Increment _
429
and Unclamp Functions
.nl'l,<'Vlrv't in Absolute and Incremental Mode,
,130
430
430
AND OFFSETS
431
Work Offset and B Axis
Tool Length Oflset and B Axis
431
432
TO MACHINE ZERO
411
INDEXING AND A SUBPROGRAM
412
COMPLETE PROGRAM EXAMPLE
412
MATIC PALLET CHANGER·
434
434
436
437
Tab Ie of Contents
Program StruclU re
BORING MILL.
47 . WRITING A CNC PROGRAM
WRITING.
XIX
438
438
439
439
439
441
441
RUNNING THE FIRST PART
459
PROGRAM CHANGES
Program Upgrading
Program Updating .
Documentation Change,
460
ALTERNATE MACHINE SELECTION.
461
MACHINE WARM UP PROGRAM
462
eNC MACHINING AND SAFETY.
462
463
460
461
461
'JGRAM OUTPUT FORMATTING
443
SHUTTING DOWN A CNC MACHINE
Emergency Stop Switch,
Parking Machine Slides
Setting the Control System,
Turning the Power Off,
PROGRAMS
Length Reduction.
Mode and Tape Mode
445
EQUIPMENT MAINTENANCE
464
51 - INTERFACING TO DEVICES
465
442
442
442
48 - PROGRAM DOCUMENTS
445
4<16
447
- '~,A FILES
447
- --
DOCUMENTATION
Documentation,
Documentation .
DeSCription
448
AND TOOLING SHEETS.
Sheet
449
.-
_.::UMENTATION FILE FOLDER
:, ',-:atlon Methods
'":'''llor'S Suggestions
and Storage
w
PROGRAM VERIFICATION
448
448
449
450
450
451
451
451
452
452
453
CTION OF ERRORS.
Measures
Measures
453
VERIFICATION,
454
ERRORS
454
Errors .
Errors.
',iMON PROGRAMMING ERRORS
Input Errors
"dation Ermrs
Errors .
: 'i!ilncous Error:J ,
- eNC MACHINING
:HJNING A NEW PART
Integrity
463
464
464
464
453
453
455
455
456
456
456
456
456
457
457
458
458
RS~32CINTERFACE .
465
PUNCHED TAPE
Tape Reader and Puncher
Leader and Trailer
Tape Iden11fication
Non-printable Characters
Storage and Handling,
466
DISTRIBUTED NUMERICAL CONTROL
468
TERMINOLOGY OF COMMUNICATIONS
Baud Rate
Parity
Data Bits"
Start and Stop Bits ,
469
DATA SEITING
469
CON NECTING CABLES
Null Modem
Cabling for Fanuc and PC
470
52 - MATH IN CNC PROGRAMMING
466
468
468
468
468
469
469
469
469
470
470
471
BASIC ELEMENTS
Arithmetic and Algebra .
Order of Calculations,
471
GEOMETRY
Circle
PI Constant"
Circumference of a Circle
Length of Arc ,
Quadrants
472
POLYGONS
474
TAPERS
Taper Definition
Taper Per Foot
Taper Ratio.
Taper Calculations - English Un its
Taper Calculations - tv-letnc
475
475
476
476
476
476
CALCULATIONS OF TRIANGLES.
477
471
471
47?
473
473
473
473
XX
477
478
478
479
S;ne ~ Cosine - Tangent
Inverse Trigonometric Functions
Degrees and Decimal
Pythagorean Theorem
Solvfng Rjght
Hardware Specifications.
Hardware Requirements,
Features,
and
480
488
480
Post Processor
L188
480
IMPORTANT FEATURES.
489
481
CONCLUSION.
482
482
53 - CNC AND CAD/CAM
483
ADVANCED CALCULATIONS
487
488
489
489
489
User Interlace,
CAD Interface,
489
MANAGEMENT,
490
483
PROGRAMMING MANUALLY?
TOOL PATH GEOMETRY
TOOL PATH GENERATION
COMPLETE ENVIRONMENT
Multi Machine Support ,
Associative Operations
Job Setup
Tooling List and Job CommenlS,
Connection Between Computers
Text Editor
for Solids
Software Specifications ,
490
PMENT
490
483
483
THE END AND
484
484
484
A - RE
485
485
485
485
485
486
486
486
486
486
487
INNING.
NeE TABLES
491
491
Metric Fine
494
494
495
495
495
Index
497
Metric
rse Threads
NUMERICAL CONTROL
Numerical Co~trol technology as it is known today,
emerged
nud 20th
It can be traced to the year
of1952,
u.s. Air Force,
names
Parsons
and the Massachusetts
of Technology in
MA,
It was not
production manufacturing until
1960's.
real boom came
of CNC,
the
of 1972,
a decade
v.:ith
introduction of
micro computers. The
hIstOry and development of this fascinating technology has
been well documented
publications.
In the manufacturing field, and particularly in the area of
working,
Control
has . . "' . . ."''"' ....
SOlnethuJll"Z of a revolution.
in the
computw
ers became standard
in every company and in
the machine
equipped with Numerical
SVS1leIn fOWld their special place in the
shops.
recent evolution of
electronics
the
never ceasing computer development, including its impact
on Numerical Control,
brought
changes to
the manufacturing sector in general
metalworking industry in particular.
DEFINITION OF NUMERICAL CONTROL
In
publications and articles,
descriptions
have been used during the
to defme what Numerical
Control It would be
to try to
yet another
defInition, just
the purpose this handbook. Many of
defmitions
the same
same basic COl1lcer:)t.
use different
The
of all the known definitions can be summed
simple statement:
are
of the
of alphaselected symbols, for
a decimal
sign or the parenthesis symbols. All in"'''''HV''':> are urn·.......... in a logical
a predetermined
collection of all instructions necessary to maa part is called an NC Program,
Program, or a
""w,t:rY,I'1'" Such a
can be
for a future
repeatedly to
identical machining reUI.-UUHl)
• Ne and eNC Technology
In ~trict
to the terminology. there is a
ence m the meaning
abbreviations NC and CNC.
NC
for the
original Numerical Control
technology, whereby
abbreviation
stands for the
newer Co~nputeriz~d Numerical Control technology, a
mode~ spm-off of lts older
However, practice,
eNC IS the
abbreviation. To clarify the proper usaf each tenn, look at the major
between
CNC ,.."~ ..~~,,
Both
perform the same tasks,
bon of
the purpose machining a
cases, the internal design of the
system
the
logical instructions that process the data. At this point
ends.
to the CNC system) uses a
The
system (as
fLXed logical functions,
that are built-in and
nently wired
the control
These LI..llI',",U'JJJ"
not be changed by the programmer or
machine
tor. Because of
ftxed wiring
logic,
control
IS synonymous with the term 'hardwired',
The
can interpret a part program, but it does not alVH...."AF>.~.., to the
using the
away from the
typically in an
environment.
the NC
quires the compulsory use of punched tapes for
information.
t?e
The
CNC
uses an internal micro
but not the
NC system,
(i.e., a computer). This
storing a variety of
routines that are capable
logical
That means
programmer or the machine '"'''"'''....,.~,''..
can change the
on the control itself (at
machine), with instantaneous results.
flexibility is
greatest advantage of
CNC systems
probably
key element that
to such a
use of the technology in modern manufacturing. The CNC programs and
the logical
are stored on special computer chips,
as software
rather
by
c.onnections, such as
that control the logical
hOns. contrast to the
system, the
system is synonymous with the term 'softwired'.
When describing a particular
that
to the
control technology, it is customary to use
or
in mind
NC can also mean
CNC 1n everyday talk, but
can never
to the
1
2
Chapter 1
technology, described in this handbook under the abbreviation ofNe. The
'C'stands for Computerized, and it is
not applicable to
hardwired
All
manufactured today are of the
design, Abbreviations
such as C&C or C 'n are not correct and reflect poorly on
anybody
uses them
CONVENTIONAL AND CNC MACHINING
What makes
CNC machining superior to the conventional methods? Is it superior at all? Where are
benefits? If the CNC and the conventional machining processes are
a common general approach to machining a part will -....-.M1.
2.
3.
4.
5.
6.
Obtain and study
drawing
Select the most suitable machining method
Decide on the setup method (work holding)
Select the cutting tools
Establish
and
Machine
part
This
same
both types of macrunmg.
IS m
way how
data
are input. A feedrate 10 inches per minute (10 mlmin) is
the same in manual or CNC applications, but the method of
applying it is not. The same can be
about a coolant it
can be activated
a knob, pushing a switch or
programming a special
All
will result in
a coolant rushing out of a
a certain amount of knowledge on
part
user is
required.
alL
working, particularly meta! cutting, is mainly a skill, but it is also, to a great
an art
and a profession of large number of people. So
appli~
of Computerized Numerical Control. Like any skill
or art or profession,
it to the
detail is necessary to be successful. It takes more than technical know 1to be a CNC machinist or a CNC
Work
I>v?,"'....."...... ,'... and
what is
called a
'gut-feel', is a much needed supplement to any skill.
HV"...........
In a conventional machining, the
operator sets
up the machine and moves each cutting
using one or
both hands, to produce the required part. The design of a
machine tool offers many features that help the
process of machining a
- levers,
and
a15, to name just a few.
same body
are repeated by the
every
in the batch. However,
the word 'same this context really means 'similar
than 'identical '. Humans are not capable to
every
the same at all times - that is the
of maPeople cannot work at the same per[orrnam;e leve!
all the
without a rest. All of US have some good and
some bad moments. The results
these moments, when
applied to
a part, are
to predict. There
will
some differences and
within each
batch of
The parts will not always be exactly the
same.
dimensional tolerances and <""""f",,,,,,
'-'UU.H..." .
Ish quality are the most typical problems in conventional
machining. Individual machinists may
own
'proven' methods, different from
a f their feHow
leagues. Combination of
and other factors create a
great amount of
machining under numerical control does away with
the majority of inconsistencies. It does not require the same
physical
as
machining. Numerically
contToned machining does not need any levers or dials or
handles, at least not in the same sense as conventional machining does.
the
has
it
can
used
number of
over,
consistent
That does not mean there are no limiting
cutting tools do wear out,
material blank in
one batch is not identical to the material
another
batch, the setups may vary, etc.
factors should be
considered and compensated for, whenever lICI.'C~~ru
emergence of the numerical control technology does
not mean an instant, or even a long tenn, demise of all manual
There are times when a traditional machining method is preferable to a computerized method. For example, a simple one time job may be done more efficiently
on a
machine
a CNC machine. Certain
of machining jobs will beneHt from manual or semiautomachining, rather than
controlled machining.
CNC machine
are not meant to replace
every manual machine, only to supplement
In many
the
whether
ing will be done on a CNC machine or not is based on
number of required parts and nothing
Although the
volume of parts machined as a
is always an important
criteria, it should never be the only factor. Consideration
should
be
to
complexity, tolerances,
the required
of
fmish, etc. Often, a
complex part will benefit from CNC machining, while
relatively
parts will not.
Keep in mind that numerical control has never machined
a single part by
Numerical
is only a process
or a method that enables a machine tool to used in a productive, accurate and consistent
NUMERICAL CONTROL ADVANTAGES
What are the
advantages of numerical control?
It is important to know which areas of machining will
benefit from it
which are
done the conventional
It is absurd to think that a two
power
mill
win over jobs that are currently done on a twenty times
more powerful manual mill. Equally unreasonable are exof
improvements
cutting speeds
over a conventional machine. the machining
and tooling conditions are the same, the cutting rime will be
close in
cases.
NUMER
CONTROL
3
of the
areas
expect improvement:
o
Setup time reduction
Cl
lead
o
o
o
o
Accuracy and repeatability
o
the CNC user can and
lead time, required to
and manufacture several
fixtures for conventional machi.nes can
be
by preparing a part program
the ~se of
plified fixluring.
reduction
Contouring of
shapes
Simplified tooling and work holding
cutting time
General productivity increase
area offers only a potential improvement. Individual users will
different
of actual improvement, depending on the
oil-site, the
CNC
used,
setup methods, complexity of
fixturing,
or cutting tools, management philosophy
level of
engineering
individual attitudes, etc.
• Setup Time Reduction
• Accuracy and Repeatability
high degree
and repeatability of
has
the single major benefit to
users. Whether the part program is stored on a disk or in the
~omputer
or even on a tape (the
method),
Il ah~'ays
the same.
program can
changed
at wlll, but on.ce proven, nO
are usually required
more. A gIven
can be reused as many times as
nec:de,:t without
a single bit
it conlains.
to allow
such changeable factors as tool
program
wear and operating temperatures. it has to stored safely,
but generally very little'
from
CNC programmer or
will required. The high accuracy of
CNC machmes and
repeatability allows high quality
to
produced consistently
lime.
• Contouring of Complex Shapes
CNC
and machining centers are capable of cona variety of shapes. Many CNC users acquired their
only to able to handle
A
are CNC applications in
and automo-
tive , , ,The use of some form of computerized programming IS Virtually mandatory for any
dimensional
tool path at''''''''''''
of the
the serup time
should not
Modular lixturing, SI<l,n{llU'{l
tooling,
locators, automatic tool
pallets and
other advanced features,
the setup time more efficient
With a
a comparable
of a conventional
good knowledge
modern manufacturing, productivity
can be increased significantly.
, The
of parts machined under one setup is
Important. order 10 assess the cost a
time. If a
number of
is machined in one setup, the setup
cost per part can
very"
A very
red~ctio~ can b~ achieved by grouping several different operDtlons IOto a .smgle setup. Even if the
lime is longer, it
may be Justified when compared to
time required to
setup
conventional machines.
•
lead Time Reduction
a part program is written and proven. it is ready 10
!n the
even at a
nOtice. Although
l~e lead
tor the
run is usually
it is virtually
ml for any
run.
if an
to be modified. it
part
requires
the lead
can be done usually quickly,
shapes,
as
can be
:virhou.t the additional expense of making a model
tracmg. Mirrored parts can
achieved literally at the switch of
a bulton,
of programs is a lot simpler than storage
of patterns,
models,
olher pattern
making tools.
• Simplified Tooling and Work Holding
Nonstandard and 'homemade' looling that clutters the
benches and drawers around a conventional machine can
beelimin~led by
looling,
designed
. num~ncal
applications. Multi-step
such as
pilot dnlls, step
combination tools, counter borers
and
are
with several individual ;:'l<lIIU<l1
tools.
tools are
cheaper and
to
than special and nonstandard tools.
measures
have
many tool
to keep a low or even a
nonexistent inventory, increasing
delivery
to the
customer. Standard, off-the-shelf looling can usually obtained faster then nonstandard
LVVi""J'.,
. and work holding for CNC machines have only
one. ~aJor purpose - to hold the part rigidly
in the same
pOSitIOn for all
within a batch. Fixtures
for
CNC work do nOI normally
jigs, pilot
and
hole locating
4
pter 1
• Cutting Time and Productivity Increase
machine is commonly
consistent. Unlike a
the operator's skill, experito changes) the CNe
machining is under
control
a computer. The small
amount of manual work is restricted to the setup and loading and unloading
batch runs, the high
cost of the unproductive time is spread among many parts,
main benefit of a consistent
making it less
cutting time is
jobs, where the production
to individual machine tools
scheduling and work
can be done very "'v"''''''''''''''
is
The main reason COlnp:anlces
machines is strictly prr,nnrn
invesilmellt. Also,
on
of every
having a competitive
technology
offers
plant manager.
in
improvement
a
excellent means to
the
overall
productivity
of the manufactured
Like any means, it has to
When more and more
wisely and
just having a CNC
companies use the CNC
anymore. The commachine does not offer the extra
how to use the
who
panies that get forward are
technology efficiently and
it to
competitive in
the global economy.
To reach the goal of a
essential that users understand the h""";",,,,,,,... nM
on which CNC technology is
many forms, for example, un(jen.tarldulg
cuitry, complex ladder diagrams, \.-UI.IILJIL,lll;;;1
ogy, machine design, machining onnC11Dles
and many others. Each one has to
by the person in charge. In this Hil11UUIUU.I\..
on the
that relate directly to the
understanding the most common
Machining Centers and the lathes
the Turning Centers). The
should be very important to every
matool operator and this goal is also reflected in the
handbook approach as well as in
numerous
TYPES OF CNC MACHINE TOOLS
ni1ffef'ent kinds of CNC machines cover an ChllClllCH
variety. Their numbers are rapidly
developmentadvances. It is .
applications, they would
of some
groups CNC
Cl
and Machining centers
Cl
and Turning Centers
Cl
Drilling machines
mills and Profilers
Cl
Cl
EDM machines
o Punch presses and Shears
cutting machines
Cl
Cl
and Laser profilers
o
Water
o
Cylindrical grinders
Q
Cl
and Spinning machines, etc.
centers and lathes dominate
industry. These two groups share
market just about equally. Some industries may
a
of machines, depending on their
higher need
one
that there are many different
needs. One must
kinds of lathes and equally many different kinds of machining centers.
the programming process for a
vertical
is
to the one for a horizontal machine or a simple
mill. Even between different machine groups, there is a
amount of general
hons and the
is generally the same.
For example, a contour
with an end mill has a lot
common with a contour cut
a
• Mills and Machining Centers
Standard number axes on a milling machine is three set on a milling system is althe X, Y and Z axes.
ways stationary,
on a
machine table. The
cutting tool
it can move up and down (or in and
out), but it does not physically follow the tool path.
CNC milling machines CNC mills - sometimes
are usually small, simple
without a tool changer
is often
or other automatic features.
quite low. In industry, they are
maintenance purposes, or small
usually designed for contouring,
CNC machining centers are far more
drills and mills,
benefit the user gets out
ability to
several diverse operations
drilling, boring, counter
facing and contour milling can be
CNC program. In addition,
automatic tool changing,
minimize idle time, indexing to a different side
a rotary movement of additional axes,
CNC machining centers can
with special software that controls the speeds and
of the cutting tool, automatic in-process ",,,,,,oil'''''
adjustment and other production "XU'I'Ul'.... Ul'J;:,
devices.
NUMERICAL CONTROL
5
There are two basic
machining
machining
center. They are the
centers. The major difference
two types is the
nature of work that can be
on them efficiently. For a
CNC machining center,
most suitable type of
work are flat parts, either mounted to
ble, or held in a vise or a chuck.
cbining on two or more
in a
sirable to be done on a CNC horizontal U14'.llll.lll
example is a pump
and
shapes. Some multi-face ULa...'U.llllli,!:;
done on a CNC vertical machining center ...'-I ..... I-'IJ .......
a
table.
prc)gr.:imrnulg process is the same
both designs,
(usually a B axis) is added to the horidesign. Ths axis is either a
lHU';;;1\.U.1J;:. axis) for the table, or a fully rotary
taneous contouring.
an
handbook concentrates on the CNC
centers applications, with a special ""...
horizontal setup and machining.
melmO(lS are also applicable to the small
tapping machines, but the "",.r'rr,..,'..,......... " ...
restrictions.
'CIVIl
•
PERSONN
FOR eNC
machine tools have no
cannot evaluate a
with
skills and
control,
sk1lls are usually
- one doing the
machining. Their
depend on the company
as
product manufactured
is quite distinct, although many
the two functions into a one, often
companies
called a CNC ProgrammerlOperat01:
• CNC Programmer
The CNC programmer is
the person who
the
most responsibility in
shop. This person
is often responsible for
numerical control
is held respontechnology in the plant.
sible for problems
operations. Although
duties may vary, the ~ ..",rr..-.,_... ""~ is also responsible for a
variety of tasks
usage of the CNC
machines, In fact, this
accountable for the
production and quality of
operations.
and Turning Centers
is usually a machine tool with two axes,
the horizontal Z axis.
distinguishes it from a mill is that
cutmachine center line. In addition,
is normally stationary, mounted in a sliding twTet.
follows the contour of
programmed
tool path.
the CNC lathes with a milling attachment, so
called live tooling. the milling tool has its own motor
rotates while
spindle is stationary.
I"nn,"I>',..,.., lathe design can be horizontal or
more common than the
purpose in
for either
For
horizontal group can be
as a bar type, chucker type or a
to
combinations are
aca CNC lathe an extremely flexible maaccessories such as a tailstock, steady
part catchers, pullout-fingers
rests or fol1ow#up
milling attachment are popular compoeven a third
nents of the CNC
~
lathe can be very versatile
so versatile in
that it is often caUed a CNC Turning
Center. AU text
examples in this handbook
use the more
tenn CNC lathe, yet still
ing aU its rr'ln,('Ip.1m h"",,,,,,h ..u,,,
analyze,
dam into a
the CNC pro01"1!1 ....... ",..I",. must be
to decide upon the best manufacturmethodology in all respects.
\"Ullv\"lvU
In addition to the machining skills,
programmer
has to have an understanding of mathematical principles,
arcs and anmainly application of equations.
Equally important is the
of trigonometry.
with computerized progranuning)
knowledge of
manual programming methods is absolutely
to the
the
thorough understanding of
control this output.
important quality of a truly
"'''''1'">'\''''''P1'" is his or her ability to listen to
the CNC operators,
are the first prerequisite to h"""'(lI"'I"""
programmer must be flexible
ClllLHll1t);!, quality,
6
Chapter 1
• CNC Machine Operator
The CNe machine tool operator is a complementary position to the CNe programmer. The programmer and the
operator may exist in a single person., as is the case in many
small shops. Although the majority of duties performed by
a conventional machine operator has been transferred to
the CNC programmer, the CNC operator has many unique
responsibilities. In typical cases, the operator is responsible
for the tool and machine setup, for the changing of the
parts, often even for some in-process inspection. Many
companies expect quality control at the machine - and the
operator of any machine tool, manual or computerized, is
also responsible for the quality of the work done on that
machine. One of the very important responsibilities of the
CNe machine operator is to report fmdings about each program to the programmer. Even with the best knowledge,
skills, attitudes and intentions, the 'fmal' program can always be improved. The CNC operator, being the one who
is the closest to the actual machining, knows precisely what
extent such improvements can be.
SAFETY RELATED TO CNC WORK
On the wan of many companies is a safety poster with a
simple, yet powerful message:
The first rule of safety is to follow all safety rules
The heading of this section does not indicate whether the
safety is oriented at the programming or the machining
level. The reason is that the safety is totally independent. It
stands on its own and it governs behavior of everybody in a
machine shop and outside of it. At fIrst sight, it may appear
that safety is something related to the machining and the
machine operation, perhaps to the setup as well. That is
defInitely true but hardly presents a complete picture.
Safety is the most important element in programming,
setup, machining, tooling, ftxturing, inspection, shipping.
and you-name-it operation within a typical machine shop
daily work. Safety can never be overemphasized. Com~
panies talk about safety, conduct safety meetings, display
posters, make speeches, call experts. This mass of information and instructions is presented to all of us for some very
good reasons. Quite a few are based on past tragic occurrences - many laws, rules and regulations have been written
as a result of inquests and inquiries into serious accidents.
At fIrst sight, it may seem that in CNC work, the safety is
a secondary issue. 111ere is a lot of automation, a part program that runs over and over again., tooling that has ben
used in the past, u simple setup, etc. All this can lead to
complacency and false assumption that safety is taken care
of. This is a view that can have serious consequences.
Safety is a large subject but a few points that relate to the
CNC work are important. Every machinist should know
the hazards of mechanical and electrical devices. The fIrst
step towards a safe work place is with a clean work area,
where no chips, oil spills and other debris are allowed to
accumulate on the floor. Taking care of personal safety is
equally important. Loose clothing,jewelry, ties, scarfs, unprotected long hair, improper use of gloves and similar
infractions, is dangerous in machining environment. Protection of eyes, ears, hands and feet is strongly recommended.
While a machine is operating, protective devices should
be in place and no moving parts should be exposed. Special
care should be taken around rotating spindles and automatic tool changers. Other devices that could pose a hazard
are pallet changers, chip conveyors, high voltage areas,
hoists, etc. Discollllectillg allY interlocks or other safety
features is dangerous - and also illegal, without appropriate
skills and authorization.
In programming, observation of safety rules is also important. A tool motion can be programmed in many ways.
Speeds and feeds have to be realistic, not just mathematically 'correct'. Depth of cut, width of cut, the tool characteristics, all have a profound effect on overall safety.
All these ideas are just a very short summary and a reminder that safety should always be taken seriously.
CNCMILLING
Many
types
machines are
in industhe majority of them are
machining centers
and CNC lathes. They are
by wire EDM, fabricating machines and machines special
Although
the
this handbook is on the two
that dominate the market, many
can be applied to
equipment.
try,
CNC MACHINES - MILLING
The description of CNC milling
is so
it
can fill a thick book all by itself. All machine tools from a
knee lype milling machine up to a five
profiler
can included in (his
They
in
features,
suitability for
work, etc., but they do all
one
common denominator - their primary axes are the X and Y
axes this reason, they are called
machines.
• Types of Milling Machines
Milling machines can divided imo Ihree categories:
o
By the number of axes - two, three or more
o By the orientation of axes - vertical or horizontal
o By the presence or absence of a tool ...h ..... "',"r
Milling machines where the spindle motion is up and
down, are categorized as vertical machines. Milling machines where the spindle motion is in
out, are categoas horizontal machines - see Figure 2-1 and
the category of the
machines are also wire EDM
machine tools, laser and water jet cutting
name
cutters. burners, routers, etc. Although
do not qualify
as milling type machine tools, we mention them because
the majority of programming techniques applicable to the
mills is
to
machines types as well. The
example is a contouring operation, a
common La
many CNC machines.
the purpose
be defmed:
this handbook, a milling machine can
Milling machine is a machine capable of a simultaneous
cutting motion,
an end mill as the primary cutting
Figure 2-/
Schematic representation of a CNC vertical machining center
at least two axes at the same time
This definition eliminates all CNC
presses, since
covers pOSItioning
not profiling. The
nition also eliminates wire EDM machines
a
of
burners,
they are capable of a profiling action but not
an end mill. Users
these machine tools will still
from m:tny
covered
The
ciples are adaptable to the majority of
machine tools.
For
EDM uses a very small cutter
in the
of a
A
cUlling machine uses
beam as its cutter, also having a known diameter bUL
term keifis used
The
will be concentrated
on metal cutting machine
of end
mills as the primary tool
contouring.
mill
can be
in many ways, first look will
or available
machines.
'I"
j'>
I
Figure 2·2
Schematic representation of a CNC horizontal machining center
7
8
2
simplified
not really reflect reality
current state of art in .a...... "'... tool manufacturing.
changing. New and
machine tool industry is
more powerful machines are V_'''"",'' __ and produced by
manufacturers worldwide.
more features.
The majority of modern machines designed for milling
are capable of doing a multitude of machining tasks, not
machines are also capaonly the traditional milling.
of many other metal
operations, mainly drillng, thread cutting
many others. They may
with a multi-tool
azine (also known as a
a fully
a pallet
changer (abbreviated as ATC)
viated as APC). a powerful computerized conlrol unit
brevlated as CNC), and so on. Some machine
may
as adaptive control.
have additional features,
terface, automatic loading
unloading, probing ",,,,,,rpo..,...
high speed machining
and other
modis - can machine tools of
ern technology. The
capabilities be
as simpleCNC milling
In two words - certainly not. Milling machines that have at
some of
built-in. have ,."u·"'''''""
new breed of
tools - CNC An/l,r".,,·,
This lenn is strictly
related - a manual machining
cel1Jer is a description thal does nul exist.
• Machine Axes
machining center is described by its specifications
manuas provided by the machine tool manufacturer.
lists many
as a quick method of
comparison between one machine and another. It is not unusual to find a slightly
information in the
tool.
brochure - after all, it is a
In the area of
chine tools are
systems, three most common ma-
Q
eNC Vertical Machining Center - VMC
Q
CNC Horizontal Machining Center· HMC
Q
CNC Horizontal Boring Mill
type, except
the major differences will
the
for indexing or full rotary
axes, additional
the type of work suitable for individual
lion of the most common type of a machining center - the
Vertical Machining Center (VMC) a fairly accurate sample
other
group.
• Vertical Machining Centers
Vertical
of work,
done on
for flat type
of machining is
setup.
A vertical
machining center can
be used with
an optional
axis. usually a
head mounted on
mounted either verthe main table. The rotary head can
tically or horizontally, depending on the
results and
the
type. This fourth
can
either for indexing or a full rotary molion. In
combination with a
supplied), the fourth
in the vertical
"nr""",,, can be
long parts that
need support at both ends.
Milling machines and machining centers have at least
The machines become more flexiaxes - X, Y
iflhey
usually an
lary axis (the A
horizontal models).
higher
with five or more axes. A
found on
chine wilh five ;'lxes.
he a hnring mill that
jor axes, plus a
axis (usually the B
parallel to the Z
(usually the W axis).
true
complex and flexible five-axis profiling [ling machine is
the type used in
industry. where a multi-axis. simultaneous
is necessary to
complex
shapes and
and various
maJonty
vertical
centers most
tors work with are those with an empty table and three-axes
configuration.
two and a
machine is used.
From the programming perspective, there are at least two
mentioning:
At times,
three and a
machine or a
terms refer to
where simultaneous
limitations. For
a
Y and Z axis as primary axes. plus
The indexing tadesignated as an A
ble is used
posllioning. but il cannot rotate simultaneously with the motion of primary axes. That type of a
called a 'three and a half axIS ' machine.
machine Ihal is
a more complex but
a
table, is
as a four
can move simultaneously
motion of the
axes,
is a good
with the
example of a true 'four ax.is· machine tool.
the type of
of all axes
vertical
o ONE· programming always takes
from the viewpoint
means the view is
as if looking straight down, at ninety degrees towards
the machine table for development of the tool motion.
Programmers always view the top of part!
spindle, not the
Q
TWO· various markers located somewhere on the machine
show the positive and the
motion of the machine
axes. For programming,
markers should be ignored!
These indicate operating directions, not programming
directions. As a matter of fact, typically the programming
directions are exactly the opposite of the markers on the
tooL
CNC MILLING
9
Vertical and Horizontal Machining
- Typical Specifications
.-
......
_-
...
Vertical Machining Center
Description
1=
m
,
Horizontal Machining Center
I~
Number of axes
3 axes IXYZ)
4 axes IXYZB}
Table dimensions
780 x 400 mm
31 x 16 inches
500 x 500 mm
20 )( 20 inches
Number of tools
20
36
Maximum travel- X axis
575 mm
22.5 inches
725mm
28.5 inches
Maximum travel- Y axis
380 mm
15 inches
22 inches
470 mm
560mm
18.5 inches
560 mm
22 inches
N/A
0.001 degree
60-8000 rpm
40 - 4000 rpm
AC 7.5/5.5 kW
AC 10/7 HP
AC 11/8 kW
AC15/11HP
150 - 625 mm
inches
150 - 710 mm
6 - 28 inches
Spindle center-to-column distance· Y axis
430mm
17 inches
30 560 mm
1.2·
inches
Spindle taper
No. 40
No. 50
Maximum travel- Zaxis
Table indexing angle
Spindle speed
Spindle output
Spindle nu:>t:-tlJ-t~1.1 distan ... ", - Zaxis
6-
Tool shank
CAT50
2 - 10000 mm/min
0.100 - 393 in/min
30000 mm/min (XY) mm/min IZl
1181 in/min IXY) 945 in/min (Z)
Rapid traverse rate
Tool selection
memory
...
Maximum tool diameter
Maximum
__
1 - 10000 mmlmin
0.04 - 393 in/min
30000 mm/min (XYI - 24000
1181 in/min (XV)- 945 iI\Imin
Random memory
80 mm (150 w/empty pockets)
3.15 inches (5.9 w/empty pockets)
1 mm
4.1 inches
300mm
11.8
350 mm
13.75 inches
length
Maximum tool weight
• Horizontal Machining Centers
Horizontal CNC Machining Centers are also
as multi-tool and versatile machines. and are
bieal paris, where
majority of machining has to
on more than one
in a single setup.
(2)
6 kg
20
131bs
44
There arc many applica£ions in lhis area. Common exam-
as pump housings,
cases,
blocks and so on.
machining
centers always include a special
ing table and arc
equipped with a pallet
and other
are large
manifolds,
10
Chapter 2
Because
their flexibility and complexity, CNC
zonlal machining centers are priced significantly
than vertical CNC machining centers.
the programming point
view, there are several
mainly relating to the Automatic Tool
the indexing table,
- in some cases - to the additional
for example, the
changer. All
differences are relatively minor. Wriling a program for
horizontal machining centers is no different than writing a
for venical machining center!'..
eli
• Horizontal Boring Mill
Horizontal boring mill is
another
machine. It
closely resembles a CNC horizontal machining center, but
have its own
Iy, a horizontal
mill is
by the lack
some common features, such as
Automatic
Changer. As Ihe name of
the machine
its primary purpose is boring operations, mainly lengthy
that reason, the reach of
is extended by a specially designed quill. Anthe
other typical feature is an axis parallel to the Z axis, called
Ihe W axis. Although
is, in
the fifth
nation (X, y,
W), a horizontal boring mill cannot be
called a true
axis machine.
Z axis (quill) and the W
(awards
axis (table) work in the
other. so Ihey can be used
large parts and hard-to-reach
areas. It
means, that during drilling, the machine table
moves
an
quill.
quill is a physical part
of the spmdle. It is in the spindle where the culling 1001 ro"'lies - but
in-nnd-out motions are done by the table.
method offered on horizontal
Think of the
mills - if the quill were to be very
it would lose
strength and rigidity.
belter way was to split the tradItional single Z axis movement into two - the quill extension
the Z axis will move only
of the way £Owards lhe
and the table itself, the new axis, will move another
parl of the way towards
the part Ihal
area
chine tool resources.
spindle.
bOlh meet in the
be machined using all the ma-
Horizontal boring mill may be called a
machine, but certainly nol as-axis CNC
the count of the axes is
Programming
CNC
mills are
similar to Ihe horizontal and
machining centers.
• Typical Specifications
On the preceding page is a comprehensive chart showi
the typical specifications
a CNC Vertical Machining
Cellterand a CNC Horizontal Machining Centel:
ifications are side by side in two
not for any comparison
are two
different
types and comparison is no\ possible
all features. In order to compare individual machine tools
within a
category, machine tool
provided by the machine manufacturer
serve as the basis
for comparison.
specifications are contained a
of
verifiable data, mainly technical in nature,
describes
lhe individual machine by
main features. Machine tool
buyers frequently compare many brochures of several
fcrcnt machines as parr of the pre
process.
agers
process planners compare individual machines in
the machine shop and assign the available workload 10 the
most suitable machine.
A fair and accurate comparison can be made between two
vertical
ining centers or between two horizontal machining centers, but cannOI be done
to compare
(ween two differenl
types.
In 11 typical
sped
chart, additional dala
may be listed, not included in
earlier chart In this handbook, the focus is on only those specifications Ihat are
interest \0 the CNC
and the CNC operator.
CNC TURNING
CNC MACHIN
• TURNING
or it turret
IS a common
In
machine shop. A lathe is used
as shafts.
machimng
or conical work,
wheels, bores, threads, etc. The most common lathe
operation is removal material from a round
Illrning tool for external culling. A lathe can
ror internal operations such as boring, as well as for
threading, etc., if a
cutting tool is
are usually
in machining power
lathes, hutlhey do have a
carousel that holds
cutting tools. An
lathe has often
one
or two CUlling tools
at a lime, but has more machining power.
Typical lathe work controlled by a CNC system uses maknown in industry as the CNC Turning
- or
more commonly - the CNC
term 'turning
is
curate overall descnption of a
can be used for a
number of machining opduring a
example, in addition to
lathe
as turning and
a
lathe can be used for drilling, grooving,
knurting and even burn
It can also be used in
ent modes, such as chuck
work,
centers. Many other combinations also exist
are designed to hold
tools in special
can have a milling
indexable chuck, a sub
a tailstock, a steadyrest
many other features
associated with a
lathe design.
more than four axes ore
common. With
constant advances in machine
technologies, more
CNC
appear on the market that are designed to do a
number of operations in a
many of them
(tonally reserved for a mill or a
center.
• Types of eNC lathes
lathes can
by the type of
the number of a xes.
two
types are
lathe and the horizontal CNC lathe. Of
the two,
horizontal type is by
the most common in
manufacturing and machine shops. A
CNC lathe
(incorrectly called a vertical boring mill) is somewhat less
common but is irreplaceable for a
work. For
a CNC
there are no
differences in
the
approach between
two lathe types.
•
of Axes
The most common distinction
CNC lathes is
by the number of programmable axes. Vertical CNC lathes
have two axes in almost all
The much
more common CNC horizontal
commonly designed
with two programmable axes, are
available wilh three,
four or
axes,
adding extra
to manufacturing of more complex parts.
A
lathe can funhcr
described by the
type
o
FRONT lathe
oREAR
... an engine lathe type
... a unique slant bed
SIan! bed type is very popular
chips to
operator and, in case an accident,
down
a
area, towards the chip
its design allows
Between the
of flat bed and
type lathes,
front and rear lathes, horizontal and venicallalhe designs,
there is another variety of a lathe. This
describes
CNC lathes by
number of axis, which probably the
simplesl and most common method
identification.
AXES DESIGNATION
A typical CNC
is designed with two standard axes one axis is the X
other axis is lhe Z axis. Both axes
are perpendicular to
other and represent the
two-axis lathe motions.
X axis also represents
I ravel of the cutting tool,
Z
represents
nal morion. All varieties of
tools are
can be
turret (a special too)
or
Because of this
lurret loaded with all CUIZ axes, which means all
Following the established
and machining
of making a hole by
or punching, is the Z
of the milling ma~
the only machine
of drilling, boring.
CNC lathe work, the
oriemation
a
type of lathe is
downwards motion
axis, and left and
motion for the Z axis, when
looking from the machinist's position. This view is shown
.
following three illustrations Figure 3-1, Figure
3-3.
11
12
Chapter 3
HEADSTOCK
I
CHUCK
/
.
I
!
/
JAWS
!". ---- TOOL
X+
.....t
"
TAILSTOCK
x-
QUILL
Figure 3-1
Typical configuration of a two axis slant bed eNG lathe - rear type
x+
t
Z- . . . . . Z+
"
.....t
XX-
"
X+
Figure 3-2
Typical configuration of a CNC lathe with two turrets
Figure 3-3
Schematic representation of a vertical eNC lathe
is true for both the front and rear lathes and for lathes
with
or more axes. The chuck
is
vertically to the horizontal spindle center line for all horizontal
lathes. Vertical lathes, due to their design, are rotated
90°, where the chuck face is oriented horizontally to the
vertical spindle center line.
In addition to the X and Z primary axes, the
of each additional axis,
lathes have individual
third axis,
for
example, the C axis is usually
milling operations, using so called live tooling. More
tails on the subject of coordinate system and machine geometry are available ill Ihe next
• Two-axis Lathe
This is the most common type of CNC
The work
u!\ually a chuck, is
on the left
holding
of
machine (as viewed by the operator). The rear type,
with
slant bed, is
most popular design for general
work.
some special
for
in the petroleum
industry (where turning tube ends is a common work). a
bed is usually more suitable. The CUlling lools are held
in a specially designed indexing turret that can hold
more tools. Many such lathes
six, eight, len,
also have two turrets.
Advanced
1001 designs incorporate tool storage
away from the work area, similar to the design of machining centers.
'even hundreds, of cutting tools may
stored and used
a single CNC program. Many lathes
also incorporate a quick changing tooling system.
• Three-axis Lathe
Three~axls lathe is essentially a two-axis lathe with an
ditional
This
has own
usually as a
in absolute mode (H
in incremental mode), and
C
is fully programmable. Normnlly, the third axis is used for
cross-milling
slot CUlling. bolt circle holes drilling,
helical slots, etc.
axis can replace some simple operations on a milling machine, reducing
setup time for the job. Some limitations apply (0
many models,
example, the milling or drilling operations can (ake place only at positions projecting from the
tool center
La the spindle center line (within a machinplane), although
adjustments.
has own power source but the power raLThe third
is relatively lower when compared with the majority of
machining centers. Another limitation may the smallest
increment of the third axis, particularly on the
three
axis lathes. Smallest increment of one degree is certainly
an increment of two or five (j"'l'rf"'~
more useful
better is an increment of 0.1'\ 0.01 0, and commonly 0.00 1°
on the
models. Usually the lathes with three axes ofa
fine radial increment that allows a simultaneous
rotary motion,
with low increment values are usually
designed with an oriented spindle stop only.
From the perspective ofCNC part programming, the
ditional knowledge required is a subject not difficult to
learn. General principles of milling apply and many programming features are also available, for
fixed
and other
CNC TURNING
13
• four-axis lathe
There is more in
a four-axis CNC lathe is a
to proa three-axis lathe. As a matter of
lathe is nothing more than programming
lathes at the same time. That may sound
the principle of a
CNC lathe
are actually two controls
one
each pair (set)
axes.
used to do the external - or
(OD) and another program to do the
- roughing (ID). Since a
and can be
pair of axes independently,
at the same time, doing two different operations
simultaneously. The main keys to a
4-axis lathe
programming is coordination of the (ools and their operations, liming of the tool motions
a
sense of
compromise.
cannot work all the
reasons, both
Kf':.c.ml<,e of this
programming fea(typically MiscellUres
as synchronized
how much (ime
laneous Function), the ability to
each tool requires to complete
etc., are required. There is a level of l"(wnnr'l"Im
because only
one spindle speed can be
both active cuuing tools,
although feedrate is
both pairs of axes.
This means that some
operations simply cannot
be done simultaneously.
promotional brochure than
in fact, in a well
technical information,
(he machine tool.
are the features and
the CNC machine tool manufacturer considers .m.,Art..:. ... !
the customer.
In the majority of brochures, there are practical
can b e '
a particular CNC machine, a
lathe in the
•
Machine Specifications
A typical
bed
may
from an actual
lathe, with two axes and a slant
Description
Number of axes
Two (X, Z) or three (X, Z and C)
Maximum swing over bed
diameter
length
12
Not every lathe job benelits from the 4-axis machining.
are cases when it IS more costly to run a job on a
lathe inefficiently
it
very efficient to run
on a 2-axis
Axis travel in Xaxis
• Six-axis lathe
Axis travel in Z axis
Six-axis CNC lathes are
twin turret and a set of
axes per turre!. This
corporales many tool
of them power
as well as back-machin
Programming these
lalhes is similar to programming a three-axis lathe twice.
The control system automatically provides synchronization, when IIvl.,'V~~<'l.1
A small \0
CNC lathe is popular
and industries with simi
applications.
FEATURES AND SPECIFICATIONS
a
promotional brochure
useful in many respects. In most
is impressive, the printing,
and the use of colors is
well done. IS the purpose of the brochure La make a
marketing tool and attract the potential buyer.
A look at a
CNC machine
Specification
Indexing time
0.1 second
Rapid traverse rate X axis
mm/min
in/min
0,01 • 500 mm/rev
,0001 • 19.68 in/rev
Main spindle motor
Spindle speed
35·3500 rpm
Minimum input increment
Motorized
Number of rotating tools
12
Rotating tool speed
30 . 3600 (Imin
Milling motor
AC 3.7/2.2 kW
AC 5/2.95 HP
• M16 metric
·5/8 inches
3
It is very important to understand the specifications and
of the CNC machine lools in
shop. Many feato the control system, many others to the matool itself. In CNC programming, many imponanl
are based on one or
of
features, for
example number of tool stations available, maximum spinothers.
• Control Features
in understanding the
description of a
lathe is the look at some control
unique 10
how they differ form a typical
control.
of control features is described in more detail
Q
circular) can
Q
Dwell can use the p. U or X address (G04)
Q
Tool
Q
1=,,,,,£1.,,.,,, s~!lection (normal) in mm/rev or in/rev
a
Feedrate
a
Rapid traverse rate different for X and Z axes
Q
Multiple repetitive cycles for turning, boring, facing, contour
repeat, grooving, and threading are available
a
Feedrate
is common from 0 to 200% in 10%
increments (on some lathes only from 0 to 150%)
o
X axis can
Q
Tailstock can be programmable
5,
At
some fealures and codes
nOI make
sense - they are included for ,,,r,"'''''1> only. Com-
mon
typical features are listed:
Q
X
Q
Constant surface speed leSS) is standard control
(G96 for CSS and G97 for r/min)
Q
Absolute programming mode is X or Z or C
Q
nr:rl~m,.'ntlll nrn"'''"rnnllnn mode is U or War H
of various forms (including taper and
performed, depending on the control model
a
Automatic
uses 4-digit identification
(special) in mlmin or inlmin
2m" .. "rv, and corner rounding
R and II Kin
a diameter, nat a radius
a
Thread
available with six-decimal
place accuracy (for inch units)
a
Least input increment in X
is 0.001 mm or .0001
inches on diameter· one half of that value per side
COORDINATE GEOMETRY
a
in
/lates. System of coordinates is
on a
over four
mathematical principles dating
are those that
most important of
can be applied to Ihe CNC technology today. In various
these principublications on mathematics and
the rea/number syspies nrc lisled under the headings
(ell! and the rec/angular coordinates.
The length of
division on the scale re[>re~,e
unit of measurement in a convenient and
ceptcd
It may come as a surprise that
used
day.
example, a simpJe ruler used in
on the number scale concept, regardless of meaWeight scales using lons, pounds,
of mass are other
uses the same
as
RECTANGULAR COORDINATE
REAL NUMBER SYSTEM
coordimlte system IS a
M
to
2D point, using the XY coordinates, or a spa-
key to understanding
point, using the XYZ coordinates. [t was first
17th century by a French
and
......... ,"'" Rene Descartes (I
I
us an alternative to the rectangular
(he knowledge of arithmetic.
key knowledge in this area is
/lumber system. Within
ten llvuiluble numerals , _ ' " , , " ' v l
can be used in any of the
called
o
Zero integer.. .
0
r:J
Positive integers ...
(with or without sign)
L 2,
o
Negative integers ...
(minus sign required)
o
Fractions ...
1/8, 3/16. 9/32, 35/64
o
Decimal fractions
0.1
Coordinate System
10,12943, +45
" ..T
-381, ·25,-77
T
.546875. 3.5
At! groups are used
the mainstream of just
modern life. In CNC programming,
primary goal is to
usc the numbers to 'Iranslate' the drawing, based on its
menslons, into t). cutter
Computerized Numerical Control means control by the
All information in a drawing
numbers using a
has to be translated into a
program, using primarily
numbers.
are
used Lo describe commands,
functions, comments,
so on. The mathematical rn.,r,·'n.
of a real number
can he expressed graphically on a
straight line,
scale, where all divisions
4-1.
have the same
Figure 4·1
Graphical representation of the Number Scale
-,
•
.
-;
Figure 4-2
Rectangular coordinate system
The concepts used in design,
and in numerical
point can be mathecontrol are over 400 years old. A
matically defined on a plane (two coordinate values) or in
space (three coordinate values).
defin ition of one point
IS
!O another poinl as a distance parallcl with one of
axes that are perpendicular to each olher. In a plane,
only two axes are required, in the space, all three axes must
represents an exacllospecified. In programming,
If such a location is on a
the point is defined
as a 20 point, along two axes. the location is in a space,
lhe poilH is defilled as a
three axes,
15
16
4
When two number scales that intersect at right angles are
used, mathematical
for a recTangular coordinate system is
terms
from
tion, and all have an important role in CNC programming.
understanding is very important for further
• Axes and Planes
• Point of Origin
Another term that emerged from the rectangular
nate
is called
poil11 of origin, or just origin. 11 is
the point where lhe two perpendicular axes intersect.
is
point
a zero coordinate value in each {lxis,
fled a.<;
planar XOYO and
XOYOZO 4-4.
AY
of
number
an axis.
This old principle, when applied to
programming,
means that at least two axes nvo number scales - will be
mathematical definition of an
-I
1'1
1--+
1
1
1-1-1" 1- -1-1- ....
X axis
T
definition can
enhanced
a statement thaI an
axis can also be a line of reference. In CNC programming,
an
as a reference all the lime. The definition
contains
word
'. A plane is a term
in 2D applications, while a solid object is used in 3D applications.
Mathematical definition of a plane is:
the top viewpoint of the
looking straight
down on the illustration Figure 4-3, a viewing direction is
established. This is often called viewing a plane.
A plane is a 2D entity -
letter X identifies
horizon-
'1--1-"
I -I
-I
ORIGIN
Figure 4-4
Point of origin - intersection of axes
This intersection has a special meaning in CNC programming.
acquires a new name, lypically the
gram reference point. Other terms are also
program
zero,
poim, workpiece zero, part zero, with
the same meaning and purpose.
• Quadrants
Viewing the two intersecting axes and the new
four
distinct areas can be clearly identified.
area is
bounded by two axes.
areas are called quadrants.
Mathematically dcfincd,
Yaxis
I I- 1-
I
1 +-1-
X axis
The word quadrant (from the Latin word quadrans or
quadrall1is,
the fourth parI), suggests four
uniquely defined areas or quadrants. Looking down in the
top
at the two intersecting axes, the following definiapply to quadrants.
are mathematically correct
and are used in CNC/CAD/CAM applications:
Figure 4-3
Quadrant I
UPPER RIGHT
Axis designation· viewing plane
Mathematical
is fully implemented in CNC
Quadrant II
UPPER LEFT
Quadrant III
LOWER LEFT
Quadrant IV
LOWER RIGHT
lal
the Jetter Y identifies its vertical axis. 111is plane IS
called
XY plane. Defined mathematically, (he horizontal axis is always listed as the first
of the pair. In
and CNC programming. this plane is also known as the
Top View or a Plan View. Other planes arc
in
CNC, but not to the same extent as in CAD/CAM work.
quadrants are defined in the
lion from
horizontal X axis and the naming convention
uses Romal! numbers, not Arabic numbers normally used.
GEOMETRY
17
counting starts at the positive
of the horizontal
4-5 illustrates the definitions.
Y+
.,
P2+
... Yaxis
II
I
1--1'- -+ -I
_
t
x-
Quadrant I
X+Y+
-u'+
"
-1--1-+ --i--I-JiIo.
-r--I-~1~~I-~-r-I--~.. I-
x+
..,.. P1
- ---- .....
X
P4
+
.. I
Quadrant III - Quadrant IV
x-yX+Y-
Figure 4·5
Quadrants in the
Any point
zero. Any
cation of the
distance
and their identification
is determined solely
point in a particular quadrant and its
relative to the origin - Figure
COORDI
X AXIS
Y AXIS
ON
,
""""""""~,--"--
..
,
,-""""",
+
QUADRANT III
+
Figure 4·6
Algebraic signs for a point location in plane quadrants
IMPORTANT:
... If the defined point lies exactly on the Xaxis,
it has the Yvalue
to zero (YO).
If the point
on the Y axis,
it has the X value
to zero (XO).
... If the point lies
on both X and Yaxes,
both X and Yvalues are zero IXO YO).
0
XOYOZO is the point
itive values are written
W",UlIlI
Coordinate definition of points within the rectangular coordinate
system (point PI = Origin XOYO)
If these directions were
hand, they would "",..r"''',... ''"
of thumb or finger
in the X direction,
middle
over a
from
root
would point
the Y direction and
,,--"""""""""""""''''''
QUADRANT II
•
::: X4.0 Y-3.0
::: X-S.O Y-4.S
P6 ::: X-5.0 YO.Q
Figure 4-7
value can be positive,
QUADRANT I
o
P1 ::: XQ.Q
- P2- ::: XQ.Q
P3 ::: X5.5 YS.O
---""""
POINT
o
T
In part programmmg,
the plus sign - Figure
• Right Hand Coordinate System
In {he illustrations of the number scale, quadrallfs and
axes, the origin
into two portions. The
zero point - the point of origin - separates the positive section of the axis from the
section. In the right-hand
coordinate system, the
at the origin and
is directed towards
rig III
upwards for the
Y axis and towards lhe
viewpoint for
Z
Opposite directions are
majority of CNC
are programmed using
the so called absolute
method, that is based on
the point of origin XOYOZO. This absolute method of
gramming follows very
of rectangular coordinate geometry and aU
covered in this chapter.
MACHINE GEOMETRY
Machine geometry is the
tween the fixed point of the
a/the part. TypicaJ
machine uses
hand coordinate system.
and negative
is determined by an
VIewing conit is always the
vention. The basic rule for the Z
along which a simple hole can machined Wilh a sinpoint tool, such as a drill, reamer,
or a laser beam.
Figure 4-8 illustrates the standard orientation of an
type machine tools.
TTlU,' TlU,,",
UH'"",,,,'VlI
• Axis Orientation - Milling
A typical 3-axis machine uses
controlled axes of
motion. They are defined as
and the Z
X
to
of the
is parallel to
dimension
the Z axis is the spindle movement. On a
longitudimachining center, the X axis is
the Y axis is the saddle cross direction and
Chapter 4
, X+
•
REAR LATHE
,
FRONT LATHE
VERTICAL
~--I"""-
X+
Figure 4-10
Typical machine axes of a eNe lathe (turning
Figure 4-8
Standard orientation of planes and eNe machine tool axes
the Z axis is the spindle direction.
horizontal machining
centers, the terminology is changed due to the design of
these machines. The X axis is
table longitudinal direction, the Y
is the column direction
the Z axis is the
spindle direction. Horizontal machine can be
as a
machine rotnted in space by ninety degrees. The
additional feature of a horizontal machining center is the
indexing B axis. Typical machine axes applied to CNC vertical machines are illustrated in
4-9.
r~~"'-""""
TOP VIEW
ISOMETRIC VIEW
Figure 4-9
Typical machine axes of a vertical eNe machining center
• Axis Orientation· Turning
Most CNC lathes have two axes, X and Z. More axes are
available, but they are not important at this point. A special
third axis, the C axis. is designed for milling operations
typical CNC lathe.
(live tooling) and is an option on
What is more common for CNC lathes in industry, is the
double orientation of
axes. Lathes are distinguished
as front and a rear lathes. An example of a
lathe is
similar to the conventional engine lathe. All the slant bed
types
a lathe are
the rear kind. Identification of the
axes have often not followed
principles.
Another variety. a venical CNC lathe, is basicaHy a horiand
zan tal lathe rotated 90 0 • Typical axes for the
vertical machine axes, as applied to turning, are illustrated
in Figure 4-10.
• Additional Axes
A CNC machine of any type can designed with one or
more additional axes. normally designated as
secondary axes using the U, V and W letters. These axes are normally parallel to
primary X, Y and Z axes respectively.
For a
or an indexing applications,
additional axes
rotated about the
are defined as A, B and C axes, as
X, Y and Z axes,
in their respective order. Positive direction of a rotary
an indexing)
is
direction required to advance a right handed screw in the positive X. Y
or Z axis. The relationship of the primary and the secondary (or supplementary) axes is shown
1.
Primary
axes
__ Secondary
axes
Arc center
1..\--+---+--+--+--+ - - vectors
Rotary
axes
,
X axis
related
Yaxis
related
I
Zaxis
related
4-11
Relationship of the primary and the sec:oncfarv
axes
center modifiers (sometimes
the arc center
vectors) are not true axes, yet they are also
to the
primary axes
This subject will
described in the
section on Circular Interpolation, in Chapter
CONTROL SYSTEM
A
unit equipped witn a
control system is commonly known as a
an analogy of the machine tool as the
system,
control unit is its
are no levers, no knobs and no
machine the way they function on COniVCr1lIIO£
and lathes. All the machine
and hundreds of other tasks are
by a
programmer and controlled by a computer that is maof the CNC unit To make a program for a CNC machine tool means to make a program for
system.
the machine tool is a major
as well, but
it is the
unit thai
of the prostructure and its syntax.
In order to fully understand
CNC programming process, it is important to understand not only the intricacies of
to machine a pan, what tools to select, what speeds
to use, how to
many other features. It is equally
the computer, the
CNC unit, actually
to be an expert
in electronics or a
I shows an
actual Fanuc control
The machine
own
panel, with all the
and button needed to operate
the CNC machine and all its features. A typical operation
panel is illustrated in
Another item required
the system. the handle, will be described as well.
HELP KEY
\.
GE Fanuc Series 16-M
\
(OFF I
I
1--1
\
OPERATION
MENU
ON I OFF BUTTONS,
Figure 5·1
A typical example of 8 Fanuc control panel. actual layout and features will vary on different models (Fanuc 16M)
19
20
5
GENERAL DESCRIPTION
control unit - the
work in conjunction
anything useful on its own.
if the program itself
tons and keys are
by
control over the program "''''''''''''''.'''
a brief look at any
reveals that there are
two basic components - one is
operation paJlel, full
rotary switches, toggle
and push buttons. The
other component is the display screen with a keyboard or a
keypad. The programmer who does not normally work on
CNC machine will
if ever, have a reason to use
the operation panel or the display screen. They are
machine operator. and
at the machine to the
the
as well as to control the activiof the machine.
• Operation Panel
Depending on
CNC machine,
ing table covers
most typical and common
found on the modern operation panel. There are some
of a machining center
a
differences for the
but both operation
are similar. As with any
reference book, it always a good idea to double
with
specifications and recommendations. It is common
machines
In
have some special
maShould the CNC
interested in
chine operation? Is
for the
to
know and understand all
of the conlIol system?
is only one answer to both questions - definizely
CYCLE
x
z
y
D
ERRORS
4
MOO M01 M30
OPTIONAL
STOP
M-S-T
LOCK
ON
BLOCK
SKIP
ON
@
@
@
OFF
OFF
OFF
o
ALARM
o
o 0
0
MACHINE
LOCK
ON
ON
OFF
DRY
RUN
ON
@
@
OFF
OFF
OFF
AUTO
ID MDI
70
60
50
175
TAPE
150
125
1
80
60
40
30
20
15
10
EDIT
MODE
Y
Z
X
20
10 0
600
- 800
1000
1200
1500
2000
4000
0
90
4030
400
5
80
ccw
D
EDIT
...!
,-_._-
80
OVERRIDE %,
N
90
110
0
120
CYCLE START
OVERRIDE %
Figure 5·2
A typical operation panel of a CNC macnmlllO center actual
FEEDHOLD
AUTO
features wiN vary on different models
EMGSTOP
CONTROL
21
Description
Feature
ONI
switch
Start
Emergency
Stop
Power and control switch for
the main power and the control unit
Starts program execution
Or MDT command
AUTO Mode
automatic operations
MEMORY
Allows program execution from the
memory of the CNC unit
mode
all machine
and
turns off power to the control unit
motion of all axes
Feedhold
Single Block
Allows program run one block at a time
Optional Stop
Temporarily stops the program
execution (MOl required in program)
Block Skip
Ignores blocks preceded with
a forward slash (I) in the program
Enables program testing at fast
mode
EDlT
MANUAL
Mode
JOG Mode
Memory
Access
Spindle
Override
Overrides the programmed spindle
usually within 50-120% range
Error lights
Feedrate
Override
Overrides the programmed feedrate,
usually within 0·200% range
Chuck
Shows current status of the chuck
Clamp
(Outside I Inside
Clamp
Coolant
Switch
Shows current status of table
computer or a punched tape
Allows
to bt: made to a
program stored in the CNC memory
Allows manual
Selects
mode for setup
(switch) to allow program editing
Red
an error
is some
may not be listed, vinual\y all of
table are somewhat related to the CNC proMany control systems
unique
of their
own. These features must
known to
The program supplied to the machine should
not rigid - it should 'user friendly'.
those in
• Screen Display and Keyboard
Coolant control ON I
I AUTO
Gear
Shows current status of working
Selection
gear range selection
Spindle
Rotation
Indicates spindle rotation direction
or counterclockwise)
Spindle
Orientation
Manual orientation of [he spindle
Tool Change
Switch allowing a manual tool
Position
Switches and
relating to setup of
the machine from reference position
Handle
Manual
Generator (MPG).
used for Axis Select and Handle
Increment switches
Tailstock
Switch
switch to manually
Tailstock and/or
IJUOUI'v"1 the tails!ock
Indexing
Table Switch
Manually indexes machine table
MOl Mode
Allows program execution from an
external device, such as a desktop
RAPID Mode
feedrales (without a mounted part)
Dry Run
Description
Feature
setup
mode
The screen display is
'window' to the computer. Any
the
program can be viewed, including the status
control, current tool position, various offsets, parameters,
even a graphic representation of the Tool Path. On all CNC
units, individual monochrome or color screens can be selected to have the desired display at any time, using the inkeys (keyboard pads and soft keys). Setting for internationallanguages is also possible.
The keyboard pads and soft keys are used to input instructions to
control.
can
modified or deleted, new programs can
Using
keyboard input, not only the machine axes motion can be
controlled, but the spindle speed and feed rate as well
Changing
internal
evaluating various
diagnostics are more specific means of control, often restricted to service people. Keyboard and screen are used to
set
program origin and to hook up to
devices,
as a connection with another computer. There are
many other options.
keyboard allows
use of
fers, digits and symbols for data entry. Not every keyboard
allows the use of all the alphabet letters or all available
symbols. Some control panel keys have a description of an
operatiol1, rather than a letter, digit or symbol,
example,
Read
Punch
or the Offset
22
Chapter 5
• Handle
SYSTEM fEATURES
machine has a rotary
handle that can move one
by as little as the
least increment of the control system. The official Fanuc
name for the handle is Manual Pulse Gen.erator. Associwith the handle is the Axis Select switch
duplicated on the operation
as well as on the handle) and
is the least increment X I, X 10
the range of increment
X I(0). The
X in this case is the multiplier and
stRnds for
limes'. One handle division will move the seaxis by X times the minimum increment of the active
of measurement. In Figure
and the following table
are the details
a typical handle.
y
X
Z
...... AXIS
SELECT
x1 x10
x100
The CNC unit is
more than a sophisticated spepurpose computer.
'special purpose' in this case is
a computer capabll' of controlling the
of a matool, such as a lathe or a machining center. It means
the computer
to designed
a company
has expertise in Ihis type of special purpose computers. Unlike
many business types
each CNC unit is made
customer is typically
maa particular customer.
chine manufacturer, not the end user. The manufacturer
certain requirements that the control system
to
requirements that reflect the uniqueness of the machines they build. The basic conlrol does not change, but
some customized features may
added
taken away)
for a specific
the
system IS
to
the
manufacturer, more features are added to the
system. They mainly relate to the design
capabilities of
the machine.
A
example is a CNC unit for two machines that are
the same in all
except one. One
a
manual lool changer, the other
an automatic 1001
changer. order to support the automatic tool changer, the
CNC unit must have special features
. that are not
for a machine without Ihe rool changer. The more
complex the CNC system is, the more expensive it Users
that do not require all
sophisticated features, do not pay
a
for
they do not need.
•
Parameter Settings
infonnalion that establishes the built-in connection
between the
control and
machine tool is stored as
special data in
called the system parameters. Some of the
in this handbook is quite ~pecialized
listed for reference only. Programmers with
limited experience
not
to know
parameters
in a great depth. The original factory
are sufficient
for most machining jobs.
5~3
An example of a detached handle, called the Manual Pulse
Generator (MPG), With a typical fayout and features.
Layout and features may vory on different machine models.
When (he parameter screen is displayed, it shows the
rameler number with some data in a row. Each row numone bYle,
digit in the
is called a
word bit is
the
Binary digiT
is
smal
unit of a parameter input. Numbering
starts with O.
from the
to the left:
II
One handle division motion is ...
Handle
Multiplier
Xl
Xl0
Xl00
Metric units
"
"
:
for English units
The Fanuc control system parameters belong to one of
three groups, specified within an allowed range:
0.001 mm
.0001 inch
0.010 mm
.0010
o
codes
0.100 mm
.0100 inch
o
Units inputs
o
Setting values
CONTROL SYSTEM
The groups use different input values.
binary input
can only have an input of a 0 or I for the bit data format, 0
10 +127 for
byte type. Units inpur has a broader scope the unit can
in mm,
mmimin, in/min,
milliseconds, etc. A value can also be specified within a
given range, for example, a number within the
of
0-99, or 0-99999, or + 127 to -127, etc ..
A typical example of a binary input is a selection between two options,
instance, a feature called dry run
can set only as effective or ineffective. To select a
ence, an arbitrary bit number of a parameter has be set to 0
to make the dry run effective and to I to make it ineffective,
UniTs inpur, for example, is used to selthe increment system - the dimensional units, Computers in general do no!
distinguish between inch and metric, just numbers, It is up
to the user and the
setting, whether the control
will
0.00] mm or .0001 inches as the
menL Another example is a parameter selling that stores
the maximum feedrate
each axis, the maximum spindle
speed, etc. Such values must never be set higher than the
machine can support. An indexing axis with a minimum
crement of 1°, will not become a rotary
with ,00 I 0 increment, just because the parameter is selto a lower
even if it is possible. Such a setting is wrong and can
cause serious damage!
To better understand what the CNC system parameters
can do,
is an abbreviated Ilsting of parameter classififor a typical
comrol system (many them are
meaningful to the
technicians only);
Parameters related to Setting
Parameters related to Axis Control Data
Parameters related to Chopping
Parameters related to the Coordinate System
Parameters related to Feedrate
l-':::Ir'Am;::tT",r<: related to Acceleration/Deceleration Control
Parameters related to Servo
Parameters related to DVDO
Parameters related to MOl, EOIT. and CRT
Parameters related to Programs
Parameters related to Serial Spindle Output
Parameters related to Graphic Display
Parameters related to I/O interface
Parameters related to Stroke Limit
Parameters related to Pitch Error Compensation
Parameters related to Inclination Compensation
Parameters related to Straightness Compensation
Parameters related to Spindle Control
Parameters related to Tool Offset
Parameters related to Canned Cycle
Parameters related to Scaling and Coordinate Rotation
Parameters related to Automatic Corner Override
Parameters related to Involute Interpolation
I-'::lr::!mpte:>r!:! related to Uni-directional Positioning
Parameters related to Custom Macro IUser Macro)
Parameters related to Program
23
Parameters related to High-Speed Skip Signal Input
Parameters
to Automatic Tool Compensation
Parameters related to T001 life Management
Parameters related to Turret Axis Control
Parameters related to High Precision Contour Control
Parameters related to Service
... and other parameters
Quite a
parameters have nothing to do with daily programming and are listed only as an actual example, All system
should be set or
only by a qualified person,
as an experienced
technician. A
programmer or operator should not modify any parameter
settings. These changes require not only qualifications but
authorization as well. Keep the list of
control, in a safe place, just in case.
settings away from
Many parameters are periodically updated
program processing. The CNC operator is usually not aware
that this activity is going on at aiL There is no real need to
monitor this activity. The safest
to observe is that once
have
set by a qualified technician, any
temporary changes required for a given work should be
done through the CNC program. If permanent changes are
required, an authorized person should
assigned to do
them - nobody
• System Defaults
Many parameter settings
in the control at the time
of purchase have been entered by the manufacturer as either the only
the most suitable choices, or the most
not mean they will be the
common selections. That
settings - it means they were selected on the
their common usage, Many settings are rather conservative in
values, for safety reas»ns.
The set of parameter values established at the time of installation are called the default seHings. The English word
'default' is a derivative of a
word 'defalu', that can
be translated as 'assumed'. When
main
to the
control is turned on, there are no set values passed to parameters from a program, since no program has yet been
used. However, certain
active automatiwithout an external program.
a culler radius offset is automatically canceled at the startup of (he
control system, Also canceled are the fixed cycle mode and
tool length offset. The control
'that certain conditions are preferable to others, Many operators will agree
with most of these initial settings, although not necessarily
with
of them. Some settings are customizable by a
of a parameter settings. Such settings will . . """"''''''A
permanent and create a /lew 'default'.
24
5
A computer is fast and accurate but has no intelligence.
People are
slow and make elTors, but have one unique
ability - they think. A computer is just a machine that does
not assume anything, does not consider, does not feel computer does nOl think. A computer
not do anything
that a human effort and ingeolli.ty has not
during the
design process, in form of hardware and software.
When the
the
software sets certain existing
to their default condition,
by engineers. Not all system parameters,
only
parameters can have an assumed condition - a
condition that is known as the default value (condition).
example, a tool motion has three basic modes - a
rapid motion, a linear motion and a circular motion. The
default motion
is controlled by a parameter. Only
one setling can be active at the startup. Which one? The answer depends on the parameter setting. Many parameters
can be
to a desired state. Only the rapid or the linear
mode can be set as default in the example. Since the rapid
motion is the first motion in {he program, it seems to make
sense La make it a default wail'
Most controls are set (0 the linear motion as Ihe default
(GO I command), to be in
at the start - strictly for
safety reasons. When the machine axes are moved manually, the parameter selling has no effect. If a manual input of
an axis command value takes place. either through the program or from the control panel, a tool motion results. If the
motion command is nm specified, the system will use the
command mode that had been preset as the default in
parameters.
the default mode is a linear motion GO I,
the
is an error condition, faulting the system for the
lack of a Jeedrate!
is no cutting feed rate in effect,
which the GO I requires. Had the default setting been the
rapid motion GOO, a rapid motion would be performed. as it
no!
programmed
It is beneficial to know the default settings of all controls
in the shop_ Unless there is a good reason to do nrn....
defaults for similar controls should be the same.
Modem methods
measuring memory capacity prefer
to use bytes as the unit, rather that a length of an obsolete
tape. A byte is the smallest unit of storage capacity and is
very roughly equivalent to one character in the program.
The memory capacity of the control system should
enough to store the longest CNC program '"''',. . '''£''''''''
on a regular basis. That requires some planning
machine is purchased.
example, in three dimensional mold work or high speed machining, the cost of additional memory capacity may very high. Although any
cost is a relative term, there are reliable and inexpensive alwell worth looking into.
One alternative is running the CNC program from a personal
An
communication software
and cabling is required to connect the computer with the
CNC system.
simplest version is to transfer the CNC
program from ODe computer to the other. More sophisticated possibility includes software and cables that can actually run the machine from the personal computer, without
luading it 10 the memory of
CNC first This method is
often called 'dripleeding' or 'bitwise input', When operfrom the personal computer, the CNC program can be
as long as the capacity of the storage device, typically the
hard drive.
Most CNC programs will fit into the internal memory of
control system. Many controls use the
of available
or the equivalent length of
are
some formulas that can be used to get at least the approximate memory capacity calculations:
C) Formula 1 :
find the program length in meters,/When the capacity
is known in
use the following formula:
n>Jl
• Memory Capacity
CNC programs can be stored in the control
size is only limited by the capacity of the control.
capacity is
in a variety of ways, originally as
the equivalent length of tape in meters or feet, lalely as the
number oj bytes or the number of screen pages. A common
minimum
capacity of a CNC lathe control is 20 m
of tape (66 ft).
is an old fashioned method thal somehow persisted in staying with us. On CNC milling systems,
the memory requirements based on the same criteria are
generally
and the typical minimum memory capacity
is 80 m or
ft Optionally, larger memory capacity
can be added to the control system. The minimum memory
capacity the control varies from one machine to anotheralways
control specifications carefully.
",rr\('l""'1"1"1
~ where ...
Sm = Storage capacity in meters
No = Memory capacity (number of characters)
C) Formula 2 .
To find the length program in/eel. when the capacity is
known in charaCters, use the following fOlTnula:
IG'i" where ...
5,
Storage capacity in feet
No :: Memory capacity (number of characters)
CONTROL SYSTEM
~ Formula 3 .
To find the number of characters in a given program, if
the system memory capacity is known in meters:
lIE where ...
C
Number of available characters
m == Memory capacity in meters
Virtually the same results can be achieved by a slightly
restructured formula:
2S
block are processed as a single inSlrllClion. The blocks are
received by
control system in sequential order, from the
top down and in the order they appear in the program.
NormaDy, a CNC machine is run in a continuous mode,
while
blocks are processed automatically, one after another. This contim1ily I!; important for production, but not
practical when proving a new
for example.
disable the continuous program execution, a Single
Block switch is provided on the operation panel. In
sinblock
only one block of the program will be
is
On the optime the C)'cle
eration panel, the single block mode can used separately
that make
or in combination with other
provmg
and more accurate.
• feedhold
Q Formula 4:
To find
of characters, if the system memory
is known in feer, use the following formula:
IGf' where ...
C
= Number of available characters
f
== Memory capacity in feet
Latest
controls show the available memory as the
number of free screen display pages. This type of data is
not easy to convert as the others.
In cases
the available memory capacity is too
small to accept a
program, several techniques are
available to minimize the problem, for example, the prolength reduction methods,
in Chapter 50.
MANUAL PROGRAM INTERRUPTION
If a program needs Lo interrupted in the middle of processing, the control system offers several ways to do that,
the
operation panel. The most common features of this type are toggle
or push buttons for a
single block operation,feedhold and the emerge/lcy SlOp.
• Single Block Operation
normal purpose of a program is to control the machine tool automatically and sequentially in a continuous
of
commands mode. Every program is a
or instructions - written as individual
of code,
blocks. Blocks and their conct!pts will be described in the
following chaplers. All
in a
Feedhold is a special push button located on
operation
panel, usuatly dose to the Cycle Start bulton. When this
button is pressed during a
linear or circular axes motion, it will immediately SLOp the motion.
action applies to all axes active at the lime.
is convenient
for a machine setup or a first
run. Some types of molion
the function of
feedhold or disable it altogether. For example, threading or tapping modes make the
switch inoperative.
Activating feedhold at the machine will not change any
other program values - it will only affect
motion. The
will illuminated (in
light), as long as
feedhold
It IS
The CNC programmer can override the feedhold from within the program, for special purposes.
• Emergency Stop
Every CNC machine has at least one special mushroom
push bUHon, red in color, that is located in an accessible place on the machine. It is marked the Emergency
SLOP or E-Sl0p. When this buuon is pressed, all machine ac/ivities will cease
The main power
will
interrupted and the
will have to
restarted.
emergency stop switch is a mandatory safety feature
on all CNC machines.
Pressing the emergency stop button is not always the best
or even the only way LO stop a machine operation. In fact,
the latest controls offer other features. far less severe, designed to prevent a collision between a cutting tool and the
part or fixture. Previously discussed feedhold button is only
one option, along with other features. If the emergency stop
must be used at all, it should be
as the
resort, when
any other action would require unacceptably
time.
panic, if something does
wrong.
There is no need
some machine
the effect of Emergency Stop
is not always apparent.
example, the spindle requires a
certain time
deceleration to slap.
26
5
MANUAL DATA INPUT - MOl
A CNC
is not always operated by the means of a
program. During a pan setup, the CNC operator has to do a
number of
that require physical movements of
the machine slides, rotation
spindle, tool change) etc.
There are no mechanical devices on a CNC machine. The
handle (Manual Pulse GeneralOr) is an electronic, not a
unit. In
to operate a CNC machine without conventional mechanical devices the control system
fers a feature eaHed the Manual DaTa inpUl - or MOL
The Manual Data Input
the input of a program
into the system one program inSTruction at a time. If
(00
instructions were to be input repeatedly. such as a
would be very inefficient.
long program, the
During a setup and
similar purposes, one or a few
structions at a time will benefil from the MDL
access the MDI
!.he MDI key on the operation
panel must be selected. That opens the screen display with
the current status of the system. Not all, but the majority of
codes are allowed in the MDI mode. Their
is identical to the
of a CNC program in written form, This is one area where the CNC operator acts as a
CNC programmer. It is
important that the operator is
trained at least in the
CNC programming, certainly to the point of being able to handle the setup instructions for Manual Data Input.
PROGRAM DATA OVERRIDE
All CNC units are designed with a number of special rotary swttches that
one common feature - they allow
the CNC operator to override the programmed
of the
spindle or the programmed speed of
axis motion. For
example, a 15 in/min feedrate in the program produces a
slight
A knowledgeable operator will know that by
increasing the feedrate or decreasing the spindle speed, the
chaner may be eliminated. It is possible to
Ihe
or the spindle
by editing the program, but
this method is not very
A certain 'experimentation'
be necessary duri the actual cut to find the optimum
value. The manual override switches come to
the rescue,
they can be
by trial during
operation. There are four override switches found on most
control panels:
o
Rapid feedrare override (rapid traverse)
(modifies the rapid motion of the machine toof)
o Spindle speed override
(modifies the programmed spindle T/min)
o
Feedrate override (cutting feedrate)
(modifies the programmed feedrate)
o Dry run mode
(changes cutting motions to a variable speed)
Override
can
used individually or together.
control to make the work
They are availahle on
operator
for both the operator and the programmer.
does not need 10 'experiment' with speeds and feeds by
constantly editing the program and tne programmer has a
certain latitude in seuing reasonable values for the cuttino
fcedrales and the spindle speed. The presence of the over~
switches is not a licence to program unreasonable
cutllng values. The overrides are fine tuning tools only program must always renee! the machining conditions of
the work. The usage of
switches does nut make
any program changes, but
the CNC operator the
port,unily to edit the program later to
the optimum
cuttmg
Used properly, the
switches
amount of valuable programming time as
can save a
well as the setup time-at the CNC machine.
• Rapid Motion Override
Rapid motions are selected in (he CNC
by a preparatory command without a specified
If a ma~hine is d~siglied to move at 500 in/min (12700 mm/min)
10 the rapId mode, this rate will never appear in the program. Instead. you call the rapid motion mode by
ming a special preparatory command GOO. During
program execution, all motions in the GOO mode will be at the
manufacturer's fixed rate. The same program will run faster
on a
with high
motion rating then on a machine with low rapid motion
some
During setup, the rapid motion rare may
control for program proving. when high rapid rates are uncomfortab~ 10 work with. After the program had been
proven, raptd rate can be applied at its maximum. CNC machines are equipped with a rapid override switch to allow
temporary rapid motion settings. Located on the control
panel, this switch can be st![ 10 one of the four
as the percentage of the max
Three of them arc
mum rate, typically as 100%, 50% and 25%. By switching
~o one of them. the rapid motion rate changes. For example,
)fthe maximum rapid rate is 500 inJmin or 12700 mm/min,
the
reduced rates are
inJmin or 6350 mmlmin at
the 50% selling and 125 in/min or 31
mm/min at the
25% setting.
oflhe reduced rates is more comfonable
to work with
setup.
The fourth position of the switch offen has no percentage
and is identified as an F I or by n small symbol. In
this seLting, the rapid motion rale is even slower than that
Why is it not idenli fled as
or 1
for example? The reason is simple - the control system allows a
selection as to what the value will
Jt may he
a setting of between 0 and 100%.
default seuin a is
the mOSI logical - usually 10% of the maximum r:pid traverse rate.
setting should never be higher than 25%
can be done only through a setting of a system
ler. Make sure that all persons who work on such a machine
are aware of the
CONTROL SYSTEM
• Spindle Speed Override
same logic used for the application the rapid rate
override can be used
the spindle speed override. The re-
quired
can be established during the actual
by using the spindle speed override switch, located on the
control panel. For example, if the programmed spindle
speed of 1000 rlmin is loa high or LOa [ow, it may be
changed temporarily by
switch.
the actual cutting, the CNC operator may experiment with the spindle
speed
switch to tind the optimum speed for the
given cutting conditions.
method is a much faster thall
'experimenting' with the program values.
spindle speed
switch can
on
some controls or selectable in increments of 10%, typically
50-120% of the programmed spindle
within the
A
programmed at 1000 r/min can be overridden during machining to 500, 600, 700,800,900,.1000,
1100 and! 200 r/min. This
range allows the CNC operator
flexibility
the spindle rotation to
suit the CUlling conditions.
is a catch, however. The
optimized spindle speed chnnge may apply \0 only one tool
of Ihe many used in the
No CNC operator can be
to watch for that
tool and switch the
speed up or down when
A simple human oversight
may ruin the part, the cutting 1001 or both.
recommended method is to find out the optimum speed for
1001. write it down. then change the program
so all the tools can be
at the 100% spindle override
for production.
on the
Comparison of
switch with the increments on switches for the rapid traverse override
earlier) and the feedrate ",,,,,,.lt1,,
next),
more limited
The reason
spindle speed range of 50% to I
is safety.
illustrate with a rather
example. no operatOr
would want La mill, drill or cut any material at 0
spindle rotation), possibly combined
a heavy feedrate.
]n
to
into 100%
speed in the program, D. new spindle
has to be calculated. If a programmed spindle speed of 1200 rlmin
a
tool is always set to 80%. it should be edited in the
\0960 r/min, then
at 100%. The formula is quite
pie:
/'
~ where ...
So ::::: Optimized - or new r/min
Sp
p
=
Originally programmed r/min
Percentage of spindle override
Overriding the programmed spindle speed on the CNC
machine should have only one purpose to
the
spindle
rotation for
best cutting conditions.
• Feedrate Override
The most commonly used override switch is one that
FOT
milling controls,
changes
the feed rate programmed in in/min or mlmin.
lathe
controls, the feed rate is programmed in itt/rev or in mnt/rev.
The [ceurate per minute on
is used only in cases
when the spindle is not rotaling and the
needs to be
controlled.
The new feedrate calculation, based on the
""A/~r""'" selling, i~ similar to that for spindle speed:
~ where ...
Fn
= Optimized - or new-
Fp
p ==
Originally programmed tP'j>,fifl'llh"
Percentage of feedrate
can overridden within a large range, Iypically
from 0% to 200% or at least 0% to 150%. When the
'·"'"..n ...... ,.,. override
is set to 0%, the CNC machine
will stop the cutting motion. Some CNC machines do nOI
have the 0% percent setting and start at 10%.
maximum of 150% or 200% CUlling feedrate will cut I
or
than the
value.
There are situations, where the use of a feed rate
would
the pari or the cutting tool - or both. Typical
examples are various tapping cycles and single point
threading. These operations require spmdle rotation synchronized with the feed rate. In such cases.
ineffective. The
override will
override will
effective. if standard motion commands 000 and GO I
are used to program aoy lapping or tread cutting mOlions.
poimilireading command G32, tapping fixed cycles
and G84, as well as lathe threading cycles 092 and
076 havc the feedrate override cancellation built into the
software. All these and other related
are dein the handbook, in more
• Dry Run Operation
Dry run IS a special kind of override. II is activated from
the control
by the Dry Run switch. It only has a direct
effect on
and allows much higher feedrate
that used for actual machining. In praaice. it means the
program can be executed much faster than using a feedrate
at the maximum
No actual
place when the dry run
is in effect.
What is Ihe purpose of the dry run and what are its
tits? Its purpose is to test the integrity of
program
The benefits are
CNC operator cuts the first
mainly in Ihe time saved during program proving when no
a dry run. the part is normachining takes place.
mally 1101 mounted in the
lfthe part is mounted in
5
the
device and
dry run is used as well. it is very
important to provide sufficient clearances. Usually, it
means moving the tool away from the parr.
program is
then executed 'dry', without actual cutling. without a
ant, just in the air. Because of the heavy feed rates in the dry
run, the part cannot he machined safely.
a
run,
the program can be checked
all possible errors except
those that
to the actual contact of the
tool with
the material.
The dry run is a very efficient setup aid to
all integrity of the CNC program. Once the
is
proven during a dry run, the CNC operator can concentrate
on
sections of the program that contain actual machining, Dry run can used in combination with
features of the operation panel.
• Sequence Return
Sequence Return IS a function controlled by a switch or a
key on the control panel.
purpose is to enable the CNC
operator to start a program from the middle of an intermemorupted program. Certain programmed functions
(usually the last
and feed),
have to be Input by the Manual Data Input key. The operation of this
function is closely lied to the machine tool design. More
formation on the
can be
in the machine tool
manual. This function is very handy when a tool breaks
during processing of long programs. It can save valuable
production time, if
properly.
• Auxiliary Functions lock
ore three
available to the operation of a
CNC machine that are part of the 'auxiliary junctions'
group. These functions are:
• Z Axis Neglect
Another very useful tool for testing
programs
on CNC machining centers (not lathes) is a toggle switch
located on the operation panel called the Z Axis Neglecr or
Ignore. As
when this switch is
activated, any motion
for the
will not
be performed. Why the axis? Since the X and Y axes are
used to profile a
of the part
most common contouring operations), would make no sense to temporarily
cancel either one of
axes.
neglecting (disabling)
Z
temporarily,
CNC operator can concentrate
on
the
of the part contour, without worrying about the depth. Needless to say, this method of program testing must take place without a mounted part (and
normally without a coolant as well), Be careful here! It is
important to
or disable the switch at (he right time.
lf the Z axis motion is disabled before the Cycle Start key is
all following Z
commands will
ignored. If
motion is enabled or disabled during program ",.I"\"I'C<'_
ing, the position the Z
may
inaccurate.
Z
switch may be
in bolh
manual
and automatic modes of operation, Just make sure that the
motion along the Z axis is returned Lo the enabled mode,
once the program proving is
Some CNC machines require resetting of the Z axis position
+ Manual Absolute Setting
If this feature is
on the control (some controls
use it automatically), it
(he
operator to resume a program in the middle of
Manual absolute can save
particularly wIlen processing long
Manual Ahsolure setting switch is not a typical
some extent, it is functionally
to the Sequence Return setting. Check
machine tool documentation
using either of these two features.
Miscellaneous functions lock
Locks M functions
Spindle functions lock
locks S functions
Tool functions lock
Locks T functions
described
in this chapter, auxiliary functions
generally relate to the technological aspects of the CNC
They control such machine functions as
spindle rotation, spindle orientation, coolant selection, tool
changing, indexing table, pallets and many others. To a
lesser degree, they also control some program functions,
such as compulsory or optional program SLOp. subprogram
flow, program closing and others.
When
auxiliary functions are locked,
machine related miscellaneous functions M, all spindle functions S
all 1001 functions T will be suspended. Some machine
1001 manufacturers
the name MST Lock rather than
Auxiliary Functions Lock.
MST is an acronym
the
first letters from the words Miscellaneous, Spindle and
Tool,
LO the program functions that will be locked.
The applications of these locking funclions are limited to
the job setup and program proving only and are not used for
production machining.
• Machine lock
Machine Lock function is yet another control feature
So far, we have looked at the Z axis Neprogram provi
glect function and the locking of the auxiliary functions.
Neglect function will
the
Remember that the Z
motion of the Z axis only and the Auxiliwy Functions Lock
(also known as Ihe MST lock) locks the miscellaneous
functions, the spindle functions
lool
Another function, also available through the control panel, is
called the Machine Lock. When this function IS enabled,
the motion of all axes is locked. It may seem
to test
CONTROL SYSTEM
a
locking all the tool motions, but there is a
good reason to use this
It
CNC operator
the chance to test the program with virtually no chance of a
collision.
When the machine lock is enabled, only the axis motion
is locked. All other program functions are
mally, including the tool
and spindle
used alone or in combination with
This function can
other functions in order to dlscover possible program errors. Probably the mostlypical errors are
errors and
the various toot offset functions.
• Practical Applications
Many of the control features described in
used in conjunction with each other. A
is
Run used in conjunction with the Z
Neglect or the
Auxiliary Functions Lock. By knowing what function are
available, the CNC operator
a
to
needs of the moment There are many areas of equal imporlance on which the CNC operator has to concentrate when
setting up a new
or
Many
lures of the control unit are
to
the operator's
easier. They allow concentration on one or two items at
than (he complexity of the whole program.
in a reasonable
These
have
now is the lime to look at some practical applications.
During the initialization of a new program run, a good
CNC operator will take certain precautions as a maHer of
facL Forexample, the first part of the job will mosllike!y be
tested with a rapid motion set to 25% or 50% of the available rapid rate. This relatively slow setting allows the operator to monitor the integrity of the program processing, as
well as specific details. The details may include items such
as a possibility of insufficient
between
tool
and the material, checking if the
Path looks reasonable, and so on.
The CNC operator will have a number of tasks to perfonn
simultaneously. Some
the Lasks include monitoring the
spindle
feed rate , tool motions, tool changes, coolant, etc. A careful and conscious approach results building the confidence in the integrity of the CNC program. It
may be
second or even the third pan of the job when the
CNC operator starts thinking of the optimization
cutling values, such as
spindle speed and the culting
This optimization will truly reflect the ideal speeds
a particular workpiece under
setup.
A production supervisor should not arbitrarily
an
override selling
than 100%. Many
consider
the CNC program as an unchangeable document They
the attitude that what is wrilten is infallible - which is
not always true. Often, the
operator may
no
other choice bur 10 override the programmed values. What
is mosl imporranl, is the modification
the program that
reflects the optimized cutting conditions.
29
the machine operator finds what values must be
changed in the program itself, the program must edited
to reflect these changes. Not only for the job currently
worked on, but also for
repetition of the job in Ihe fulUre. After all, it should be the goal of every programmer
and CNC operator to run any job at one hundred
efficiency. This efficiency is most likely
as a comoperator and the programmer. A good
bined effort of
CNC programmer will always make the effort to
100% efficiency at
desk and then improve the
even
SYSTEM OPTIONS
Optional features on a
system are like options on a
car. Whal is an option at one dealership, maybe a
feature at another. Marketing
and corporate philosophies have a lot to do with this
Here is a look al some conlrol features Ihal mayor may
nol be
as optional on a
system. BUI
some important disclaimer first:
This handbook covers the subject matter relating
to the majority of control features, regardless of whether they
are sold as a standard or an optional feature ofthe system.
It is up to the user to find out what exact options are installed
on a particular control system.
• Graphic Display
Graphic representation of the tool path on the display
screen is one of
most important, as well as sought after,
control options. Do not confuse (his oplion with any type of
conversational programming, which also uses a ,..,.,."'''.~
tool path interface, In the absence
a computer
programming (CAM), a
display on the conLrol
panel is a major benefit. Whether in monochrome or in
color, the convenience of seeing the 1001 motions before acmaChining is much appreciated by CNC
and
alike.
A typIcal graphics option shows the
axes and
two cursors for zooming. When the tool path is tested, individual tools are distinguished by different colors, if available or different intensity. Rapid motions are represented
by a dashed line lype. cutting motions by a
line
lype. If the graphics function is applied during machining,
the lool motions can
watched on the display screen very helpful
CNC machines
oily
and scratched safety shields.
Upwards or downwards
the display allows for
evaluation of a tool motion
or
detail areas. Many
controls
include actuallOol path simulation, where the
shape of the part and
cuLting 1001 can be set first, then
seen on the screen.
Chapter 5
• In-Process Gauging
During many unattended machining operations, such as
in manufacturing cells or Agile manufacturing, a periodic
checking and adjusting dimensional tolerances of the part
IS imperative.
the cUlling 1001 wears out, or perhaps because
causes, the dimensions may fa!! into the
'out-of-tolerance' zone. Using a
device
a suitable
quite a satprogram, the In-Process Gauging option
isfactory solution. The CNC part program for the
In-Process Gauging option will
'Some quite unique
written
and will
formal features - it will
be using another option of the control system - the Custom
Macros (somt!iimes called the User Macros), which offer
variable lype
I f a company or a CNC machine shop is a user of the InGauging option, there are good chances that other
to the CNC
control options are
installed and
programmer. Some of Ihe most typical options are probing
software, tool life management. macros, etc. This technology goes a lillie too far beyond standard CNC programming, although it is closely related and frequently used.
Companies that already use
numerical control technolwill be well advised to look into these options to recompetitive in their lield,
• Stored Stroke limits
Definition an area on a CNC lathe or a
on a
\0 work within, can be stored
machining center that is
as a control system
sTored stroke limit.
These stored stroke
are designed to
a collimachine tool
sion between the cutting tool and a fixture,
or the part. The area (2D) or the cube (3D) can be defined
as either enabled for
cutler entry or disabled for the cutor, if
ler entry. It can set manually on the
able, by a program input. Some controls allow only one
area or cube to be defined, others allow more.
unit
a
When this option is in effect and the
motion in (he program that takes place within the forbidden
zone, an error condition results and the machining is interrupted. A typical applications may include zones occupied
by a tuilstock, a fixture, a chuck. a rotary table,
even an
unusually shaped part.
•
Drawing Dimensions Input
An option that seems somewhat
is the programming method by using input of
dimensions from
an engineering drawing. The ability to input known coordinates, radii, chamfers and given angles directly from the
drawing makes it an attractive option. This ability is somewhat
by poor program portability. Such an
option must be installed on all
in the shop, in order \0 use the programmed features efficiently.
• Machining Cvcles
Both the milling and the turning controls offer a variety
of machining cycles. Typical machining
for milling
operations are calJedfixed cycles, also known as the canned
cycles. They simplify simple poinl-Io-point machining operations such as drilling, reaming, boring, backboring and
CNC
cycles for face
ing, pocket milling,
patterns, etc.
CNC lathes
have many machining cycles available
to remove material by
roughing, profile finishing, facing, taper cutting, grooving and threading. Fanuc
conlrols call
cycles Multiple Repetitive Cycles.
Allihese
are designed for
programming and
faster dlanges at the machine. They are built in Ihe conlrol
and cannot be changed. Programmer supplies the cutting
by using
approduring the program
priate cycle call command. All the processi ng is done automatically, by the CNC system. Of course, there will always
special programming
that cannol use any cycles
and have to be programmed manually or with the use of an
external computer.
• Cutting Tool Animation
Many of the graphic tool path displays delined earl icr, are
represented by simple lines and arcs. The currenltool posiline or arc endpoinl on
tion is usually the location of
screen. Although this method of displaying the motion of
the CUlling tool graphically is certainly useful, there are two
to il. The
of lhe cutting tool and the
material being removed cannot be seen on the screen and a
1001 path simulation may help a bit. Many modern controls
incorporate a
feature called CUllillg Tool Allima~
lion. If
on the
il shows Ihe blank of the
part, the mounting device and the tool shape. As the program is executed, the
operator has a very accurate visual aid in program proving. Each graphic element is
by a different color, for even a better
blank
the mounting device and
preset for exact proportions and a variety tool shapes can
be stored for repetitive use. This option is a good example
of CAD/CAM-like features built into a stand-alone control
system.
• Connection to External Devices
The CNC computer Caft be connected to an external
usually another computer, Every CNC unit has one or
to
more connectors, specifically designed for
peripheral
The most common
is
RS-232 (EIA standard), designed for communications between two computers. Setting up the connection with external
is a specialized application. The CNC operator
uses such a connection to transfer programs and other seltings between two computers, usually for slorage and
backup purposes.
PROGRAM PLANNING
The development of any CNC program begins with a
very carefully planned process. Such a process starts with
ng drawing (technical print) of the required
part released for production. Before the part is machined.
several
have (0 be considered and carefully evaluated.
The more effort is put inlo
stage of the
program, the
results may be
at the
drawing
The initial part information is not limited to
and the material
- it also
conditions not covered in the drawing,
as pre- and
machining,
grinding allowances,
features, requirements for
hardening, next machine setup, and others. Collecting all
this information provides enough
(0 start planning
the
program.
STEPS IN PROGRAM PLANNING
MACHINE TOOLS fEATURES
The
required in program planning are decided by
the nature of the work. There is no useful fonnula for all
jobs, but some basic
should considered:
No amount
initial information is useful if
CNC
is nOI suitable for
job.
program
nlng, programmer concentrates on a parlieu/ar machine
a particular
Each part has to be
tool,
(he
machine has LO large
to handle the
of the part, the pan should nOl be heavier
than the maximum weight allowed.
control system
must be capable to provide the needed
path,
so on.
o Initial information / Machine tools features
o
Part complexity
o
Manual programming /
.nfTmllr...
programming
o Typical programming procedure
drawing /
CJ
o
data
Methods sheet / Material specifications
o Machining sequence
o
Tooling selection
o
Part
o Technological decisions
o Work sketch and calculations
o Quality considerations in CNC I'IT/'Inflllmrn"nn
steps in the list are suggestions only - a guideline.
be adapted for
job and to the specific conditions the work.
are quite tlexible and should
INITIAL INFORMATION
Most drawings define only
shape and
of the completed part and nonnally do not specify data about the
Initial blank material. For progrnmmi
a good knowledge
of the
is an essential start - mainly in terms of its
size, type, shape, condition, han.lness, etc. The
and
material data are the primary information about the part. At
(his point,
program can be planned.
objective of
such a plan is to use the inilial information and establish the
most efficient method of machinmg. with all
con- mainly part accuracy, productivity, san~ty and
converHcnce.
In most cases, the CNC equipment is already available in
the shop. Very
companies go
buy a new CNC machine just to suit a particular job. Such cases are rather rare
and happen only if
moke economic scnse.
• Machine Type and Size
The most important considerations in
planning
machine, partIcularly
are the type and the size the
ils work
or work area. Other
equally'
machine power rating, spindle speed
number of 1001 stations, 1001 changing system,
accessories. etc. Typically, small CNC mahave higher spindle speeds
lower power
large machines
lower spindle speeds available,
their power
• Control System
The control system is the
of a CNC
Being
familiar wilh all
standard and oplional features availableren all controls is a must. This knowledge allows
use of a variety of
programml
as
machining
subprograms, macros
timesaving features a modern CNC system.
A programmer
not
to physically run a CNC
machine. Yet, the programs will become better and more
with good understanding of the machine and its
control system. Program development
programknowledge of the CNC machine operation.
31
32
Chapter 6
of the main concerns in program plannin o should be
the operator's perception of the
. To a la~ge degree,
such a perception is quite subjective, in (he sense that
operators will express their personal preferences. On
the other hand, every operator appreciates an error-free,
well documented and professionally
part
p.rogram, consistently and one after
A poorly deof
Signed program is disliked by any operator,
personal
PART COMPLEXITY
• Disadvantages
There are some disadvantages associated with manual
program~ing. Perhaps the most common is the length of
reqUIred to actually develop a fully functioning CNC
program. The manual calculations, verifications and other
related activities in manual programming are very time
Other
also very high on the list,
~re a large percentage of errors, a lack of tool path verification, (he difficulty in making
to a
and
many others.
• Advantages
At the
drawing, material and the available CNC
equipment are
the complexity of the
ming task become,s much
How difficult to program the part manually? What are the capabilities of
machines? What are the costs? Many questions have to be
before starting the
Simple progr(lmming jobs may be assigned to a
experienced
or the CNC operator. It makes
sense from
management perspective
it is
a
good way to gain experience.
will
from a computerDifficult or
ized programming
'technologies such as Computer
Aided Design (CAD) and Computer Aided Manufacturing
(CAM) have been a
part of the manufacturing
cess for many years. The cost of a CAD/CAM system is
only a fraction of what il used to be only a few years ago.
small shops now find that the benefits offered bv modern technology are too significant to
ignored.
programming systems are availahle various computers and
can
virtually
job. For a typical machine shop, a
Windows based programming soft ware can very benefiA typical example of this kind of application is the
popular and powerful Masfercam™, from CNC Software, Inc., Tolland,
are
others.
On
positive side, manual part programming does have
qUi,le a few un~atched qualities. Manual programming is
so Intense that It requIres the total involvement the CNC
programmer and yet offers virtually unlimited freedom in
the development of the program structure. Programming
it teaches a
manually does have some disadvantages,
tight discipline
in program development.
It forces the programmer to understand programming techniques to the lasl detail. In fact, many useful skills learned
in manual programming are directly applied to CAD/CAM
programmIng. Programmer
to know what is happening
at all times and why it is happening, Very important is the
tn-depth understanding of every detail during the program
development.
Contrary to many beliefs, a thorough knowledge of manual programming methods is absolutely essential
efficient management of CAD/CAM programming,
J
MANUAL PROGRAMMING
Manual programming (without a computer)
been the
most common method
preparing a
program for
many years. The fatest CNC controls make manual
or
gramming much easier than ever before by using
repetitive machining
variable type programming,
graphic tool motion simulation, standard mathematical input and other time saving features.
manual programming, all calculations are done by hand. with the aid of a
pocket
no
programming i~ used. Programmed data can transferred to the CNC machine via a
cable,
an inexpensive desktop or a laptop computer.
is
and more rellable than other methods,
Short programs can
manually, by keyboard
entry; directly at the machine. A punched tape
to
the popular media of the past but has virtually disappeared
machine shops.
CAD/CAM AND CNC
The nee~ for i
efficiency and accuracy in CNC
programming has been
major reason for development
of a variety of methods that use a computer Lo prepare part
Computer assisted CNC programming has been
around for.many years.
in the form of language based
programming, such as APyrM or Compact IITM. Since the
late 1970's, CAD/CAM has played a significant role by
adding the visual aspect to the programming process. The
acronym CAD/CAM means Computer Aided Design and
Computer Aided Manufacturing. The first three letters
(CAD) cover the area of engineering
drafting.
"' ........ 'u .. '" three
(CAM), cover the area
crized manufacturing, where
programming is only a
sman
whole subject of CAD/CAM covers much
more
just design. drafting and programming. It is a
part of modern
also known as ClM - Computer
Integrated Manufacturing.
In
area of
have
major role for a long
Machine controls have
more sophisticated, incorporating
latest techni,ques of
data
tool path graphics, machining
can now be prepared with the usc
PROGRAM PLANNING
computers, using graphical interface.
is
no
an
even small machine
can afford a
systems are also
programming system in house.
popular because of their flexibility. A typical computerized
programming system
not have to be dedicated only to
programming - all related tasks. often done by the pro""lnr'ln"l'''r can
implemented on the same computer. For
of
example, cuning tool inventory managemenl,
part programs, material information sheets, setup sheets
and tooling sheets, etc. The same computer could also
used for uploading and downloadIng CNC programs.
33
the price, may handle to an absolute
If the control system can handle il, manual programming is the way
to the ultimate control over such a project, when
other
methods may not suitable.
with a well customized and
computerized
system, how can the
program
output be exactly as intended? How can the CNC operator
change any part of the program on the machine, without
knowing its
and
• Integration
The keyword in the acronym CIM is - integration. It
means putting all the elements of manufacturing together
work with them as a single unit and more efficiently.
The main
behind a successful integration is to avoid
duplication. One of the most important rules of using a
CAD/CAM computer software is:
When a drawing is made in a CAD software (such as
AutoCAD), then done again in a CAM software (such as
Mastercam), there is a duplication. Duplication breeds er-
rors. In order to avoid duplication, most of the CAD
tems incorporate a transfer method of the design to the seCAM system to be
for CNC programming.
Typical transfers are achieved through special DXF or
lOES files. The DXF stands for Data Exchange Files or
Drawing
and the IGES abbreviation is a
Specification
short form of Initial Graphics
Once the geometry is transferred from the CAD system to
the CAM system, only the tool path related process is
needed.
a
kind of formatter),
the computer
will prepare a part program, ready to
be loaded directly to the CNC machine.
• future of Manual Programming
It may seem that the manual
is on the
cline. terms of actual use, this is probably true.
il is necessary to keep in perspective that any computerized
technology is
on
already well established melhof manual programming. Manual programming for
CNC machines serves as the source
new technology
- it is (he very
concept on which
computeropens the
programming is
door for developmem of more powerful
and soft~
ware applications.
The manual programming may
somewhat
frequently today and eventually will be used even less - but
knowing it well - really understanding it - is and always
will the key (0 control the power of CAM software.
are some special
computers cannot
everything.
programming projects that a CAM software, regardless of
TYPICAL PROGRAMMING PROCEDURE
Planning a CNC program is no different than any other
- it must
planning - at home, at work, or
in a logical
methodical
The first
sion~ relate to what tasks have to be done and what goals
have to be reached. The other decisions relate to how to
achieve the set goals in an efficient and safe manner. Such a
progressive method not only isolates individual problems
as they develop, it also forces their solution before the next
step can be taken.
foHowing items form a fairly common and logical
sequence of tasks done in CNC programming. The items
are only in a
offered for further
This order may
changed to reflect special conditions or
working habits. Some items may be missing or redundant:
1. Study of initial information (drawing and methods)
2. Material stock (blank) evaluation
3. Machine tool specifications
4. Control system features
5. Sequence of machining operations
6. Tooling selection and arrangement of cutting tools
7. Setup of the part
8. Technological data (speeds, feedrates, etc.)
9. Determination of the tool path
10. Working sketches and mathematical calculations
11. Program writing
preparation for
to CNC
12. Program testing and debugging
13. Program documentation
There is only one
in CNC program planning and that
is the completion
all instructions in the form of a prothat will result in an error-free,
and efficient CNC
machining.
suggested procedures
some
changes for example, should the tooling
selected before or after the pall setup is determined? Can the manual
the
part programming methods
efficiently?
worki sketches necessary? Do not be afraid to modify
any so called ideal procedure either temporarily, for a
given job, QT permanently. to reflect a particular CNC prostyle. Remember, there are ItO ideal procedures.
34
Chapter 6
PART DRAWING
The parl drawing is the single most important document
used in CNC programming. It visually identifies the shape,
dimensions, tolerances,
tinish and many other requirements for the completed item. Drawings of complex
parts often cover many sheets, with different views, details
and sections. The programmer first evaluates all the drawdata first, then isolates Ihose that are relevant for the development of a particular
Unfortunately, many
the actual CNC manufacdrafting methods do not
turing
They reflect the designer's thinking, rather
than the method manufacturing. Such drawings are
erally correct in technical sense, but they are harder to study
by the
and may need to
'interprered'to be
of any
in CNC programming. Typical examples are
of a datum point
methods of applying dimensions,
that can be used as a program reference point and the view
orientation in which the part is drawn. In the CAD/CAM
environment,
traditional
between
design, drafting and CNC programming mUSI be eliminated, Just as it
helps the programmer to understand designer's intentions,
it helps the designer to understand the basics of CNC programming, Both, the designer and the programmer have to
understand
other's methods and find common ground
that makes the whole process of design and manufacturing
,...",,,"',."',.... and
title block supvisions. special instructions, etc. Data in
ply crucial information for CNC programming
can be
used for program documentation to make easier cross
Not all title block information is needed in programming, but may
used for program documentation.
Revision dates in a drawing are associated with the title
block. They are important to the programmer, as they indicate how carrent is the
version. Only the latesl ver"
sian of
part design is important to manufacturing.
• Dimensioning
Dimensions on the part drawing are either in
metric units. Individual dimensions can be
a certain datum point or they can he
from the previous dimension. Often, both types of dimensions are mixed in the same drawing. When writing the
more
to
all conprogram. it
secutive - or incremental dimensions intO datum - or absolute - dimensions. Most CNC programs benefit from drawings using datum, or absolute
Similarly,
when developing a subprogram for tool path translation, an
incremental method of programming may ,be the right
choice - and the choice depends on the application. The
mosl common
for CNC machines
uses the absolute dimensioning method (Figure 6-2),
mainly because of the editing ease within the CNC system.
----
• Title Block
The title block 6- / - is typical to all professional
infordrawings. lts purpose is to collect all
mation related to the particular drawing.
170
a
170
By
,
110 .-
lI
bl
Dr.:
Date:
Chk.:
Drawing number:
App ..
6·1
A title block 8xa'mDIB of an .mn,iflFlF!rinn drawing
and contents of a title block
coman the eype of manufacturing and internal
usually a recl.angular box, positioned in
the corner of the drawing, divided into several
boxes,
The contents of the title block include such items as the pari
name and part number. drawing number, material data, rc-
6-2
Program using ABSOLUTE dimensions
Only one change in the program is necessary
With the absolute system of dimensioning, many program changes can be done by a single modification. Incremental method requires alleast two modifications.
differences between the two dimensioning systcms cnn be
compared in
6-2, using the absolute dimensioning
using the incremental dimenmethod, and in
word incremel1tal is more common in
sioning
CNC. in drafting the equivalent word would be relative.
Both illustrations show the a) figure before revision, and
the b) figure after revision,
PROGRAM PLANNING
35
---,60 ._",......:I
60
al
."
70! ----.--' 40 ---' 60 ---
Figure 6-3
Program using INCREMENTAL dimensions
Two (or more)
in the program are necessary
Fractions
Drawings in English units
contain fractions, A
tional dimension was sometimes used to identify a
importam dimensional tolerances (such as :1:,030 inches from
the nominal
number of digits following (he
mal point often indicated a tolerance (the more digits specified, the
the tolerance range).
methods are
not an ISO standard
are
nO use in programming.
Fractional dimensions have to be changed inlo their decimal equivalents, The number of decimal places in the
is determined by
minimum increment of {he conIroL A dimension of 3-3/4 is
as
and a
dimension of 5-11/64 inches is programmed as 5,1719, its
closest rounding. Many companies have upgraded their
to the ISO system and
to
principles of CNC dimensioning. In this respect, drawings usthe metric units are much more practicaL
Some dimensioning problems are related (0 an improper
designers
use of a CAD software. such as AutoCAD.
do not change the default setting of the number of decimal
dimension ends up with four decimal
places (inches) or three decimal
(metric), This is a
poor practice and should be avoided. The best approach is
to
for all dimensions
require them. and even use Geometric Diflumsioning and
Tolerancing standards (GDT) ,
•
e A drawing dimension specifies a hole as
075+0.00/-0.05 mm. What actual dimension
should appear in the program?
There are some choices. The dimension on the high side
mlly be programmed as X75,0 and X74,95 on the low
of the
A middle value of X74,975 is also a
Each selection is mathematically correct A creative
programmer looks not only for the mathematical points,
but for the technical points as well.
cutting
of a
tool wears out wilh more parts machined. That means the
machine operator has to fine-tune the machined size by using the tool wear
available on most CNC systems,
during machining
is
Such a manual
acceptable. but when done too often, it slows down the production and adds to the overall costs.
A particular programming approach can control the frequency of such manual adjustments to a great
Consider the
mm mentioned
If il is an external diameter, the tool edge wear will cause the actual dimension
during machining to become larger. In the case of an internal diameter, the actual dimension will become smaller as
the CUlling
wears out By programming X74,95 for
the external
(the bottom Iimil) or X75,O for the inlerna] diameter (the top limi!), the wear of the cutting
will move into the tolerance range, rather than away
it The
lool offset adjustment by
machine operfrequently. Another apator may still be required, but
proach is to select the middle
of the tolerance
this method will also
a positive effect but more manual adjustments may
necessary during machining,
•
Surface finish
Precision parts require a certain degree of surface finish
quality, Technical drawing indicates the
finish for
various features (he part
drawings indicate the
in micro inches, where micro inch =, 00000)",
Metric drawings use specifications expressed in microns.
where 1 micron:: 0,001 mm, Symbol for a micron is a
Greek letter )1. Some drawings use symbols - Figure 6-4,
Tolerances
For quality
machining work, most part
have a
range of acceptable deviaLion fTom
the nominal size, within its system of reference,
example, an English
of +,0011-,000
will be different from a mel ric tolerance
+0.1/-0.0 mm. Dimenmu,<;1
sions of this type are usually critical dimensions
be maintained during CNC machining. It may be true thai
CNC operator is ultimately responsible
maintaining
the part
within the tolerances (providing Ihe program
is correct) - but it is equally true, that the CNC programmer
can
the
operatoro's task
Consider the
following example for a CNC lathe:
Figure 6-4
Surface finish marks in a drawing:
English (top) and metric (bottom)
36
6
The most important factors influencing the quality of surface finish are spindle speed,
cutting tool radius
and
amount of material removed. Generally, a larger
cuLter radius and slower
contribute towards finer
surface finishes. The
time will be longer but can often
be
by elimination of any subsequent operations such
as grinding, honing or lapping.
• Drawing Revisions
Another important section
the drawing, often overlooked by CNC programmers, shows the
..... ,,<u,!",'''''' (known as revisions) made on the drawing up to a
date.
or
the designer identifies such changes, usually with both
the previous and the new value exampl~:
REV' • 3 / DIMENSION 5.75 WAS 5. 65
Only the latest
are important to the program development. Make sure the program not only reflects the
current engineering design, but also is identified some
unique way to distinguish it from any previous
versions. Many programmers keep a copy of the part
ing corresponding to the program in the files, thus preventing a possible misunderstanding later.
• Special Instructions
METHODS SHEET
Some companies have a staff qualified manufacturing
for determitechnologists or process planners
of the manufacturing process.
people dcvc\op
a
of machining .
detailing the route of
each part through the manufacturing steps. They allocate
the work to individual machines, develop machining seand setup methods,
tooling, etc. Their
(routing
that
structions arc written in a methods
accompanies the part through all
of manufacturing,
a
is available,
typically in a plastic folder. If
copy should become a part of the documentation. One of
purposes of a methods sheet is to provide
CNC programmer with as much information as possible to shorten
the turnover between programs.
greatest advantage of
a methods sheet in programming is its comprehensive covof all required operations, both CNC
tional, thus offering a
overview the
turing process. A good quality methods sheet will save a lot
of decisions - it is made by a manufacturing
who
specializes in work detailing. The ideal
is
one
recommended manufacturing process
closely matches establlshed part programming methods.
For whatever reason, a large number of CNC machine
shops does not use methods sheets, routing sheets or
lar documentation.
CNC programmer acts as a . . .
as well. Such an environment offers a certain degree of flexibility but demands a large degree of knowledge, skills
responsibility at
same time.
H ..' ' - ' ' - ' ' ' "
Many drawings also include special instructions and
comments that cannot
with the traditional
drafting symbols and are
spelled out mClleoemlenlly, in words. Such instructions are very important for
CNC program planning, as they may significantly influence the
example, an I"ll"mpn!
the part is identified as aground
or diameter.
drawing dimension always shows thejinished
In the
program, this dimension muSI be adjusted for any grinding
allowance necessary - an allowance
by the programmer and written as a special instruction in the proAnother example of a special instruction required in
program
to
machining performed
part
assembly.
example. a certain hole on the drawing
should be drilled and tapped and is dimensioned
same
way as
other hole, but a special instruction indicates the
drilling and tapping must done when
part is
during assembly. Operations relating to such a hole are not
programmed and if any overlook of a small instruction
in unusable pan.
such as this, may
Many drawing instructions use a special pointer called a
Usually it is a line, with an arrow on the
pointing towards
ar~ that it
to. For
a leader
may be pointing to a
with the caption:
~12
- REAM 2 HOLES
is a
has 12 mm
to ream 2 holes with a reamer that
MATERIAL SPECIFICATIONS
Also important consideration in program planning is evaluation of the malerial stock. Typical material is raw and
bar, billet, plate, forging.
etc).
unmachined
Some
may
already premachined, routed from
another machine or operation. It may
solid or hollow,
with a small or a
amount to removed by CNC machining. The
shape of the material
the
setup mounting method. The
of malerial (steel, cast
iron, brass,
will influence not only the
of cultools, but
cutting conditions for machining as well.
• Material Uniformity
Another important consideration, often neglected by
and
alike, is the uniformity material
specifications Within a particular batch or from one batch to
another. For
a ' ordered
two suppliers La
slightly different
PROGRAM PLANNING
37
even
A similar example is a macut into sjngl~ pieces on a saw, where the length of
varies beyond an acceptable range. This inconsistency between blank parts makes programming more
difficult and lime consuming. It also creates potentially unmachining conuiLions. If
problems are encounthe best planning
is to place emphasis on
safety than on
time. At worst, there
will some air Ctming or
needed cutting feed,
but no cuts will be too heavy
to handle.
approach is to
non-uniform material
groups and make
programs for each group,
properly identified. The
method is to cover all known
predictable inconsistencies
program control, for
using the block skip function.
• Machinability Rating
IS
important aspect of
machinability. Charts with SUj;(g<::ste:a
feeds for
major tooling
most common
in programming, parwhen an unknown
is used, The suggested
values are a
starting point, and can be optimized later,
when the material properties are
known.
is given in units
terms surface feet
or CS), periphper minute; constant sUlface speed
eml
or just surface speed are
For metric
meters per mindesignation of the machinability
ute (m/min) are used. In both cases,
spindle speed
(r/min)
lOol diameter (for a
or a given part
a lathe) is calculated,
common formuI-<n,,,,I1<", system, the spindle
can be calcuper minute (r/min):
Machinability rating in the English
per minute (ftimin). Often
MACHINING SEQUENCE
Machining sequence
Technical skill
help in program
some common sense
sequence of
proach is equally
must have a logical
example. drilling must
programmed before
roughing operations before
second, etc. Within this
finishing. first operation
order, further
of the order of individual
motions is required for a particular tooL For example,
in turning, a face cut may be
on the part first,
then roughing all material on
wili take place.
method is to program a roughing
for the
meter, then face and
with
of the diaa center drill
for some
but in another
a
drill may be a
on which method is
CNC programming assignment has to be considered individually, based
on Ihe criteria of safety and
approach for
machining seis the evaluation of all
In gen"'''~'''r''''''''' should be planned in
a
that the cutonce selected, wi1l do as much
as possible,
a tool
On most CNC
less time is
np.p,(1p('l for positioning the tool than for a tool change. Another
is in benefits
by programming
all heavy
first, then the
semifinishing or
finishing operations. It may mean an extra tool change or
two, but this method minimizes any shift of the material in
the holding
while machining. Another important
factor is the current position of a tool when a
operation is completed. For example, when
a pattern
holes in
of 1
the next tool
as a boring
bar, reamer or a tap) should be
order of
4-3-2-1 to
Figure 6-5.
T02::: Drill
Hole4
calculation, the
For a
Hole 4
Figure 6-5
Il3r' where ...
r/min
12
1000
fVmin
= Revolutions per minute (spindle
=
meters to millimeters
= Peripheral speed in feet per minute
mlmin = Peripheral speed in meters per minute
value of 3.141593 ....
n: (pi) =
D
""''''"1''''!'1' may have to be
feet to inches
(milling) or
(turning) - in inches or mm
verse
tools and the setup method.
not be practical in subprograms.
Program planning is not an independent
dividual
- it is a very interdependent and
cally coherent approach to achieve a certain
re-
6
TOOLING SELECTION
tool holders and cutting
is another important
in planning a CNC
category of tooling covers n lot more than Ihe cutting lools and 1001 holders
- it includes an extensive line of
including nufixlures, chucks, indexing tables, clamps,
Cutting lools remany other holding
attention, due to
variety available
In
selec-
cutting tool itself is
tion. It should be selected by two
o
Efficiency of usage
Q
Safety in operation
Many supervisors responsible
CNC programming try
to make the existing tooling work at all times. Often they
the fact that a suitable new lool may do the job faster
and more economically, A
knowledge of tooling
and its applications is a
technical profession - the
should know
principles of cutcases, a tooling .."' ......&>~'~M
tool applications.
tive may provide additional
assistance.
of usage is also a
The arrangement of
subject of serious
in CNC program planning.
On CNC lathes, each
tool is assigned to a
turret station, making sure
disTribution of lools is
anced between short and
tools (such as short
tools versus long
This is important for
of a possible
during CUlling or tool
Another concern should be the order in which
particularly for machines that
indexing. Mos:t
where the
All tool offset
and other program
be documented in a
known as the looling sheel.
a document serves as a guide to the operator
job
resetup. It should include at least the basic
lating to the
tool. For example, the documentation
may include
its length and diameter,
the number
and offset
and
feed selected
and other relevant information.
PART SETUP
Another
in program planning
to
setup - how to mount the raw or premachined material,
how
what supponing tools and devices should
many operations are required to complete as
machining sequences as possible, where (0 select a
etc.
is necessary and it should be done
are designed to
more productive. Mulfispmdle '''''~'''III'''~
can handle two or more parts at the same
tures, such as barfeeder for a lathe, an
or dual setup on the table,
added as well.
• Setup Sheet
At this
of program planning, once the setup is demaking a setup sheet is a good
A setup sheet
can
a simple sketch, designed mostly
the use at the
machine, that shows the part orientation when mounted in a
tool offset numbers
by the program,
idenlificaof course, all
Other information in
setup sheet
to some
establ ished
planning stages of
of clamps, bored jaws 1"I ...n"' ... <"
Setup sheet and tooling
can
source of Information. Most ,"", ..,,,,.~h_
own various versions.
TECHNOLOGICAL DECISIONS
The next stage of CNC "',." ...... ,,'""
lection of spindle speeds,
application, etc. All
tors will have their Influence.
of spindle speeds is
of the cutter and
speeds and feeds. the
help determine what amount
can be removed
~afely, elc. Other factors
(he program design
mclude tool extensions, setup rigidity, culling tool material
and its condition. Not to be overlooked is the proper selection of cutting fluids and lubricants - they, too, are
1ant for the part quality.
• Cutter
The key factor
understanding this principle is to visualize the tool ",,,,,,\.1,,, not (he machine mOllon.
most
noticeable
programming a machining
to a lathe is the cutter rotation comIn both cases, the
in terms of the cutter .nn,lJ111'U
PLANNING
39
require more than
roughing and
is to isolate the area that
tool do both operations? Can all
Is the lool wear a problem?
the surface finish
achieved? When programming ooncutting rapid motions, take the same care as with
motions. A particular
should be lO minimize
tool motions and ensure
'-UlIklll'"
Figure 6-6
Contouring too! path motion - as intended (lathe or miff)
The tool path
all profiling tools has to
into consideration the cutter radius. either by
equidistant path
center of the radius or
ler radius offset.
machines for milling and
provided with
linear interpolation and
lar interpolation, all as
features. To
more
complex paths,
as a helical milling motion, a special
option has to
in the control unit Two
of
typical tool
o
Point-to-paint
81so called
Positioning
o
Continuous
a/so called
Contouring
a point location operations, such
as drilling,
and similar operations; conrinuous path generates a profile (contour).
case,
the programmed data
to the po~ition of the culter
when a certain
is
This position is called
the tool
6-7.
• Machine Power Rating
Machine tools are
power. Heavy cuts require more power than
cuts, A depth or width of a cut
that is too large can
tool and stall the machine.
Such cases are 1I1"1<~f"f"f'nl
must be prevented, The
CNC machine specifications
the power rating of the
motor at the machine
rating is in kW (kilowans) or HP (horsepower). Formulas are available for
power ratings, calculating
removal rate, tool wear
faclors, etc. Useful is
ofkWandHP
on I HP = 550 foot-pounds
second):
1 kW= 1.341 HP
of
in
can be comis not always
in everyday programming.
experience is often a bener teacher than formulas.
• Coolants and lubricants
When the lool contacts the
of Lime, a great amount of
overheated. becomes
possibilities. a
1
(\End
T
r"
-i:-- ,6
/.
for an extended peM.!,;;.l''vU''''vIJ. The cutand may break. To
must be used.
Water soluble oil is the most common coolant. A propcoolant dissipates
the cUlting edge
it
acts as a lubricant
of lubricaremoval easier.
lion is to reduce friction and make the
flood of the coolant should
at
cutting edge,
with a
pipe or through a coolant
in the tool.
6-7
Contouring too! path motion with tdefltifil~d contour change points
start and end positions
profile are identified
and so are (he positions fQr
contour change. Each tarposition is called the contour change point, which has
to be cnIcuiated. The order of
locutions in the program is very important. That means the tool position] is
the target position commencing at the Start point, position
2 is the target position beginning at point I, position 3 is the
from point 2 and so on, until the End
is
.-.,.,,,,,,,., If the contour is
be in X
Y axes. In turning,
Z axes.
operator is responsible for a """""VI"
the machine.
coolant should
r'f'r'f'lIT,m,f'n(lp.t1 proportions. Water
to preserve the
CNC n"I"\Or~lmYrlpr
not. Ceramic
nn,r"'CfIl'-Jl'(f dry, without a
cast
flood coolant, but air blast or oil mist
may be allowed.
coolant functions vary between machines. so check the machine reference
details.
40
Chapter 6
• Identification Methods
The
of cUlling fluids
outweigh their inconveniences. CUHing
are often messy, the cutting edge
cannot
seen,
may
wet and
old
all problems recoolant smells.
proper
lated to coolants can tie controlled.
is when to turn the
A coolant related programming
coolant on in the
As the coolant function MOS
only turns on tbe pump motor,
sure the coolant actually reaches the tool edge
contact with work. Programming the coolant on
is better than late.
A
sketch can be done directly in the drawing
or on paper, Every
is associated with mathematical
calculations. Using color
or point numbering as
identification methods offers
and
organization. Rather (han writing coordinates at
contour change
drawing, use point reference numbers and crepain! in
ate a
coordinate sheet fonn
numbers, as illustrated in Figure
Position I
X axis
Yaxis
Z axis
WORK SKETCH AND CALCULATIONS
Manually
progTams require some mathematical
calculations.
part of
preparation intimidates
programmers but is a necessary
Many
contours will require more calculations, but not more complex calculations. Almost any math problem in CNC
gramming can be solved by the use of
algebra
and trigonometry. Advanced
of mathematics - anageometry, spherical trigonometry, calculus, surface
calculations, etc. - are required for programming complex
molds,
similar
In such cases, a CAD/CAM
system is necessary.
6-8
Coordinate
- blank form Ino data)
Such (\ sheet can be used for milling or turning, by filling
only the
icable
The aim is to develop a consistent programming style from one program to another.
Fill-in all values, even those that do not
A compleled coordinate sheet is a
reference
6-9,
Lriangle can
calThose who can
a right
of the
culations for almost any CNC program. At
handbook is an
of some common math problems.
When working with more difficult contours, it is often not
the solution i{selfthat is
it is the ability to arrive at
the solution, The
must have the ability Lo see
exactly what triangle
to be
It is not
to
do
intermediate calculations before the required copoint can be established.
any lype often benefit from a pictorial
Calculations
representation. Such calculations usually need a working
should
sketch.
sketch can done by
in an approximate
Larger sketch scales are
to
work with. Scaling
sketch has one great advantage - you
can immediately see rhe
dimensions
the others, the relationship
should be smaller or larger
of individual elements, the ~hape of an extremely small
tail, etc. However,
you should never
use the sketch for:
er use a scaled sketch to
Scaling a sketch is a
and unprofessional
that creates more problems than it
ness or incompetence.
Coordinate sheet example - filled form for milling tool path
QUALITY IN CNC PROGRAMMING
An important consideration in
is a perapproach and attitudes,
attitudes
a significant influence on the program development. Ask yourself
some questions. Are you attentive to detail, well
Can a
be improved, is it safe, it
cient?
program quality is more than writing an error
program.
complexity is only related to your
knowledge
and wilr
to solve problems. It
should be a
goa! to
a program
is the
Set your standards high!
program
PART PROGRAM STRUCTURE
A
program is composed of a series of sequentiaJ instructions related to
machining of a parI. Each
tion is specified in a format the CNC system can accept,
Each·
must also conform to
terpret and
the machine tool specifications. This input method of a procan be defined as an arrangement of
machining
formal
the CNC
related inSlrUCliolls. written in
tool.
and aimed at a particular
have a different format. bUI most are
differences
among
manufacturers, even those
same control
This is common,
plac.e upon the
demands individual machine
control manufacturer 10 accommodate many original
machine
features. Such variations are usually minor but
programming.
BASIC PROGRAMMING TERMS
field of CNC
its own terminology and
terms and its jargon. It has its own abbreviations
expressions Ihal only the people in the. field lmderstand. CNC
programming is only a
of the
'zed
machining and it has a
The
majority of them
the program.
There are fOllr
terms used in
They appear in professional
books,
lUres and so on. These words are the key to
the
CNC
Word
....
Program
A character is the smallest unit of CNC program. It can
have one of
o Digit
o
Symbol
available for use in a program
are used in two modes - one
for integer values
a
point),
for real
(numbers with a decimal
positive or negative values.
Numbers can
controls,
numbers can
with or without the decimal pOint. Numbers applied in either mode can only be entered within the range that is allowed by the control system.
Letters
The 26lelters
English alphahet are 1)11 available for
programming, at leasl in theory. Most control
letters
reject others. For example. a
accept only
CNC la(he control will
the letter as
Y axis is
unique to milling
(milling machines and machining centers). Capital letters are normal designation in
programming, but some controls accept low case
ters with the same meaning as their
case equivalent.
If in doubt, use CAPITAL letters only!
Svmbols
Several symbols are used for programming. in addition (0
the digits
letters. The most common symbols are the
decimal point, minus
percent sign, parenthesis and
options.
• Word
• Character
Letter
There are ten digits, 0 10
to create numbers. The
others, depending on the
Each term is very common
important in
programming
deserves
own detailed explanation.
o
Digits
Characters are combined into meaningful words. This
combination of digits,
and symbols IS
led the
alpha-/wmerical program input.
A program word is a combination of alpha-numerical
creating a single
to the
sys-
tem. Normally, each word begins with a
letter that is
followed by a number representing a
code or the
axes position, feevalue. Typical words indicate
speed. preparatory
misceLlaneous ftmelions and many Olhcr definitions .
• Block
Just like the word is
as a single instruclion to
block is used as a multiple instruction. A
the control
consists individin a logical
a sequence
or simply a block - is composed one or several words and each word is composed
or two or more
41
42
Chapter 7
In the control system,
must be
allOlhers.
iOlhe MDI (Manual
II/pur) mode al the control,
block
(0 end with a
cial End-Of Block code (symbol), This
is
as
EOB on the control panel. When preparing the program on
a computer, (he EHler key on the keyboard will terminate
the block
the same result (similar to the old Carriage
on typewrirers). When writing a program on paper
each
block should occupy only a single line
on
paper.
program block contains a series of single instructions that are executed together.
• Program
The parI program structure varies
different controls,
but
logical approach
not
one control
to
A CNC program usually
with a program
number or similar identification, followed by the blocks
Instructions in a logical order.
program ends with a
SlOp code or a program termination symbol,
as the
percent sigll %. Internal clocumentation and
(he operator
be placed in strategic places wi
The
format has evolved
cantly during the
formats
emerged.
PROGRAMMING FORMATS
the early days of
control, three formalS
had become significant in their time. They are listed in the
order of their original introduction:
NC only no decimal
c
6 IF
Words
F2 7 5'. 0'
N15,
011
Block
N 5 GO: 1~y - '6 ~~~_L-"!..~_~_ 2J.!' 5 . ~_O:
Figure 7·'
Typical word address programming format
The
!cHer in
of the word and mllst always
is correct,
are allowed wlthill a
the word, meaning
block
written
is no\. No spaces
characters.)
but
are only allowed before
[he
numerical assignment. This
varies greatly and
on the preceding <1UlHC;~.:>.
It may represent a sequence number N, a n ...""1"I" . ."'I," .... '
mand
a
function M, an
number D or H. a coordinate word
Y or the feed rate
function F, the spindle function S, the tool function etc.
one word is a series characters (at least two) that
define a single instruction to
control
and the machine.
above
typical
have the following meaning in a
o
Tab
o
Fixed
NC only· no decimal point
G01
PreparaJOI)! comml1J1ti
o
Word Address Format
NC or eNC - decimal point
IDO
D2S
Miscellalleous funCTion
Offiel nwnber selecfion mills
XS.75
Coordinale word
mos
Sequence Illlmher(block Illunber)
HOI
YO
Tool length
92500
SpiJuUe speedjuJlctioJl
z-s .14
CoordflllJJe word - Jleg(llive value
F12.0
Feedmlejunction
Tool funclioll . kl1hes
TooljilJlClioll- mills
Format
Only the very' early control
use the tab sequential or jixed formats. Both of them disappeared in the early
1970's and arc now
They have been replaced by
the much more convenient Word Address Formal.
WORD ADDRESS FORMAT
The word address formal is
on a combination of
one JeHer and one or more digits - Figure 7-1.
In some applications, such a combination can be
mented by a symbol,' such as a minus
or a
point. Each teller,
or symbol represents one character
in the
and Ihe control memory. This unique alcreates l) word, where the letter
the address, lowed
numerical
with or without
symbols. The word address
\0 a specitic register of
the
memory. Some
arc:
GOI M30 D2S
Z-S.14 F12.0
XS.75
TOSOS
NiOS HOI
T05 /MOl
YO S2500
B180.0
TOSOS
TOS
/MO 1
value
IIwnber
CoordiJlaJe word· zero l/aJue
",:!block skip symbol
B180.0
Individual
arc instructions grouped together to
form sequences of programming code. Each
will process a
of instructions simullaneously,
unit
a sequence block or simply a block. The
blocks arranged in a logical
that is required to machine a complete part or a complete operation is the part
program
known as a
program.
PART PROGRAM STRUCTURE
43
The next block
position
a rapid tool motion to (he
X 13.0Y4.6, with a coolant turned on:
N25 G90 GOO Xl3.0 Y4.6 MOS
t6f' where ...
N25
G90
GOO
X13.Q Y4.S
MOB
Sequence or block number
Absolute mode
motion mode
Coordinate location
ON function
Address X accepts positive or negative data with the maximum
of five digits in front of a decimal point and three digits
maximum behind the deCImal point - decimal point is allowed.
The
of a decimal point in the notation means the
decimal point is not used; the absence of a plus
sign in
the notalion means that the
value cannot be negative - a lack
means a positive value
implication.
These samples format notalion explain the shorthand:
G2
Two digits maximum, no decimal point or sign
N5
digits maximum, no decimal point or sign
Five digits maximum, no decimal point or
The control will process anyone block as a complete unit
- never partially. Most controls
in a block, as long as the block
a random word order
lS
first
fORMAT NOTATION
Each word can only
written in a specific
The
number of digits allowed In a word, depending on
address and maximum number of decimal places, is set by the
control manufacturer. No! all
can be
Only
ters with an assigned meaning can be programmed, except
in a comment. Symbols can be used in only some words,
and their position in
word is
Some
are
in custom macros. Control limitations are imporused
tant. Symbols supplement the
and letfers and provide
with an additional
Typical
symbols are
sign, decimal point,
a few others. All symbols are listed in a
• Short Forms
Control manufacturers often specify the input format in
an abbreviated
- Figure 7-2.
X ± 5
F3.2 Five digits maximum,
digits maximum in front of
the decimal point, two digits maximum behind the
decimal point,
point is
no sign is used
Be careful when evaluating the shorthand notations from
a manual. There are no industry standards and not all conmanufacLUrers use the same methods, so the
the short forms may vary significantly.
list
dresses,
format
and description is listed in the
notations based on a
following tables. They
typical Fanuc control system.
• Milling System Format
The
description
for
pending on the input units. The table below lists
formal descriptions (metric format is in parenthesis, applicable). Listed are format notations for milling units. The
column is the format
first column is the address, the
notation and
third column is a description:
Address Notation
--
Number of digits
decimal pOint
--
Decimal paint allowed
_---.-
-----..
A+5.3
degrees·
B
8+5.3
Rotary or Indexing axis - unit is
- used about the Y axis
0
02
Cutter radius offset number
(sometimes uses address H)
F
F5.3
Feedrate runction - may vary
Number of digits
decimal point
G
Positive or negative
value possible
H
number (tool position and/or
1001 length
Described address
1+4.4
(1+5.3)
Figure 7-2
Word address format notation - X axis format in metric mode shown
The full
description
each
would
unnecessarily too long. Consider the following complete
nnd not abbreviated description of the address X· as a coorin (he metric system:
dinate
that is
Rotary or
A
3
4I·-iII-iII-4I-e
Description
Arc center modifier for X axis
Shift amount in fixed
(X)
Corner vector selection for
X axis (old type of controls)
Arc center modifier for Y axis
J
J+4.4
(J+5.3)
Shift amount in fixed cycles
Corner vector selection for
Y axis
type of controls)
7
Notation
Description
,,~,"~,~ ~"""~"~~'"
K
K+4.4
(K+S.3)
Arc center modifier for Z axis
D
Fixed cycle repetition count
Subprogram repetition COUnt
L
M
"
M2
Program number (EIA)
Number of divisions in G73
044
Depth of Cul in
I and
Relief amount in G74 and G75
Depth of first thread in G76
(053)
E2.6
Precision feedrate for '''p,>",....~
F
F2.6
Feedrale function
G
G2
Preparatory commands
Miscellaneous function
Block number or sequence number
N
04
or (:4 for ISO)
P4
p
Subprogram number call
Custom macro number call
1+4.4
(1+5.3)
Dwell time in milliseconds
Arc center modifier for Z axis
Taper height in Z for cycles
Z axis relief in G73
K
Direction of chamfering
Motion amount in Z in G75
Thread depth in G76
Depth of peck in fixed cycles
Q
in fixed cycles
Arc radius designation
s
S5
Spindle
T
14
Tool function
L
L4
Subprogram repetition count
M
M2
Miscellaneous function
N
N5
Block number or sequence number
o
04
Program number (ErA)
or (:4 for ISO)
in r/min
Subprogram number call
Custom macro number call
Offset number with G I0
p
-----ooi
X axis coordinate value
designation
y
Y+4.4
(Y+5.3)
z
Z+4.4
IZ+5.3}
conds
value
u
• Turning System ............. ,'+
Ihis one is for lalhe systems.
Similar chart as for
same
are included only
A number of definltions are
the met~
for convenience. Notation is in
to the address.
ric notation is in parenthesis, if
Address
Notation
A
A3
c
(C I 5.3)
C+4.4
Direction of
Motion amount in X in G74
G73 and G83
x
X axis
Arc center modifier
Taper height in X for
X axis relief in G73
Work offset number - used with G 10
Block number in main program when
used with M99
R
may vary
w
x
Description
input
Chamfer for direct
input
z
axis
US.3
Dwell function with G04
W+4.4
(W+S.3)
Incremental value in Z axis
Stock allowance in Z axis
X+4.4
(X+5.J)
Absolute value in X axis
X5.J
Dwell function with G04
PART PROG RAM
45
• Multiple Word Addresses
One
that is
in both
dance different meanings for some
This is a
necessary feature of a word address format. After all, there
are only 26
in the English
but more than
that number of commands and functions. As new contTol
features are added, even more variations may be necessary.
Some
the addresses
an established meaning
(for example, X, Y and Z are coordinate
that giving
would be confusing. Many
them an additional
ters, on the other
are not used very often and a multimeaning for
is quite
(addresses I, J, K,
for example). In addition, the meaning of
varIes
the milling and turning systems.
The
system has to have sam!; means of accepting
a particular word with a precisely defined meaning in the
In most cases, the preparatory command G will
the
at other times it will be the
or a setting of
table lists
symbols are
only with
custom macro option. These symbols cannot
used in
s(andard programming, as they would cause an error. Typical standard symbols are found on the computer keyboard.
Crrl,
and All character combinations are not allowed.
• Plus and Minus Sign
One of the most common
- plus or
can be either
or negative.
convenience, virtually all
systems allow for an omission of
for all
values. This
IS
positive
the control
Positive
lerm i nrlicating an MS\lmed positive value, if no
grammed in a word:
X+125.0
parameters.
must always be programmed. If the
(in this case the tool position):
In addition to the basic symbols,
symbols for
applic(ltions.
scribes all symbols available on the
X-12S.0
Xl2S.0
X+12S.0
Comment
Description
X125.0
""''','''ES, the number becomes positive, with an
SYMBOLS IN PROGRAMMING
Symbol
is {he same as
Fractional
Negative value
Posimte value
Positive value (-+- sign is ignored)
Symbols supplement the
and digits and are an integral part the program structure.
of a number
PROGRAM HEADER
Positive value or
addition sign in Fanuc macros
*
Minus sign
Negative value or
subtraction
in Fanuc macros
Multiplication
Multiplication
in
Fanllc macros
Block skip function symbol or
divisioll sign in Fanuc macros
/
Comments or messages
providing
are enclosed in
of inlernal documentation is
to both the programmer and
operator. A series of comments at the
top is defined as the program
where
lures are identified.
next
sample of items that may be used in
(FILE m:ME ••.•••.••..••...••••••••• 01234. NC)
(LAST VERSION DATE ................ 07-DEC-Ol)
VERSION TIME •••••...•••••••••• ,. 19: 43)
(PROGRAMMER ...................... PETER
(MACHINE ••••••••.••..••••••••••••• OKK - VMC)
(CONTROL •••••••••••.•••••••••••••• F.ANOC 15M)
!I
;1 SelmiCI)lon
I
#
I Sharp sign
Variable definition or call in Fan
macros
Equality in Fanuc macros
(UNITS ••••••.•••.•••.••..••••.••••...
(JOB NUMBER •••••••••••••••••••••••••••• 4321)
(OPERATION ••.•••••••••••.••.. DRILL-BORE-TAP)
(STOCK MATERIAL ...•............ H.R.S. PLATE)
SIZE •••••••••••••••••••• 8 X 6 X
".-,J"'"......... ZERO ••••••••••...••• XO - LEFT
(
YO - BOTT EDGE)
(
ZO - TOP FACE )
(STATUS • • • • . • • • • • • • • • • • . • • • • • •• NOT VERIFIED)
46
Chapter 7
Within the program, each tool
identified as well.
the X
change
Y axes. If Ihe absolute position is unknown,
block to the incremental verSlon:
(*** T03 - 1/4-20 PLUG TAP ***)
N88 G91 G28 XO YO
Other comments and
to the operator can be
added La the program as required.
If a 1001 has 10
repeated, make sure not 10 include the
1001 change block for the current tool. Many CNC systems
TYPICAL PROGRAM STRUCTURE
Although iL may be a bit early to show a complete program, it wiH do no harm to look at a typical program structure. Developing a
structure is absolutely essential it is going to be
lime. Each block of the
program is identified with a comment
Note - Program blocks use only sample block numbers.
Blocks in parentheses are not required for fixed cycles. The
XY value in the block N88 should be
current position
00701
MAX 15 CHARS)
is
a machine with
The program structure
random tool selection mode
a typical control system,
with some minor changes to be expected, Study
flow of
the program, rather than its exact contents. Note the
tiveness of blocks for
lool and
note the addition of
a blank line (empty block) between individual
easier orientation in the program.
(PROGRAM NUMBER AND IDl
(BRIEF PROGRAM DESCRIPTION)
(PROGRAMMER AND DATE OF LAST REVISION)
(BLANK LINE)
(UNITS SETTING IN A SEPARATE BLOCK)
(INITIAL SETTINGS AND CANCELLATIONS)
(TOOL TOl INTO ~TING POSITION)
(TOl INTO SPINDLE)
(TOl RESTART BLOCK - T02 INTO WAITmG POSITION)
(TOOL LG OFFSET - CL.E.AR ABOVE WORK - COOLANT ON)
(FEED TO Z DEPTH IF NOT A cYCLE)
(SAMPLE PROGRAM STRUCTURE)
SMID - 07-DEC-01}
N1 G20
N2 G17 G40 GSO G49
N3 T01
N4 MOG
N5 GSO G54 GOO X.• Y.• S .• MOl T02
NG G43 Z2.0 H01 MOB
(N? GOI Z-.. F •. )
(---
will
an alarm if the 1001 change command cannot
find
tool in the
the following program example, the lOa! repeat blocks will be NS, N38 and N67.
CUTTING MOTIONS WITH TOOL TOl ----)
N33 GOO GaO Z2.0 MOS
N34 G2S Z2.0 MOS
(CLEAR ABOVE PART - COOLANT OFF)
(HOME IN Z ONLY-SPINDLE OFF)
(OPTIONAL STOP)
N3S MOl
(-- BLANK LINE --)
(TOOL T02 INTO WAITIN'G POSITION - CHECK ONLY)
(T02 INTO SPINDLE)
(T02 RESTART BLOCK - T03 INTO WAITmG POSITION)
(TOOL LG OFFSE.'T - CLEAR ABOVE WORK - COOLANT ON)
TO Z DEPTH IF NOT A
N36 T02
N37 M06
N38 G90 G54 GOO X.. Y.. S .. MO) T03
N39 G43 Z2.0 H02 MOB
(N40 GOl Z- •• F •• )
(-- - CUTTING MOTIONS WITH TOOL TOA
---)
N62 GOO GSO Z2.0 M09
N63 G2B Z2.0 MOS
N64 MOl
N6S T03
N66 M06
,
N67 G90 G54 GOO X •• Y •• S .• M03 TOl
N6S G43 Z2.0 H03 MOS
(N69 G01 Z- .• F .. )
(CLEAR ABOVE PART - COOLANT OFF)
(HOME IN Z ONLY - SPINDLE OFF)
{OPTIONAL STOP}
(-- BLANK LINE --)
(TOOL T03 INTO WAITIN'G POSITION - CHECK ONLY)
(T03 INTO SPINDLE)
(T03 RESTART BLOCK - TOl INTO WAITING POSITION)
(TOOL LG OFFSET
CLEAR ABOVE WORK - COOLANT ON)
(FEED TO Z DEPTH IF NOT A CYCLE)
(- -- CUTTING MOTIONS WITH TOOL TO) ----}
Na6 GOO GSO Z2.0 M09
NB7 G28 Z2.0 MOS
NBS G2S X •. Y ..
Na9 M30
%
(CLEAR ABOVE PART ~ COOLANT OFF)
(HOME IN' Z ONLY - SPINDLE OFF)
(HOME IN XY ONLY)
(END OF PROGRAM)
(STOP CODE - END OF FILE TR.1\NSFER)
PREPARATORY COMMANDS
The program address G identities a preparClfory command, often called the G code. This address has one and
only objective - that is to
or to prepare the control
system to a certain desired condition, or (0 a certain mode
or a state of operation.
example, the address GOO prefor
machine tool, the address
sets a rapid motion
G81
the drilling cycle. etc.
term preparatory
command indicates meaning a G code will prepare the
control to accept the programming instructions fol/.owing
the G
in a specific way.
C Example C:
N3 G90 GOO
N4
NS •••
N6
N7 X13.0 YlO.O
C Example 0:
N2 G90
DESCRIPTION AND PURPOSE
N3
GOO
N4 , ••
NS .••
A one block example will illustrate the purpose of the
commands in the following program entry:
N7 X13. 0 Y10.O
a
look at this block shows that the coordinates X J3.0Y 10.0 relate to the erul position of
cutting
tool, when the block
is executed (i.e., processed by Ihe
control). The block does no! indicate whether the coordinates are in the Clbsohl{e or the
mode. It
not
whether the values are in
English or the
metric units. Neither it indicates whether the motion to this
specified target position is a rapid motion or a linear motion. If a look at the block cannot
the
of
the block contents, neither can Ihe control system. The supplied information in such a block is incompleTe, therefore
unusable by itself. Some additional
for the
block are required.
in order to make the block N7 a tool destiFor
nation in a rapid mode using absolute dimensions, all these
instructions - or commands - must be specified before
block or within
block:
C Example A :
N7 G90 GOO X13.0 Y10.O
C Example B.
N3 G90
N4
NS
N6
N7 GOO X13.0 Y10.O
N6 ••.
N7 X13.0 YlO.O
All four examples have the same machining result, providing that there is no change of allY G code mode between
blocks N4 and N6 in the examples B, C and D.
Modal and non-modal
will described shortly.
Each conlrol
has
own list available G
Many G codes are very common and can be found on virtually all controls. others are unique to the particular control
even the machine tooL Because of the nature of
machining applications. the
of lypical G codes Will
different for the milling systems and Ihe turning systems.
The same applies for other types of machines. Each group
G codes must
kept "pn,"'r~IP
Check machine documentation for available G codes!
APPLICATIONS FOR MILLING
The G code table on the next page is a considerably
tailed list of the most common preparatory commands
for programming CNC milling
and CNC machining centers. The listed G codes may not be applicable
to a particular machine and control system, so consult the
machine
control
manual to make sure. Some
G codes listed are a
option that must available on
the machine and in the control system.
47
Chapter 8
G code
G code
GOO
Rapid positioning
GOl
Li near interpolation
G02
Circular intcrpolallon clockwise
G03
Circular interpolation counterclockwise
Local coordinate
Work coordinme
GlO
G55
Work coordinate
G56
Work coordinate offset 3
G57
Work coordinale offset 4
G58
Work coordinate offset 5
Gll
Data Seni ng mode cancel
G59
G15
Polar Coordinate Command cancel
GSO
G16
Polar Coordinate Command
G61
G17
G62
Automatic comer override mode
G18
G63
Tappi ng mode
G19
G64
CUlling mode
G65
Custom macro call
G20
English units or input
G66
G21
G22
check ON
G67
G23
Stored stroke check OFF
G68
G25
Spindle
fluctuation detection ON
G69
G26
Spindle
fluctuation detection OFF
G73
G27
Machine zero position check
G74
Lert hand threading cycle
G76
Fine
GSO
Fixed cycle cancel
2)
G31
Skip function
G40
Culler radius compensation cancel
compensation -
eep hole drilling cycle)
decrease
compensation - double increase
G48
G49
Tool length offset cancel
Scoling funclion cancel
G98
runction
G99
Return 10 R level in a fixed
PREPARATORY COMMANDS
49
G code
Description
APPLICATIONS FOR TURNING
Fanuc lathe controls use three G code group Lypes - A, B
Type A is
most common; in this handbook,
all examples and explanations are
A group, including
Types A
table below. Only one type can set at a
~nd B. can be sel by a control
but lype C
IS optIOnal. Generally, mOSl
codes arc identical, only a
few are different In the A and B types. More details on the
G code
is listed at the
of this
G54
and
Description
G code
Work coordinate offset 2
G56
Work coordinate offset 3
G57
Work coordinate offset 4
Work coordinate offset 5
G59
Work coordinate offset 6
G61
stop mode
GOO
Rapid posilioning
G62
GOl
Linear illterpolation
G64
Circular
Work coordinate offset I
clockwise
G03
Circular interpolation counterclockwise
G04
Dwell (as a separate block)
G09
Exact Stop check - one block only
Gl0
Programmable data input
Gll
Data Selling mode cancel
Custom macro modal call
for double turrets cancel
Setting)
- Z axis direction
units of input
G23
Stored stroke check
G25
Spindle speed fluctuation detection ON
G26
s
Spindle
nuctuation detection OFF
(Group type A)
Machine zero posilion check
G28
Machine zero return (reference poinl I)
G90
Absolute command
(G roup type B)
G29
Return from machine zero
G91
Incremental command
(Group IYpe B)
point 2)
G92
Toul pUSilioli
- conSlant lead
G94
G35
Circular threading CW
G94
G36
Circular
895
G40
Tool nose radius offset cancel
G41
Tool nOse radius offset lefl
G42
CCW
osc radius compensation
G96
CUlling cycle B
(Group type A)
fvpe D)
Constant surface speed mode
Ie per minute
50
8
Most of the preparatory commands are Ul~'i..U::'::'c;u
individual applications, for
Inrerpolation, G02 and G03 under
Interpolation,
etc. In this section, G codes are described in general, reof the type of machine or
unit.
G CO
IN A PROGRAM BLOCK
Note
rapid motion command GOO does it
in the program? Just once - in
In fact, so is
command for absolute
reason neither GOO nor G90 has been
is v ....... QI.I,)1.both
remain active from the moment of their
first
in the program. The cerm
is
to
this characteristic.
Unlike the miscellaneous
and described in
next cm~ptl:r
rator·y commands may be used in a
block, providing
with each other:
they are not in a logical con
N25 G90 GOO G54 X6.75 Y10.S
This method of program writing is severa! blocks shorter
single block
tation
~ Example C - modified (as processed I :
N3 G90 GOO xso.o Y30.0
N4 G90 GOO XO
N5 G90 GOO Y2QO.O
N25 G90
N26 GOO
N27 054
N28 X6. 75 Yl0.5
Both methods will
during a '-v........ ..
processing. However,
example, when
in a single block mode,
block will require pressing the
Cycle Start key to activate the
The shorter method is
more practical, not only
length, but for the
connection between individual commands within
block.
general considerations
rules of application
to G codes used with other data in a block. The most
of
is
of modality.
• Modality of
Earlier, the following
C was used to
the general placement of G codes into a program block:
~ Example
to repeat a
example
interpre-
c· original:
N6 G90 GOO XlSO.O Y:220.0
N7 G90 GOO X130.0 YlOO.O
program does not have any practical application by
from one location to another at a rapid rate, but it
the modality
commands. The
of modal values is to
unnecessary duplicaof programming modes. G
are used so often. thal
tedious. Fortunately.
writing them in the program can
(he majority of G codes can
only once, providing
they are modal. In the control
specifications, prepaas modal and unmodal.
ratory commands are
• Conflicting Commands in a Block
The purpose of preparatory commands is to select from
two or more modes of
If the rapid motion command GOO is
it
command
to a
tool mn'!,nn
[0 have a rapid motion and
same time, it is
to
N3 G90 GOO
N4
N5
N6
N7 X13.0 YlO.O
If the structure is changed slightly and filled with
data, these
may be the result:
~ Example C - modified (as programmed) :
N3 G90 GOO XS.O Y3.O
N4 xo
NS Y:2O.O
N6 XlS.O Y22.0
N7 Xl3.0 YlO.O
N74 GOl GOO X3.S Y6.125 F20.0
In the example.
two commands GO 1 and GOO are m
conniCL As GOO is the latter one in the block. it will
come
feedrale is ignored in this block.
N74 GOO GOl X3.S Y6.12S F20.0
This is
exact
of the previous
front, therefore the G01 will
the GOO is in
motion will take place as a
of 20.0 in/min.
Here.
precemotion at
PREPARATORY
51
• Word Order in a Block
GROUPING OF COMMANDS
G codes are normally programmed at Ihe beginning of a
other significant data:
block, after the block number,
N40 G91 GOl Z-O.62S Fa.S
This is a traditional order,
on
that if the
the control
purpose of the G codes is to
to a cenain condition, the ",,..c,,,,,..,,...,I,,,,,,,,,
always be placed
that only non~conflicting
block. Strictly
there is
to:
N40 G91 Z-O.62S Fa.S GOl
unusual, but quite correct.
next method of positioning a G
is nol the case
in a block:
of conflicting G codes in one
forefront. Il makes sense,
motion commands
as GOO,
, G02 and
same
is not so
or€~oarat;orv commands. For example, can the lool
command G43 be programmed in the same
as
cutter
offset command G41 or
The answer is
but leI's look at the reasOn why.
two-digit
codes in one
from the same
f1icl with
recognizes preparatory commands
into arbitrary groups. Each
has a Fanuc assigned
governing the
simple. If two or more G codes
the same block, they are in con-
N40 Z·O.625 F8.S GOl G9l
• Group Numbers
Watchfor situations like this! What
case IS
Ihat
cutting motion G01, the
depth Z
will
combined and executed using the current
If current mode is absolute,
Z
executed as an absolute value, not an mcrernell1reason for this exception is
values in the same block.
can a
feature, jf used carefully. A typical correct
feature can be illustrated in this example:
The G
(G20)
N45 G90 GOO G54 Xl.O Yl.0 51500 M03
(G90)
N46 G43 ZO.l H02
N47 GOl Z~0.25 F5.0
N48 X2. 5 G91 Yl. S
(G90 MIXE:D WITH G91)
N49
through N47 are all in the aU:'U1Ul\.,
N48 is executed, the absolute
the axes X
Y is 1.0,1.0.
the
target location is
"V"'VIUl.... position of X2.5 combined
with
of 1,5 inches along the Y axis.
will be X2.5Y2.5, making a
45" motion. this case, the G91 will remain in effect for
all subsequent blocks, unlil the G90 is programmed. Most
likely, the block N48 WIll be written in absolute mode:
are typically numbered from 00 to
different control models,
tealtur(~s It can even be higher for the newest controls or
more G codes are required. One of
one and perhaps the mosl
these groups - the most
important as well - is the Croup 00.
All preparatory commands in the 00 group are not modal,
unmodal or non-modal.
sometimes using [he
They are only active in
in which they were proare to be effective in
grammed. If unmodal G
consecutive
they must
programmed in
those blocks. In majority of unmodal
this
titian will not
pause measured in
duration within the
no longer.
is no
need to prodwell in two or more consecutive blocks. After all,
what is the benefit of the next three blocks?
N56 G04 P2000
NS7 G04 P3000
NS8 G04 PlOOO
All three blocks contain the same
another. The program can
by simply entering the total dwell
N48 X2. 5 Y2. S
N56 G04 P6000
Normally,
is no reason to switch between the two
in some
unpleasant surprises.
modes. It can
There are some V""'''......HV. when this special
in subprograms.
brings benefits. for
following groups are typical for the
Applications for milling and turning
distinguished by the M and T letters
column of the table:
control
Chapter a
52
Type
00
Unmodal
G codes
Motion Commands,
G04 G09 GIO
GIl G27 G28 G29
G30 G31 G37
G45 G46 G47 G48
G52 G53 G65
GSl G60 G92
GSO
G70 G71 G72 G73
G74 G75 G76
GOO GOI G02 G03
G32 G35 G36
G90 G92 G94
01
Cutting Cycles
02
Selection
03
Dimensioning Mode
G90 G91
(U and W for lathes)
04
Stored Strokes
G22 G23
05
Feedrate
G93 G94 G95
G20 G2l
Radius
Offset
08
09
Tool Length
Offset
Cycles
from Group 09. In a
MIT
MIT
M
G CODE TYPES
T
T
T
MIT
T
T
M
M
T
MIT
T
MIT
G40 G41 G42
G43 G44 G49
M
G73 G74 G76 GSO
G81 G82 Ga3 GB4
Ga5 Ga6 G87 GSS
Ga9
M
M
M
M
10
M
11
M
T
12
Coordinate
System
5 G56 G57
GSa G59
13
Cutting Modes
G6l G62 G64
G63
MIT
G66 G67
MIT
G6a G69
M
G96 G97
T
17
byO
MIT
MIT
-----+---1
Gl9
Group 01 is 1101
summary ...
M
18
Input
GlS GI6
M
24
Speed
Fluctuation
G25 G26
MIT
group relationship makes a perfect sense in all cases.
One possible exception is Group aI for Motion Commands
and Group 09 for
The relationship
these
two groups is this - if a G code from Group 01 is specified
in any ofthe fixed cycle
09, the
is immediately
but
opposite is not true. In
words, an active motion command is nO!
by a
cycle.
Fanuc control system
a nexible selection of preparatory commands. This fnct distinguishes Fanuc from
many other controls.
the fact that Fanuc conit only
sense to
the
trols are used
standard control configuration to follow established style
A typical example is the selection of diof each
mensional
In Europe, Japan and
other counmetric system is the standard. In
America,
common system of dimensioning still uses {he English
both
are substantial in the world trade, a
clever control manufacturer tries to reach them both. Almost all control manufacturers offer a selection
the dimensional
But
and similar controls also
selection
programming codes that were in
Fanuc reached the worldwide market.
The
Fanuc controls use is a simple method of paBy
the speci fie system parameter,
rameter
one of two or three 0
types can
selected,
one
is typical
a particular geographical user. Although
majority of the G codes are
same for
lype, the
most typical iIluslIation are G
used
English and
metric selection of units. Many earlier US controls used
070 for
units and G71 for
units.
tern has
020 and
1 codes for
and metric
Setting up a parameter, the G
type
is the most
practical can be
Such a practice, if done at all.
should done only once and only when the conlIol is installed,
any programs have been wriuen
il.
Change of
G code type at random is a guaranteed way
to create an organizational nightmare.
in mind that a
of one code meaning will affect the meaoing of another
Using
units
for a lathe, if G70
means an English input of dimensions, you cannot use it to
program a roughing
Fanuc provides a
code.
Always
with the
G code
All G
this handbook use the default group of
Type A, and
the most common group.
• G Codes and Decimal Point
include a G code with a
1 (Rotation copy) or
(Parallel copy). Several preparatory commands in this
group are related to a particular machine tool or are not typical
to described in this handbook.
MISCELLANEOUS FUNCTIONS
..'"".... '"'.~., M a CNC
neous jUnction, sometimes
all
a miscellaa
functions are related to
CNC machine - quite a few are related to
the
lun'-UIJfI.\
Not
of a
of
itself. The more sui tab Ie term miscellaneous
is used throughout this UW1UL'VVr....
DESCRIPTION AND PURPOSE
the structure ofa CNe prclgr(!Jlt.progl1lmmers ofcertain aspects of the
ten
some means of
machine operation or controlling
flow. Without
availability of such means,
program would be
mcomplete and impossible to run.
let's look at the
18neOlIS functions
to
operation of the ma- the true machinefonctions.
All
for metal removal by
have certain common features and capabilities. For example,
can
three - and only three ble
Q
normal rotation
o
Spindle reverse rotation
o
Spindle
three possibilities, there is a
"'''''.,,"', .... orientation, also a machine
tion.
example is a coolant. Coolant can only
controlled as being ON or being OFF.
operations are typical to most CNC
All
with an M function, fonowed by no more
although some control
allow the
M function, Fanuc 16/18,
example .
• Machino Related Functions
spetwo
other
and
Various physical
machine must be
controlled by the program, to ensure fully automated machining. These functions
use the M address and
include the following
0
Spindle rotation
CW Of CCW
0
Gear range change
low 1 Medium 1High
0
Automatic tool change
ATC
0
Automatic
0
Caolant operation
0
Tailstock or quill motion
or OFF
IN or OUT
These operations vary be1:'wef~11 machines, due to the different designs by various
manufacturers. A machine design, from the
point of view, is
on a certain primary
application. A CNC milling machine will
functions related to
center or a CNC lathe, A
machine than a
numerically controlled
wire cutting machine will
many unique
typical to that kind of machining and
on no other machine.
........"..&L.......... for the same type of work,
Even two
for example, two
vertical machining center, will
each other, if they have a
have functions ditterjent
ferent CNC
SlgOJ.tllCaIltly different I'InlMI'ITHI
ferent
the same manutactlmer
also have
functions, even with the same
model of the CNC <II'UC!,rpTn
• Program Related Functions
In addition to the machine
some M functions
are
to control the execution
program. An interruption of a program execution
an M function,
during the change
such as a part
Another example is a
where one proone or more subprograms. In such a case, each
to have a program
the number of
etc, M functions
previous "'''''''Ull-''.... ''',
ous
falls lnto two
ular application:
o
Control of the machine functions
o
Control of the program execution
miscellaneon a partic-
TIlls handbook covers only the most common miscellaneous functions, used by the majority controls, Unfortu~
nately, there are many functions that vary between maand the control system.
functions are called
machine specific junctions.
reason, always consult
the documentation for the
machine model and its
control system
54
9
TYPICAL APPLICATIONS
learning the functions, note
type of activity
these functions
regardless of whether such activity relates to
machine or
program. Also nOle Ihe ahundance
two way toggle modes, such as ON and OFF, IN
OUT, Forward and Backward, etc. Always check your
manual
- for
reasons of consistency,
M functions in this hoodbook are based on the following table:
:ription
"""'=
MOO
Compulsory program stop
MOl
Optional program stop
M02
End of program (usually with reset. no rewind)
M04
Spindle rotation reverse
MOS
Spindle stop
M03 ~ rotation normal
6
Automatic lool change (ATC)
M07
Coolant mist ON
MOS
Coolant ON (coolant pump motor ON)
M09
Coolant OFF (coolant pump molor OFF)
M19
;pindle orientation
M30
Program end (always with reset and rewind)
M48
Feedrate override cancel OFF
(deactivated)
M49
Feedrate override cancel ON
(activated)
M60
Automatic pallet change (A
M78
B axis clamp
(nonstandard)
M79
B axis unci amp
(nonsfandard)
M98
Subprogram call
M99
end
Description
MOO
Compulsory program stop
MOl
Optional program stop
End of program (usually with reset, no rewind)
M03
MOS
Spindle stop
I
MOS
Coolant ON (coolant pump molar ON)
M09
Coolam OFF (coolant pump motor OFF)
Ml0
open
Ml1
Chuck close
M12
il<;lo{'k quill IN
M13
TailSlock quill OUT
M17
Turret indexing rurward
MIS
Turret indexing reverse
M19
;pi
M21
Tailstock forward
M22
Tailstock backward
M23
Thread gradual pull-out ON
M24
Thrcad gradual pull-om OFF
M30
Program end (always with reset and rewind)
M41
Low gear selection
M42
Medium gear selection 1
M43
Medium gear selection 2
M44
High gear selection
M48
FeedralC override cancel OFF
( deactivated)
M49
Feedrate override cancel ON
(activated)
M9a
;ubprugl"uB call
M99
Subprogr{lm end
oriental ion (optional}
• Special MDI functions
• Applications for TurRing
M code
Spindle rotation reverse
Mo;-r Coolant mist ON
• Applications for Milling
M code
M04
Spindle rotation normal
'''''IF''"'''' M functions cannot be used in
CNC n,..r,or~m
at all. This group is
in the Manual Data Input mode
exclusively (MDl). An example of such a: function is a step
by
tool
for machining
for service
'rnr\<'tH" only, never in the program. These functions are
outside of the scope of this handbook.
• Application Groups
The two major categories, described
can further
into several groups,
on the specific
of the miscellaneous functions within each group. A
(ypical distribution
is contained in the following table:
be
MISCELLANEOUS FUNCTIONS
55
method of programming certain
is in a block that contains a tool
turning the coolant on and - at the same time the cuuing tool to a certain part location
there is no conflict between
may look something like this:
Typical M-functions
Group
..... "·uv,, •.)
Program
4 MOS
Spindle
Tool change
M06
Coolant
M07 MOB M09
Accessories
M10 M11
Ml.2 M13
Ml.7 MiS
M21 M22
M78 M79
Threading
M23 M24
N56 GOO X12.98S4 Y9.474 MOB
or
moat this combination - a Z
with the program stop function
M44
Gear ranges
M48 M49
M98 M99
M60
NG19 GOl Z-12.S4S6 F20.0 MOO
This is a
more
situation and two answers are
needed. One is what exactly will happen. the other is when
exactly it will
when the MOO function is activated.
and three questions to
There are
1.
The table does nOI cover aU M functions or even all possible groups. Neither
it
between machmes.
On the other hand, il does indicate
types of applications
the miscellaneous functions are
for in everyday CNC
programmIng.
The miscellaneous functions
used throughout the book.
than olhers, reflecting
functions that do not l"""",......".·~ ..-.r\nn
control system are
not
However, the concepts for their
most control systems
In this chapter, only the more general functions are covin significant detail. Remaining
are described in the sections covering individual apAt this stage. the stress is on the
and
of the most common miscellaneous
M FUNCTIONS IN A BLOCK
If a miscellaneous function is programmed in a block
with no other data supplementing it, only
itself will be executed. For example,
N45 MOl
block is correct - an M function
entry. Unlike the preparatory comonly one M function is allowed in a block
allows multiple M functions in the same
error will occur (latest controls only).
place immediately, when
.""y,,,,U,,,,,, - at the start of the block?
2.
Will the
place while the tool
is on the way - during a motion?
3.
Will the program
command is
One of the
Even if a practical
apparent at this
system interprets
miscellaneous function.
place when the motion
- at the end of the block?
- but which one?
examples may nol be
to know how the control
a tool motion and a
Each M function is designed logically - it is also designed
to make a common sense.
The actual startup of a M function is
groups - not three:
Q
M function activates at the start of a
(simultaneously with the tool
Q
M function activates at
into two
of a
(when the tool motion has been cOl1nDl~!ted
""''''",n will be
during
executhere is no logic to it. What is the logical startup
ON function M08 in the block N56
at
correct answer is that the coolant will be
same time as the tool motion begins. The correct answer
the example block N319 is that the MOO
function will be activated after the tool ~,., .. ,.". .
completed. Makes sense? Yes, but what about
functions. how do they behave in a block?
them next.
Chapter 9
•
Startup of M Functions
M functions completed in ONE BLOCK
""='"'=~==-==9
Take a look at the list of typical M functions.. Add a tool
motion to
try to determine the way lhe function is
going to behave, based on the previous nOles. A bit of logical thinking provides a good chance to arrive at
righ!
Com pare) he two following groups to confirm:
t. no rewind)
Mfunctions activated at the START OF A BLOCK
UNTil CANCELED or ALTERED
Automatic too! change (ATC)
Coolant mist ON
Spindle rolation reverse
Coolant ON (coolant pump motor ON)
M functions activated at the
OF A BLOCK
lVIUV
Compulsory program stop
M01
Optional
M02
End of program (usually with reset no rewind)
M05
Spindle stop
M09
Coolant OFF (cool an! pump motor OFF)
M30
Program end (always with resel and rewind)
M60
Automalic pallet change (APC)
SLOp
If there is an uncertainty about how the function will interact with the lool motion,
safest choice is to program
That way the function
the M
as a separate
will always be processed before or after
relevant program block. In the majority of applications this will be a
SOltllion.
•
Duration of M Functions
Knowledge of when the M function
effect is logically followed by the question about how long the function
will be active. Some miscellaneous functions are active
only in the block they appear. Others will continue to in
until canceled by another miscellaneous function.
the preparatory G comThis is similar to the modality
however the word modal is not usually used with M
an example of a function duration, take misfunctions.
cellaneous functions MOO or MOl. Either one will active
for one block only. The coolant ON function M08, will be
until a canceling or an altering function is programmed.
anyone of the following functions
will cancel the coolant ON mode - MOO, MO l, M02, M09
and M30. Compare these two tables:
The classification is quite logical and shows some common sense. There is. no
to
individual M
best place to find
functions and
exact actlv!tles.
out for certain, is to study manuals supplied with the CNC
run right on the machine.
and watch the
PROGRAM fUNCTIONS
Miscellaneous functions that control program processing
temporarily
can
used either to interrupt
(in Ihe middle of a program) or permanently the end of a
program), Several functions are available for Ihis purpose.
• Program Stop
The MOO function is defined as an unconditional or compulsory program stop. Any time the control system encounters lhis function during program processing, all automatic operations of the machine tool will stop:
o
Motion of all axes
o
Rotation of the spindle
o Coolant function
o
Further program execution
Thc control will ItO! be reset when the MOO function is
prclce:5scQ, All
program data currently active are
(feedrate.
spindle
etc.).
program processing can only resumed by activating
the spindle
the Cycle Starr key. The MOO function
rotation
coolant function they have to be
grammed in subsequent blocks.
FUNCTIONS
MOO function can be
as an individual
block or in a block
commands, usually'
motion. If the MOO
is programmed together
with a motion command, the motion will be completed
then (he program stop will
effective:
c::> MOO programmed after a motion command "
N38 GOO X13.5682
N39 MOO
c::> MOO programmed with a motion command:
N39
GOO X13.5682 MOO
In both cases, the motion
will
first, before the program
is executed. The
between the two examples is apparent only in a
block processing mode (for example, during a trial
will be no practical difference in aula mode pro(Single Block switch set to OFF).
Practical Usage
program stop
CNC operator's job
common use is a
the part is still
During the stop, the part
sions or the lool condition can be checked. Chips accumulated in a bored or drilled hole can be removed, for example, before another
operation can start,
as
blind hole tapping.
program stop function is also necessary to
the current setup in the middle of a
for
to reverse a part. A
tool
also requires the
in the
an optional program stop MO I,
The control
described next. The main rule of using MOO is
need of a
manual
every parl machined. Manual lool
change in a
qualifies for MOO.
part
check may oOl
if is infreneeds it. A
choice. Although
quent. MOl will
is slight, the actual
between the two
cycle time can
significant for large
When usi'ng the MOO function, always inform the operator why the function
been used and what purpose is.
Make the
known to avoid a
This intent
can be
to the operator in two ways:
refer to the block
that contains
MOO
describe the manual
BLOCK N3 9 •..••. REMOVE CHIPS
57
o
In the program itself, issue a comment section with the
necessary information.
comment section must be
enclosed in
(three versions shown):
[Al
109 MOO (REMmr.E CHIPS)
[8]
N39 Xl3. 5682 MOO (REMOVE CHIPS)
[C]
108 Xl3.5682 MOO
(REJM'O'.i'E CHIPS)
Anyone of the
methods will give Ihe
operator
the necessary information. From the two options, the second one [B], the comment section in the program, is
The built-in
can be read directly from the
screen
control paneL
• Optional Program Stop
The miscellaneous
MO I is an optional or a COIIdirional program stop. It is similar to MOO function,
the MOO function, when MOl funcone diffe.rence.
lion is encountered in the program, the
processing
will nOl SlOp,
the operator
the control
panel. The Optional SlOP toggle switch or a button key located on the
Clln be set to either ON or
in the program is
When the
setting of
will determine
will
or continues to
Optional Stop switch setting
Result of MOl
ON
OFF
When
the MOl function behaves
the MOO function. The motion of
coolant
and any further
execution will be
temporarily interrupted. Feedrate, coordinate settings,
setting, etc., are
. The further prospindle
program can only be reactivated by (he Cycle
All programming rules for the MOO function also
MOl function.
is to program
MOl function at the end of
followed by a blank line with no
If the program processing can continue witham Slopping, the Optional Stop switch will be set to
and no production
time is lost. If there is a need to
program temporarily at the end of a tool, the switch will be set to ON and
100i. The lime loss is
stops at the end of
under the
for example, to
a dimension or the
58
Chapter 9
• Program End
the
Percent Sign
program must include a
of current program.
M functions available but
a distinct
M02 and
are two
are similar,
The M02 function will terwill cause no return to the first
minate the program,
block at the program top. The function M30 wililerminate
the program as well but it will cause a return to the
lOp. The word t return' is often replaced by
word 'rewind'. It is a leftover
the limes when a reel-to-reel
tape
was common on NC
tape had to
be rewound when the program has
completed for
M30 function provided this
capability.
When the control reads the program end function M02 or
M30, it
all axis motions, spindle rotation, coolant
function
usually resets the system to
default conditions. On some controls the reset may not be automaTic
any programmer should be aware of it.
U the program
with the M02 function, the control
remains at the program end, ready for the next Cycle Stan.
On modem CNC equipment there is no need for M02 at all,
except for backward compatibility. This function was
in addition to M30
those machines (mainly NC
had tape
without
using a short
tape.
(railer of
tape was spliced 10 the tape
creating a closed loop. When the program was finished, the start
of the
was next to the
so no rewind was necessary.
and M30.
Long
could not use loops and
So
for the history or M02 - just
percent sign (%) after M30 is a special stop code.
This symbol terminates the loading of a
from an
external
It is
the
• Subprogram End
last M
a
is M99.
mary usage is in the subprograms. Typically, the M99 function will
a subprogram and return to
processing of the previous program, If M99 is
in a standard
program, it creates a program with no end such a situation
is called an endless loop, M99 should be used only
not in
standard
MACHINE FUNCTIONS
Miscellaneous functions relating to
operation of the
tool are
of another group. This section
the most important of them in detail.
• Coolant Functions
Most metal removal operations
that the cUlting
tool is flooded with a suitable coolant In order to control
the flow of coolant in
program,
are three
neous functions usually provided for (his purpose:
M07
Flood ON
Is M02 the Same 8S M30 ?
On most
controls, a system parameter can be set
to make
M02 function
the same meaning as that of
M30,
setting can
It
rewind capabilities,
in situations where an old program can be used on a mawith a new
without
Tn a
if the end of
is terminated by the
M30 function, the rewind
performed; if the M02
function is used, the rewind will not be performed.
When writing
program, make sure the last
program contains nothing else but M30 as the
end (sequence block is allowed to start the block):
N65 . . .
N66 G91 G2S xo YO
N67 mo
%
(E:tiID OF PRQGR.ll.M)
On some controls, the M30 function can be used together
with the axes motion - NOT recommended !:
Mist or Flood OFF
Misl is
combination of a small amount of cutting oil
mixed with compressed
It depends on
machine tool
manufacturer whether
function is standard for a particular
machine tool or not. Some
mixture oil and air with air only. or with oil
only,
etc. In these cases, it is typical that an additional equipment
is built into
machine. If this option exists on the machine, the most common miscellaneous function to
the oil
or air is M07.
function similar to M07 is M08 - coolant flooding .
.This is by far the most common
application in CNC
programming. It is standard for virtually all
machine.
The coolant, usually a
mixture
oil and
water, is premixed and
in the
tank of the machine tool. Flooding
cuning edge of
tool is important for three reasons:
o
N65 . . .
N66 G91 G28 XO YO M30
%
Mis! ON
OF PRQGR.ll.M)
Heat dissipation
o Chip removal
o Lubrication
FUNCTIONS
primary reason La use a coolant flood aimed at the
cutting
is to dissipate
cutting.
reason is to remove
cutting area, using coolant pressure, Finally,
also acts as a lubricant to ease the friction
cutting tool and material. Lubrication helps to extend tool
life and
the surface finish.
initial tool approach towards the part or during
nal return to the tool change position, the coolant is normally not
turn off (he cootant function, use
M09 function - coolant off. M09 wi lllurn off the oil mist or
supply and nothing else. In reality, the M09 function
will shut off (he coolant pump motor.
the rhree coolant related functions may
in
blocks or together with an
are subtle but important differences in
of the program processing. The
explain the differences:
A - oil mist is turned ON, if
C)
N110 M07
a There will be no coolant splashing outside of
work area (outside of the machine)
a
will never be a situation when
the coolant reaches a hot edge of the tool
IS
function is programmed in the
an inconvenience.
wet area
chine may present unsafe working
quickly corrected. Even more "Pro"""
when the coolant suddenly starts
that has already entered the material.
perature at the cutting edge may cause
damage the part. Carbide tools are
by temperature changes than
possibility can be prevented
the M08 function a few blocks
the actual cutting
block. Long pipes or insufficient coolant pressure on the
flooding.
machine may delay the start of
•
C) Example B - coolant is turned ON :
Spindle functions
Chapter 12 - Spindle
trolling the machine
neous functions that are
rotation and
N340 MOS
=
Example C - coolant is turned OFF:
all aspects of conprogram. Miscellathe spindle control its
Most spindles can rotate in
NSOO M09
(CW) and
C) Example 0 - axis motion and
Lion is always relative to a
viewpoint is
lion along the spindle center
lion in such a view is
as M04. assuming the
ON:
N230 GOO Xll.5 Y10.O MOS
=
Coolant should always be programmed with two
lant considerations in mind:
E - axis motion and
OFF.
N4QO GOO Zl.O M09
The examples show
cessing. The gen;;ral rules
o
Coolant ON or OFF in 8 :>e:IJ'I1TClIe:
the block in which it is
o
Coolant ON, when programmed with the axes motion,
becomes active simultaneously with the axes motion
(Example 0)
o
Coolant OFF, programmed with the axes motion,
becomes effective only upon completion of
the axes motion {Example E)
pro-
The main purpose M08 funclion is to turn the coolant
pump motor on. It
that the CUlling
receives any coolant
On large machines with
long coolant pipes, or
with low coolant pump
is to
expected before the coolant
pump and cutting lOol.
clockwise
of rota·
point of view. The
spindle
as the
towards itsface. CW rotaas M03, CCW direction
rotated either way.
0\.L1,llV<.U\J
The drilling and milling Lypes of machines use this established convention
commonly. The same convention is
LO
lathes. On a CNC milling machine or a
machining center, it is more practical to look towards the
part from the spindle side rather than from the
horizontal type), the more
the tailstock towards the spindle, because that
(0 how the CNC machine operator stands in
nu.H'l/p, M03 and M04 spindle
the same way as for machining cenis the fact that left hand tools
are
In
more
than in
milling applications. Make an
to
manual for a
machine carefully in
12.
Spindle function (0 program a spindle
is
function will stop the spindle from rotating,
the rotation direction. On many machines.
neous
MOS must also be programmed
the spindle rotation:
60
9
M03
<: •••
CW)
Machining at the current location .•• :>
M05
<:. • •
M04
<. . .
a tool change ... :>
(SPDmLE CCW)
at the current location ... :>
may also be required
on CNC lathes. A spindle SLOP
. an axis motion, will take
completed.
spindle control function is the function M 19,
spindle orienTation. Some control
call it the spindle key lock function. Regardless of the
the M 19 function will cause the spindle to SLOp in
position. This function is used mostly during
seldom in the program. The spindle must be
in two main situations:
o
Automatic tool change (ATC)
o
Tool shift during a boring ",",or<>+i,,"
and
boring cycles only)
For example, most rougbing " ....",..".i"'.~"
the spindle more than the
low range is usually a better selection.
medium or high range is better,
high
can be more beneficial to the metal removing
distribution of (he miscellaneous functions
has
entirely on the number of gear ranges the CNC
available. Number of ranges IS I, 2, 3 or 4.
foJlowi
shows typical distribution of the M
the actual commands in a machine tool manual.
Ranges
Gear
N/A
None programmed
2 available
M41
M42
Low range
High range
3
M41
M42
M43
Low range
Medium range
High range
M41
M42
M43
M44
law range
Medium range 1
Medium range 2
High range
thumb is that the higber (he gear range, the
is possible and less spindle power is reis also true. Normally, the ."pindle rota be stopped to change a gear, but conanyway. In doubt, stop the spindle
the
then restart the spindle.
sequence and
cutting tool holdthe M 19 with the
first,
is necessary for certain boring
on mill
To exit a bored hole with a
1001 away from the finished cylindrical wall, the
spindle must
the tool cutting bit must be
aQd then the tool can be
from the hole. A
similar approach is
back boring operations. However,
use fixed cycles in the
program, where
is built in. For more
details, Chapter
M function
• Machine Ar.r.fHrt~n
The majority of " .. ,,,"'''',,<.1,
functions is used for some
physical operation of the
tool <.>"'\..""""Ul
this group, the more common
ready covered, specifically
changes. The remaining M
scribed in delail elsewhere in
description is offered
are:
chine related M
In conclusion. the M 19
gram. It IS aVailable as a ... r~''''''''''''''''
chine operator for
M function
• Gear Range Selection
M06
M60
Description
M
Automatic
M
M23 M24
Thread gradual pull-out ON I OFF
T
M98 M99
Subprogram call J Subprogram
SE~UENCE BLOCK
Each line in a CNC program is called a block. In
terminology established
a block was
as a
CNC system.
single instruction processed by
A
block, a
n block is normally one
written line in
copy, or a
line typed in a text
and terminated by the Enter key.
This line can contain one or more program words - words
that result in
definition
a single i
to the
machine. Such a program instruction may contain a
of
commands, coordinate words,
(001 functions
coolant function, speeds and
commands, position registration, offsets of different
English, (he contents of one block will
kinds, etc. In
be
as a single unit before the control
block. When the whole CNC program is proindividual instructions
the system will
(blocks) as one complete machine
step. Each
program consists of a series of
necessary to complete a
machining process.
overall program
number of blocks
length will always depend on
and their
BLOCK STRUCTURE
As many program words as
are allowed in a
block. Some controls impose a limit on the number
in one
is only a
maximum
Fanuc and
controls,
in practice.
The only restriction is that two or more duplicated words
(functions or commands) cannot
in the same block
of G
example, only one
(with the
miscellaneous M function
do exist) or only one
coordinate word for the X
in a 5i
block are
al
The order of
words within a block follows a fairly free
required words
may be in
providing that
block (the
N address) is written as (he firs!
Although
order of individual words in a block is allowed to be in
order, it is a standard practice to place words in a
ora block. ft
the CNC
to
and understand.
dependent on
block slructure is
and the type of the eNC machine. A
may conlain the following inslructions, in the
Not all
data are
to be
specified every lime.
o
Block number
N
o
Preparatory commands
G
a
Auxiliary functions
M
o
Axis motion commands
XYZABCUVW ...
o
Words related to axes
I J K R Q ...
o Speed,
or tool function
S FT
contents of tile program block will
between matools of di
kinds. but
the majority of
general rules will
be followed, regardless of
CNC system or the
tool
• BuHding the Block Structure
program has to
built with the
same thoughts
the same care as any other important
structure, for
a building. a car, or an
It
starts with
planning. Decisions
to be
as lO
what
and what will not
of the program block,
to a building, car,
or other structure. Also,
have to
as to what order commands instructions - nrc
to be established within thc block
many other
The next few examples compare a typical structure
operablocks
milling operations and blocks for
tions.
block is
as a separate
• Brock Structure for Milling
In milling operations. the structure of a typical
machining center
block will renee! the realities of a
or a
machine.
C Milling block examples:
Nll G43 Z2.0 S780 M03 HOl
{EXAMPLE
N98 GOl X2.1S Y4.575 F13.0
(EXAMPLE 2)
The first milling example in block NIl, is an illustration
of a 1001 length offset
applied
with the
ndle rotation
dIe speed and
example in block
shows a typical prong instruction for a simple linear CUlling motion.
the linear interpolation method and a suitable CUlling
61
62
Chapter 10
<:> Turning block examples:
N67 GOO G42
5 ZO.l T0202 MOS
N23 G02 X7.5 Z-2.8 RO.5 FO.012
1)
(E.XAMPLE 2)
rectory more descriptive
useful. The program description can be read on
display screen
provides an easidentification of
program stored.
If program name is
than the
characters
recommended, no error is generated, hut only the firsl sixteen
will be displayed. Make sure 10 avoid
names that can
ambiguous when displayed.
names, they appear 10 be
these two
In
lathe examples. block N67
a rapid motion to an XZ position, as well as a few other ("''''''nm,<ln,'l<:
the tool nose
offset startup
activation of the tool
(T0202),
the coolant ON function M08. The example in block
is a typical circular interpolation block
with a
OJ.005 (LOWER SUPPORT A.RM: - OP 1)
01006 (LOWER SUPPORT A.RM: - OP 2)
PROGRAM IDENTIFICATION
the control screen display can show only the
siXfeen characters
the
name, the "'''IV'''!H'''''
names will be ambiguous when
A CNC
can
identified by its
and, on
some controls, also by its name. The identification by
number is
in order to store more than
in the CNC memory.
name, if
can be used to make a brief description of
proreadable on the control screen display.
• Program Number
The
is commonly a
Ihecontrol system from the
are available for the
number - the
letter a for
formal,
colon l : J for
ASCII (ISO) formal. In memory operation,
the control system always displays program number with
the letter
The block containing the
number is
not always necessary to include in the
If the program uses program numbers.
typical
specified within an allowed range. Programs
Fanuc controls must be within the range of I - 9999, program
zero (00 or 00000) is not allowed. Some
not allowed
controls allow a 5-digit program number.
are decimal poim or a negative sign in the program
of leading zeros is
- for '-'h<"JJ~J'\;'.
I, 0001.
00001 are all
entries, in this
case for a program number one.
• Program Name
the latest
control systems, the name of Ihc
can bc i
in addition to
program
not instead of the program number, The program name (or
a brief
of the program) can
to sixteen
long (spaces and symbols are
The program name must be on
same line (in
same block) as
the program number:
01001 (DWG. A-124D IT. 2)
This
has the advantage that when
directory of
Ihe memory is displayed on the screen, the name of the proappears next to the program
making
di-
01005
SUPPORT
01006 (LOWER SUPPORT AR)
eliminate this problem, use an
that is within the
characters
data:
01005 (LWR SOPP ARM OP1)
01006 (LWR SUPP A.RM: OP2)
If a more detailed description is
to
the description
split over one or more comment lines:
01005 (LWR SOPP A.RM:
(OPERATION 1 - ROUGHING)
The comments in the block or blocks following the
screen lislnumber will not appear on
but still will be a useful aid to
CNC operator.
be displayed during the
execution and,
course, in a hard copy printout.
Keep the
names short and descriptive - their purpose is to
the CNC
in
of programs
in the control memory. The
data to
in
program name are the drawing number or
number,
parl name. operation, etc. Data not
are the
name, control mo.del,
name, date or
company or customer's name and similar descriptions.
On many controls,
program into the
memory, the CNC
the
numon the
the
in the
CNC program. It can be a
that just bappens \0 be
available in (he system, or it can be a number that has a
unique meaning, perhaps indicating a
group (for exall programs that begin with
belong to
the group associated with a single customer). Subprograms
must always
stared under
number specified by the
CNC
Innovative use of program numbers
may also serve 10 keep track of programs developed for
each
or part.
SEQUENCE
63
•
SEQUENCE NUMBERS
Individual sequence blocks in the
program can be
referenced wilh a number for
orientation within
program. The program address
a block number is the
leuer
followed by up to five digits - from
I to
9999 or 99999, depending on the
block number
be N I to
for the older
controls and N I Lo
for the newer controls. Some
rather old
accept block
in the three
only, NI - N999.
N address must
be the firs! word in the block.
an easier orientation in programs that use SUbprograms,
there should be no duplication of the
between the
lwo lypes of
For example, a
program starting with N I
a subprogram also starting with Nl
cause a confusing situation. Technically, there is nothing
with such a designalion. Refer to
for
on
In
•
Sequence Block format
program input format notation for a
using the address N. is N5 for (he more
and N4 or even N3
older controls.
number
is
not allowed. neither is a minus
a fractional number or
a block number using a
point. Minimum block increment number must
be an integer allowed is one (N 1,
N4, N5. etc.). A
Increment is allowed
its seleclion
on the
personal programming style or
established
within the company. The typical sequence block
ments
then one are:
Program
2
N2, N4, N6, NS,
5
N5, N10, N15, N20,
.••
10
N10, N20, N30, N40,
.•.
100
N100, N20Q, N300, N400,
Sequence Number Command
column represents seIn the following table, the
quence numbers the way
are used normally.
second column shows the
numbers
in a forine control system, as applied to
mal acceptable to
a CNC program:
Increment
-
.
block number
I~
- - <- " " " " - « - <
1
N1
2
N2
5
NS
10
N10
50
N50
100
N100
99999
N99999
like to start with
of the
NIOO, usually programmed in the incremenLS of I
10, or less. There is nothing wrong with this
a large start and increment. but the CNC
too long, too soon,
In all cases of block incremenLS
than one, the pur·
pose of
program is the same - to
for additional
blocks to be filled-in between
blocks, jf
a
comes, The need may
while proving or optimizing the program on the
machine, where an addition to
the existing
II be required. Although
new
blocks (the ones inserled) will not be in the oruer ur an
equal increment, at least they will
numerically ascending. For
a face cut on a lathe
one cut (Example A) was
by the
operator for two cuts
(Example
=
Example A - one face cut:
numbers (block numbers) in a CNC
al least one likely
several advantages
On the positive
the block
program search greatly simplified
repetition on (he machine. They
the program
to read on
CNC display screen
copy. That means both
or on the
programmer
the operator benefit
On the
side, block
will
the
available computer memory of the
That means a
of programs can
stored in the memory,
programs may not fit in their entirety.
N40 GOO G41 Xl.S zo T0303 Moe
NSO GOl X-0.07 FO.Ol
N60 GOO WO.l M09
mo G40 Xl. S
=
Example B - two
cuts:
N40 GOO G4l Xl.5 ZO.05 T0303 MOS
N50 aOl X-O.07 FO.Ol
N60 GOO WO.1
N61 X3.5
N62 ZO
N63 GOl X-0.07
N64 GOO WO.l M09
mo G40 Xl.S
64
10
"""'1"1"''' in
N40 and
N6l to
this handbook is 10 I"Il"f,a!"lOlm
if an addition is needed,
will have no
numbers at all (check if the control
system allows block numbers to be omitted, most do),
Q Example A - one face cut:
N40 GOO G4l X3.5 zo T0303 MOS
N41 GOl X-O.07 FO.Ol
N42 GOO WO.l
N43 G40 X3.S
Q Example B . two face cuts:
N40 GOO G4l X3.5 zo.os T0303 MOS
N41 GOl X-D.07 FO.Ol
N4.2 GOO WO. 1
X3.S
ZO
GOl X-O.07
GOO WO.l
N43 G40 X3.5
Note that the program is a lillie smaller and the additional
or
arc quite visual and noticeable when
displayed on the screen.
Leading zeros may (and should) be omitted in
- for example. NOOOO8 can
(he
zeros
reduce the
zeros must always be written, to
for sl1ch similnri
8S N08 and N80.
use of block numbers in a program is optional, as
shown in the earlier example. A program containing
is easier to
CNC operator,
functions in program editing can be used
depend on the
numu"..... ..,.'" repetitive cycles
the significant blocks
•
Numbering Increment
Block numbers in a prog(am can
in any physical order
- they can also be
programming
UI..,",<l ..",,,, they are logical
numbers in
serves no useful purpose
neither do duplinumbers. If the program contains dupl icate
and a block number
is initiated at the
control system will only
for the first
the particular block number, which mayor
block required.
search will have
'""1-"_"'"........ from the string found
reason for the
in the sequence
numbering-is to
to the CNC operator
the program has
into the
block sequence number
not affect the order of
program processing, regardless of the increment.
if
the blocks are numbered in a
or mixed
the part
will always be
sequentially, on
the
of the block
nO!
mcnt of 5 or lOis the most
to 4 to 9
That should more than sufficient for the
program modifications.
programmers who use a computer hased
programming system, just a few
relating to (he
gramming of sequence numbers. Although the computer
programming
allows
start number of the block
and its
to almost any
adhere to the
start and
numbers of on.e (N I, N2, N3, ... ). The
is (0 keep an accomputer based
\"""""U<X.J,, of the part geometry
the cutting tool
program is modi
manually, the part
Ua.'·LlV''''''" is not accurate any more. Any CNC
program
should al ways be reflected in the source of
the program, as well as its result - never in
result alone.
•
long Programs and Block Numbers
are always
to
into a CNC
limited capacity. In such cases, the program
lenoth may be shortened by omitting the block numbers altog~ther or - even
- by programming them only in the
significant blocks. The significant blocks are those that
have to be numbered for the purpose of
search, a
(001 repetition, or
procedure Lha[
on program
numbers, such as a machining cycle or tool
In these
cases, select
of two or
the operator's
numbers will
convenience.
limited use of
Increase the
length, but for
reason.
rr all
block numbers have been omitted in the
program, the search on the machine control will
ralher difficult. The CNC
will have no
lion but to search for
next occurrence of a particular
dress within (l bJock.
Y, Z, etc., rather than a sequence block
method
unnecessarily prolong
Of BLOCK CHARACTER
of the control
specifications,
ual sequence blocks must separated by a special
characler or by its
known as Ihe
EOB or E-O-B.
most computer
""h~'''''''IP!" is generated by
key on the
the program is input to
control by MDI
on the control
the EOB
the block. The
symbol on
appears as a semicolon [ ; ].
SEQUENCE BLOCK
The semicolon symbol on the screen is only a graphic
representation of the end-or-block character and is never
entered literally in the CNC program.
stances it should be included in the program
older control systems have an asterisk [ * J as
symbol for the end-of-block, rather then the ... m,,..."'"
Many controls use other symbols. that
of block, for example, some use the
any case, remember the symbol is only the
!he end-of-block character, not its actual
STARTUP BLOCK OR SAFE BLOCK
A startup block (sometimes called a
or a slalUS
block) is a
sequence block. It
one Of more
(usually preparatory commands of
thal
the control system into a
state. This block is placed at the
or even allhe beginning of each
is
processed duriog a repetition of a program
a tool within a program). In the CNC program. the
startup block usually precedes any motion block or
as well as the tool change or tool index block.
to be searched for, if the program or
n"""',o,f1 cutting 1001 is to be repeated during a machine opSuch a block will be slightly different for the milland
systems, due to the unique requirements of
in this handbook, in. the Chapter 5, one
covstate of {he control system when the main
on, which sets the system default condishould never count on
they can be easily changed by
without the programmer's knowlsetthe machine
who designed the conshould always assume
approach and will not
programmer will try to preconditions under the program control,
rather that
ng on the defaults of the CNC system.
Such an approach is not only much safer, it will also result
in the
that are
10 use during the setup, the
tool path provi ng and
tool repetition due to the tool
breakage, dimensional adjustments, etc. It is also very
beneficial to the CNC
particularly to
(hose with limited
applications listed,
the startup block will not
machining cycle time
at all. Another
block is that the proone machine tool to andefault setting of a par-
65
The name safe block - which is another name
for the
startup block - does not become
nuuie safe. Regardless of
name,
tain control settings for the program or
slart the program in a
state.
tries that set the initial status are the
(English/metric and absolute/incremental),
any active cycle, cancellation of the
cutter
offset mode, the plane selection for milling, the
fault selection for lathes, etc. The presented
some
blocks for both milling and turning 1'1"\">11"1'\1
At the beginning of the program for milling, a startup
may be programmed with the following contents:
Nl GOO G17 G20 G40 G54 G64 GSO G90 G98
N I block is the first sequence number, GOO
rapid mode, G 17 establishes the XY plane selection,
selects the English units, G40 cancels any active cutter raoffset, G64 sets a continuous cutting mode, G80 cancels any active fixed cycle, G90 selects the absolute mode,
G98 will retract to the initial level in a
conditions apply only when the startup
as the first major block in the CNC
"LlIJ""'I..ILII"'''' program changes will become
block in which the change is
command is effective by
any subsequent
cancel the GO I command.
of GOO. G02, or
a CNC lathe program, the startup
G codes:
Nl G20 GOO G40 G99
block number, G20 selects the English
the rapid mode, 040 cancels any
tool nose radius offset, and the G99 selects feed rate per revolulion mode,
to Ihe absolute or incremental
the
controls use
system is usually not
absolute dimensioning and the
addresses X and Z
addresses U and W for
incremental dimensioning. For
lathe controls that do nol
U and W addresses,
(he standard G91
is
values in X
and Z axes. As in the
of the words
programmed in
by subsequent change of
Some controls """'AM""
the same line. For
grammed with other G
G codes in separate
Nl G20 017 G40 G49 Gao
two or more blocks can
Nl G20
N2 G17 G40 G49 GSO
o
or
on
not be proare not sure, place the
66
10
PROGRAM COMMENTS
CONFLICTING WORDS IN A BLOCK
Various comments and messages in the program can be
blocks, or as
parts of an existing block, mostly in cases when the mesis short. In either case, the
must enclosed
in parenthesis (for ASCIIIISQ
included within (he program body as
e Example A :
NJ30 MOO
'Set the English system of dimensions, also set the
system of dimensions and set the XY plane'.
8:
N330 MOO
(REVERSE PART /
CHECK
e Example C:
N330 MOO
PART /
CHECK TOOL)
of a message or comment
the machine operator of a
every time the program rpClrn,>"
such message ~nr\P<~lrc ;omnlents
at a
understanding the
for documenting the program.
IS
11:.'.:>~.al::.\;;':> and comments relate (0
changes, chip removal from a hole, dimencutting tool condition check and
others.
or a comment block should be
only if
1'P-1T11,,"'n task is not clear from the program
to
what happens in each block. 1Vle~ssages
comments should be brief and focused, as
a
memory
in the CNC memory.
perspective, a
at the
drawing information
This subject has
7 - here is just a reminder:
nrrn,u'PrI
01001 (SHAFT
DWG B451)
(SHAFT TOOLING - OP 1 - 3 J1U'J CHUCK)
(TOl - ROUGH TOOL - 1/32R - 80 DEG)
(T02 - FINISH TOOL
1/32R - 55 DEG)
(T03 - OD GROOVING TOOL - 0.125 WIDE)
(T04 - OD THREADING TOOL - 60 DEG)
Nl G20 G99
N2 •••
CNC unit is limited,
usi ng comment
cal. It will
listed in proper
required details.
Nl G20 G21 G17
What
contains is simpJy not logically possible.
It instructs the control to:
(REVERSE
e
In a program
not impossible. For'
the first block of
the following words:
Definitely not
actually happen
a
statement? The
lection of
possible, the
mensional
Fanuc systems
unit will
words within
same
the section dealing with the
groups have been
preparatory commands - G codes, in Chapter 8.
If the computer system
two or more words that belong to the same group, it will not return an error
it will automatically
the last word of the group. In
the example of conflicting dimensional selection, it will
the preparatory
G21 of metric
sions - thal becomes
That
not
the selection required.
than
sive luck,
program
the example illustrating
and metric
tion, the preparatory command G was used. What would
happen if, for example. the address X was used? Consider
following example:
N120 GOl X11.774 X10.994 Y7.0S0 F1S.O
are two X addresses in the same
control
will not accept the second X value. but it will
an alarm (error). Why? Because there is a
difference
"''''.',,,''',>,.. the programming rules for a G
as such and
the coordinate system words.
allow to
as many G codes in the same block as
providare not in conflict with each other. But the same
"""",11"1'\1 system will not allow to program more
one coward of the same address for
block.
rules may also apply. For example, the words io
a block may
programmed in any
providing the N
aa(lre~;S is the first one listed. For example,
following
block is
(but very nontraditional in its
Nj40 Z-O.75 Yll.56 Fl0.0 x6.S45 GOl
SEQUENCE
67
practices, be sure to
block in a logical order.
word and is usually folaxes in their alphabetical oraxes or modifiers (1.., L, K..),
miscellaneous [unctions
words. and the feedrate word
as the last item. Select only those words needed for the indIvidual block:
N340 GOl X6.84S Yl1.S6 Z-O.7S F10.O
Two other possibilities
tention in programming
the following block be
that may require a special athow
N150 GOl G90 X5.5 G9l Yi.7 F12.0
There is an
the absolute and inmodes. Most Fanuc controls wi I] process this
exactly the way it is written.
X axis target posibut the Y axis will
tion will be reached in absolute
be an incremental distance,
from (he current position of the cutter. It may not
approach, but it
offers advantages in some cases.
- the sequence
block following the block N ]50 will
in the incremental
mode, since G91 is specified
command!
The other programming
block programmed in the
dealing with this subject
that an arc or a circle can
modifiers I, J and K (depending
control system is used). It also
input, using the address R, can
following examples are correct,
1.5
radius:
or a turnthat a direct raBoth of the
in a 90° arc with a
e With I and J arc modifiers:
N21 GOl XlS.3S Yll.348
N22 G02 XlS.as Y12.848 11.5 JO
N23 GOl ...
e With the direct radius R address:
N2l GOl X1S.35 Yll.348
N22 G02 Xl6.85 Y12.848 Rl.5
N23 GOl
N22 G02 Xlo.85 Y12.848 11.5 JO Rl.S
or
answer may be surprising - in both cases, the f'("\",lfV'Il
the 1and J values and will only
the
R.
order of address definition is irrelevant in
case. The address R has a higher control
ity
I and J addresses, if programmed in
same
block. All examples assume that the conlrol
ports
R radius input.
MODAL PROGRAMMING VALUES
are modal. The word modal is
word 'mode' and means that the
comin this mode after it has been used in the
once. It can
be canceled by another modal command of the same group. Without this feature, a
using
interpolation in absolute mode with a
of J 8.0 in/min, would contain the absolute command
the linear molion command GO I and the
F 18.0 in
every block. With
modal values, the programming output is much
Virtually all controls accept modal
two examples illustrate the
commands.
ferences:
e Example A without modal values:
Nl2 G90 GOl Xl 5 Y3.4 FIB.O
Nl3 G90 Gal XS.O Y3.4 F18.0
N14 G90 GOl XS.O YO.S F1B.O
NlS G90 G01 Xl.S Y6.5 F18.0
Nl6 G90 GOl Xl.S Y3.4 F18.0
Nl7 G90 GOO Xl.S Y3.4 Zl.O
e Example B - with modal values:
Nl2 G90 GOl Xl.S Y3.4 F18.0
Nl3 XS.O
N14 YO.S
Nl5 X1.5
Nl6 Y3.4
Nl7 GOO Zl. 0
identical result.. , Compare
Both examples will
corresponding block
each block of the
the modal commands are
of the
B
not
to
..... ,..,"'""'11"/1 in the CNC program. In fact,
in everyday programming,
program commands used
are modal. The exceptions are
program Instructions,
whose functionality starts and
in (he same block (for
example dwell, machine zero
certain machining instructions, such as tool
table. etc.). The M
functions behave in a
example, if the
program contains a machine zero return two consecutive
it
look like this:
blocks (usually for safety
N83 G2B Zl.O M09
N84 G28 XS.37S Y4.0 MOS
N22 G02 Xl6.85 Y12.848 Rl.5 11.5 JO
G28 cannot be removed from
command is not
N84, because the
repeated.
68
Chapter 10
EXECUTION PRIORITY
Functions (hat will be executed simultaneously with the
cutting tool motion:
There are special cases, mentioned earlier, where the order of commands in the block determines the priority in
which the commands are executed. To complete the subject
of a block, let's look at another situation.
M03
Here are two unrelated blocks used as examples:
N410 GOO X22.0 Y34.6 S8S0 M03
and
NS60 GOO ZS.O MOS
In the block N4J 0, the rapid motion is programmed together with two spindle commands. What will actually
happen during the program execution? It is very important
to know when Ihe spindle will be activated in relationship
to the cutting tool motion. On Fanuc and many other controls, the spindle function will take effect simultaneously
with the tool motion.
In the block N560, a Z axis tool motion is programmed
(ZS.O), this lime together with the spindle stop function
(M05). Here. the result will be different. The spindle will
be stopped only when the motion is one hundred percent
completed. Chapter 9 covering Miscellaneous Func/ions
explains this subject.
Similar situations exist with a number of miscellaneeus
functions (M codes), and any programmer should find out
exactly how a particular machine and control system handle a motion combined with an M function address in the
same block. Here is a refresher in the form of a list of the
most common results:
M04
M07
MOS
Functions that will be executed after the cutting tool motion has been completed:
MOO
MOl
MOS
M09
M98
Be careful here - if in doubt, program it safe. Some miscellaneous functions require an additional condition, such
as another command or function to be active For example,
M03 and M04 will only work if the spindle function S is in
effect (spindle is rotating). Other miscellaneous functions
should be programmed in separate blocks, many of them
for logical or safety reasons:
Functions indicating the eod of a program or a subprogram (M02, M30, M99) should stand on their own and
not combined with other commands in the same block, except in special cases. Functions relating to a mechanical activity of the machine tool (M06, M 10, Mil, MI9. M60)
should be programmed without any motion in effect., for
safety. 1n the case of M 19 (spindle orientation), the spindle
rotation must be stopped first, otherwise machine may get
damaged. Not all M functions are lisled in the examples,
but they should provide a good understanding of how they
may work, when programmed together with a motion. The
chapter describing the miscellaneous functions also covers
lhe duration of typical functions within a program block.
It never hurts to play it safe and always program these
possible troublemakers in a sequence block containing no
tool motion. For the mechanical functions, make sure the
program is structured in such a way that it provides safe
working conditions - these funClions are oriented mainly
towards the machine setup.
INPUT OF DIMENSIONS
Addresses in a CNC program that relate to the tool position at a given moment are called the coordinate words. Coordinate words always take a dimensional value, using the
currently selected units, English or metric. Typical coordinate words are X ,Y, Z, L J, K, R, etc. They are the basis of
all dimensions in CNC programs. Tens, hundreds, even
thousands of values may have to be calculated to make the
program do what it is intended to do - to accurately machine a complete part.
The dimensions in a program assume two attributes:
o
Dimensional units
... English Dr Metric
D
Dimensional references
... Absolute or Incremental
The units of dimensions in a program can be of two kinds
- metric or English. The reference of dimensions can be either absolute or incremental.
Fractional values, for example 1/8, are not allowed in a
CNC program. In the metric format, millimeters and mefers
are used as units, in the English format it is incites andfeet
that are used as units. Regardless of the format selected, the
number of decimal places can be controlled, the suppression of leading and trailing zeros can be set and the decimal
point can be programed or omitted, as applicable 10 a particular CNC system.
ENGLISH AND METRIC UNITS
Drawing dimensions can be used in the program in either
English or metric units. This handbook uses the combined
examples of both the English system, common in the USA,
to some extent in Canada and one or two other clluntries.
The metric system is common in Europe, Japan and the rest
of the world. With the economy reaching global markets, it
is imponant to understand both systems. The use of metric
system is on the increase even in countries that still use the
English units of measurement, mainly the United Slates.
Machines that come equipped with Fanuc controls can be
programmed in either mode. The initial CNC system selection (known as the default condition) is controlled by a parilmeter setting of the control system, but can be overridden
by a preparatory command written in the part program. The
default condition is usually set by the machine tool
manufacturers or disuibutors (sometimes even by the CNC
dealers) and is based on the engineering decisions of the
manufacturer, as well as the demands of their customers.
During the program development, it is imperative to consider the impact of default conditions of the control system
on program execution. The default conditions come into effect the moment the CNC machine tool has been turned on.
Once a command is issued in the MDI mode or in a program, the default value may be overwritten and will remain
changed from that point on. The dimensional unit selection
in the CNC program will change the default value (that is
the internal control setting). In other words, if the English
unit selection is made, the control system will remain in
that mode until a metric selection command is entered.
That can be done either through the MOl mode, a program
block, or a system parameter. This applies even for situations when the power has been turned offand then on again!
To select a specific dimensional input, regardless of the
default conditions, a preparatory a command is required at
the beginning of the CNC program:
G20
Selects English units (inches and feet)
G21
Selects metric units
(millimeters and meters)
Without specifying the preparatory command in the program, control system will default to the status of current parameter setting. Both preparatory command selections are
modal. which means the selected a code remains active
until [he opposite G code is programmed - so the meuic
s~stem is active until the English system replaces it and
vIce versa.
This reality may suggest a certain freedom of switching
between the two units anywhere in the program, almost at
random and indiscriminately. This is not true. All controls,
including Fanuc, are based on the metric system, partially
because of the Japanese influence, but mainly because the
metric system is more accurate. Any 'switching' by the use
of the G20 or 021 command does not necessarily produce
any real conversion of one unit into the other, but merely
shifts the decimal point, not the actual digits. At best, only
some conversions take place, not all. For example, G20 or
G21 selection will convert one measuring unit to another
on some - bul not all - offset screens.
The following two examples will illustrate the incorrect
result of changing G21 to G20 and 020 to 021 WIthin the
same program. Read the comments for each block - you
may find a few surprises:
69
70
Chapter 11
c::> Example 1 - from metric to
G21
GOO X60. 0
units:
• Comparable Unit Values
are many units available in
the metric and
In CNC programming, only a very small
of them is used. The
are based on a milapplication. The Engdepending on
for the different
IniTial wUt selection (metric)
X value ,,. arrPI,,)(p/J
Previous value will change into 6.0 incites
(real translalion is 60 I'I1m 2.3622047 inches)
G20
c::> Example 2 - from English to
G20
1niJ.ial unit seleclion
GOO X6.0
X value
units:
G21
Both examples illustrate
problem
by
switching between the two dimensional units in the same
program. For this reason, always use only one unit of
If the program calls a
dimensioning in a
subprogram, the rule
to subprograms as well:
In
it is unwise to
control system aTe n ..",';.",;
system will
trol functions will work.
fecled by the change
Dimensional words (X, Y, Z axes, I, J, K modifiers, etc.)
o
Constant Surface
o
Feedrate function
o
Offset values
and tool preset
(eSS - for CNC lathes)
F
Hand 0 offsets for milling
a
number of rlol"i..,.,,,1
o
Screen position
o
Manual pulse generator· the HANDLE (value of flllIll<;!II'lII1'l.
a
Some control system parameters
dimensional units can
The initial selection
setting. The control status
done by a system
turned on is the same as is was at
when the power
power shut off If neither G20 nor
I is
the time of the
accepts the dimensional units seprogrammed,
lecled by a .-.<;>'-""',1"1 ..:J"",,,H.,,,. If G20 or G21 is ""lI.lU\AJ
command will always
the program, the
system parameter "'.... LUIl;"'.
ority over
- the control ""<:1"""'"
mer makes
preting them, but it
the units setting in a ",,, ... ,,r,,t
Always
motion, offset selection, or
fore any
and G54 La G59).
nate system
produce incorrect results.
low this
ng unils for different jobs.
when frequently
mm
Meter
m
Inch
in
Foot
ft
Many programming terms use
abbreviations.
terms between the two
mensional systems (older terms are in
next table shows the
even if the
selection of the
difference how some confollowing functions will
one system of units to the
o
Millimeter
Metric
English
mlmin (also MPM)
ftlmin (also FPM or SFPM)
mm/min
in/min (also IPM or fpm)
mm/rev
in/rev {also IPR or ipr}
mm/tooth
(also IPT or ipt)
HP
kW
ABSOLUTE AND INCREMENTAL MODES
A dimension in either input units must have a rn",."h"-",
point of reference.
example, if X3S.0
In
program and the
units are millimeters,
statement does nol i
where the dimension of mm has
needs more information to
correctly.
There are two
In
o
Reference to a common point on the part
... known as the
for ABSOLUTE input
o
Reference to a
point on the part
... known as the last tool position for INCREMENTAL input
In the example, the dimension X35.0 (and any
as
well) can
from a selected fixed point on the
part, called
or program zero, or program
point - all
terms have the same meaning.
value
can
be measured from
the
tool
current position for the next
cannot distinguish one
two
statement alone, so some
added to the program.
INPUT OF DIMENSIONS
71
All dimensions in a CNC program measured from the
common poinl (origin) are absolute dimensions. as illustrated in Figure JJ-J, and al I dimensions ina program measured from the current position (last point) are incremental
dimensions, as illustrated in Figure J /-2.
0
2
0
3
, I
-
1
cF~ 1r1_
,/I~
/:
/
•
--- '
I
I
ORIGIN,I
-
Preparatory Commands 690 and G91
There are I wo preparatory commands available for the input of dimensional values, G90 and G91. to distinguish between two availabJe modes:
G90
Absolute mode of dimensioning
G91
Incremental mode of dimensioning
---
'4
0
0
-
•
•
It is a good programming practice to always inclurle the
required setting in lhe CNC program, not to count on any
default setting in the control system. It may come as a
surprise that the common default setting of the control system is the incremental mode, rather than the absolute mode.
After all. absolute programming has a lot more advantages
than incremental programming and is far more popular. In
addition, even if the incremental programming is used
frequently, the program still starts up in the absolute mode.
The question is why the incremental default? The reason is
- as in many cases of defaults - the machining safety. Follow this reasoning:
Figure 71·1
Absolute dimensioning - measured from part origin
G90 command will be used in the program
-- -01
,/L-______________________
Both commands are modal, lherefore they will cancel
each other. The control system uses an initial default setting
when powered on, which is usually the incremental mode.
This setling can be changed by a system parameter that presets the computer at the power startup or a reset. For individual CNC programs, the system setting can be controlled
by including the proper preparatory command in the program, using either one of two available commands - the
G90 or G91.
~
__ _
=I===:I==I==.!
//~/ :J:. :_~:_:_ _
:START AND END
Figure 11-2
Incremental dimensioning - measured from the current tool location
G91 command will be used in the progrom
Absolute dimensions in the program represent
the target locations of the cutting tool from origin
Incremental dimensions in the program represent
the actual amount and direction of the cutting tool
motion from the current location
Since the dimensional address X in the example, written
us X35.0, is programmed the same way for either point of
reference, some additional means must be available \0 the
programmer. Without them. the control system would use a
default selling of a system parameter, not always reflecting
the programmer's intentions. The selection of the dimensioning mode is controlled by two modal G commands.
Consider a typical start of a new program loaded into the
machine control unil. The control had just been turned on,
the part is safely mounted, the cutting tool is at the home
position, offsets are set and the program is ready to start.
Such a program is mosllikely written in the more practical
absolute mode. Everything seems fine, except that the absolute G90 command is missing in the program. WhaT will
happen at the machine? Think before an answer and think
logically_
When the first tool motion command is processed, the
chances are that the tool target values will be positive or
have small negative values. Because the dimensional input
mode is missing in the program, the control system 'assumes'lhe mode as incremental, which is the default value
of the system parameter. The lool motion, generally in X
and Y axes only, will take place to either the overtravel
area, in the case of positive target values, or by a small
amOlJnl, in the case of neg<1li ve target values. In either case,
the chances are that no damage will be done to the machine
or the part. Of course, there is no guarantee, so always program with safety in mind.
G91 is the standard default mode for input of dimensions,
72
Chapter 11
• Absolute Data Input - G90
In the absolute programming mode, all
are
of origin.
origin is the promeasured from Ihe
gram
poinT also known as program zero. The actual
the
is the di fference bet ween
current absolute position the tool and the previous absoposition. The
[+] plus or H
refer
to the quadrant of
coordinates, nor
direction
motion. Positive
does not have to written for any
address. AI!
z.ero values. such as XO. YO or ZO
to
the
at program
point, not to the
motion itself. The zero value of any axis must
written
• Combinations in a Single Block
many Fanuc
the absolute and incremental
modes can be combined in a single nrr'O'f':~rn
cial programming purposes. This
usual, but
are significant benefits this advanced
is in one mode only plication. Normally. the
either in the absolute mode or
incremental mode. On
controls, for
to the opposite mode, the
motion command must programmed in a
block.
do not
to program an inSuch controls, for
cremental motion along one axis and an absolute motion
along
other axis in the same block.
do allow to program both
in the same
All that needs to be done is to
specify the G90 or the G91 preparatory
before
the significant
address.
Most
absolute
The preparatory command G90
mode remains modal until the
command 091
is programmed. the absolute
there will no motion for
that is omitted in the program.
main advantage
programming is tbe ease
of modification by the programmer or
CNC operator. A change of one dimension does not
any other
menslOns m
program.
lathes with Fanuc controls, the common repreof the absolute
is the axis
as X
command. Some lathes
Fanuc controls.
• Incremental Data Input - G91
programmmg,
a
mode, all program dimensions are
as de"'<:l,elln-", distances into a specified direction (equivalent to
'on the control
The actual motion of the
is the speC! fied amount along
with the direction indicated as
or negative.
rPI,'7TH'P
signs + or - specify direction of the tool motion, not
the quadrant of rectangular coordinates_ Plus
for positive values does not have to be written, but
sign must
used. All zero input values, such as XO, YO or ZO mean
there will be no tool motion aiong that axis, and do not have
to written at all. If a zero axis value is programmed in inmode, it will
preparatory comincremental
is G91 and remains modal until the absolute
is programmed.
will be no
motion for any axis omitted in the
block.
The main advantage of
programs is their
portability between individual
of a
An
program can called at different locations of
the part, even in different programs. It is mostly
when
developing
or repealing an equal distance.
For
controlled CNC lathes, the common representation
incremental
is the axis designation as U
and W, without the G91 command. Some lathes
use
I, but not those with
controls.
G91 are not
For lathe work, where G90
is between the X
U axes and the Z and Waxes.
The X and Z contain the absolute values. U
Ware the
incremental values. Both types can be wriuen in the same
block without a problem. Here are some typical examples
for both applications:
C Milling example;
N68 GOl G90 X12.5031 G91 Y4.S111 Fle.S
The milling
shows a motion
the cutter has
La reach the absolute position of 12.5037 inches and - at
the same rime to move
Y axis by
177 inches in the
Note
position
commands G90 and G91 in the block - it is
Important, but it may not work on all
C Turning example:
N60 GOl X13.S6 W-2.S FO.013
example
a
lathe shows a tool
motion,
where the cutting tool has to reach the diameter of 13.56
inches and - at/he same time to move 2.5 inches into
the
Z
direction.
by the neremer
tal
address W.
or G91 is not nonnally
the Group A
G codes is the most common
one ~nd does not
G code
of dimensional mode selection.
is a switch
the absolute
mode in a CNC program, me programmer
must be careful not to remain in the 'wrong' mode
man
The switch
(he modes is
Iy temporary, for a specific
It may
one block or
several blocks.
thatLhe original selling for (he proRemember that both the absolute and
.nf'rp,...,pnt,:; modes are modalremaIn In
unby the opposite
IN
OF DIMENSIONS
73
DIAMETER PROGRAMMING
MINIMUM MOTION INCREMENT
All dimensions along
Minimum increment (also called the leas! increment) is
the smallest amount of an a.:ds movement the control syslem is capable supporting. The minimum increment is
the smallest amount thai can be programmed within the selected
input. Depending on the dimensional
Ihe minimum
increment is exin millimeters
system or in
system.
on a CNC lathe can be
as
This approach simplifies
programming and
Normally, the defauh
ler programming. The
changed to interpret the X
the program
to read.
controls is
system parameter can
as a radius inpul:
GOO X4. 0
GOO X2. 0
Dia.me/erdimellsioll
, .. when sel 17)' {J {Ifl1'ffJl1l'lf'Y
R(Jf/ilis
... when set by (j paroJlleler
value is rnrrpt·,
setting. The diameter
is easier to
by both the programmer and operator,
use the diameter di
for cylindrical
suring diameters at
machine is common.
cerlain caution - if the diameter programming is used, all tool
wear offsets for
X
must be treated as applicable to
the diameter oJfhe
not to il$ single
(radius value).
0.001 mm
of minimum
most com0.0001 inches for metunits respectively.
a typical CNC
increment for the X axis is also 0.00 I mm or
but is measured on the diameter - that means a
mm or .00005 inches minimum increment per
is much more tlexjble
machining
the metric
than in the English
are O.OOl mm
Minimum increment
Converted equivalent
-
For example,
two sections of the following metric
programs are
- note Ihal Ihey bOlh starr in the ab~
solute mode and only the diameters
different:
Q Example 1 - Absolute diameters:
.~
0.001 mm
.00003947 inches
.0001 inches
0.00254
the metric system
system, which
less accurale
J54% more accarale
the English system
..
metric system,
(ABSOLUTE START)
FORMAT OF DIMENSIONAL INPUT
year of 1959 is
numerical
......."'''''~'"' have taken
format of dimensional
X116.0
GOO ..
Q Example 2 - Incremental diameters:
mo.o
Metric
In the
mode, the intended X
mOlion will
Inlhe
U
as a distance and
be programmed as
on n
direction to
GOO G42 X85.0 Z2.0 T0404 MOS
GOl z-24.0 FO.3
Minimum increment
.0001 inch
Another
consideration,
very imporLant, is the
the absolute or the incremental
mode of dimensional input. The diameter programming,
represents the part
IS
where the X
much more common in the absolute mode. In those cases.
when an incremental
is required.
that all
incremental dimensions in the program must
be specified per dial1letel; lIot
radius.
GOO G42 X8S.0 Z2.0 T0404 MOS
GOl Z-24.0 FO.3
X9S.0
Z-40.0
X1l2.0
Z-120.0
Units system
considered to be the
Since that lime,
that intluenced the nrr,ot":lm
Even to this day,
data can be
one of the four possible ways:
(ABSOLUTE START)
(X95.0)
Z-40.0
Q
Full address format
o
leading zeros suppression
ill 7 . 0
(Xll.2 • 0)
o
Z-120.0
U4.0
GOO ..
(Xl16.0)
o Decimal
zeros
in
74
Chapter 11
In
to understand
format
back some years may be beneficial.
control
(mainly the old NC systems as compared to the more modern CNC
were nOl able to accept the
input
of dimensions - the decimal point formal - but the
accept all the earlier
formats,
even
decimal format is most common. The reason
iscompatjbility with lheexisting programs (old programs).
decimal point programming method is
latest of
available,
systems thaI allow
point
programming can also accept programs written many years
earlier (assumed that the control and machine tool are also
compatible). The reverse is nor true.
Since
leading zeros suppression and the trailing zeros
suppression are mutually exclusive. which one
be
programmed for
Without a decimal poim? As it
depends on
setting the control system or
(he designation of (he status by the control manufacturer,
the actual
stnLuS must be known.
status determines which zeros can suppressed. It may be the zeroes
zeros allhe end of a dimension withallhe beginning or
out a decimal poin!. In the extremely unlikely evenl
the
system is
with
zero suppression feature
as the only
programming the decimal point will not
be possible.
illustrate
results of zero suppression.
will be
earlier
is a very imponant issue,
knowing how the
interprets a number that
110 decimal poim is
for all
motion commands and
Jr the English input .625 inches is to programmed in
the leading zero suppression format
applied to the X
it will
in the program as:
• fun Address format
X6250
The full format of a dimensional
English
metnotation of +44 in
That means ali eight
digits have to
len for the
words X, y, Z, I. J, K, etc. For example, the
English
of .625,
applied to
X axis, will
be written as:
The same dimension
rOs suppressed, will
inches with the trailing zein Ihe
as:
X0000625
The metric units input of 0.42 mm, also applied 10 the
axis, is written with the lending zeros suppressed as:
X00006250
X420
the X axis,
dimension of 0.42 mm,
written as:
when
to
The same dimension of 0.42 mm with the
suppressed will appear in the program a,,\:
zeros
X00000420
X0000042
full formal programming is applicable only to
early control un its, but is correct even today.
programmed
was usually
without the
designation, which is determined by position of the dimension
within the block. For modern CNC programming. the full
format is obsolete and is used here
reference
format will
quite
comparison. Yes,
modern programs, but don't used it as a standard.
•
Zero Suppression
Zero suppression
is a great improvement over
full programming
It was
<ldaptation of a new
format that reduced the number of zeros in thedimensional
input Many
controls still support the method of
7~ro suppression. but only for reasons of compatibility with
old and proven programs.
Zero suppression means that either
leading or
trailing zeros of
maximum
input do not
have [0 be written in the CNC
The result is a great
reduction in
program
The default
has
been done by the control manufacturer, although
default mode can be optionally set by a
parameter.
Don 'I
allY
WiThoul a
reason!
Although the examples above illustrate only one small
ieation, the impression
leading zero suppresis more practical than the trailing zero suppression is
quite
Many older control systems are indeed set
(rarily 10
the
zero suppression as the default,
because its practicality.
is the reason why - study it
carefully, although today the subject is more trivial than
On
other hand. if even one decimal point is
omitted (forgOlten) in the program, this knowledge becomes very useful and
subject is not trivial any more.
Preference for Leading
Suppression
the
dimensional input the
syslem can accept
eight digits, withoUl a
decimal point, ranging from 00000001 to 99999999:
o
Minimum:
0000.0001 inches
o
Maximum:
9999.9999 inches
or 00000.001 mm
or 99999.999 mm
is nol written. If the program uses zero
suppression
either type, a comparison of input values
should be useful:
INPUT OF DIMENSIONS
Input
Decimal point
75
- inches
leading zeros
suppression
Trailing zeros
suppression
the
I can
programmed with the X
fo!lowed by
the
of eight digits, always positive. If
control
system
the decimal point, there is no confusion. If
the leading or the trailing zeros have to
is very important
XO.OOOl
Xl
XOOOOOOOl
XO.OOl
XIO
XOOOOOOl
XO.Ol
XIOO
XODOOOl
XO.l
X1000
00001
Xl. 0
XlODOO
0001
a
No trailing zeros
X000005
XOOl
a
Decimal point
XO.5 or X.5
XOI
XI0000000
Xl
leading zero suppression is much more common, bebencfits numbcrs with a small
parI
than a large integer part.
the metric input the resulls will
a
X0000050
a No
zeros
X500
Note thaI
the format is the same
dwell as for the
words. The programmed formal
will always adhere to the notation of the address.
dwell is expressed by the
dentally, in some
P address, which
a decimal point at all and
the leading zero suppression
must be programmed
will be equal to P500.
mode in effect.
• Decimal Point Programming
Input value comparison - millimeters
point
dwell
Leading zeros
suppression
XOOOOOOOl
XOOOOOOl
XOOOOOl
Xl-O
XlOOO
XOOOOl
XIO.O
XIOOOO
XOOOl
XlOO.O
XlOOOOO
XOOl
XlOOO.O
X1000000
XOl
XIOOOO.O
XIOOOOOOO
Xl
time.
important for example,
the
programmer forgets to
point or
CNC operator forgets to punch it in?
- and common - errors that can be avoided
good knowledge.
complete the section on zero suppression, let's look at
a program input that uses an axis letter but no/ as a
nate word. A
command will be
to explain.
Chapter 24 covers
the delails relating to the dwell
gramming.
use the basic format and one second dwell
The dwell formal is
the dwelling
This format tells us that
All modem
will use the decimal point for
dimensional input
the decimal point, particularly for program
a fractional portion,
makes the CNC program much
to develop and to
read at a later date.
From all the available nT"""""'"",
used. not all can be
The ones that can arc those
millimeters or seconds
The following two
mal point is allowed in
controls:
thedeciand tum-
control programs:
X, Y, Z, I, J, K, A,
R
=> Turning control programs:
X, Z, U, W, I, K, R, C,
F
The control system that supports
option of programming the decimal point, can also
dimensional values
without a decimal poin£, to allow
with older
programs. In such cases, it is
the
principles of programming
and
the traiJing zeros. If they are used rrw'r",1'"
explanations). there will be no problem to
the various
dimensional formats to any other
old or
new. If possible, program the
as a standard
approach.
76
11
compatibility enables many
users to load
their old
in
format), into the new
not the other way around usually with
or no modifications at all
Some
units do not have the ability to
an paper tape
they have no tape
convert
any tapes that contain good programs, there are two options
if
- one, have someone to install a tape reader in
possible and
(probably not).
to store the contenls of a tape in the memory
computer.
much better
able software
possible.
cializing in
in the metric system assume 0.00 I
mm mInImUm
while in the English
the
increment is .000 I
an inch (leading zero suppression
mode is in effect as a default);
• Input Comparison
Differences in the input format for both
and
metric dimensioning can be seen clearly. One more time,
the same examples will
shown. as before:
Q English
Full format
No leading zeros
No trailing zeros
Decimal point
input of .625 inches:
X00006250
X6250
X0000625
XO.625 or X.625
Q Metric example input of 0.42 mm :
Full format
No leading zeros
No trailing zeros
Decimal point
X00000420
X420
X0000042
XO.42 or X.42
CALCULATOR TYPE INPUT
In some
is
is
Y12 • 56
Y12.56
Yl25 600 ..Jor English units
Y12560
.. .jormefriculliis
without the decimal
the same block:
such as woodworking or
(especially metric)
not require decimal
only whole numbers. In these
cases, the decimal point would always be followed with a
zero. Fanuc provides a solution to such situations by the
feature called calculator input. Using this feature can
shorten program size.
N230 X4.0 Y-10
This may be beneficial
extreme conservation of
system memory. For
X4.0 word WIll
fewer characters than the
X40000 - on the other hand,
the Y-IO is shorter
decimal poin! equivalent of
y-o.OO I (both examples are in English units). If all
before or after the decimal
are zeros, (hey do not
10
wriUen:
xO.s
:::
Y40.0
Z-O.l
F12.0
X.5
X40.
calculator type input
parameter. Once the parameter is
the trailing zeros do not
to
example,
will
the normally expected
selling of a system
the decimal point and
they will asas X25.0, not
H l r . . . ",,, -
In case the input value
the decimal point, it
can written as usually.
means the values with a decimal point will be interpreted correctly and numbers withou(
decimal point will be treated as major units only
or millimeters). Here are some
Z-.l
;:;
Standard Input
F12.
RO.125 ::: R.12S
... etc.
Any zero value must be written example, XO cannot
written as X only. In this
all the program examples use the decimal point
whenever possible.
Many programmers prefer to nrr"',"'!\rT\ zeros as in the left
of the example. They
memory. but they are
for learning.
i·
Calculator Input
X345.0
X345
XL 0
Xl
YO.67
YO.67
Z7.4B
Z7.48
Normally, the control system is set to the
suppression mode and the non-decimal
preted as
of the smallest units.
Z 1000 in
I mode will be equivalent to .0
SPINDLE CONTROL
machines, machining centers
mateuse spindle rotation when removing
a
rotation may be that of the cutting tool
or
itself (lathes). In both cases, the.
spindle and the working feed rate of the
to be strictly controlled by the program.
require instructions that relate to the
selection of a suitable speed of the machine spindle and a
a given job.
methods to control the spindle and cutting
they all depend mainly on the type of the
CNC
the current machining application. In
this chapter, we look at the spindle control ancl its programming appl '('<lInn,,,,!
SPINDLE FUNCTION
to spindle speed is conS. The programis usually within the range of
point is allowed:
51
10
59999
machines is not unusuaJ to
For many high
to five digits. in the range
have spindle
available
of I to 99999, within
S
On
CNC lalhes, all three alternatives may
on the control system. For the CNC mill'
terns, peripheral spindle speed is not applicable,
spindle speed code number and the direct spindle speed
are.
spindle speed selection by special code number is
an obsolete concept, no! required on modern controls.
I-'..... JJIUllII5
ndle speed designation S is not
",,..,,,,.,,,,,,,,,,,,,,.rl by itself. In addition to the
additional
are attributes that control
is
if the spindle
programming instruction is not
spindle function stands by itself in
not include all information {he control
for
spindle data. A spindle speed
example, to 400 r/min or 400 mlmin or 400
on (he machining application), does not
information, namely,lhe spindle rotaMost
can be rotated in two directions clockwise or counterclockwise, depending on the type and
setup of the cutting tool used. The spindle rolation has to be
specified in
in addition to the spindle speed
are two miscellaneous functions provided by
that controllhe direction of tile spindle-
DIRECTION OF SPINDLE ROTATION
51 to 599999
and left, up and down. clockand similar directional terms, is
/lIe relative to some known reference.
as clockwise (CW), or as
some established and standard
this case a reference point of
VLa'UUll
• Spindle Speed Input
The address S relates to
and must always
the CNC program.
are
the numeric value (input) of the
o Spindle speed code number
spindle function,
numeric value in
alternatives as to what
function may be:
.. old controls· obsolete
o
Direct spindle speed
.. r/min
o
Peripheral spindle speed
.. ftlmin or mlmin
The direction
rotation is always relative to the
from the spindle side of the
poim of view that IS ",;) ••:lUlI',.
that contains the spindle.
machine. This part a
headstock. Looking
and is generally called
from the machine
area
the direction along
establishes the corspindle center line and towards
rect viewpoint for
and CCW rotation of the
spindle. For CNC
CNC machining centers,
is quite simple
to understand.
are exactly the
same, and will
77
78
•
Chapter 12
Direction for Milling
It may be rather impractical to look down along the center
line of the spindle, perpendicularly towards the part. The
common standard view is from the operator's position, facing the front of a vertical machine. Based on this view, the
terms clockwise and counterclockwise can be used accurately, as they relate to the spindle rotation - Figure 12-1.
Although the descriptions CW and CCW in the iHustration appear to be opposite to the direction of arrows, they
are correcL The reason is that there are two possible points
of View, and they are both using the spindle center line as
{he viewing axis, Only one of the viewpoints matches the
standard definition and is, therefore, correct. The definition
of spindle rotation for lathes is exactly the same as for machining centers.
To establish spindle rotation as CW and CCW,
M04
M03
look from the headstock towards the spindle face.
The first and proper method will establish the relative
viewpoint starting at the headstock area of the lathe. From
this position, looking towards the tailstock area, or into the
same general orea, the clockwise and counterclockwise directions are established correctly.
The second method of viewing establishes the relative
viewpoint starting at the tailstock area, facing the chuck.
This is an incorrect view!
R/H tool - CCW
R/H tool- CW
Compare the following two illustrations - Figure 12-3
shows the view from the headstock, Figure 12-4 shows the
view from the tailstock and arrows must be reversed.
Figure 12-1
Direction of spindle rotation.
Front view of a vertical machining center is shown
•
Direction for Turning
A comparable approach would seem logical for the CNC
lathes as welL After all, the operator also faces the front of a
machine, same as when facing a venical machining center.
Figure 12-2 shows a front view of a typical CNC lathe.
CW= M03
CCW= M04
Figure 12-3
Spindle rotation direction as viewp.d from the headstock
Headstock
cw
ccw
y
Tailstock
CW= M03
Figure 12-2
Typical view of a slant bed two axis CNC larhe.
CWand CCW directions only appear to be reversed
CCW= M04
Figure 12-4
Spindle rotation direction as viewed from the taifstock
SPINDLE CONTROL
• Direction Specification
If
spindle rotation is clockwise, M03 function is used
in the program - if the rotation is counterclockwise, M04
function is used in the program.
the spindle speed S in the program is dependent on
the spindle rotation function M03 or M04. their
ship in a CNC program is important
S and spindle
function
spindle speed
M03 or M04 must always
accepted by the control system together. One without the other will not mean anything
to the control, particularly when the machine is switched
on. There are at leasllwo correct ways to program tbe spindle
and spindle rotation:
o
If the spindle speed and rotation are programmed together
in the same block, the spindle speed and the spindle
rotation will start simultaneously
o
If the spindle speed and rotation are programmed in
separate blocks, the spindle will nat start rotating until both
the speed and
rotation commands have been processed
• Spindle Startup
The following examples demonstrate a number of correct
starts for the spindle speed and
rotation 10
All examples assume that
is no active setting of
spindle speed
either through a previous program or
through the Manual DaJa Input (MDI). On
machines,
there is no
or default
speed when the machine power turned on.
<:> Example A - Milling application:
m G20
N'2 G17 G40 GSO
NJ G90 GOO G54 X14.0 Y9.S
N4 G43 Zl. 0 Hal S600 M03 (SPEE.'O WITH ....".·A·'·'
N5 •••
This example is one the preferred
for milling
applications. Both the spindle speed and spindle rotation
are set with the Z axis mOlion towards the
Equally
motionpopular method is to start the spindle with the
in the example:
Nl G90 GOO GS4 X14.0 Y9.S S600 M03
Selection is a matter of personal preference.
020 in a
separate block in not necessary for Panuc controls.
e Example B - Milling application:
N1 G20
N'2 Gl' G40 GSO
N3 G90 GOO G54 Xl4. 0 Y9. 5 S600
(SPEED ONLY)
N4 G43 Zl.O HO 1 MO)
(ROTATION STARTS)
N5 ...
79
second example B is technical1y correct, but logically flawed. There is no benefit in splitting
spindle
speed and spindle rotation into two blocks. This
makes the program harder to interpret.
e
C - Milling application:
N1 G20
N2 G17 G40 GBO
N3 GOO G90 G54 X14.0 Y9.S M03
N4 G43 Zl.O HOl
N5 GOl ZO.l FSO.O S600
N6 ••.
(ROTATiON SET)
(NO ROTATION)
(ROTATION STARTS)
Again, the C example is not wrong, but it is not
tical either. There is no danger. if the machine pewer has
been switched on just prior to running this program. On the
other hand, M03 will
the spindle rotation, if another program was processed earlier. This could create a
possibly dangerous situation, so foHow a simple rule:
e Example 0 - Turning application with GSO :
N1 G20
N2 GSO X13.625 Z4.0 T0100
N3 G96 S420 M03
(SPEED SET - ROTATION STARTS)
N4 •.•
This is the preferred example for
lathes, if the
G50 setting method is used. Because
spindle
is
se~ as CSS - Constant Surface Speed, the control system
WIll calculate the actual revolutions per minute (r/min)
current part
based on the CSS value of 420 (ftlmin) and
at XI
The next example E is correct but not
recommended
caution box above).
e Example E Turning application with G50 .
N1 G20
N2 GSO X13.62S Z4.0 TOlOO M03
N3 GOO X6.0 ZO.l
(ROTATION SET)
(NO ROTATION)
N4 G96 GOl ZO FO.04 T010l S420 (ROTAT. STARTS)
NS ...
Q Example F - Turning application without G50 :
N1 G20 T0100
N2 G96 5420 M03
N3 GOO •••
(SPEED SET - ROTATION
In
more contemporary example (GSO is not used as a
position
command anymore), the machine spindle
speed will be calculated for a tool offset
stored in the
Work Geometry Offsel register of the control system.
system will perform the ca1culation of actual r/min when
the block N2 is
80
These examples are only
correct methods for
a spindle start. All contain
rotation at the beginning of a program
milling and turning applications. The
beginning of a program has
been selected intentionally, IJ"'-''"'''''''-' for any first tool in the
program. there is no active
or rotation in effect (normally carried on from a
tool). However, the control unit may still store
and rotation from the
last tool of the previous
Any toolfollowing
programmed speed "'-:I<::L"'"
tool. If onJy the 31..1'11"":''-'
for the next tool,
assume the last
rotation direction. If only the
direction code M03 or M04 is programmed, the
speed S will
the same as
the previous tool.
Be careful if a program
program stop functions MOO Or MOl, or the
function M05. Any
one of them will automatically stop the spindle. It means to
be absolutely sure as to when
rotation will take
spindle
place and what it will be.
speed selection and its rotation the same block and for
tool. Both functions are
connected and placing
within a sing1e block w i l l '
and
logical program structure.
SPINDLE STOP
NormaHy, most work requires a
speed. In some cases, a
desirable. For example, before
change or reverse a part in the middle
a program, the
spindle must be stopped first. The spindle must also be
during a tapping operation and at
of proSome miscellaneous functions will stop the spindle
rotation automaticaHy (for example, the functions MOO,
MOl, M02 and M30). Spindle rotation will
during certain fixed cycles.
the spindle stop should always
Counting on other functions to
is a
programming practice.
in programming, to slop the
spindle rotation. use function MOS.
the clockwise or the counterclockwise
V\(l,lIV'1. Because M05 does not do anything
(unlike other functions that also stop the spindle, such as
MOO, MOl, M02, M30 and others), it is used for situations,
must be stopped without
other programmed activities. Some typical
in tapping. tool motion to the . ".".,AlI."
tion, turret
position, or after machine zero
depending on the application. Using one of the
cellaneous functions that automatically stop
the
is not required. On tile
......t,nT<;Ifn exactly what is required, in a particular
Chapter 12
but it will
method may result in a slightly longer
easier to read and maintain it, mainly
with limited experience.
can be
asa
Nl.20 MaS
block containing the tool motion, such as
Nl.20 Z1.0 M05
The motion will always be completed first, then the spindle will be
This is a safety feature built inlo
control
remember to program M03 or
.,.n .... rlll", rotation,
SPINDLE ORIENTATION
The last M
relates to a spindle activity,
is M 19,
is most commonly used to set a machine spindle
an
position. Other M codes may
be valid,
on the control system. for example
M20 on same
spindle orientation function is
a very specialized
seldom appearing in the program itself.
MI9 function is used, it is mainly during
setup, in the Manual Data Input mode (MDI). This function is exclusive to
milling systems, because only specially eqllipped
may require it. The function
can only be used when
spindle is stationary, usually
ter the spindle
When the control system executes the M 19 function, the following action will
The spindle will
tum in both
clockwise and
a short period.
the internal
activated. In some
is audible. The spindle
cases, the
will be locked in a
and rotating it by hand,
will not be
exact locking position is deterby the machine tool
indicated by the
setting angle - Figure
Figure 12-5
Spindle orientation angle is defined bV the ma,~fll'I'"
manufacturer and cannot be changed
SPINDLE CONTROL
81
In CNC machine lool operation, the MI9 function enables
machine
to place a tool into the
manually and guarantees a proper 1001 holder orientation.
Later chapters will provide more
about
Ofland
applications,
example. in
point
boring
SPINDLE SPEED - R/MIN
programming CNC machining centers, designate
the spindle
directly in revolutions per minute (rlmin).
A basic
that contains spindle speed 200 rlmin, for
require this
enu-y:
N230 S200 M03
CNC
centers (oat all) use tool holders
that can be placed into
magazine only one way. To
~chieve this goal, the 1001 holder has a special notch
of the spindle built-in,
matches
internal
Figure
In order to find the
the holder that has
the
there is a small dimple on
notch side.
deis intentional.
format is typical to milling controls,
nO peripheral speed is used. There is no need to use ~ sp~i~l preparatory command to
the rlmin setllng. It IS the
a mInimUm
control default. The r/min value must
crement of one.
or
values are not allowed
the r/min must always within the range of any
A few machining centers may be equipped with the option of a
spindle
selection - direct r/min
a
peripheral speed. In this case, as
as for all
gramming, a proper preparatory command is used to.
guish which
is active.
is used
penpheral
direct
of r/min. The distincspeeds, G97
tion between them is discussed next.
SPINDLE SPEED - SURFACE
Figure 12-6
Built-in notch in 8 tool holder used for correct tool
orientation in the spindle - not a/l machines
this feature
tools with
flutes (cutting edges),
as
drills, end mills, reamers, face mills, etc., the orientation of
cutting edge
to the
spindle
is not
that important. However,
.
point . such a~
ing bars, orienlation of
cuttmg edge dunng setup lS extremely important,
when
fixed
are used. The two
cycles that use the built-in
orientation, G76
G87, the
retracts from
mahole without rotating. In
to prevent damage to
the finished
the tool retraction must
controlled.
Spindle orientation guarantees that the tool will shift away
from the finished bore into a clear direction. An accurate
setup is ne1ces,sary
Those machines
spindle either way still
shift when
or G87
tool holder
the
proper setting tools that
cycles are programmeu.
Programmed spindle speed should be based on the machined material and the cutting tool diameter (machining
centers), or
part diameter (lathes).
rule is
that the larger the
the slower the spindle r/min
must
Spindle speed should never guessed - it
always be calculated.
a calculation will
the spindle
is directly proportional to the programmed
An incorrect spindle speed will have a
negative
on both the tool and the
• Material Machinability
spindle speed, each
material
a sugtool material. This
machinability rating for a
is either a percentage of some common material,
such as mild
, or a direct rating in terms
periphor sUiface speed. Surface speed is specified in
eral
feet per minute (ftlmin) in
units,
in meters
system.
minute (nt/min) in
for jtlmin is FPM, meaning Feet Per Minute. The
amounts of
speeds indicate
level of machining
difficulty with a given tool material. The
(he surface
speed, the more difficult it is LO machine the
material.
Note the
on the words 'given fool material'. To
comparisons meaningful
fair, they must be
with the same type of cutting tool, for
tools will
much
speeds for high speed
lower then
for cobalt
tools and. course, for
carbide tools_
Chapter 12
on the surface speed
(he cutler diameter (or
part diameter for lathes), machine spindle speed can be calculated in revolutions per
one mathematical
for English units
another when
are programmed.
Itir where ...
= Spindle speed in revolutions per minute
= Multiplying
- meters to mm
= Peripheral
in mlmin
= Constant3.1415927
= Dia.meter in mm (cutter diameter
r/min
1000
m/min
1t
o
or part diameter for
• Spindle Speed - English Units
peripheral
To calculate the spindle
the material
as well as the
type must
tool or the part:
speed is 30 mlmin
meter is 15 mm:
=
=
=
(1000 x 30)
636.6
637 r/min
I
A
version of the
tive and almost as accurate as
the cutting tool
.1415 x 15)
is an acceptable allemaformula:
n",,'I"'(''''
Itir where ...
rim in
Spindle speed in revolutions
Multiplying factor - feetto
Peripheral speed in
12
ft/min
1t
:::
D
Constant 3.1415927
Diameter in inches (cutter
or part diameter for turning)
for milling,
is 150 fUmin,
Peripheral
for the selected
and the cutting tool diameter is I
:::
(12 x 150) /
327.4
327 r/m.in
(3.1415 x L 75)
Many
applications can use a
mula, without losing any significant accuracy:
r I min =
3.82 x ft I min
D
ILl."" .. " . the 3.82 constant may
as an easier calculation
a
units must be applied "'Y'r,nG>rl
not be correct.
• Spindle Speed - Metric Units
When metric
previous formula is
is
in the program,
same, but
units are
Again, by replacing the constant 31
with constant 320
somewhat inaccurate, but
within an acceptable
most
(or even 300), the r/min will
CONSTANT SURFACE
lathes, the machining
is different
from
process. The turning tool has no diameter
to the
and the diameter of a boring bar has no
It is the part diameter that is
spindle
used for
calculations. As the
machined,
changes constantly.
cut or during roughing operations
during a
eterchanges
in Figure 12-7.
the spindle
is not practical of the many
should be selected to
is to use the sUrface
r/min? The
the lathe
is only a half of the
To select a
The other half is to communicate this selection to
trol system. The
has to be set to the surface
mode, not the rlmin
Operations IlS drilling,
tapping, etc., are common on a lathe and
distinguish between
direct r/min in the
the choice of
face speed or
per minute must be
This is done with preparatory commands G96 and
prior 10 the spindJe function:
SPINDLE CONTROL
G96 S •• M03
83
o Example 1 :
Swface speed selected
G97 S •• M03
""rl-""c> speed is set right after
milling. this distinction normally does not
GSO (or
and
spindle speed in rlmin is always assumed.
By
the
G96 for
turning
boring, the control enters
a special
known as the ConstaJlt Surface Speed or CSs. In this
the
spindle revolutions will
and
diameter
cut (curautomatically, depending on
rent diameter).
automatic Constant Surface Speed is
built in
systems
for most CNC lathes.
It is a feature that not only saves programming time, it
allows
tool to remove constant amount of material at all
cutting too)
excessive wear
"".-/''''"'''' finish.
a typical example,
a facing cut
starts at
(06.2), and faces the part to the centerline (or
slightly below). G96
was used
program.
6000
was the
spindle
of the
coordinate setting,
command:
N1 G20
GSO X16.0 ZS.O T0100
N3 G96 MOO MOl
~
In this quite common application, the actual spindle
speed will be
on the current diameter of 16 inches,
In
r/min in block
In some cases, this will
be too low. Consider another example:
o
2:
On large CNC lathes, GSO
of the X
diameter
is quite large,
024.0
the previous example,
target diameter the next tool motion was nat important, but in
case it is.
example:
N1 G20
N2 GSO X24.0 ZS.O T0100
N3 G96 S400 M03
ftlmin
N4 GOO X20.0 TOIOl MOB
8375
06.20 231 r/min
-""'-- 06.00 :::; 239 r/min
6000 r/min
:::: 260 r/min
max. spindle
speed
05.00:: 286 r/min
,~,- 04.50:: 318 r/min
,,'~- 04.00 :::;
rIm in
:::; 409 r/min
- 03.00:::; 477 r/min
- - - 02.50 :::; 573 r/min
02.00 ::::
r/min
01.50 :::;
r/min
01.00:: 1432 r/min
- ' ' ' - 00.50 2865 ,!min
00.25 := 5730 r/min
~ 00.00 ::::; 6000 r/min :: spindle max.
Figure 12-7
i-IfR1Tlnlll at a
cut using constant surface speed mode 696
Althougb only selected diameters are shown in the illustration, along with their
revolutions per
ute, the updating
is constant. Note the sharp increase in r/min as
tool moves
to machine center
When the
reaches XO (00.0), the speed will be at
its maximum, within the current gear
As this speed
may be too high in some cases, the control system allows
setting of a
maximum, described
a
speed
a
lathe,
options. In
following
examples,
important ones will be examined. The gear
tions are omitted for all examples.
are
most
func-
In the
2, the
1001 position is at X24.0
the tool motion terminates at X20.0, both values are
ters_
translates to an actual motion of only
the X24.0, the spindle will rotate at 64 r/min, at X20.0 it
will rolate at 76 r/min. The difference is very
to warrant any
programming. [t is different, however, if
the starting position is at a
diameter,
a tool moves
to a much smaller
diameter.
o Example
From
initial position of 024.0 .
move to a
small
of 2.0 .
the tool will
N1 G20
N2 GSO X24.0 ZS.O TOIOO
N3 G96 S400 M03
N4 GOO X2.0 TOlOl MOB
Spindle speed at the start of program (block N3) will
the same as in previous example, at 64 r/min. In the next
block (N4), the
calculated for
inch will
764
rfmin, automatically calculated by the control. This rather
in spindle speeds may have an
effect
large
on some
What may happen is that
cutting
tool will reach the 02,0 inch before the spindle speed fully
to the
764 rfmin.
tool may start removing material at a speed much slower than intended. In
order La correct the problem, the CNC program
to be
modified:
84
12
e Example 3b :
The modification
in block N3.lnstead
speed mode, program
gramminga
rect rlmin for the
inches, based on 400
to calculated first,
surface speed. The
setting will be .... ,..("~'ml1nprl a subsequent
N1 G20
N2 G50 X24.0 Z5.0 TOIOO
N3 G97 S764 M03
N4 GOO X2. 0 TOIOl MOe
Whenever the
mode is active
reaches spindle center
at XO) the result will LLY"''''...........
be the highest spindle
possible, within the
gear range. It is
but that is exactly what will
happen. Such
when the part is weD
mounted, does not
chuck or fIXture lOO
out, the tool is strong
and so on. When
is mounted in a special
or an eccentric setup is
the part has a long
or when some other adverse conditions are present,
maximum spindle
at
center line may be too high for operating safety.
N5 G96 S400
is a simple solution to this problem, using a
and other ""_"rA'~
mode can be
highest limit,
E>"_'~L~O feature available
the example, at the 024.0 (X24.0 in N2), the actual
the 02.0 (Xl.O in N4),
would be only 64 r/:min.
will be 764. The
tool may reach X2.0 pobefore the spindle speed
accelerated to full 764
if it is not calculated and programmed earlier.
CNe lathe does not
modern lathes have a
to wait before ac-
until the spindle
fully accelerated.
Modern CNC lathes today do not use the G50 setting and
In this case, the acuse the Geometry Offset setting
diameter at machine zero position is normally
tual
this case,
not known. Some experience can
program a short dwell
the actual cutting.
• Maximum Spindle Speed :t8t[lng
CNC lathe operates
Constant Suiface
the spindle speed is
to the curdiameter. The smaller
diameter is, the
spindle speed will be.
natural question is
- what
happen if the tool diameter is
It may seem
but there are at
impossible to ever program a zero
least two cases when that is the case.
the first case, zero diameter i~ t'lT'l'1,~,ml'1nl"l1
ter line
All drilling, center
similar
are programmed at
(XO).
are always n"'(,'C1T~ITT1Tnf"n
using 097 con:uru:ma.
is controlled directly,
not change.
"'..."'."4..... case of a zero diameter is when facing off a
solid part all the; way to the center
is a different
diameter
situation.
all operations at XO, the
does not
because a direct r/min is proi gramnle<1
During a
cutting operation., the aIa1meter V'lX<U1.5"'"
the
material removal continues
center line. No,
eX~Ha.:ullea .......... ,,....... Any calculation
zero, will result in
~ at the center line
tIl
. .'".....,. . . . ~ to Figure 12-7 for H'W'UU""~'"
mrevolutions per
.. _,,~.,~~ spindle
ma:u.mlUI11 setting is
clamping. Do not
position register
program function
setting is normally G50.
called maximum spinthis G50 with its other
is an example:
01201 (SPINDLE SPEED c::t.AWP)
Nt G20 TOIOO
(1500 R/MIN MAX)
SPINDLE RANGE)
AND 400 Fl' /MIN)
N2 G50 X9.0 Z5.0 S1500
N3 M42
N4 G96 8400 M03
NS GOO G41 X5. 5 ZO TOIOl MOB
N6 GOl X-O. 07 Fa. 012
,~._. CENTER L.I.NE)
N7 GOO ZO.1
N8 G40 X9.0 Z5.0 TOIOO
N9 M01
What actually happens in program 0120 I? Block N 1 se.......0 ....' ... units of measurement.
critical block N2
o
only the tool coordinate position, as in:
GSa X9. 0 ZS. 0
o
Also sets the maximum
to
as
GSa X9.0 ZS.O 81500
a
During
motion, tool nose
ant function are activated. The spindle
be
a formula described
ter~
N6 is the actual
cut.
0.012 inlrev, the tool tip
reality, the end point is
spindle center line. The
programming
must be taken into consideration
with the tool nose
offset and to the machine center
will hapline. A
later explains what
pen during
SPINDLE CONTROL
Block N7 moves the tool tip .J 00 inches away from the
face, at a rapid rate. ]n the remaining two blocks, the tool
will rapid to the indexing position with a cancellation of radius offset in N8 and an optional program stop is provided
in block N9.
Now, think of what happens in blocks N5 and N6. The
spindle will rotate at the speed of 278 rlmin at the 05.5.
Since the CSS mode is in effect, as the tool tip faces off the
part. the diameter is becoming smaller and smaller while
the r/min is constantly increasinJr
Wirhout the maximum spindle speed limit in block N2,
the spindle speed at the center line will be equivalent \0 the
maximum rlmin available within M42 gear range. A typical
speed may be 3500 rlmin or higher.
With the preset maximum spindle speed limit of 1500
rlmin (GSa S 15(0), the spindle will be constantly increasing its speed, but only until it reaches the 1500 preset rlmin,
then it will remain at that speed for the rest of cut.
At the control, CNC operator can easi Iy change the maximum limit value, to reflect true setup conditions or to optimize the cutting values.
Spindle speed is preset (or clamped) to the maximum
Y/min setting, by programming the S [unclion together wilh
the GSO preparatory command. If the S function is in a
block not containing GSa, the control will interpret it as a
new spindle speed (eSS or r/min), active from that block
on. This error nwy be very costly!
N1S GSO XS.S Z2.5
Single meaning
N40 GSO Z4.75 S700
Double meaning
From lhese examples. G50 command should be easy to
understand. There are two, completely independent, mean~ngs?f the G50 command. Either one can be programmed
In a StOgIe block, or they can be separated into two individual blocks.
~f the CNC lathe supports G92 instead of G50, keep in
mmd that they have exactly the same meaning and purpose.
On lathes, the G50 command is more common than the
G92 command but programming method is the same.
• Part Diameter Calculation in CSS
Often, knowing at what diameter the spindle will actually
be c1~mped can be a useful information. Such knowledge
may mfluence the preset value of spindle speed clamp. To
find oul at what diameter the Constant Surface Speed will
remain fixed, the formula that finds the r/min at a given diameter must be reversed:
D =
I@" where ...
o
= Diameter where CSS stops (in inches)
= Multiplying factor - feet to inches
ftlmin = Active surface speed
1t
= Constant 3.1415927
r/min = Preset maximum spindle speed
12
Use caution when presetting maximum r/min of the spindle!
The maximum spindle speed can be clamped in a separate block or in a block that also includes the current tool
coordinate setting. In the example 0120 I, block N2 contains both settings. Typically. the combined setting is useful
at the beginning of a tool, the separate block selling is useful if the need arises to change the maximum spindle speed
in the middle of a tool, for instance, between facing and
turning cuts using the same tool.
To program the GSa command as a separate block, anywhere in the program, just issue the preparatory command
combined with the spindle speed preset value. Such a block
will have no effect whatsoever on any active coordinate setting, it represents just another meaning of GSa command.
The following examples are all correct applications of G50
command for both, the coordinate setting and/or the maximum spindle speed preset:
N12 GSO X20. 0 Z3. 0 SlSOO
Double mealling
N38 GSO S1250
SillglemeaniJlg
12 x ft I min
11 x r I min
o Example - English units:
If the preset value in the program is GSO S 1000 and the
surface speed is selected as G96 S350. the CSS will be
clamped when it reaches the 01.3369 inches:
D
::
(12
x 350) /
(n
x 1000).
1.3369015
01. 3369
The formula may be shortened:
D ==
3.82 x ft I min
r I min
For completeness, the formulas based on the English system, can be adapted to a metric environment:
D ::= 1000 x m I min
1t x
r I min
86
12
If these requirements are met, the most important source
data is
spindle speed actually used during machining.
I1iilf' where ...
Diameter
Muftiplying
stops (in
- meters to mm
Ac:t:ive surface speed
=
D
1000 =
mlmin =
=
1t
r/min
requirements
3.1415927
maximum spindle speed
::::
Just
optinrum spindle speed is known, the cutting
(eSS) can be calculated and used
any other tool
the English version, you may shorten
met-
ric formula as well:
In a nutshe14 the whole subject can be quickly
up by categorizing it as a
- that of Constant
Suiface Speed, also
as the Cuting Speed (CS), when
tool or part diameter
the spindle
are known.
there on, it is a simple matter of IV1..111UllQ.
ft I min =
- Metric
the preset value in the program is
S1200 and the
surface speed is selected as G96 S165, the ess will be
damped when it reaches the
mm
D =
::::
::::
are met
e EXAMPLE:
drill works very
speed in ftlmin?
(1000 x 165) / (1t x 1200)
43.767609
043.768 nm
:
at 756
IS
(3.14 x 0.625 x 756) / 12 : 123.64
• CSS Calculation
The Constant Suiface
(CSS) is required
most
tunung and boring
on a CNe lathe. It is also the
cutlnng data, from
spindle speed
is calculated for
all machining center operations.
Now - consider a very common scenario - the CNe
tor has
the current
conditions, J.U....'! ..."'W.1J:l;
the
speed., so they are
favorable. Can
COlllQl1nOIlS be applied to subsequent jobs?
they can - ........'VlF' .." that certain
Machine
-what
part setup are equivalent
Q
tools are equivalent
Q
Malerial conditions are equivalent
Q
well at 1850
is
m/min = (3.14 x 7 x 1850) / 1000 = 40.66
will be satisfied:
Q
requirements
C EXAMPLE:
Other common conditions are satisfied
DeD.em ofusing
is a significant respent at the CNC machine, usully required
to find and 'fine-tune'
or part opttI1lli!:aU()D
optirmnn spindle speed during
FEEDRATE CONTROL
Feedrate is the closest programming companion to the
spindle function. While
spindle function controls
spindle speed and the
rotation direction. feedrate
controls how fast the
move, usually to remove exhandbook, the rapid
materiaJ (stock). In
tioning, sometimes called a rapid motion or rapid traverse
motion, is not considered a true feed rate and
be described
in Chapter 20.
Cutting feed rate is the
at which the
ing tool removes the m"f"YI~1 bV cutting action.
The cutting action
be a rotary motion of the
(drilling and milling. for example), the
molion of
part (lathe operations), or other action (flame cutting.
cutting, water
electric
etc.). The feedrale
function is
in the CNC
to select the
value. suitable for the
o
o
word in the program is
the address F, followed
of digits. The number
of digits following the
F depends on the feedrate
mode and the machine tool application. Decimal place is
allowed.
in CNC ......nil'Y"1:Ilm""
For miHing applications, aJl cutting feedrale in
linear
and
interpolation mode is programmed in inches
(in/min) or in millimeters per minute (mmiminJ.
of the
is the
a cutting tool
travel in one minute. This value is modal and is
only by another F address word.
main
of the
feedrale
minute is thai it is not dependent on
spindle
useful in milling operations, usmakes it
ing a large variety of tool diameters. Standard abbreviafeedrate
minute are:
CJ
Inches per minute
in/min (or older
CJ
Millimeters per minute
mm/min
Feedrate per
Feedrate per revolution
for
The most common
of machines. CNC machining
centers and lathes, can
programmed in either feed rate
mode. In practice, it is much more common to use the
jeedrale per minute on machining centers and the jeedrate
revolution on
lathes.
There is a significant
chining centers and lathes.
in G codes
for ma-
most typical format for feedrate
minute is F3.1
English system and F4.1 for
metric system.
For example,
of 1 inches per
be programmed as 5.5. In
metric system,
amount of
mm/min will
in the
F250.0. A
different programming
expected
special machine designs.
important item to remember
feedrate is tbe
feedrate values.
feedrate range
of the control
always
that of the machine
servo system.
example, the feedrate range
a Fanuc
CNC
is between .000 I and 24000.0 jn/min or
0.0001 and 240000.0 mm/min. Note that
difference
tween
two umts IS
a decimal point
not an actual translation. In programming, only
feedrates that
specified
can be used. Such a
belong within
feed rate wHi
smaller than
the control
range of the
FEED RATE
Milling
Turning
Group A
Turning
Group B
Turning
Group C
Per minute
G94
G98
G94
G94
revolution
a
• feed rate per Minute
FEEDRATE CONTROL
Two feed rate types are
FEEDRATE FUNCTION
G99
G95
In milling, the programming command (0 code) for the
per minute is
For most
it is set autype of a
time jeed rate. It is
handbook.
feedrate is
the inverse
is not discussed in
tomatically, by the
written in the
default and
not have to
For lathe operations, feed rate per
A, the 0
for
seldom. In
is G98,
Groups Band C it is G94.
use primarily jeedraJe per revolution mode.
88
• Feedrate per Revolution
o
For
CI
CNC lathe work, the feedrate is not measured
terms lime,
as the
distance the tool
in
one spindle revolution (rotation). ThisJeedrate per revolution is common on lathes (099 for Group A). Its vaJue is
modal and another feed rate
cancels it (usually the
G98). Lathes can
be programmed injeedrate per minute (098), to control the feedrate when the spindle is stationary.
standard abbreviations are used for JeedraJe
per revolution:
a
Inches per revolution
in/rev ~or older ipr)
o
Millimeters per revolution
mrn/rev
feedrate per revolution is four
decimal places in thc
system
three decimal
places in the metric system. This format means the feed rate
of 0.083333 inJrev wili be applied jn the CNC program as
FO.0833 on most
The metric
example of
0.42937 mrnJrev will be programmed as F0,429 on most
controls. Many modern control systems accept fecdratc of
up to
decimal
for English units
five
for metric
careful when rounding feedrate values. For
boring operation, reasonably
feedrates are
quite sufficient. Only in'
point threading, the feed rate
is critical for a proper thread lead, particularly for
long or very
can
programmed with up to
decimal places feedrate precision
for threading only.
The programming
for the feedrate per revolution is G99. For most lathes, this is the system default, so it
does not have to written in the
unless the opposite
command G98 is also
It is
more common to program a feedrate per
minUle (098) for a
lathe program, than it is to proafeedrate per revolution (095) in a milling program.
reason is that on a CNC lathe,
command controls
example,
the feed rate while the spindle is not rotating.
a barfeed operation, a part stopper is used to 'push'
the
to a
position in
chuck or a collet, or a
pull-put
to 'pull' the bar OuL Rapid feed would be too
and feedrate
revolution is not applicable.
per minute is
instead. In cases
G98
099 commands are used in the lathe program as required.
Both commands are modal and one cancels the other.
FEEDRATE SELECTION
To
the
feed rate, one that is most suitable
a
given job, some general knowledge of machining is useful.
is an important
of
process and
be done
A
depends on
many factors, most notably on:
o
speed - in rev/min
Tool diameter! M J or the tool nose radius [ T J
requirements of
o
Cutting tool geometry
o
Machining forces
part
o Setup of the part
o Tool overhang (extension)
o
Length of the cunlng motion
o Amount of material removal
or width of cut)
o Method of milling (climb or conventional)
o Number of flutes in the material (for milling cutters)
o
considerations
The last item is safety,
a programming responsibility number one, to assure
safety
the people and
equipment. Safe speeds and
are only two aspects of
safety awareness in CNC programming.
ACCELERATION AND DECELERATION
During a contouring operation, the direction of the cutis nothing unting motion is changed quite often.
usuaJ about it, with all the intersections,
points
In contouring, it means that in
to
and
gram a sharp comer on a
the tool motion aJong
X
axis in one block will
to
into a motion along
the Y axis in
next
make the change
one
X mocutting motion to another, the control must stop
tion first, then start
Y motion. Since it is impossible to
start at a full
instantly, without an acceleration,
and equally impossible to stop a feedrate WIthout a deceleration, a possible
error may occur.
error
cause
corners on the profile to be cut with an undesirable overshoot, particularly during very high TO"'''''''',,"
or extremely narrow angles. It only occurs during a cutting
motion in 001,
003 modes. not the rapid motion
mode 000. During the rapid mOlion, the deceleration is automatic - and
from the part.
In a routine CNC machining,
ever encountering such an error,
it will likely
within
two commands
is a small chance of
if the error is
controls provide
problem:
Exact stops increase
For
used
on older machines, they may be required in some cases.
FEE
CONTROL
•
89
Command
of two commands that control the feedrate
machining
comers is G09 command - Exact
This is an unmodal command and has to be repealed in evit is required.
ery block.
0] 30 I, there is no provision
That may cause uneven cor-
01304
CUTTING)
N13 GOO X1S.0 Y12.0
Nl4 G61 GOl X19.0 F90.0
N15 Y16.0
N16 XlS.O
Nl7 Y12.0
Nl8 G64
A'""''''.... ' ... A''' of F90.0 (in/min);
in re-
01301 (NORMAL CUTTING)
~3
GOO X1S.0 Y12.0
N14 G01 X19.0 F90.0
N15 Y16.0
N16 Xl5.0
N17 Y12.0
By adding the GOg exact
will
the motion in that
motion in the
will start.
01302
(G09
I'"'r'l"I""l'TU':!'
~3
GOO X1S.0 Y12.0
N14 G09 G01 X19.0 F90.0
N15 G09 Y16.0
~6 G09 X1S.0
N17 Yl2.0
Example 01302
11
comer Ilt all three positions of the part. only one corner is
for sharpness, program the G09 command in the block that terminates at that corner (program 0 I
01303 (G09 C'U'I'T1NG
N13 GOO X1S.0 Y12.0
N14 G01 X19.0 F90.0
N15 G09 Y16. 0
N16 X15.0
Nl7 Y12.0
The G09 command is useful only if a
require the deceleration for a sharp corner.
all corners must be
the constant
the G09 is not very efficient.
• Exact Stop Mode Command
The second command that corrects an error at
ners is G61 - Exact SlOP Mode. It is
than G09 and functions identically. The
that G61 is a modal command that remains in
is canceled by the G64 cutting mode
ens the programming time. but not the cycle
when the G09 would be
too
too
same program, making it
point
f\
Target point
GOg I G61 USED
Figure 13-1
Feedrate control around comer Exact Stop commands
The overshoot is
for clarity
• Automatic Corner Override
While a cutter radius
is in
for a milling cutter,
the feed rate at the contour
points is normally not
overridden. In a case like this,
command
the cutting feedG62 can be used to automatically
rate at the corners of a part. This command is active until
the G61 command (exact stop
the
comG64
(cutting mode)
mand (tapping mode), or
is programmed.
• Tapping Mode
90
Chapter 13
• Cutting Mode
When the cutting mode G64 is programmed or is active
it represents the normal cutting mode.
by system
When
command is active.
exact stop check 061
will not be performed, neither will the automatic corner
G62 or the
mode G63. That means the acceleration and
will be done
and the
feedrate
will be effective.
is the most common default
for the control
The CUlling mode can be
(exact stop
G62 command
corner override mode) or G63 command (tapping mode).
The G64
is not usualJy programmed, unless
one or more of the other feed rate
are used in the
same
To compare the
064 modes,
see il
in Figure
It is important to understand that the effeclive
rawill decrease in
for all internal arcs
crease in size for
arcs. Since the
rate does not change automatically during
cutter radius
it must
adjusted in
program. Usually.
offset
this adjustment is not necessary,
in cases where the
surface finish is of great importance or the culler radius is
This consideration applies only to
motions. not to linear
• Circular Motion feedrates
feedrates for circular motions is generally
linear feedrates. In fact, most programs do not
feed rate for
circular tool motions. If the
part surface finish is important. the 'normal'
must
be adjusted
or lower. with consideration of (he cutter
radius, the
radius cutting
or
arc) and
the cutting conditions. The
cutter radius,
cutting feed rate
programmed arcs will
more reason
some correction,
same as
In case of arc
(after applying cutter
may be much larger or much
smaller than the arc programmed to drawing dimensions.
The
for compensated arc motions is
on the linear motion
Look for a more
explanation in
29, with an
and
First,
is (he standard
calculating
a linear feedrate:
G62 USED
G64
Figure 13·2
Corner override mode 662 and default 654 cutting mode
CONSTANT fEEDRATE
In Chapter 29,
lEi" where ...
feedrate (in/min or mm/min)
Spindle speed
Feedrate per tooth (cutting edge)
Number of cutting edges (flutes or inserts)
FI
==
r/min : : :
F.
n
:::;
chapter are
explanations
wining Q constant cutting feed rate
inside and outside
arcs, [rom
practical
of view. At this point, the
eus is on the understanding the constant "''''''',n''''''''>
than its applicaJion.
In programming, normal process is to
the coordinate values for all the contour
paints, based on the
part
The cutter
produces the center
line
the tool path is typically disregarded. When
gramming arcs to the drawing dimensions, rather than to
the center line of the cutter, the feed rate applied to the programmed arc
relates to the
radius, no'
the actual
cut at the tool center,
the cutter radius
is
and the
path
arc is offset
the cutter radius, the actual arc radius
that is cut can be
smaller or larger. depending on the
offset value for
tool motion.
outside arcs, the
wards. to a higher
lEi" where ...
F.
F~
R
=
Outside radius of the part
= Cutter radius
up-
FEEDRATE CONTROL
91
\ ......
\
arcs, the
wards, to a lower value:
is generally adjusted
x (R
dOW~
r)
R
Ilii" where ...
F,
F,
R
r =
Feedrate for
arc
Linear feedrate
Inside radius of the part
Cutter radius
MAXIMUM fEEDRATE
maximum programmable jeedrate for the CNC mais determined by the machine manufacturer, not
manufacturer. For
although
machine may
several times
to all
but there are addiconsiderations for CNC lathes, where
revolution is the main method of programtool.
• Maximum feed rate Considerations
The maximum cutting feedrate per
rp.;:tr./"'tpl1 by the programmed spindle
maximum rapid traverse rate of
It is quite
to
the feed rate per revolution too high withit. This problem is most common in sin-
A
cannot deliver heavier
than the
maximum it was designed for, the results will not be accurate.
results could be unacceptable, When unusually heavy
and fast spindle
are used in
the same progF.dffi, it is advisable to
the final
feedrate does not exceed the maximum
the given
It can be
drare per revolution, according to
fEEDHOlD AND OVERRIDE
While running a program,
programmed
be ~emporarily suspended or changed by using one of two
avatlable features of
system. One is
jeedhold switch. the
is a jeedrate override
Both switches are standard
allow the CNC operator to
control the
feedrate during program
operation panel.
They are
• Feedhofd Switch
FeedhoLd is a push button
can be toggled between
ON and Feedhold
It can be
modes.
rate
revolution. On many
not only a cutting feed with 00l,
003 in effectprogram funcstop the rapid motion GOO.
will remain active during a feedhold state,
i"P,'I'II1.f'l11'l
machining operations, the feedhold function
is automatically disabled and
ineffective. This is
tapping and threading,
G84 and 074
cycles on machining centers
threading operathe 032, 092 and
•
feed rate Override Switch
is nonnally
by means of a
switch. located on the control panel of the
13-3.
'O~
Q,iJ
100 110
'\~",\ \
I
'<0
// ~
Figura 13-3
Typical feedrare override switch
Jri" where ...
r/min =
The Rmtlx is
Max. allowed feedrate per revolution in/rev
of the maximum feedrate,
' '>I •• I''1'''1'l from the X and the Z
in revolutions per minute
in in/min or mmlmin. depending on the
38 nre details
to
input units
In
feedrate limits for threading,
This rotary switch has marked settings or
indicating the
oj programmed jeedrate, A typical
range of a
override is 0 to 200%,
0 may be
no motion at all or the slowes( motion, depending on the
machine.
200%
doubles all programmed
rates. A programmed
of 12.0 in/min (FI
is the
100% feedrate. If
override switch is set to 80%, the actual cutting
will 9.6 in/min, If the
110%, the actual
will be 13.2
92
Chapter 13
simple logic
to metric "'\f<'I''''f'''n
programmed feed rate 300 mmlmin, it ....... rrlm/
An 80%
override results in 240 mm/min cutting
setting is
feed rate and a 110%
to 330 mm/min
cutting tool.
a
",
feed rate override switch works equally well forfeedrevolution.
example, the programmed feedrate
.014 in/rev will
in actual feedrate of .0126
in/rev with 90% feed rate
and .01
in/rev with
130%
override. If a
feed rate
revolution is required, be
the
setFor example, programmed
is FO.0I2, in
revolution. A change by one division on the
,,'"" ....... '1... dial will
increase or
the programmed
by a full 10
Therefore,
feedrate
etc. In
will be .0108 at 90%, .0120 at 100%, .0132 at I
feedrate is not required, bUl
in
will not
for exama feedrate of .0 I in/rev, because of
fIxed 10%
crements on the override switch.
rates
threading
Feedrate ",,"'.......... ,,'"
tapping
and G74 on
single point threading
G92 and
milling
tapping mode is used
mand G63, both the feedrate
the feedhold
functions are disabled - through the program .I
UI.:lUL/I/::U.
offers two
override functions
for cutting
other than tapping or threading
They are M48 and M49. These are programmable functions,
may not be
for all
<"""Ip.rn
• feed rate Override functions
Although the
function uses the address F. two
miscellaneous functions M can be used in the
On the operagram to set the feed rate override ON or
lion panel, a switch is provided for feed rate override. If the
CNC
decides that programmed feedrate has to be
or decreased, this switch is very
other hand, during machining
handy. On
the cutting feed rate must be
as programmed,
"uj.. ......,'np switch
to
set to I 00% only. not to any
are special tapping operations without
A good
cycles, using GOl and GOO preparatory commands.
Lions M48 and
are used precisely for such
cancel function is OFF,
which means feed rate override is active
Feed nil t!
M49
Feedrate override cancel function is ON.
which means feedrate override is inaclive
M48 function
the CNC nn,"'"",,'nr to use the
rate override switch freely; the
function will cause
to be
of the
on the control panel. The
two functions is
tapping or
most common usage of
threading without a cycle, where the exact programmed
feed rate must
be maintained. The following examshows the
teChnique:
mo 8500 M03
(usnro TAP 12 TPI)
N14 GOO X5.0 Y4.0 Moe
N15 ZO.25
N16 M49
(DISABLE FEEDRATE OVERRIDE)
N17 GOl Z-O.62S F41.0 MOS
N18 ZO.25 M04
N19 M48
(ENABLE FEEDRATE OVERRI:DE)
mo GOO X.• Y•• M05
N21 MOl
The tapping occurs between blocks N 16 and N]9
override is disabled for
the
E ADDRESS IN THREADING
Some older
rather
lathes use
feed rate address E for
the more common address F.
feed rate function E is similar to the F function. It also
thread lead
per revolution, in in/rev
or in mmJrev, hut it ha.." a
decimal place accuracy.
control system model 6T, for
the
e English - Fanuc
F
0.0001
E :::: O. 000001
e Metric - Fanuc
F '" 0.001
E
::0
0.0001
control:
/()
10
50.0000 in/rev
50.000000
control:
to
500.000
10
500.0000 rrm/rev
models, FS-OII 011 J/1S/16T, the
On the newest
is no E address),
the safest way
are similar
the available
specifications
is to lookup
control system.
The E address is redundant on the newer controls and is
retained only
compatibility with older programs that
be used on machines equipped with newer controls.
available
feedrate ranges
between
ferenl control systems,
depend on
type of feed
screw
input units
in the
TOOL FUNCTION
ly controlled machine using an automatic
must have a special tool functlon (f7ifnc£ion)
used in the program. This function controls the
of the cutting tool, depending on the Iype of machine tool.
are noticeable differences between T
on CNC machining centers and those used
are also differences between si
Ihe same machine type. The normal program.,rlri ..",-.- for {he tool function uses the address T.
machining centers. the T function
the tool number only. For the
indexing to (he tool stalion
number.
T FUNCTION FOR MACHINING CENTERS
All vertical and horizontal CNC machining centers
called the All/omalic Tool
In the program or MDI mode on
uses the function T, where the T
tool number selected by the programmer.
describe the tool number itself. On
with a manual tool change. the tool
required al all.
a
programming for a particular
center begins, the type of the (001 selection for that machine
must be known. Thert~ are twu major Iypes uf luul selCX:lion
in automatic tool change
o
Fixed type
o
Random memory type
TOOL READY POSITION
F;gure 14-1
Typical side view of a 20-tool ma(,aZifle
as small as len or
on special
cenler may
machines will
or oval (larger
It consists of a
where the tool holder
setup. Each pocket is
is important to know
for each pocket The
during
and auloor MOL The number
of tools that
To understand the
is to understand the general
tool selection, available for many rnn,nJ>'"""
centers.
• Tool Storage Magazine
A typical CNC machining center
is designed with a special 100/
a 1001 carousel), [hat contains all
gram. This magazine is not a
tools, but many
used tools there at all limes, If
magazine is illustrated in
or horizontal)
""... rn"",nH'<" called
by the profor the
(he commonly
typical 20-tool
Within the travel of
lion, used Cor
aligned with the tool
waiting position,
tion, or just the lool (,1U11HJ'P
is one special posi-
position is
the
tool-ready posi-
93
94
• fixed Tool Selection
A machining center that uses a fixed tool selection rethe CNC
to place all
into
that match the tool numbers.
example. (001
number I (called as TO I in the
must be
into the magazine pocket number I, lool
7 (cal~ed
as T07 in the program) must be placea-~b.e magazme
pocket
7, and so 00.
magazine pocket is mounted on a side of the
from the work area (work
With the fixed
selection, the control system
no way
of determining which 1001 number is in which magazine
pocket
at any
The CNC
has to
match the
numbers with the magazine
numbers
during setup. This
of a tool selection is commonly
machining centers, or on some
found on many older
centers.
inexpensive
)..."""uu~, usually
the lool is
easy the T
function
is used in
program, that will the tool
number selected during a tool change.
example,
N67 T04 M06
or
N67 M06 T04
or
N67 T04
N68 M06
means to bring
number 4 into the spindle (the
las(
is preferred). What will
to the (001 that
is in the spindle at
The M06
cha~ge
.
will cause the
tool to return to the magazme pocket It
came from,
the new tool will be loaded.
the
tool
takes the
way to select
new tool,
Today, this type of a tool selection is considered impracliand
in a long run. There is a significant time
during tool
because the
tool has to wait
until the
lool is found in
magazine and placed
into the
The programmer can somewhat improve
the
by selecting
and
tool numnot necessarily in the order
Examin this handbook are based on a more modern type of
the random memory.
tool selection,
• Random Memory Tool Selection
This
is the most common on modern machining
centers. It also stores alltool5 required to machine a part in
the tool magazine
away
machining area.
CNC
identifies
by a T
usually in
order of usage. Calling the required tool
number by
program will physically move the tool to the
Chapter 14
position
the too!
This can
simultaneously,
the machine using another
to
cut a part. Actual tool change can take place anytime later.
The is
concept of
next tool waiting where the T
function
to the next tool, not the current tool. In the
the next tool can made
by
simple blocks:
(MroCE TOOL 4 READY)
T04
<... Mac:i111'unf! wiIh previous 1001 ... >
M06
T15
(ACTUAL TOOL CHANGE - T04 m SPDmLE)
(MAKE NEXT TOOL
<... fVU7r""'I1'" with 10014 - 7D4 ... >
first block, the 1'04 tool was called into the walting
of the tool
while
previous
was
CUlling. When
machining
been completed, actual tool
will take place, where T04 will become the
active tool. Immediately,
system will
for
the next tool (TIS in the example) and
it into the
waiting position, while T04 is cutting.
In
example illustrates that the T function will not
any physicallool change at a!1. For that, the ~utomatic ~ool
change junction - M06 - also
later In
secMn,
is needed and must be programmed.
Do not confuse the meaning of
T
with the
tool selection
the same
T used with the
random tool
The former means the actual number of the
pocket, the latter means the tool number of
next tool. The
call is programmed earlier
than it is needed. so the
sysl~m can
for that
tool while another tool is
productive work.
• Registering 1001 Numbers
and CNC
in "",,..,.rll
can process
data
quickly and with
precision.
the CNC work, the required
input first, to make the computer work in our
. In the
to
random tool selection method. the CNC operator lS
any tool into any magazil1e
as long as
actual setting is
into the
unit, in the form
control
is no need to worry too
much about system parameters,just acceplthem as the collection
various system
Registering tool numits own entry screen.
operator will
the required tools into
writes down the
numbers (which tool number is in which pocket number),
and
the information into the system. Such an operation is a normal
of
machine tool
and various shortcuts can
used.
TOOL FUNCTION
• Programming Format
95
Q Example:
Programming format for the T function used on milli~g
systems depends on the maximum number of lools aVaIl-
N81 TOl
able for the CNC machine. Most machining centers have
N82 M06
number of available tools under 100, although very large
machines will have more tool magazines available (even
several hundred~. In the ex~m~l~s, two-digit tool function
will used, covenng tools wlthm~ range of TO J to T99.
In a typical program, the TOI tool command will call the
1001 identified in the setup sheet or a tooling sheet as tool
number 1; T02 will call tool number 2, T20 will call tool
number 20, elc. Leading zeros for tool number designation
may be omitted, if desired - TOI can be written as Tl, T02
as 1'2, etc. Trailing zeros must always be .written, for exampJe, T20 must be written as T20, otherwIse the system WIll
assume the leading zero and call the tool number 2 (T2
equals to T02, not T20).
•
Empty Tool or Dummy Tool
Often, an empty spindle, free of any tool, is required. For
Ihis purpose, an empty tool station has to be assigned. Such
a tool will also have to be identified by a unique number,
even if no physical tool is used. If the magazine pocket or
the spindle contains no tool, an empty tool number is necessary for maintaining the continuity of (001 changes from
one part to another. This nonexistent tool is often called the
dummy tool or the empty tool.
The number of an empty tool should be selected as higher
than the maximum number of tools. For example, if a machining center has 24 tool pockets, the empty 1001 should be
identified as TIS or higher. It is a good practice to identify
such a tool by the largest number within the T function formal. For example, with a two digit format, the empty tool
should be identified as 1'99, with a three digit format as
T999. This number is easy to remember and is visible in the
program.
As a rule, do not identify the empty tool as TOO - alllools
not assign.ed may be registered as TOO. There ~re, howeve.r,
machine tools that do allow the use of TOO, WIthout POSSlble complications.
TOOL CHANGE FUNCTION - MOS
The tool function T, as applied to CNC machining centers, will not cause the actual 1001 change - the miscellaneous function M06 must be used in the program to do thaL
The purpose of tool change function, i~ to exc.h.ange the tool
in the spindle with the tool in the wallmg pOSItIon. The purpose of the T function for milling systems is La. r?tate th.e
magazine and place the selected tool into the wall!n~ POSItion, where the actual tool change can lake place. ThIS next
tool search happens while the control processes blocks following the T function call.
N83 TO 2
=
loaded in the wairi.ng posilion
... brings TO) imD the spiJulJe
, .. rnakes 7D2 ready = Irxuled in the wailing position
... Innkes T01 ready
The three blocks appear to be simple enough, but let's explore them anyway. In block N81, the tool addressed as
TOl in the program will be placed to the waiting position.
The next block, N82, will activate the actual tool change tool TO I will be placed into the spindle, ready to be used for
machining. Immediately following the actual tool change
is T02 in block N83. This block will cause the control system to search for the next (001, T02 in the example, to be
placed into the waiting position. The search will ~ake place
simultaneously with the program data followmg block
N83, usually a too! motion to the culling position at the
part. There will be no time lost, on the contrary, this method
assures that the tool changing times will be always the
same (the so called chip-to-chip time).
Some programmers prefer to shorten the program somewhat by programming the tool change command together
with the next tool search in the same block. This method
saves one block of program for each tool:
N81 TOl
N82 M06 T02
The results will be identical - the choice is personal.
Some machine tools wilJ not accept the shortened two-block
version and the three-block version must be programmed.
If in doubt, always use the three-block version.
• Conditions for Tool Change
Before calling the M06 tool change function in the program, always create safe conditions. Most machines have a
light located on the control panel for visual confirmation
thai the tool is at the tool change position.
The safe automatic tool change can take place only if
these conditions are established:
o
The machine axes had been zeroed
o
The spindle must be fully retracted:
( a) In Z axis at machine zero for vertical machines
( b) In Y axis at machine zero for horizontal machines
U
The X and Y axis positions of the tool
must be selected in a clear area
o
The next tool must be previously
selected by a T function
Chapter 14
---- . - - - - - - A
program sample illustrates the tool
(ween tools in (he middle of tile program
illustrated in Figures
10
MAGAZINE
SPIN
Q Example for illustrations:
N51
N52
E
T03
( • •• T02 IN SPJlNDLE)
( • •• TO 3 READY FOR TOOL c:.Hll1NGl~)
(MACHINING WITH
(RETRACT FROM ",,,,,,,,,,,,,,,\
N75 GOO Zl. 0
N76 G28 Zl.0 MOS
N77 MOl
(T02
(OPTIONAL
(BLANK LINE BETWEEN
N78 T03
(T03 CALL REl?E1!,TElDI
N79 M06
OUT - T03 IN THE SPJCNDLE)
NBO G90 G54 GOO X-lS.S6 Y14.43 9700 M03 T04
"4
t
N81 . .
N76 represents the end of machinIt will cause tool T02 to move
..
zero
ATe
same
optional program stop
lows in the block N77.
Front view of the machine
14·2
- Blocks N51 to N78
ATC
TOOL MAGAZI
(MACHINING WITH T03)
SPINDLE
In the following block N78, the can for
this is not necessary, but may come very
tool
Block N79 is the actual tool
in the spindle will be replaced with T03 that
rently in the
posluon.
in block N80. the rapid motion in X and Y axes
first motion of T03. with
ON. Note
at
block end. To save lime. the next tool should
placed into the waiting position as soon as possible after
(he tool 1''''''''''''''
T02
note that when T02 is """'''1.1''''''
N77. il is
still in the spindle! There are
who
not follow
If the tool change is
right after
block (machine zero return)
the MOl
it will be more difficult for
" . . ..,'.. ot,...... to repeat the
tool that just finished working, if it n .. (·r\Tm~'"
Front view
AUTOMATIC TOOL CHANGER - ATC
Figure 14-3
ATC example - Block N79
TOOL MAGAZI
SPINDLE
references to Automatic
were made in some examples.
on various machines and
to
\ /
method of programming
times quite a bit. The machine
will automatically index
the proper order. Everything
Programmer and operator
with the type of ATC on all
'
Changer (ATe)
designs of
from one
to say, the
10
under program control.
thoroughly familiar
centers in the shop .
• Typical ATC System
Front view of
machine
Figure 14-4
ATC example - Block NBD (new tool waiting == next tool)
A typical Automatic Tool
system may have a
double swing arm, one
the .... I""fYI. tool, another for
outgoing tool. IL will
on Random Mem01)' selection (described
which mean:-.; the next 1001
can be moved to a
and be ready for a tool
TOOL FUNCTION
97
change, while the current tool works. This machine feature
always guarantees the same tool change time. The typical
lime for the tool changing cycle can be very fast on modern
CNC machines, often measured in fractions of a second.
The maximum number of tools thaI C(ln be 10(lded into
the tool magazine varies greatly, from as few as IOta as
many as 400 or more. A small CNC vertical machining
center may have typically 10 to 30 tools. Larger machining
centers will have a greater tool capacity.
Of~toOI
Apart
changer features, programmer and machine operator should be also aware of other technical considerations that' may influence the \00\ change under program control. They relate to the physical characteristics of
cutting tools when mounted in the tool holder:
o
Maximum tool diameter
o
Maximum tool length
• Maximum Tool length
The tool length in relation to the ATC, is the projection of
a cUlling tool from the spindle gauge line towards the part.
The longer the tool length, the more important it is to pay
attention to the Z axis clearance during the 1001 change.
Any physical contact of the tool with the machine, the fixture or the part is extremely undesirable. Such a condition
could be very dangerous - there is not much that can be
done to interrupt the ATC cycle, except pressing the Emergency Switch, which is usually too late. Figure 14-6 illustrates the concept of the tool length.
GAUGE LINE
o Maximum tool weight
TOOL
NGTH
• Maximum Tool Diameter
The maximum tool diameter that can be used without any
special considerations is specified by the machine manufacturer. It assumes that a maximum diameter of a certain
size may be used in every pocket of the lool magazine.
Many machine manufacturers allow for a slightly larger
tool diameter to be used, providing the two adjacent magazi ne pockets are empty (Figure 14-5).
J (
I,
i OVERSIZE TOOL;
\
I
/
/ Empty pocket
Figure 14-5
The adjacent pockets must be empty for a large tool diameter.
For example, a machine description lists the maximum
tool diameter with adjacent lools as 4 inches (100 mm). If
both adjacent pockets are empty, the maximum tooJ diameter can be increased to 5.9 inches (150 mm), which may be
quite a large increase. By using tools with a larger than recommended diameter, there is a decrease in the actual number of tools that can be placed in the tool magazine.
Adjacent pockets must be empty for oversize tools!
Figure 14·6
The concept of too/length
• Maximum Tool Weight
Mosl programmers will usually consider the tool diameter and the tool length, when developing a new program.
However, some programmers will easily forget to consider
the tool overall weight. Weight of the cutling tool does nol
generally makes a difference in programming, because the
majority of tools are lighter than the maximum recommended weight. Keep in mind that the ATC is largely a mechanical device, and as such has certain load limitations.
The weight of the lool is always the combined weight of the
cutting tool and the tool holder, including collets, screws,
pull studs and similar parts.
Do not exceed the recommended tool weight during setup!
For example, a given CNC machining center may have
the maximum recommended tool weight specified as 22
pounds or about 10 kg. If even a slightly heavier tool is
used, for example 24 lb. (l 0.8 Kg), the ATC should not be
used at all- use a manual tool change for that tool only. The
machine spindle may be able to withstand a slight weight
increase but the tool changer may not. Since the word
'slight' is only relative, the best advice in this case is - do
not overdo it! If in doubt, always consult the manufacturer's recommendations. Examples in this chapter illustrate how to program such a unusual Lool change, providing
lhe tool weight is safe.
98
..........
-.~~-
• ATC Cycle
an example, the following
is
to a
typical CNC vertical machining center and may
a little
different for some machines. Always study individual steps
of lh~1:C operalion - often, that knowledge will resolve a
problem on lool jam during the tool changing. This is a
possible time loss that can be
Some machines
have a step-by-step cycle
with a
rotary
switch, usually localed near the 100\ magazine.
In the following example, a tool changer with a double
the cutting (001 from
arm swing system is used. It will
the waiting position and exchange it with the tool currently
in the machine
ATC is a process that will execute the following orof steps when the tool change function M06 is programmed. All steps
are quite typical, bUI not necessarily standard for
CNC machining center. so
them only as a close example:
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Spindle orients
T00\ pot moves down
Arm rotates 60 degrees CCW
Tool is unclamped lin the magazine and spindle)
Arm moves down
Arms rotates 180 degrees CW
Arm moves up
Tool is clamped
Arm rotates 60 degrees CW
The rack returns
Tool pot moves up
example is only presented as general information its logic has 10
adapted to each
The instruction manual for the machine usually lists relevant dcabout Ihe ATC.
Regardless of the machine 1001 used, two conditions are
to perform the ATC correctly:
always
o The spindle must be stopped (with the M05 function)
o The tool changing axis must be at the home position
(machine
position)
For CNC vertical machining centers, the tool changing
Z axis. for the horizontal machining centers it is
the Y axis. The M06 function will also stop the spindle.
never count on it. It is strongly recommended to stop the
spindle with the MOS function (spindle stop) before the tool
cycle is
aXIs IS
Chapter 14
• MDI Operation
A programmer
not have to know every
related
to the automatic tool changer actual operation. It is not a vital knowledge, although it may quite a useful knowledge
in many applications. On the other hand, a CNC
operator should know each and eVel) step of the
inside oul.
1.
.....
Incidentally,
step of the tool
can usually executed through the MDI (Manual Data Input), usfunctions are only
for
special M functions.
!>ervice
via the MDl operation and cannot be
used in a
program. The benefit of this feature is that a
\001 changing problem can be traced to its cause and corrected
there. Check instructions for each machine to
get details about
functions.
PROGRAMMING THE ATC
A number of possibilities exists in relation to the auto-marie tool
Some of the important ones are
number of tools used. what tool number is
to the
spindle (if any) at the start of ajob, whether a manual tool
elc.
change is required, whether an extra large tool is
In (he next several examples. some typical options will be
examples can be used directly. if the CNC
(001 uses exactly the same formal, or they can be
adapled to a particular working environment. For the following examples, some conditions must be established that
will help to understand the subject of programming a lOoi
change much better.
To program
ATe successfully, that is needed is
programming format for three tools - theftrs! tool
the
tools used in the middle of the program and the last tool
used in the program.
make the whole concept even easto understand.
examples will use only four tool numbers tool number will represent one of the four available programming formats:
o TOl
tool designation represents the
first tool used in the CNC program
o T02 '"
tool designation represents any tool in
the CNC program between the first and
the last tool
o
T03
o
T99
tool designation represents the
last tool used in the CNC program
... tool designation
an empty tool
(dummy tool) as an empty tool pocket
identification
In all examples, the
tools will always
used,
the empty tool only if required. Hopefully, these examples
will illustrate the concept of many possible
applicalions. Another
situation is in situations
only
one tool is used in
CNC program.
• Single Tool Work
Certain jobs or special operations may
only one
tool is generally mounted
in the spindle during setup and no tool t:alls Uf 1001 changes
are required in the program:
1001 to do the job. In this case,
TOOL FUNCTION
01401
(FIRST TOOL
B
. .,,,,,lo,,~c~k~N=u~m~b~er~'"==T=oO=I~W=.a,.,,i.,,t,i.n..•g..... LT 001 in Spindle
N1 G20
I .........
N2 G17 G40 G80
N3 G90 G54 GOO X •• Y •• S •• M03
N4 G43 Z •• HOl MOB
< ... TO) working ... :>
N26 GOO Z •• M09
N27 G2B Z •• MOS
N28 GOO X .• Y ••
N29 M30
%
(TO 1 MACHINING DONE)
(TOl TO Z-li0111E
(SAFE Xi!'
(END OF PRC)GRAM)
fill the table, start from the program top and
occurrence of the T address and M06 function. All
are irrelevant. In the example 01402, the
will
filled as a practical sample of usage.
• Any Tool in Spindle - Not the first
is the most common method of nr/"\"'r'lln1,1"Y1,
The operator sets aU tools in the magazine,
settings but leaves the last tool measured in the "1-"""" . . .
most machines, this tool should not the
tool.
matches this too! changing method within
following example is probably the one that
the most useful for everyday work. All
are
comments.
lool is in the way of part changing, it remains
"I.u ............ permanently for the job.
In
• Programming Several Tools
using several tools is the most typical
work. Each tool is loaded into the spindle
various ATe processes. From the
viewpoint. the various lool changing meththe cutting section of the program, only
the start
tool (before machining) or the end of the
tool (after machining).
01402
(ANY TOOL IN SPINDLE AT START)
(**** NOT THE FIRST TOOL ****)
N1 G20
N2 G17 G40 GSO Tal
N3 M06
As
the required tool can be changed
automatically, only if the Z axis is at machine zero (for vertical
or the Y axis is at machine zero
(for horizontal machining
tool position in
axes is only important to the safety
the
is no tool contact with the
the
are formatted
programs use machine
of last tool, for example:
zero return
N393 GOO Z •• M09
N394 G28 Z •• MOS
N39S G28 x.. Y ••
N396 M30
TOOL WORK DONE)
TOOL TO Z HOME)
TOOL TO XY HOME)
(END OF PROGRAM)
N4 G90 GS4 GOO X •• Y •• S.. M03 '1'02 ('1'02 READY)
(APPROACH WORK)
NS G43 Z•• Hal MaS
< ... TO}
.. >
N26 GOO Z •• M09
N27 G28 Z.. MOS
N28 GOO X .• Y ••
N29 MOl
(TOl MAClUNING OONE)
(TOl TO Z HOME)
(SAFE XY POSITION)
(OPTIONAL STOP)
N30 T02
(T02 CALL REPEATED)
(T02 TO SPINDLE)
N3l M06
N32 G90 GOO GS4 X.. Y •• S.. M03 T03 (T03 READY)
N33 G43 Z •• H02 MOS
' .......·rfiJu....'..n WORK)
< ... T02 working .. . :>
%
with this practice, but
a large volume of
(INCH MODE)
(GE.'T TO 1 READY)
(TO 1 TO SPINDLE)
N46 GOO Z •• M09
NS7 G28 Z .• M05
N48 GOO X •• Y ••
N49 MOl
MACHINING DONE)
TO Z HOME)
(SAFE XY
N50 '1'03
N51 M06
N52 G90 GOO GS4 X •• Y ••
• Keeping Track of Tools
If the lool
is
easy
to keep a track of where
tool is at
moment.
In later examples, more complex (00\
will (ake
place. Keeping a
track which tool waiting and
which tool is in the spindle can
with a 3 column table with block number, 1001 waiting and tool in the spindle.
N53 G43 Z .. H03 MOS
< ... 7rJ3 working .. . :>
N66 GOO Z.. M09
N67 G28 Z •• MaS
N68 GOO X •. Y ••
N69
%
mo
(T03~
('1'03 TO Z
XY POSITION)
(END OF PRCiGRAM)
100
Chapter 14
The filled-in table below shows the status of tools for the
first part only. '?' represents any 1001 number.
Block Number
Tool Waiting
Nl
?
?
N2
Tal
?
N3
?
TOl
N4
T02
TOl
in Spindle
-
A few comments to the 01402 example. Always program MO I optional S!OP before a tool change - it will be
easier to repeat the tool, if necessary. Also note beginning
of each tool, containing the next tool search. The tool in the
block containing (he first motion has already been called compare block N4 with N30 and bluck N32 with N50, The
repetition of the (001 search at the start of each tool has lwo
reasons. It makes the program easier to read (tool is coming
imo the spindle will be known) and it allows a repetition of
the tool, regardless of which tool is currently in the spindle.
T01 WORKING
• First Tool in the Spindle
N30
T02
TOI
N31
TOl
T02
N32
T03
T02
T02 WORKING
N50
T03
T02
N51
T02
T03
N52
TOl
T03
T03 WORKING
When the second part is machined and any other part after that, the tools tracking is simplified and consistent.
Compare the next table with the previous one - there are no
question marks. The table shows where each tool is.
Block Number
Tool Waiting
Tool in Spindle
~
Nl
TOl
T03
N2
Tal
T03
N3
T03
TOl
N4
T02
T01
Program may also start with the first tool in the spindle.
This is a common practice for the ATC programming. The
fIrst tool in the program must be loaded into the spindle
during setup. In the program, the first tool is called to the
waiting station (ready position) during the last tool - not the
first tool. Then, a tool change will be required in one of the
last blocks in the program. The first tool in the program
must be firs! for all parts within the job batch.
01403
(FIRST TOOL IN SPINDLE AT START)
N1 G20
(INCH MODE)
N2 G17 G40 GSa TO::!
(GET T02 READY)
N3 G90 G54 GOO X .• Y •. S •• M03
N4 G43 Z.. HOI MOB
(APPROACH WORK)
< ... Wl working ... >
N26 GOO Z •• M09
N27 G28 Z.. MOS
N2S GOO X •. 'l ..
N29 MOl
(Tal MACHINING OONE)
(Tal TO Z HOME)
(SAFE XY POSITION)
(OPTIONAL STOP)
mo T02
(T02 CALL REPEATED)
N31 M06
(T02 TO SPINDLE)
N32 G90 G54 GOO X .. Y .• S •• M03 T03(T03 READY)
N33 G43 Z.. H02 MaS
(APPROACH WORK)
TOl WORKING
< ... m2 working .. _>
N30
T02
TOl
N31
TOl
T02
N32
T03
T02
T02 WORKING
N50
T03
T02
N51
T02
T03
N52
TOI
T03
N46
N47
N4S
N49
MOl
(T02 MACHINING OONE)
(T02 TO Z HOME)
(SAFE XY POSITION)
(OPTIONAL STOP)
NSO T03
(TO 3 CALL REJr"EATED )
N51 M06
(T03 TO SPINDLE)
NS2 G90 G54 GOO X •• Y.. S •• M03 TOl (TOl READY)
N53 G43 Z.. H03 MO]
(APPROACH WORK)
< .. " m3 working . .. >
T03 WORKING
Examples shown here use this method as is or slightly
modified. For most jobs, there is no need to make a tool
change at XY safe position, if the work area is clear of obstacles. Study this method before the others. It wiJl help to
see the logic of some more advanced methods a lot easier.
GOO Z.. M09
G28 Z •• MaS
GOO X •. Y ••
N66 GOO Z •. Ma9
N67 G28 Z .. MOS
N68 GOO x .. Y ••
N69 Ma6
mo IDO
%
(T03 MACHINING OONE)
(T03 TO Z HOME)
(SAFE XY POSITION)
(TOl TO SPINDLE)
(END OF PROGRAM)
FUNCTION
101
",,,u.,,,,,,. Since there is
method is not without a
a tool in the spindle, it
or part changing.
in such a way that
part setup (spindle
"",,.'nIT'" an obstacle dur':
is lO program the
is no IDol in the spindle
condition).
• No Tool in the Spindle
{NO TOOL IN SPINDLE AT
{INCH
{GET TOl
N2 Gl7 G40 GSO TOl
(TOl TO SPJlNDLE)
N3 M06
N4 G90 GS4 GOO X •• Y.... Sit.. M03 T02 (T02 DVJ\"",,r\
N5 843 Z.. HOI MOS
(APPROACH
< ... 10) working, .. >
N26 GOO Z •• M09
N27 G2B Z •• M05
N28 GOO X •• Y ••
N29 MOl
(TOl MAcmNING DONE)
(Tal TO Z HOME)
(SAFE XY POSITION)
STOP)
NJO T02
NJl M06
N32 G90 G54 GOO X •• Y •.
NJ3 G43 Z •• NO.2 M08
(T02 CALL REPEATED)
<. ""7D2 working
(T02 TO
S •• M03 T03(T03 READY)
(APPROACH WORK)
>
N46 GOO Z •• Mag
N47 G28 Z •• MOS
N48 GOO X •• Y ••
N49 MOl
NSO T03
N5l M06
In the next example,
dIe tool in the program
may
100 heavy or too
through the ATe
must
tool change can be done by
gram supports manual tool cl1tmf!e.
spindle at the start and end of each machined
productive than
with the first tool in the
eXlr;1
Ihe cycle time. An
empty spindle at start
used if the programto recover space above
mer has a valid reason,
the part that would otherwise occupied by
recovered space may be
for removing the
with a crane or a
programming
from the previous exsituation is not much
ample - except that there is an extra tool change at the
program. This tool
brings the first tool
into the spindle, for
of each program run.
01404
N1 G20
• first Tool in the Spindle with Manual Change
(T02 MACHINING OONE)
(T02 TO Z HOME)
(SAFE XY POSITION)
(OP"l'I(JN.!!,L STOP)
(TOl CALL REPEATED)
(T03 TO SPJlNDLE)
N52 G90 G54 GOO X.. Y •• S .. M03 T99 (T99 READY)
\.n.t:",t"J:\,.JJ:'i.....n WORK)
N53 G43 Z .. HO) MOS
to use MOO program
scribing the reason
good selection - MOO is a
the machine without
carefully, to understand how a
Follow the next
tool change can perfonned when the firsllOoJ is
in the
1'02 in
example will be changed manually by the CNC
01405
TOOL IN SPINDLE AT START)
(INCH MODE)
N1 G20
N2 G17 G40 GBO T99
(GET T99 READY)
NJ G90 G54 GOO X .• Y •• S .• M03
N4 G43 Z •• HOI MOS
(APPROACH WORK)
< ... 1D J working . .. >
N26 GOO Z •• Ma9
N27 Gl8 Z.. MOS
N2e GOO X •• Y ••
N29 MOl
(TOl MAanNING OONE)
(TOI TO Z HOME)
(SAFE XY
(OPTIONAL STOP)
(T99 CALL REI)Rl\,TTi:l))
(T99 TO SPINDLE)
NJO T99
N31 M06
N32 TO)
READY)
NJ3 MOO
(STOP AND LOAD T02 MANUALLY)
N34 G90 G54 GOO X .• Y.. S .• M03
N3S G43 Z.. HO:;! MOS
<,
T02
(NO NEXT TOOL)
WORK)
>
(T02 MAan:NING DONE)
N46 GOO Z.. M09
TO Z
N47 G28 Z •• MOS
(SAFE XY POSITION)
N48 GOO X •• Y ••
(SPINDLE ORIENTATION)
N49 MI9
(STOP AND UNLOAD TOl MANOALLY)
N50 MOO
(TO) CALL REPEATED)
N51 TO)
(T03 TO SPINDLE)
N52 M06
N53 G90 GS4 GOO X .• Y •• S.. M03 TOl (TOI READY)
(APPROACH WORK)
N54 G43 Z.. H03 MOB
< . 103 working, . , >
< ... 103 working .. " >
N66 GOO Z •• M09
N67 G28 Z •• M05
N6S GOO X •• Y ••
N69 M06
mo ICO
%
(T03 MACHINING OONE)
TO Z-HOME)
(SAFE XY' POSITION)
(T99 TO SPJlNDLE)
OF PROGRAM)
N66 GOO Z •• M09
N67 G2S Z.. MOS
N68 GOO X •• Y ••
MACHINING DONE)
(T03 TO Z HOME)
(SAFE XY POSITION)
N69 MOl
(OPTIONAL STOP)
(TOl TO SPINDLE)
NIl M30
%
(END OF PR.OGRAM)
mo M06
1
Chapter 14
Note the M19 function in
block N49.
miscellaneous function will orient the spindle to exactly the same
were used.
position as if the automatic tool changing
The CNC operator can then replace the current tool with
next tool and still maintain the tool position orientation.
This consideration is mostly important for certain boring
cycles, where the tool bit cutting
has to be positioned
away from the machined surface. a boring bar is used. it
is
to
Its cutting tip.
• No Tool in the Spindle with Manual Change
The following program is a variation on the previous example, except that there is no tool in the spindle when the
program starts.
(NO TOOL IN SPINDLE AT START)
01406
(INCH MODE)
N1. G20
(GET TOl READY)
N2 G17 G40 G80 TOl
(TOl TO SPINDLE)
N3 M06
N4 G90 G54 GOO X. _ Y.. S •• M03 T99 (T99 READY)
(APPROACH WORK)
N5 G43 Z.o HOl Moa
< ... 7rJl
(TOl MACHINING DONE)
(Tal TO Z
(SAFE XY POSITION)
(OPTIO:N1\L STOP)
(T99 CALL REPEATED)
(T99 TO SPINDLE)
(T03 READY)
N32 T03
(STOP AND LOAD T02 MANUALLY)
N33 MOO
N34 G90 G54 GOO X •• Y •• S •• M03 (NO NEXT TOOL)
N35 G43 Z .• H02 MOB
(APPROACH WORK)
N30 T99
N3l MU6
< ... 7rJ2 worJdng ... >
N46
N47
N48
N49
GOO Z .• M09
G28 Z •• MOS
GOO X •• Y ••
MJ.9
NSO MOO
Sometimes it is necessary to use a little larger
tool than the machine specifications allow. In that case, the
oversize 1001 must return to
same pocket in the tool
it came from and
two adjacent magazine
must empty. Do not use a tool that is too heavy!
In [he example 01407, the large tool is
01407
(FIRST TOOL IN SPINDLE AT START)
(INar MODE)
N1. G20
N2 G17 040 GBO T99
(GET '1'99 RE1IDY)
N3 G90 G54 GOO X .• Y •• S •• MU3
N4 G43 Z •. HOl MOB
(APPROACH WORK)
< ... 7rJJ working . .. >
N26 GOO Z •• M09
N27 G28 Z .. MaS
N28 GOO X •• Y ••
N29 MOl
(TOl MACHINING DONE)
(TOl TO Z HOME)
(SAFE XY POSITION)
(OPTIONAL STOP)
N30 T99
(T99 CALL REPEATED)
TO SPINDLE)
N32 T02
('1'02 READY)
N33 M06
(T02 TO SPINDLE)
N34 G90 G54 GOO X •• Y.. S •• M03 (NO NEXT TOOL)
N3S 043 Z.. H02 M08
(APPROACH WORK)
001 MOG
... >
N26 GOO Z •• M09
N27 G28 Z •• M05
N28 GOO X •• Y ••
N29 Mal
• First Tool in the Spindle and an Oversize Tool
(T02 MACHINING DONE)
(T02 TO Z HOME)
(SAFE XY
(SPINDLE ORIENTATION)
(STOP AND UNLOAD '1'02 MANUALLY)
('1'03 CALL REPEATED)
NSl '1'03
(T03 TO SPINDLE)
NS2 M06
N53 G90 GS4 GOO X .. Y •. S •• M03 T99(T99 READY)
(APPROACH WORK)
N54 G43 Z •• HOJ MOS
< ... 7rJ2 working .. . >
N46
N47
N48
N49
GOO Z •• MU9
G28 Z •• M05
GOO X •• Y •.
Mal
('1'02 MACHINING OONE)
(T02 TO Z HOME)
(SAFE XY POSITION)
(OPTIO:N1\L STOP)
N50 MOG
(T02 OUT OF SPINDLE TO THE SAME POT)
N5l T03
(T03 READY)
NS2 M06
(T03 TO SPIND1..E)
N53 G90 G54 GOO X •• Y •• S .. M03 Tal ('1'01 READY)
N54 G43 Z •• H03 MOB
(APPROAOi WORK)
< .. .
workiJlg .. . >
N66 GOO Z •• M09
N67 G2B Z •• MOS
N68 GOO X.. Y .•
N69 MOl
mo M06
N7l lOa
%
(T03 MACHINING DONE)
(T03 TO Z HOME)
(SAFE XY POSITION)
(OPTIONAL STOP)
(TOl TO SPINDLE)
(END OF PROGRAM)
< ... 7rJ3 working . .. >
• No Tool in the Spindle and an Oversize Tool
N66 GOO Z •• M09
N67 G28 Z •. MaS
N68 GOO X •. Y ••
N69 M01
N70 M06
N71 M30
%
('1'03 MACHINING DONE)
(T03 TO Z HOME)
(SAFE XY POSITION)
(OPTIONAL STOP)
('1'99 TO SPINDLE)
(END OF PROGRAM)
This is another tool change version. It assumes no tool in
the spindle at the program start. It also assumes the next
1001 is target" than the maximum recommended diameter,
within reason. In this case, the oversize tool must return to
exactly the same pocket it came from. It is important that
the adjacent pocket.,;; are both empty.
TOOL FUNCTION
103
• lathe Tool Station
In (he 01408 example,
the
tool.
01408
(NO TOOL m SPINDLE AT START)
(INCH MODE)
N1 G20
(GET Tal READY)
N2 G17 G40 GSO TOl
(1'01 TO SPINDLE)
N3 M06
N4 G90 G54 GOO X •• Y •• S •. M03 1'99 (1'99 READY)
(APPROACH WORK)
NS G43 Z.. Hal MOB
A
slant bed
uses a polygonal turret holding
all external and internal cutting tools in special holders.
These tool stations are similar to a tool
on a madesign
8, 10, 12 or more cutchining center.
ting tools - Figure 14-7.
< ... TOI wor/dng .. . >
N26 GOO Z •• M09
N27 G28 z.. MaS
N2e GOO X •. Y •.
N29 Mal
(TOI MACIaNING DONE)
(Tal TO Z HOME)
(SAFE XY POSITION)
(OPTIONAL STOP)
(T99 CALL REPEATED)
N30 1'99
(T99 TO SPINDLE)
N3l M06
READY)
N32 1'02
(T02 TO SPINDLE)
N33 M06
N34 G90 GS4 GOO X.. Y.. S.. MO) (NO NEXT TOOL)
(APPROACH WORK)
N3S G43 Z.. H02 MO 8
Figure 14-7
Typical view of an octagonal lathe turret
< ... T02 working.. >
N46 GOO
N47 G28
N48 GOO X .• Y •.
N49 MOl
Many
MACHINING
(T02 TO Z HOME)
(SAFE XY POSITION)
(OPTIONAL STOP)
(1'02 OUT OF SPINDLE TO THE SAME
NSO M06
(T03 READY)
N51 T03
N52 MOo
(1'03 TO SPINDLE)
READY)
N53 G90 G54 GOO X •• Y.. S •• M03 1'99
(APPROACH WORK)
NS4 G43 Z •• HOJ MOS
type
tools available
CNC lathe models start adopting the tool
to
with many more
away from
work area.
Since all tools are
held in a single turret, the one
selected
cutting will always carry along all other tools
into the work area. This may be a design whose
has
but il is still
commonly used in industry.
cause a possible
between a tool and the maor part, care must be taken not only of the active cutall orher tools mounted in
turret,
ting tool. but
collision
for ail
< ... T03 working .. . >
• Tool rndexing
N66 GOO Z .• M09
(TO 3 MACHINING DONE)
N67 G2B Z •• MOS
(1'03 TO Z HOME)
XY POSITION)
N68 GOO X .. Y ••
N69 MOl
(OPTIONAL STOP)
NiO M06
Nil M30
%
(1'99 TO SPINDLE)
{END OF PROGRAM}
To program a tool change, or rather to index the cutting
tool into the
position, the T function must be programmed according to its proper formal. For the CNC
lathe. this format calls for the address
followed
four
digits - Figure 14-8.
illustrate some of
ATe programming
methods. The
is not difficult once the tool changing
mechanics of the machining center are known.
Tool
number
is tool WEAR
number
T fUNCTION fOR LATH
r•••• _ _ __
So
rhe tool function was
as it applied to the
CNC machining centers. CNC lathes
use the tool function T, but with a completely different structure.
Tool station number
is GEOMETRY offset number
Figure 14·8
Structure of a 4-digit tool number for eNC lathes
104
Chapter 14
It is important to understand this function well. Think
about the four digits as two pairs of
ralher than four
single digits. Leading zeros within
omitted. Each pair has its own meaning:
The first pair (the first and the second digits). control the
1001 index station and the geometry offset.
display of a typical Fanuc control, there
is a
two screens, both very
in appearance.
One is called the Geometry Offset screen, the other is called
lhe Wear Offset screen. Figure 14-9 and Figure 14-10 show
examples of both screens, with typical (Le., reasonable)
sample entries.
~ Example:
TOl xx - selects the tool mounted in position one
and activates geometry oHset number one
The second pair (the third and the fourth digits), control
the tool wear offset
used with the selected tool.
~ Example.
Txx01 - "''''P'''.''
wear offset register number one
It is customary, not arbitrary. La
the pairs, if
ble. For example, tool function TO 10 I will select 1001 station number one, geometry
number one and the assotool wear offset
number one. This format is
easy 10 remember and
be used every time, if only
one
number is assigned to the tool number.
Figure 74·9
Example af rhe GEOMETRY offset screen display
OFFSET - WEAR
If two or more different wear ~l!sets~e used for the same
Lool, it is not possible to malch Ihe pairs:In such a case, two
or more different wear offset numbers must be
grammed
the same 1001
Q Example:
T0101
for turret station
,
geometry offset 01 and wear offset 01
Q Example:
T0111
for turret station 01,
geometry offset 01 and wear offset 11
The first pair is always
tool station number and the
geometry offset number. The examples assumed that tool
wear offset 11 is not
by another tool. If tool ! 1 is
~with the offset II, another suitable wear offset number
must be selected, for example 2J, and program it as TOI2l.
Most controls have 32 or more offset
for
and another
wear olfsets registers.
offset
can be applied to the CNC
by registering
value into the
TOOL OffSET REGISTERS
word offset has been mentioned already several times
with two adjectives - with the expression geometry offset
and the expression wear offset. What exactly is an offset?
What is the difference between one offset and the Olher?
figure 14-10
Example of the WEAR offset screen dispfay
• Geometry Offset
Geometry
the same as the turret
operator measures and fills-in the gestation number.
ometry
for all tools used in the program.
The
from the
zero position will
the distance from the tool reference point to the part refer14- J 1 shows a typical measurement
tool.
applied to a common
All X values will normally have diameter values and are
a typical rear lathe of the slant bed
stored as
type. The
axis values will normally be
(positive
are
but impractical). How to actually measure the geometry offset is a subject of CNC machine lOol operation training, not
Figure} 4- 12 shows a lypical measurement of the geometry offset applied to a common internal tool.
TOOL FUNCTION
105
tty relating to the geometry off13. It shows geometry offset
on the spindle center line (at XO
center drills, drills, taps,
will always be the same.
Tool tip
• Wear Offset
if-r---' TO 101
,,
Geometry
offset X (0)
tr(:JnmJ'>f,rvofiset for external (turning) tools
program, the same
are used
as
in the finished drawing. For examof 3.0000
is programmed as
not reflect any implied dimensional
X3.0, X3.00, X3.000 and X3.0000
same result. What is needed to maintain
particularly when they are
to be done with a worn out tool that is still good
to cut a few more parts? The answer is that the propath must be adjusted,fine-tuned, to match
the machining conditions. The program itself will not be
but a wear offset for the selected tool is
difference between the
measured size of the part.
J4- 14 ill ustrales the principle of the tool wear
the
tip detail
is exaggerated for prnnn<l,""
!
I
Geometry
offset X (0)
II
1/
14·12
geometry offset for internal (boring) tools
I
I
J
1/ ;- PATH
I PROGRAM
Figure 14-14
/
Programmed tool path and tool path with wear offset
Tool tip
The wear offset
only one purpose - il compensates between the programmed value, for example of the
3.0
the
as measured
The differential
register. This is
of the (001
Geometry
X (0)
figure 14-13
Typical geometry offset for center line (drilling) tools
1
• Wear Offset Adjustment
illustrate the concept
offset adjustment on a rear
lathe, T0404 in the program will be used as an examThe
is to achieve an outside diameter of 3.0 inches
and tolerance ±.OOOS.
starting value the wear offset in the
Txx04 will be zero. The relevant section
{he program
look something like this:
N31 MOl
The principle of the wear offset adjustment is logical. If
the machined diameter IS larger then the drawing dimen(he wear
is changed
the minus direction, towards the spindle center line, and
versa. This
principle applies equally to external and internal
The only practical difference is
an
external
internal diameter can be recut (see
diameter and
the lable above). Chapter 34 presents several practical examples using the wear offset creatively,
• The Rand T Settings
N32 T0400 M42
N33 G96 S450 M03
The last items are
N34 GOO G42 X3.0 ZO.! T0404 Moa
N35 GOl Z-l.S FO.Ol2
R
T columns (Geometry and
Wear). The offset screen columns are only useful during
The R column is (he radius column. the T column is
the (001 tip orientation column (Figure 14-
N36 •••
When the machined part is inspected (measured), it can
have only one of
possible inspection results:
i
m
o
o
dimension
Q
Undersize dimension
If the part is measured on
is no need to inlerfere. The tool setup and
program are working correctly.
If the
is oversize. it can usually be recut for machining
an outside diameter.
an inside diameTer. the exact oppofinish,
will apply.
recut may damage the
a concern. If (he part is undersize, it bewhich could
comes a
The aim is to prevent all subsequenl parts
from being
as well. The following table shows
Inspection results
all existing possibilities:
Measurement
External diameter
Internal diameter
ON size
Size OK
Size OK
OVER size
SCRAP
UNDER size
Recut possible
Let's go a little further. Whether the pan will be
or...JJJldersized, something has to be done to prevent this
from happening again. The action to take is adjusting the
wear offset value. Again, the emphasis
is (hal this is an
example of an outside diameter.
The
diameter X3,0 in the example may result in
3,004 diameter
That means il is 0.004 oversize - on diameter. The operator, who is in charge of the offset adjustments, will change the current 0.0000 value in the
X register of the wear
04 to -0,0040. The subsequent
cut should result in the part that will be measured within
specified tolerances.
If the part in the example is undersize, say at 2.9990
inches. the wear offset must adjusted by +,0010 in the X
part is a
positive direction. The
RADIUS
Figure 14-15
Arbitrary tool tip orientation numbers used with tool nose radius
compensation (G41 or G42 mode)
The
rule of
R
T columns is (hat they are
only effective in a tool nose radius offset mode. If no G4]
or G42 is programmed, values in these columns are irrelevant. If G411G42 command is used, non-zero values for
that tool must be set in both columns,
R column requires the tool nose radius the cutting loot the T column
the tool tip orientation number of the
tool.
Both are described in Chapter 30, in more detail.
most
common tool nose radii for turning and boring are:
1/64 of an inch =: .01
or 0,4 mm
1/32 of an inch == .0313 or 0,8 mm
3/64 of an inch == .0469 or 1,2 mm
tool lip numbers are arbitrary and indicate the tool
orientation number used to calculate the nose
tool setting in the turret.
of
REFERENCE POINTS
environment,
importance.
are three major "'.\\Ilrrm
an established mathematical
n1o""",",,n
that
Machine tool + Control system (CNC unit)
Workpiece + Drawing + Material
environment
two. If the relationship
(he sources of each ,..n'Jlrrm
+ Cutting tool
maiep!~nOent of the other
right away, consider
a MACHINE TOOL is made by a company specializing in
machine tools, usually not
or cutting tools
... this ellvironment is combined with . ..
a CONTROL SYSTEM is made by a company specializing
in the application of electronics to machine tools.
do not normally manufacture machine tools
or cutting
o PART {workpu~cells a
engineering design
developed in a company that does not manufacture
machine tools, control systems, or cutting
and
holders.
a
environments
. They have to
purposes, these relationships and interactions are based on one common denominator of each en- a reference point.
A
Relationship
Tool
The common point here is that all
cannot
useful without some 'leam
they have to interact.
work
CUTTING TOOLS are a specialty of tooling companies,
which mayor may not make cutting tool holders.
These companies do not manufacture machine tools
or CNC C:\J<::rl>nH:
is a fixed or "''''"",,",,,,,.,, arbitrary location
machine, on the rool
A fixed referis a precise location
two or more axes, deduring manufacturing
reference
are established by the
during the progralmrmnlg process. In these
three refpoint for each of
erence points are needed - one
available groups:
a Machine reference point
.. Machine zero or Home
a Part reference point
.. Program zero or Part zero
a
or Command point
In a typical language of a
shop. these reference
have somewhat more
meamng. Home posior a machine zero are
terms for machine
reference point. A program zero,
are terms commonly used
reference point. And
name tool tip or a tool command point are commonly used
{he tool reference point.
REFERENCE POINT GROUPS
The
for short.
the control
CNC machine tool
H ......... ""'"
ratings, etc.
a
table or mounted into a
or other work holding
of numbers to consider. The parr
size, its height, diameter, shape,
Finally, the third group of numtools. Each CUlling tool
its indias features that are
with the
meet when a customer buys a
\hese sources
engineering design (part). must
CNC machine. A
1001 from one manufacturer, using
machined on a
manufacturer.
tools
a control
and 1001
from yet another
sources are similar to a
fourth source.
who never played .~"'_ ... _,
tet of first
is a need to create a harmony.
both cases
By itself,
environment is not very useful. A machine
withoultools will not yield any profit; a 1001 that cannot be
is not going to benefit
manufacused on any
turing
cannot be machined without tools.
.. Tool
Tool reference point
All
have a
- they are
they are actual values
programto work with individually as well
as
107
108
Chapter 15
• Reference Point Groups Relationship
The key 10 any successful CNC program is (0 make all
to work in a coordinated way. This goal can
achieved by understanding
principles of
ence points and how Ihey work.
reference point can
have two
o
Fixed reference
o
Flexible. or floating reference point
A
point is set by the machine
Lurer as part of
hardware design
cannot be physically
by the user. A CNC machine has at
fixed
point. When it comes to
ence points for the part or the cutting tool,
programmer
of freedom. A
reference point (program
is
a flexible point,
actual
silion is in programmer's hands. The
point for the
cutting tool can
either
or flexible, depending on machine design.
MACHINE REFERENCE POINT
The machine zero point, often called the machine zero,
home
or
a machine
position, is the
of machine coordinale
location
this
may
between the
manufacturers, but
most obvious
is
individual machine
types, namely the vertical and horizontal models.
In general terms, a CNC machine
two,
or more
axes, depending on the type and model.
has a
maximum range of travel that is fixed by
manufacturer.
range is usually
for
If the CNC
erator exceeds the range on
an error condition
known as over/ravel will occur. Not a serious problem, but
one that could be
During
setup, particularly after the power has been turned on, the position of all
axes has to
preset to be
the same, from day to
day, from one part to another. On older
this prois done by setting a grid, on
machines, by
performing a machine zero return command. Fanuc and
m~flY
control systems prevent automatic operation of
a machine tool, unless the machine zero return command
been performed at least once - when the power to the
has been
on. A
safety feature.
On all CNC machines that use typical coordinate system,
end of each
the machine zero is located at the
For a lypical
vertical machining
center,
at the pan in the
plane,
is straight down
from the tool position (tool tip). Also look into the XZ
plane (operator's front
of the machine), or into
YZ
plane (operator's right-side view of the
three planes are perpendicular to
other and together
creale su t:alled work cube or work space - Figure 15-1.
Figure 15-1
Machine
and axes orientation for a vertical machine
The cubical shape shown is useful only for
understanding the
work area.
programming and
the majority of work is done with one or two axes at a
time. To understand the work area and machine zero point
in a
at the machine
the top (XZ machine
(YZ
plane). Figures
plane) and from Ihe
J5-2
J5·3 illustrate both views.
MACHINE
view
15·2
Top view of a vertical machine as viewed towards the table
Spindle /'0 ...." 0 .. 1
Gauge line
FRONT view
Figure 15-3
front view of a vertical machine as viewed from the front
the two views. In top view, the
the spindle center line shown in
right corfront view.
REFERENCE POINTS
Also note that in front
there is a dashed
idenlias the gauge line. This is an imaginary
for the
proper fit of the
holder tapered body and is set by the
machine
The inside
spindle is a
taper that
tool holder with
Any (001 holder
in the spindle will
In
the same position.
Z motion illustrated will
shortened by the
tool projection.
subject of
tool referencing is
later in this
109
This vital reference point will be used in a ....,."IT,.".."
the relationship with
reference
ence point of {he
and the drawing dimensions.
The part
is commonly known as a program zero or a part zero. Because the coordinate point that
selected by the
represents program zero can
anywhere, it is not a fixed point, but ajloQling
this point is
more details can
covprogrammer who
part zero.
- after all, it is
• Return'to Machine Zero
In manual mode, the
operator physically moves the
axes to the machine zero position. The operator IS
to register
inlo the control
if
necessary.
turn
power to the
while the
are at or very close to the machine zero pomachine
Silion.
too close will make
manual machine zero
return more difficult later,
power had
reA clearance 1.0 inch (25.0 mm) or more
each
machine zero is usually sufficient. A typical proto physically
the machine zero position will
follow these
1.
2.
3,
4.
5.
6.
7,
Turn
power on
and control}
Select machine zero return mode
the first
to move (usually Z axis)
Repeat for the all
axes
Check the
in-position indicators
Check the position screen display
display to zero, if necessary
• Program
Selection
ng the program zero, often in the comfort of
is
that will
office, a
the efficiency
setup and its machining in
the shop. Always
allenlive (0 all
are for
and against a
zero selection in a
zero point may be selected
IS not much of an advice, although true
in
terms. Within
practical restrictions
the mach.ine operations, only the most advantageous possibilities should be considered. Three such considerations
of program zero:
should govern
[) Accuracy of machining
o
Convenience of setup and operation
o
Safety of working conditions
Machitli"q Accuracy
safety reasons, the
selected axis should
machining centers and the X
In bolh cases, either axis will be moving away
work,
into the clear area. When the axis has reached machine zero
position, a small indicator light on
control panel turns
on to confirm that
axis actually
machine zero.
The machine is now at its reference position, at the machine
zero, or at the machine
point, or at homeever term is used in the
The indicator light is
confirmation for each
the machine is ready for
use, a good
will go one step further. On the posilion display screen, Ule actual
position should be
set to
roreach axis, as a standard practice, ifil
is not
to zero automatically by
control. The
butcontrol panel
the position screen
PART REfERENCE POINT
A part
for machining is
within the machine
motion \lmils. Every
must mounted in a
that
IS
suitable for
required operation and
not
change position
other part of the job run. The fixed
location of the
very important for consistent results and
It is also very important to guarantee
thaI
of the job lS set the same way as the first
is established,
part reference
can
Machining accuracy is paramount all parts must be maexactly to the same
specifications.
is also important
repeatability. All the
in the balch must the same and all subsequent jobs
must be the same as well.
Convenience of Setup Bnd Dperation
Operating
setup
can only be considered
once (he machining accuracy is assured. Working
desire. An experienced CNC nrl".O'r~imrnl"r
think of
the
has in
Defining program zero that difficult to set on the
machine or difficult to check is not
convenient. It
slows down the setup process even
Working
Safety is always important to whatever we do machine
has a
and part setup are no different. Program zero
lot to do with
the
We look allhe lypical considerations of program zero severtical
centers and lathes
ally. Differences in part
influence the
zero
selections as well.
110
•
Chapter 15
Program Zero - Machining Centers
CNC machining centers allow a variety of
methods. Depending on the type of work, some most common
setup methods usc vises, chucks, subplates
hundreds of
special fixtures. In addition. CNC milling systems allow a
setup,
increasing
available options. In
to select a program zero, all
machine axes must
considered. Machining centers with additional axes require zero point each of these axes as well, for
the
or rotary axes.
What are the most common setup methods? Most machining is done
clamped on
table, in a
or a fixture mounted on Ihe table. These basic methods can
be adapted to more complex applications.
programmer
the setup method for any
given
perhaps in cooperation with
machine
tor.
programmer
selects the program zero
protion for each program. The process of selecting
zero starts with drawing evaluation, but two steps
to be
first:
Step 1.
Study how
drawing is dimensioned,
which dimensions are critical and which are not
Step 2.
Decide on the method of part setup and holding
Program zero almost presents ilselfin the
any
make sure all critical dimensions and tolerances are
from one part to another.
dimensions
are usually not critical.
on a machine table involves
simplest
the part, some clamps and
surfaces.
run and
ing surfaces must be fixed during
measured from. The most typical setup of this kind is
on
pin
Two pins form a single row
the third pin is offset away at a right
creating a
setup corner as two locating surfaces - Figure 15-4.
MACHI
PART
part are both parallello
machine axes and perpendicular
zero (part
is at (he intersection
edges.
IJvr\<Tr"' ......
two
The
concepl is common for virtually all setups,
actual
If a part is mounted in a
vise jaws must be parallel to or
perpendicular with
machine axes
the fi;ced location
must be established with a stopper or other fixed
Since a machine
most common work holding
device
parts,
use it as a practical example of
how to
program zero. Figure 15-5 illustrates a lypical
simple engineering drawing, with all the expected dimendescriptions
material
3
1210 75
.
\
THRU
1.0 r-~
--....
!
4.0
1020
Figure 15·5
Sample
x 0.5
used lor selecting program zero """::,,.... nltJ
When selecting a
zero,
study the
The designer's dimensioning style
flaws, but it still is the engineering drawing. In the example,
dimensioning
alJ holes is
the lower left corner of
the work.
the program zero of the part
itself?
For this example,
should be no question about programming the
point
except at
lower left corner the part.
the drawing origin and
it will become the part origin as well. It also satisfies Step 1
of the program zero selection
The
2, dealing
is next. A typical setup
with work holding device
CNC machine vise could be the one iIlust.rated
15-6.
N LOCATORS
Figure 15·4
Three-pin concept 01 a parr setup (all pins have the same diameter)
Since
part touches only one point on each pin, the
setup is very accurate. Clamping is usually done with top
clamps and
The left and
bottom
of the
In the setup identified as Version 1, the part has
positioned
the vise
a left pan stopper. The
part orientation is the same as
drawing. so all drawing
will appear in the program using these drawing
dimensions. It seems that this is a winning setup - yet, this
is actually
poor.
in the
IS any
of
What is
the actual
size of
The drawing specifies a
rectangular stock of 5.00 x 3.50. The~e are open dimen10 or more and
be acceptable.
sions they can vary
REFERENCE POINTS
111
If the choice is between Version J and 2, select Version 2
and make sure all negative signs are programmed correctly.
FIXED JAW
Is there another method? In most cases there is. The final
Version 3 will offer the best of both worlds. Part program
will have all dimensions in the first quadrant, as per drawing. Also, the part reference edge wiU be against the fix.ed
jaw! What is the solution? Rotate the vise 900 and position
the part as shown - Figure 15-8) if possible.
o
o
0
MOVING JAW
y
l
~
~
<:
-:I
I
--x
<:
-:I
(!)
0
LU
Figure 15-6
A sample part mounted in a machine vise· Version 1
X
u..
Combine any acceptable tolerance with the vise design,
where one jaw is a fixed jaw and the other one is a moving
jaw, and the problem can be seen easily. The critical Yaxis
Z
0
,'"
0
>
0
0
::E
y
i
!
reference is against a moving jawl
The program zero edge should be the fixed jaw - a jaw
that does not move. Many programmers incorrectly use a
moving jaw as the reference edge. The benefit of programming in the first quadrant (al! absolute values are positive)
is attractive, but can produce inaccurate machining results,
unless the blank material is 100% percent identical for all
parts (usually not a normal case). VersiOIl 1 setup can be
improved significantly by rotating the part 1800 and aligning the part stopper to the opposite side - Figure J5-7.
FIXED JAW
o
--x
Figure 15-8
A sample part mounted in a machine vise - Version 3
To select a program zero for the Z axis. the common practice is to select the top face of the finished part. That will
make the Z axis positive above the face and negative below
the face. Another method is to select the bottom face of the
part, where it IS located in the fixture.
Special fixtures can also be used for a part setup. In order
to hold a complex part. a fixture can be custom made. In
many applications of special fixtures, the program zero position may be built into the fixture, away from the part.
Selecting a program zero for round parts or paHerns (bolt
circles, circular pockets). the most useful program zero is at
the center of (he circle - Figure J5-9.
0
o
)
nr--9--~
MOVING JAW
x:..;
I
'
(2)
~
,----- PROGRAM ZERO
f
I
~
-Q- -.-- ·¢-----~--cB· -
y
1
--x
figure 15-7
A sample part mounted in a machine vise - Version 2
In Version 2, results are consistent with the drawing. Part
orientation by 1800 has introduced another problem - the
part is located in the third quadranti All X and Y values
will be negative. Drawing dimensions can be used in the
program, but as negative. Just don', forget the minus signs.
h\!
~_¢_0
0
Figure 15-9
Common program zero for round objects is the center point
Chapter 40 describes the G52 command that may solve
many problems associated with program zero at the center.
112
Chapter 15
• Program
-lathes
is setting program zero on the
This is not a perfect selection
other advantages. The only disadvanthere is no finished face. Many opface to the setup or cut a
On
zero selection is simple,
are only two axes to consider - the vertical X axis and the
horizontal Z axis. Because of the lathe design, the X axis
program zero
is always the spindle center line.
On eNC lathes, the program zero for the X axis
MUST be on the center rine of the spindle
z
three popular methods are used:
o Chuck
o
o
.. , main face of the chuck
, ., locating face of the jaws
, ., front of the finished part
Stock
,_[tp
__l /
'.
,
_.
-
-
-
-...1
X
J
---
What are the
zero at the front
One
is that many
dimensions along Z axis
can be
directly into
program, normally with
value. A
depends on the
of cases, the CNC programmer
probably the most important, is
a
a tool motion indicates the work area, a
is in the clear area. During program devel·
opment It IS
to forget a minus sign for the Z
cutan error, ifnotcaught in time, will positool away from part, with the tails tack as a possible
obstacle. It is a wrong position, but a better one than hilling
pari. Examples in this handbook use program zero at
thefrontfinishedface, unless otherwise specified.
.
--
--
---
CHUCK
Stock
x
~
Stock
-
-
•
-
<
- - -
_.'
-~
)",,~ ~
referenc~ point is related to the lOol. In milling
•
JAW
---
TOOL REFERENCE POINT
X
!
operations, the reference point of
tool is
the intersection of the tool centerline
the
culting lip (edge).
turning and boring, the most common (001
point is an imaginary tool point of the cutting
cause most tools have a cutting
with a built-in
For tools such as drills and other point-to-point tools
in milling or lurning. the reference point is
Ireme tip
the tool, as measured along Z
15-1 J shows some common tool tip points.
-
-
P,ART
Common program lero options for 8 eNC lathe· center line is XD
a chuck
with the
On a negaadditional
drawing
Jawor fixture face presents more
face can also be touched with
tool
all parts. This location may
shapes, such as castings,
Many lathe pariS
During
the first operation, material
operation
must always be added to
Z value.
is the main
reason why CNC programmers
away from program
in special cases.
zero located on jaw or fixture
tool reference
All
toofs
are connected. An error
on another. The
to understand
REGISTER COMMANDS
reference points
CNC programcorrectly. Havharmonized to
rPt,"'rPlnrppoints for
program zero) and
tool (i.e.• tool tip)
there has to be some
to fit them together.
means to associate them
must be some means LO 'teU'the control syslem exactly where each tool is physically
within the mawork area, before it can
oldest method
to do all lhis is to register the current
of the
control system
.", .. 'nr.n r,'{"wlt ..p'n a
• Position Register Definition
A little more verbose defi
could be
of the position rell~ISli:::r
way:
Position register
location
as
FROM
the program zero,
TO ..• the tool current position,
measured along the axes
Note that the definition does not mention the machine
zero at all - instead, it mentions
POSITION REGISTER COMMAND
The
command for the tool position register is
092 for machining centers and
lathes:
ition register command
(used in milling)
ilion regisler command
in turning)
lalhe5: also lise G92
but lathes
supplied with
and similar controls normally use G50
command instead. In practical applications, both 092 and
G50
have identical meaning and the following
discussion
to both commands
In the first
part of this
the focus will
applications using
command, lathe
using G50
command will
explained later.
by a much more
and
called the Work Offsets
to U59),
described in Chapter 18, and the Tool Length OffseT (G43),
described in Chapter 19. However, there are still quite a
few older machine tools in shops that do not
the
ury of the
of commands. There are
many
but still
compames
developed years
running on
equipment. In
cases,
registration command is an
standing the
skill. This
been one
some
grammers and
found a little difficult to
stand. In reality, is a very simple command.
First, a look at some more detailed definition this command. A typical description only specifIes Position Register Command, which by itself is not very
current tool position.
is a very important distinction. The current tool position may be at machine zero,
it
may
within travel limits of
axes.
note the emphasis on from-to
By definidistance is unidirectional. between the program
direction is always
the current tool location.
zero, 10 lool
never reversed. In a
correct sign of each
value (positive, negaor zero) is always required.
!-'v" .. " " , register is only applicable in the absolute
mode programming, while G90 command is jn effect. It
has no use in the incremental
G91. In
programmmg,
do begin in
toullocation.
• Programming Format
As the name
(he command suggests,
data associated with the G92 command will
(i. e., stored) into
control system memory.
The format
command is as
In all cases, the
of each axis specifies
zero to the tool reference point (tool tip).
Programmer provides all coordinates based on the
reference point (program
discussed earlier.
ditional axis will also have to be registered with
the indexing table on
example the B axis
chining centers.
from the
113
114
Chapter 16
• Tool Position Setting
MACHINE
ZERO
only purpose of
command is to register the current 1001 posilion imo the control memory - nothing
can be seen on the absolute position
effect of
screen display. AI all
the
position display
some values for each
They could
zero or any
other values. When G92 command is
current
values of the display will
with the values
fied with G92. H an axis was not specified with
there
will
no change of display for that
At the machine.
the
has a major responsibility - to match the actual
specified in the
command.
tool seHing with the
MACHINING CENTERS APPLICATION
In programming for CNC machining centers without the
Work Coordinate SysTem feature (also known as Work Offsets), the
Register must be
for each
axis and each lOol. There are two methods:
o
The tool position is set at machine zero
18-1
Current tool position
(only XY axes shown)
machine zero
Fig ure 16-/
a G92 setup
on
tool sel at
machine zero position.
method of starting program at
machine zero is useful. There could be an advantage, for
example, if a special fixture is permanently attached to the
machine
A subplate with a
grid is a common
example. Permanently set one or more vises may also benefit. There are numerous variations on this lype of setup.
o The tool position is set away from machine zero
Which method is better? We look at both
them.
• Tool Set at Machine Zero
The first method requires that the machine zero position
be
tool change position for all axes. This is not
will
necessary and definitely very impractical. Consider il for a
moment and think why it is impractical.
A program is usually done away from the machine. but
the part position on the tabJe must be speci
• Tool Set Away from Machine Zero
second method eliminates the difficulty of the
ous
It allows the programmer to sel XY 1001
anywhere within the machine travel limits (considering
safety first) and use that position as the lool
position
for XY axes.
there is no
for
machine zero itself.
the CNC operator can setup the part anywhere on the table.
in any reasonable position, within limits of the machine
axes. Figure 16-2 shows an
a
set at a
live X axis and a positive Y axis.
G92 X12.0 Y7.5 ZS.375
Numbers in the example look innocent enough. But conCNC
al the machine, trying 10 setup
part (without a
fixture), to
12.0 inches
away from machine zero in the X axis.
the same lime,
the operator must
the same
exactly
inches
away from machine zero
Y axis. The same effort has
to be done for the Z axis as well.
without some speIt is an almosl impossible task, at
cial fixtures. It is definitely an extremely unproductive
There is no need
those numbers. they are strictly
X 12.0 could have easily been 12.5. with no
benefit
All this difficulty is encountered
has chosen the machine zero
only
tool change position (mainly in the X
reference poi nt
andY
IN1TIAL
TOOL
POSITION
MACHINE
ZERO
Figure 18·2
Current tool position
(only XY axes shown)
set away (rom machine zero
REGISTER
115
In order to place tool into the
change position, the operator physically moves the 1001 from the pro·
gram zero by amounts
in
statement. This
is a lot easier job and also much more
that
jng setup to the machine zero.
Once the lool change posilion is
the program will return to this position
a
The Z axis automatic tool change position on
chining centers musl be programmed at
the only automatic tool change
really applies 10 XY axes only.
tion, the 092 selling will be the same for all
[here is a good reason to change it.
The only major disadvantage of this method is
new tool change position is only
system while the power is on. When the power to
chine is turned off. the tool change position is lost.
nprlpn,~p.n CNC operators solve this problem by
finding the actual distance from the machine zero to
tool
position. register it once for
particular
then move the tool by that distance
for example, at the start of a new day.
• Programming Example
To illustrate how to use the position
a part program for vertical
have to be followed:
o
The cutting tool should be changed first
o
G92 must be established before any tool motions
o Tool must return to the G92 position when
all the cutting is completed
All three rules are followed in a
01601
N1 G20
N.2 G17 G40 GBO G90 TOl
N3 M06
(TOOL 1 TO SPJCNDLE)
(SE.'T CURRENT XY)
N5 GO 0 XL 0 YO. S S800 M03
(MOVE TO
No ZO.l NOS
(MOVE TO CLEAR ABOVE)
N'7 GOl Z-0.55 F5.0
(FEED TO DEPTH)
N8 X).O Y4.0 F7.0
(CUT A SLOT)
~ GOO Z11.0 N09
(RAPID TO Z MACHINE ZERO)
N4 G92 X9.7S Y6.S Z11.0
NlO X9. 7 5 Y6. 5 MaS
Nll NOl
• Position Register in Z Axis
a typical vertical machine, the Z axis must be fully re[0 the machine zero, in order to make (he automatic
tool change. The position register value is measured from
the
zero of the Z axis (usually the top of finished
to the tool reference lip, while the Z axis is at mazero position. There is no other option.
Normally, each tool will have a different Z value of the
command, assuming the tool length is different for
tool.
a rule. the XY settings will not change.
for 092 command along
shows a typical
o 1601 ill ustrates the concept.
(PROGRAM NUbmElR)
(SET ENGLISH
)
(GE.'T TOOL 1 READY)
(RAPID TO XY SET POSITION)
(OPTIONAL STOP FOR TOOL 1)
example to write but more difficult to setDon't worry about unknown program
explanations should be
at
In
setting position must always
It
not maHer
the tool
is made, at machine zero or away from it - the prosame,
of the values
will
Only one
but normally, each
Z value as the position register,
length.
LATHE APPLICATION
with Fanuc and similar controls. 050
092 command:
the
MACHI
If 092 is
a
the command is similar:
same definition and
program
Figure 76-3
machine zero fDr the Z axis
8 different setting)
116
Commands G50 and
are identical, except that they
belong to two different G
groups. Fanuc actually offers three G code
for lathe controls. Based on history,typical Japanese made controls use GSO, whereby typical US made controls
G92. A cooperative US and
Japanese venture known as
Fonuc (General Electric
and Fonuc) produces controls that are the most common in
North American'
the G50 command.
for lathe applications is
very similar to that
for the mills. However, due to
design of CNC lathes, where all tools are mounted in
turret, the projection
from the
turret holder must
possible interference must be
mounted inaclive
one that is used for
tools move
cutting. In
all
are safely out of
placed in a tool magazine. Several new designs of
lathes are available, where tool
on the lathe
resembles the milling type.
• Tool Setup
The most important
work relates to the
tions to select from, some are .....,..,C"" .. "
lathe
op-
Probably the most
to have the tool change
to the machine zero position.
POSIto move the turret 10, just
control panel
The position registcr
to machine zcro
/00 far for
have one major disadvantage it
most jobs, particularly on larger lathes
the Z axis.
imagine a tool motion ono inches or more
the Z
only to index the turret and than (he same 30 inch mobuck to continue the cutting cycle. It is not efficient at
is a solution, however.
Much more efficient method is to select
tool indexing
position
position as close lO the part as possible.
should always be based on the longest tool mounted in the
turret (usually internal tools), whether the tool is
in the
or not. If there is enough clearance
the IV"!:;'-""
will also be enough clearance
• Three-Tool Setup Groups
On a typical slant bed CNC lathe, equipped with a
Iygonal turret (6 to 14 stations), all cutting
individual stations of the turret. During tool
the
tool is in the active station.
the
used for CNC lathe
three groups
normally do:
o
Tools lAtn'''''tn on the part center line
Q
Tools working externally on the part
Q
Tools working internally on the part
for each group is understood well,
it to any tool within a group,
tools used.
• Center line Tools Setup
as center line tools are typically
standard twist drills,
carreamers, and so on. Even an end mill can
center line. All tools in this group
have a
common denominator, whereby the tool tip is
always
on
spindle cenler line, while they cut
These
must
be setup exactly at 900 to the work
face (parallel to
The position
value in the X axis is from the spindle center line
to the center line of the tool. For the Z
axis, the position
value is measured from program
Iy, the center line tools will have
zero Lo the tool
a fairly large
that means their GSO value
the Z axis wm
small, when compared to
external tools, which generally do not project too much.
Figure 16-4
a
using an indexable drill as an
for center line tools.
TOOL
of
two
position at the X
not too distant) and JUS!
On a
lathe, do not forget to keep in mind
layout of all tools in the turret, to prevent a collision with
the
chuck, or the machine.
are other, but less common, methods to
the GSO command.
a tool
16-4
Typical 550 setting for center line lathe tools
COMMANDS
REG
117
• External Tools Setup
TOOL
external machining operations such as
diameters, taper cutting,
threading, part-off and
and approaches
zero to
register value is
tool tip of the
this chapter). In case of tools
tool, G50 amuunl is usually
the insert, for safety reasons,
16-5 illustrates a typical position
tool (turning tool shown in
example).
for
AT
TOOL CHANGE POSITION
Figure 16·6
Typical G50
for internal lathe tools
For
reasons, no 1001 should extend from a turret
into the Z minus zone that is to the left of part front
a fairly long travel beyond
Z
Many
lathes
zero (about I inches or 25-50 mm).
times, this zone can entered to make a safe tool
for very
tools.
(his is a more advanced
strict safety COI1Sllaer'an,ons
no extended zone for the X axis above
(only about .02 inches or
in the
sure to
G5D setting for external farhe tools
•
Internal Tool
Internal tools are
core or other
inside of a part, in a premachined
Typically, we may first
a boring bar, but
can be used as well for various internal operations. For exand i nlemal threading are comample, an internal
mon operations on a
setup rules
Ihe
Z axis apply in the same way for internal tools as for external lools of the same
position register setting must
Along the X axis, the
tip
the insert. Figure J6-6
be made to the
setup for an internal 1001
shows a typical
example).
(boring bar shown in
16-4, 16-5 and /6-6)
All three iIIuslrations
operations (drill - tum a possible order
Note that the turret position is
for a typical
position. not necessarily as
identified as a tool
That means G50 may be set
machine zero
of the machine, even at the mawhere within
chine zero.
concern relating to long tools is {"lp~r~lnt'p
area, mcluding chuck
those tools where the
• Corner Tip Detail
Typical turning tool contains an indexable
with a
strength and surface finish
When
command is used for a Lool that
a
built-in, the programmer has to know (and also tell
operator), which edge
corresponds to, In
cases, the choice is simple.
value is meaintersection of
program zero to the
X and Z
tool shape and
in the
will vary. Figure
next page shows
settings for the
a corner radius,
most common orientations of a
including two grooving tools.
• Programming Example
The example showing how to use a position register command G50 on a lathe will be very similar to that of a machining center. First, the tool change is made, followed
with G50 setting for the
tool. When the machining
is
with (ha( tool, it
to return to the same absolute
position as specified in the
The following simplified example is
two
the fir.sl 1001 is proor",mnC'lPt1 to cut a
the
tool is programmed to
cut a 2.5 inch diameter:
118
Figure 16-7
Position
Chapter 16
setting G50 for common tool tip orientations - the heavy dot indicates XZ coordinates set by GSO X. Z. for the tool above
01602
N1 TOlOO
N2 GSO X?4S ZS.5
N3 G96 S400 M03
N4 GOO X2.? ZO TOlOl MOB
N5 GOl X-O.01 FO.OO?
N6 GOO ZO.l M09
N7
X7.4S ZS.5 TOlOO
NB MOl
N9 T0200
NlO GSO XB.3 Z4.B
Nll G96 S425 M03
Nl2 GOO X2.S ZO.l T0202 MOB
Nl3 Z-1.75 FO.OOS
N14 GOO X2. 7 H09
N15 X8.3 Z4.B T0200
N16 !rOO
%
Note blocks N2 and N7
first tool, and N 10 and
the second tool. For
tool.
pairs of
are exactly
same. What
program is
the
system here is that block N2 only registers the
current tool position, but block N7 actuaJly returns that tool
to the same posilion it came from. For
second tool.
block NIO registers the current tool position, block N15
forces the tool to return there.
N 15
important blocks to
together are the
blocks N7 and N 10. Block N7 is the tool change position
for the
tool. block NIO is the tool
register for
toot - both tool are at the same physical position
the
of file turret! The difference in the XZ values reflects the
of each tool from the
difference in the projection
turret station. All that is done
G50 command is telling
the control where
currenr
is from program zero always
that in mjnd~
POSITION COMPENSATION
In this handbook,
programming are expressed as
than not, these numbers,
well before the actual
part programming, many
are
exactly, others are known approximately and there
known diare also many that are not known at all
mensions are subject to variations
Without
it will
facility available to (he
almost impossible to setup
precisely and efficiently. Fortunately, modem controls offer many features
to
both programming and machine
an easier,
and more precise activity. A
coordinate
offsets and compensations are typical support
in programming for
can also be used for a
Like
screens,
and similar controls. there are four preparatory
available to program position com-
increase in the programmed direction
compensation amount
It is only one of several
The maIn purpose
compensation is to correct
any difference between machine zero and program zero
1001 positions. In
it is
in those cases, where
the distance between the two reference points is subject to
vanations or is not known at all. For example, when working with castings, the
zero taken from the cast surface will be subject to
change. Using position
the need to make constant
compensation will
program
of the fixture setup.
mally, the part
in a fixture on the table
whole setup is
this reason, the position
compensation is
called fixture offset or
an offset and a cornlJ(!ns:aoffset. The
lion is often
and for any practical purposes,
(Wo terms are sami!.
IJV~"LJ\.)" compensation is
that requires mput the CNC maspecifies the
number, the operator enters
machine, using appropriate
setup.
• Programming Commands
decrease in the 1pro,gn,lmrne(
the programmer and machine
'- DESCRIPTION
limited replacement of the culler
is not covered at all for its obsoleswill be on positioning of the
t~"."r,"~ the part.
D .. An ..."' ..... ,.,,.," ..
One of the oldest programming l""".IJlIl ..... U~~;) available in
is called a position
As the
name suggests, using position
functions, the
actual tool position is compensated
to its Iheorelior assumed position,
methods available to
On modern CNC
systems, this method is still
compatibility with
older programs. Today, this technique is not really needed.
It
been replaced by the much more flexible Work Offsets (Work Coordin.ate Syslem),
in the next chapter
handbook. The current chapter'describes some
can benefit from ustypical programming
ing the old-fashioned
method.
term is used in the same meaning
as the majority of users interpret it. Ppsition compensation
pensation amount
G47
Double increase in the Iprogr~lmrne(
by double the compensation amount
G48
Double decrease in the programmed direclio1n
by double the compensation amount
I
definilions are based on
stored in the control
meaning of all
are inverted. None of
is
and
are
which they appear. If required in
\;;~";Lll\;;,U in any subsequent block, if
• Programming Format
Each G code (G45 to G48) is
with a unique
position compensation number, programmed with the adH. The H address points to the memory area storage
of the control system. On most Fanuc control systems. the programmed leuercan
be D, with exactly the
same meaning. Whether the H or D
is used in the
program, depends on the
of a control system
parameter.
120
A typical programming format for position compensation function is:
G91 GOO G45 X •• H ..
or
G9l GOO G45 X •• D ..
where the appropriate G code (G45 through G48). is followed by the target position and number of the memory
storage area (using H or D address).
Note that the example uses incremental and rapid mOlion
modes and only one axis. Normally, the compensation has
to be applied to bolh X and Y axes. However, only a single
measured amount can be stored under either H or D number. Since it is most probable that the compensation value
will be different for each axis, it must be specified on separate blocks, with two different offset numbers H (or offset
numbers D), for example:
x .. H31
(illl STORES THE X VALUE)
(H32 STORES THE Y VALUE)
G91 GOO·G45 X .• D31
G45 Y •• D32
(D31 STORES THE X VALUE)
(D32 STORES THE Y VALOE)
G91 GOO G45
G45 Y •. H32
or
For the record, the H address is also used with another
type of compensation, known as the tool length offser (or
tool length compensation), described in Chapter 19. The D
address is also used with another type of compensation,
known as the cutter radius offset (or cutter radius compensation). described in Chapter 30.
The applicable preparatory G code will determine how
the address H or address D will be interpreted. In the examples. more common address H will be used - Figure 17-J.
TABLE
1
'-....
11111--_ _
H31---
MACHINE
ZERO
T
H32
.\
J"'"
PROGRAM ZERO
_. _ _ ~ _ J
\ PART
figure 17- 7
Position compensation - general concept
•
Incremental Mode
The question may arise why the compensated motion [s
in the incremental mode, Remember that the main purpose
of position compensation is to allow a correction of the distance between machine zero and program zero. The normal
use is when starting the tooJ motion from machine zero position. By default, and without any offsets, coordinate settings or active compensations. the machine zero [s the absolute zero, it is the only zero the machine control system
'knows' allhe time,
Take the following example of severa! blocks, typically
programmed at the beginning of a program with position
compensation:
N1 G20
N2 G17 GSa Tal
N3
M06
N4 G90 GOO G45 XO H31
N5 G45 YO H32
(NO x MOTION)
(NO Y MOTION)
N6
This example illustrates a motion from machine zero (the
current tool position), to program zero, which is the target
position, along XY axes, Note the absolute mode setting
090 in block N4. Assume that the control system is set (0
H31 =-12.0000 inches. The control will evaluate the block
and interpret it as programmer's intention to go to the absolute zero, specified by G90. It checks the current position,
finds it is at the absolute zero already and does nothing.
There will be no motion, regardless of the compensation
value setting, if the absolute motion is programmed to eIther XO or YO target position. If the G90 is changed to 091,
from absolute to incremental mode, there will be a motion
along the negative direction of X axis, by the distance of
exactly 12 inches and there will be a similar motion along
Y axis, in block N5. The conclusion? Use position compensation commands in the incremental mode G9 J only.
• Motion length Calculation
Let's look a little closer at how the control system interprets a position compensation block. Interpreting the way
how the control unit manipulates numbers is important for
understanding how a particular offset or compensation
works. Earlier definition has stated that a single increase is
programmed with G45 command and a single decrease
with 046 command. Both G47 and G48 commands are of
no consequence at the moment. Since both commands are
tied up with a particular axis and with a unique H address,
all possible combinations available must be evaluated:
o
Either an increase or a decrease is programmed
(G45 or G46)
o
Axis target can have a lero value, or a positive value,
or a negative value
o
Compensation amount may have a lero value,
or a positive value, or a negative value
POSITION COMPENSATION
121
In programming. it is important to set cenain standards
and consistently abide by them.
example, on vertical
machiningcenlers, the compensation is measured/rom mane zero to program zero.
means a negative
result is a
lion from the operator's viewpoint.
decision 10 set
as
It is
cruc1al to understand how the control interprets
information in a block. In
compensation, it evaluin memory called by
address H (or
ales Ihe value
D). If the value is zero. no compensation
place. If the
value of H is stored as a negative
it adds this
10
the
the axis
position and the
is the
motion length and direction.
example, assume the
memory
I stores
value of -15.0 inches. and
machine current location is at
zero position and
setting on Ihecontrol is also set to zero. Then the
will be interpreted as
-15.0 + 0 = -15.0000
the Iota I motion of negative \5.0 inches along
value of axis target
the same formula
is a non-zero and
17
l
13
,
"j,--
.'
--15 ;-'"
17-2
Figure 1 shows
for the following
example 701, The
applies to the X and Y axes exactly (he same way. In written in metric units and has
tested on
[ I M,
the H address
would
the same way). The
compensation values
and H99 were set to:
the X and Y axes respectively. The modal
were not repealed
interpreted as
01701
AND G46 TEST}
Nl G21 G17
N2 G92 XO YO ZO
N3 G90 GOO G45 XO H98
N4 G46 YO H99
NS G28 XO YO
-15.0 + 1.5 = -13.5000
However,
'-1
H98
H99 = -150.000
G91 GOO G45 Xl.S H31
will
r
H99
Position compensation applied to different target locations:
zero, positive and negative - see 01701 program Pll::l'mn/I'!
G91 GOO G45 xo H31
resulting
the X axis.
9
next example is 1/01 correct:
G91 GOO G4S X-l.5 H31
(ABS
(ABS
xo TARGET)
YO TARGET)
the motion will try 10
the
X axis direction and
result will be
overtravel. Since [he
value of X is
G45 command cannol be used and
G46 command must
instead:
N6 G91 GOO G45 XO H98
N7 G46 YO H99
N8 G28 XO YO
(INC' XO TARGET)
(INC' YO TARGET)
G91 GOO G46 X-l.S H31
N9 G90 GOO G45 X9.0 H98
NlO G46 Y17.0 H99
Nl1 G28 XO YO
(ABS X+
(ABS Y+
will be
r",'or,,'/] as
-15.0 + (-1.5) '" -15.0000 - 1.S
G45
TARGET)
TARGET)
16.5000
in the ....."" .. ":1',.....
value could
been
value.
could be quite confusing and
but it would work quite well. To see the
possibiliprogram 0 J70! is not dOl ng very much, exCCrl moving from machine zero 10 different positions and back to
machine zero (G28 command refers 10 a machine zero return and is explained separately in Chapter 2/ ).
N12 G91 GOO G4S X9.0 H98
N13 G46 Y17.0 H99
Nl4 G28 XO YO
X+
(INC' Y+ TARGET)
NlS G90 GOO G45 X-1S.O 898
Nl6 G46 Y-13.0 H99
N17 G28 XO YO
(AES X-
Nle G91 GOO G4S X-1S.0 H98
Nl9 G46 Y-13.0 H99
N20 G28 XO YO
N21 M30
%
(INC' X- TARGET)
(INCY-TARGET)
TARGET)
Y- TARGET)
122
17
control syslem will
the way it was
(symbol orr means an
the
and direction of
each motion block
or the wrong way
condition, preceded WiLh
method is described in Chapter 19 of the handbook. If the
Z axis is programmed with G45 or G46 commands, i( will
also be affected.
• Using G41 and G48
N3
G90
G90
Gn
G9l
->
->
->
->
N9 G90
NlO G90
N12 G91
Nl3 G9l
->
->
->
->
Nl5 G90
Nl6 G90
N1e G9l
Nl9 G91
->
->
->
->
N4
N6
N7
•
G45
G46
G45
G46
G45
G46
G4S
G46
G4.5
G46
G45
G46
->
->
->
->
0
0
0
no motion
no motion
X-2S0.0
Y+ OIT
->
->
->
->
+
+
+
+
X-241.0
Y+ OjT
X-241. 0
Y+
->
->
->
->
0
X+
Y-163.0
X+ OjT
Y-163.0
Position Compensation Along the Z axis
Position compensalion
usually appl
to the
X
Y axes and will nol normally be used with the
In most cases, the Z
to be controlled by another
of compensation known as the too/length
This
In the examples,
compensation feature was used
only between the
zero and program zero, as a
method
exactly is the part
on
the table. The single mClrea~;e using G45 and the
were used, because
crease using G46
the only commands npPflP{"I
Commands G47 (double increase) and G48 (double de~
crease) are only
for a very simplified cutter radius olfsel and are not covered in this handbook
of
their obsOlescence. However, they can still
used.
• Face
In a later
(Chapter 28),
milli ng wi II be explained in more detail. In thai chapter is a very
good example of how to apply position
to
offset
the face mill in a
regardThis is probably the only
use of
less of its
G45 and 046 commands in contemporary programming.
WORK OFFSETS
In position compensation, to switch machining
part to another within the same setup. the n1"I'''',,-';'rn
contain a different compensation number
zero of the previous part. Using the work
program zeros are measured from the machine zero
lion, normally up to six. but more
are
The six work coordinate systems
are available on Fanuc control
lowing preparatory commands:
When the control unit is
is normally
"'lU~I.n''-'' rl,r;.c{'nhlf'c the most modem methods to coor-
relationship between machine zero reference
the program zero reference point. We will use
Work Coordinate System feature of any modern control
whether it is called the Work Coordinate System or
the Work Offsets.
lalter term seems to be more popular
because it is a little shorter. Think of the work offsets as an
alignment bctwcen two or more coordinate systems.
Basically, the work
ent work areas as a
the
unit are
to
independvalues input into
measured from the maare up to six work
zero positions can be
relationships, using
[X]
WORK AREAS AVAILABLE
MACHINE
ZERO
some more detailed descriptions can be covered,
just what is a work coordinate system - or a work offset?
Work offset is a method that allows the CNC programmer
to
a part away from the CNC machine, without
is a
knowing its exact position on the machine table.
very SImIlar approach as in the position compensation
method, but much more advanced and flexible. In
work
system, up to six parts may be set up on the machine
each having a different work offset number.
can move the tool from one part to
with
aV"Vluc,-, ease. To achieve this goal, a
preparatory
for the active work offset is needed in
control system will do
rest.
will automatically make any adjustment for
between the two part locations.
Un1ike the position cmnOlens:aU'OI
more axes may be
offsets. although the Z
controlled independently,
offset commands. Commands
are fully described in the next
AXES MOTION LIMITS
Figure 18·1
Basic relationships of the work offset method
The same relationships illustrated for the def~ult
apply exactly the same way for the other
able work offsets 055 to G59. The values siored in the control system are always physically measured from the rnazero position 10 the program zero of the
as
determined hy lhe CNC programmer.
12
124
Chapter 18
The distance from machine zero to program zero of each
work area is measured separately along the X and Y axes
and input into the appropriate work offset register of the
control unit. Note that the measurement direction is from
machine zero to program zero, never the other way around.
If the direction is negative, the minus sign must be entered
in the offset screen.
For comparison with the position register command G92,
Figure J 8-2 shows the same part set with t.he older method
of G92 {lnd m{lchine zem a<; a ~tart point. Note the opposite
arrows designation. indicating (he direction of measurement - from program zero to machine zero.
;---- G92 [ X ) ~
MACHINE
ZERO
t
>-
Part position on the machine table is usually unknown
during the programming process. The main purpose of
work offset is to synchronize the actual position of the part
as it relates to the machine zero position.
• Additional Work Offsets
The standard number of six work coordinate offsets is
usually enough for most types of work. However. there are
jobs that may require machining with more program reference points, for example, a multi-~irlerl part on a horizonttll
machining table. What options do exist, if the job requires
ten work coordinate systems, for example?
Fanuc offers - as an option - up to 48 additional work offsets, for the total of 54 (6+48). If this option is available on
the CNC system, anyone of the 48 work offsets can be accessed by programming a special G code:
GS4.1 P..
Selection of additional work offset,
where P = I 1048
N
0)
o
(!)
PART
l
PROGRAM\
ZERO
\.
AXES MOTION UMITS
Figure 18-2
Basic relationships of the Position Register cDmmand G92
For work offsets G54 to G59, a typical entry into the coordinate offset position register will be the X axis as a negative value. the Y axis as a negative value and the Z axis as a
zero value, for the majority of vertical machining centers.
This is done by the CNC operator at the machine. Figure
18-3 shows an example of a typical control system entry.
01 (GS4)
X -12.5543
Y - 7.4462
Z
0.0000
Figure 18·3
Typical data entry for the G54 work coordinate system
By using the G54 to G59 settings in the program, the control system selects the stored measured distances and the
CUlling tool may be moved to any position within the selected work offset simultaneously in both the X and Y axes,
whenever desired.
Q G54.1 P.. example:
G54.1 Pl
G54.1 P2
GS4.1 P3
G54 1 Px..
G54.1 P48
Selection of additional work offset 1
Selection of additional work offset 2
Selection of additional work cffset 3
Selection of additional work offset x..
Selection of additional work offset 48
The utilization of additional work offsets in the program
is exactly the same as that of the standard commands:
N2 G90 GOO GS4.i Pi XS.S Y3.1 SlOOO M03
Most Fanuc controls will allow omission of the decimal
ponion of the G54.1 command. There should be no problem programming:
N2 G90 GOO G54 Pl X5.S Y3.1 S1000 M03
The presence of PI to P48 function within a block will
select an w.1Ji/ional work offset. If tbe PI to P48 parameter
is missing, the default work offset command G54 will be
selected by the control system.
WORK OffSET DEfAULT AND STARTUP
If no work offset is specified in the program and the control system supports work offsets. the control will automatically select G54 - that is the normal default selection. In
programming, it is always a good practice to program the
work offset command and other default functions. even if
the default G54 is used constantly from one program to
another. The machine operator will have a better feel for the
CNC program. Keep in mind that the control still has to
have accurate work coordinates stored in the G54 register.
WORK OFFSETS
125
In the program, the work offset may be established in two
ways - either as a separate block, with no additional information, as in this example:
N1 G54
The work offset can also be programmed as part of a
startup block, usually at the head of program or at the beginning of each tool:
N1 G17 G40 GBO G54
The most common application is to program the appropriate work offset G code in the same block as the first cutting tool motion:
N40 GOO G90 G54 X5.5 Y3.1 SlSOO M03
Figure J8-4 illustrates this concept. In (he above block
N40, the absolute position of the tool has been established
as XS.5Y3.1, within the GS4 work offset. What will actually happen when this block is processed?
.all
x = -12.5543 + 5.5 = -7.0543
Y =
-7.4462 + 3.1 = -4.3462
These calculations are absolutely unnecessary in everyday programming - they are only useful to the thorough understanding of how the control unit interprets given data.
The whole calculation is so consistent, il can be assigned
into a simple fonnula. For simplicity, the seuings of the
EXT (external or common) offset are not included in the
formula. but are explained separately. later in the chapter:
II3f' where ...
A == Actual motion length (distance-to-go displayed)
M = Measured distance from machine zero
P == Programmed absolute target position (axis value)
Be very careful when adding a negative value - mathematically, the double signs are handled according to the
standard rules:
G54 [X]--'
PLUS and PLUS becomes
a + (+ b) == a
+
b
PLUS
PLUS and MINUS becomes
0--r
I
a + (- b) = a - b
MINUS
3. 1
WoJ+------'-----I _t
1-- -5.5 --1
Figure 18-4
Direct too/ motion to a given location using G54 work Dffset
Note thaI there are no X or Y values associated with the
G54 command in the illustration. There is no need for
them. The CNC operator places the part in any suitable 10calion on the machine table, squares it up, finds how far is
the program zero away from machine zero and enters these
values into the control register, under the G54 heading. The
entry could be either manual or automatic.
Assume for a moment, that after setup, the measured distances from machine zero to program zero were X-12.5543
and Y-7 .4462. The computer will determine (he actual motion by a simple calculation - it will always add the programmed target value X to the measured value X, and the
programmed target value Y to the measured value Y.
The actual tool motion in'the block N40 will be:
MINUS and PLUS becomes
b) == a - b
a -
(-I-
a -
(- b)
MINUS
MINUS and MINUS becomes
:::
a
-I-
b
PLUS
In the example, plus and minus combination creates a
negative calculation:
-10 + (-12) = -10 - 12 = -22
If any other work offset is programmed, it will be automatically replaced by the new one, before the actual tool
motion takes place.
• Work Offset Change
A single CNC program may use one, two, or all work
offsets available. In all mulli-offset cases, the work offset
setting stores the distance/rom the machine zero to the program zero 0/ the each part in the setup.
126
Chapter 18
For example, if there are three parts mounted on the table,
each individual part will have its own program zero posilion associated with one work offset G code.
r--,...
G56 X
G55X
G54X -
I
i
Figure 18-5
Using multiple work offsets in one setup and one program.
Three parts shown in the example,
Compare all possibJe motions in Figure 18-5:
G90 GOO G54 xO YO
... will rapid from the current tool position, to the program zero position of theftrst part.
G90 GOO GSS XO YO
... will rapid from the current tool position. to the program zero position of the second part.
G90 GOO GS6 XO YO
... will rapid from the current tool position, to the program zero position of the third part.
Of course, the target position does not have to be part zero
(program zero) as shown in the exampJe - nOr1liaJly, the tool
will be moved to the first cutting position right away, to
save the cycle time. The following program exampJe will
illustrate that concept.
In the example, a single hole will be spot drilled on each
of the three parts to the calculated depth of Z-0.14 (program 01801). Study the simplicity of transition from one
work offset to another - there are no cancellations - just a
new G code, new work offset. The control will do the rest
OlSOl
Nl G20
Nt G56 XS.5 Y3.1
NB GBO ZI.0 M09
N9 G9I G54 G2a ZO MOS
NlO MOl
(SWITCH TO GS6)
(SWITCH TO GS4)
Blocks N3 through N5 relate to the tirst part, within the
G54 work offset. The block N6 will spot drill the hole of
the second part of the same setup, within the G55 work offset and the block N7 will spot drill the hole of the third part
of the same setup, within the G56 work offset. Note the return to the G54 work offset in block N9. Return to the default coordinate system is not required - it is only a suggested good practice when the tool operation is completed,
The work offset selection is modal - take care of the transitions between tools from one work offset to another.
Bringing back the default offset G54 may always be helpful
at the end of each tool.
If all these blocks are in the same program, the control
unit will automatically determine the difference between
the current too! position and the same tool position within
the next work offset. This is the greatest advantage of using
work offsets - an advantage over the position compensation
and the position register alternatives. All mounted parts
may be identical or different from each other, as long as
(hey are in the same positions for the whole setup.
• Z Axis Application
So far, there was a conspicuous absence of the Z axis
from aU discussions relating to the work offset. That was no
accident - it was intentional. Although any selected work
offset can apply to the Z axis as well, and with exactly the
same logic as for X and Y axes, there is a better way of controlling the Z axis, The method used for Z axis is in the
form of G43 and GM commands that relate speci fically to
the too/length compensation, more commonly known as
the tool length offset. This important subject is discussed
separately in the next chapler. In the majority of programming applications, the work offset is used only within the
Xy plane. This is a typicaJ control system selling and may
be represented by the following setup example of the stored
values within the control register:
(G54) X-S.76l Y-7.819 ZO
(GSS) X-1S.387 Y-14.122 zo
(GS6) X-22.733 Y-8.3S2 zo
(GS7)
The ZO offset entry is very important in the examples and
in the machine control. The specified ZO means that the coordinate setting for the Z amount (representing the height
of the part) does not change from one part to another, even
if the XY setting does.
N2 G17 G40 GSO
N3 G90 GS4 GOO XS.5 Y3.1 S1000 M03 (G54 USED)
N4 G43 ZO.l HOl ~8
NS G99 GB2 RO.l Z-O.14 P100 FB.O
N6 G55 X5. 5 Y3. 1
(SWITCH TO GSS)
The only time there is a need to consider Z axis within the
work offset setting is in those cases, where the height of
each part in the setup is different. So far, only the X Y posi~
tions were considered, as they had been the ones changing.
WORK OFFSETS
127
If the 2 amouot changes as well, that change must be con~_
sidered by modifying the coordinate register selling of the
control. This is the responsibility of the CNC operator, but
the programmer can learn an important lesson as well.
~:!'~-:-Dr;c
,...----, - r
,
G56
" _ _ M.
--
G54
........
.. ................. ""
HORIZONTAL MACHINE APPLICATION
Machining several parts in a single setup is done quite
frequently on CNC vertical machining centers. The multiple work offset concept is especially useful for CNC horizontal machi ning centers or boring mills, where many part
faces may have to be machined during a single setup.
Machining two, three, four, or more faces of the part on a
CNC horizontal machining center is a typical everyday
work in many companies. For this purpose, the work offset
selection is a welcome tool. For example, the program zero
at the pivot point of the indexing table can be set for the X
and Y axes. Program selling of the Z axis may be in the
same position (the pivot point of the indexing table) or it
can be on the face of each indexed position - either choice is
acceptable. The work offset handles this application very
nicely, up to six faces with a standard range of the G codes.
. . . . .,
TABLE
Figure 18-6
Setting of work offsets {Dr a variable part height
Figure 18-6 shows some typicaJ and common possibilities used for special parts that have a variable height within
the same tool setup. The difference between part heights
has to be always known, either from the part drawing specifications or from actual measurements at the machine.
If the previous multi-offset example for XY setting are
also adapted for the Z axis, the work offset can be set up for
parts within the same setup, but with variable heights. This
variable height is controlled by the Z axis. The result of the
setting will reflect the difference in height between the
measured Z axis surfacc for one part and thc mcasured 2
axis surface for the other parts. Based on the data in the previous example, combined with the 2 values shown in Figure 18-6, the control system settings may look like this:
(054) X-S.761 Y-7.819 ZO
(GSS) X-lS.387 Y-14.122 Z-O.40S
(056) X-22.733 Y-S.3S2 ZO.356
The important thing to know about the control of the Z
axis within the selected work offset is that It works in very
close conjunction with the tool length offset, discussed in
the next chapler (Chapter 19). Stored amount of the Z axis
setting within a work offset will be applied to the actual tool
motion and used to adjust this malian, according (0 the setting of the tool length offset. An example may help.
For instance, if the tool length offset of a particular cutting tool is measured as 2-10.0, the actual motion of such a
tool to the program zero along Z axis will be -10.0 Inches
within the 054 work offset, -10.408 within the G55 work
offset. and -9.644 within the 056 offset - all using the examples in the previous illustration, shown in Figure J8-6.
There is no significant difference in the programming approach - the switch from one work offset to another is
programmed exactly the same way as for the vertical machining applications. The only change is that the 2 axis will
be retracted (0 a clear position and the table indexing will
usually be programmed between the work offset change.
Figure 18-71l1ustrates a typical setting for four faces of a
part, where 20 is at the top of each part face. There could be
as many faces as there are table indexing positions. In either case, Ihe programming approach would be similar if
20 were at the center of indexing table, which is also quite a
common setup application. See Chapter 46 for more details relating to horizontal machining.
8180
~~8~,g
-...j
i
0,
-
I
t:O
A
1""._ _-""-,""""--,-""-,""""""
80
Figure 18-7
Example of work offsets applied fo a horizontal machining center
128
Chapter 18
EXTERNAL WORK OFFSETS
A careful look at a typical work
screen display
reveals one
offset that is identified by one of the following
work offsets, as well as any additional
will be
by the values set in the external
offset, based on the setting
.
all programmable coordinate systems will
name for
special offset is
Work
or more
often, the External Work Offset.
o 00
o 00
LATHE APPLICATIONS
(EXT)
(COM)
The two zeros - 00 that this work offset is not
one of the standard six
G54-G59.
offsets are
identified by numbers 0 I
06. The
designation
also implies that this is nol a programmable
at least
not by using the
CNC program~ing .
Fanuc Macro B option
allow programming thIS
The abbreviation EXT means External,
the abbreviation COM means Common.
machine
will have
one or the other
but not both.
a maHer of
curiosity, the COM designation is found on older
UJ!'!'''I"I-'r\v the EXT designation is more recent. The
With
computer market,
COM
abbreviation
become
facto standard abbreviation
for the word communications.
Fanuc
also supseveral communication methods, including the conwith a personal computer, some time ago,
COM
designation has
replaced with the designation
EXT, to prevent possible confusion between the two
viations
in computing.
to the same
and has the
Either ahhreviation
same purpose. On
screen
this special
is
usually located before or above
for G54.
example, as illustrated in Figure 18-8:
Originally,
work coordinate ~ystem was designed f~r
CNC machining centers only. It did not take
to apply It
to CNC lathes as well. The operation, logically and physiis identical to that for machining centers.
work
offsets
CNC lathes eliminates
awkward use
or (;92 and makes the
lathe setup
operation much
and
• Types of Offsets
main difference in applying work offsets on a
is
that seldom will there
a need for more than one
offset.
work offsets are a possibility, three or more are
used for some
special and complex
G54 to
commands are available on all modern
lathes
customary to ignore the work
in
program,
more !han one offset is
means the CNC lathe programmer
on the
G54 setting as a rule.
Two special offset features found on the
control
Wear offsets,
on the
systems nre (he Geometry
same screen dispJay, or on
screens, depending on
the control model.
• Geometry Offset
01 (G54)
00 (EXT)
X
Y
t:){tlll/ul/::
0.0000
0.0000
0.0000
of an
X -12.5543
Y
7.4462
Z 0.0000
feXl'emi~IJ work offset display (EXT ::::: COM)
difference between an
or common
is that it is not programmable with any particuwork
G code.
ly set to zero for all axes.
Any nOll-zero
work offset in a very
important way:
Geomerry
is the equivalent of a
known from
milling controls. It rpl"lf"PCf'ntc
tool reference poinllo program zero, measured from
the
zero along a selected
Typically, on a
bed CNC lathes, with the tool turret above the spindle centerline, the geometry offset
both X and Z axes will be
negative. Figure /8-9 illustrates reasonable geometry values for a drill, turning tool and
bar (TO I ,
T03).
GEOMETRY OFFSET
_. _TIP'
_ ...1
No.. X
01 .
02' -8.6470
-9,0720
04
0.0000
05
0.0000
0.0000
0.0469
0.0313
0,0000
0.0000
18·9
Typical data emries for a lathe tool GEOMETRY offset
0
3
2
0
a
WORK OFFSETS
129
• Wear Offset
TOOL SETUP
The wear offset is also known and used on milling controls, but only for the tool length offset and the cutter radius
offset, not for the work coordinate system (work offset).
On the CNC lathes, the purpose of the wear ofrsel is identical to that for machining centers. This offset compensates
for the tool wear and is also used to make fine adjustments
to the geometry offsets. As a rule, once the geometry offset
for a given tool is set, lhat setting should be Jeft unchanged.
Any adjuslments and fine lunillg of actual pan dimensions
should be done by the wear offset only.
WEAR OFFSET
No.j X OFFSET. Z OFFSET
01
02
03
04
05
0.0000
-0.0060
0.0000
0.0000
0.0000
0.0000
0.0000
0.0040
0.0000
0.0000
RADIUS
TIP
_M··t
0.0000
0.0469
0.0313
0.0000
0.0000
0
3
2
0
0
Figure 18- 70
Typical data entries for a lathe tool WEAR offset
Figure J8-10 shows some reasonable sample entries in
the wear offset registers. The tool radius and tip number
seHings appear in both displays and the display in both
screens is automalic after the oifset value input. The tool
nose radius and the tool tip orientation number are unique
to CNC lathe controls.
•
Tool and Offset Numbers
Just like tools on CNC machining centers have numbers,
they have numbers on CNC lathes as well. Usually, only
one coordinate offset is used, but different tool numbers.
Remember, the tool number for a lathe has four digits, for
example, 1'0404:
o
o
The first two digits select the tool indexing station (turret
station) and the geometry offset number. There is no
choice here. Tool in station 4, for example, will also use
geometry offset number 4.
The second two digits are for the wear offset register
number only. They do not have to be the same as the tool
number, but it makes sense to match the numbers, if
possible.
Depending on the control model and the display screen
size. the tool offset register may have a separate screen display (page) for (he geometry and wear offsets, or both offset types may be shown on the same screen display. The
work offset values (work coordinates) are always placed in
the Geometry offset column.
In the next three illustrations is a very similar layout as
that shown in Chapter 16, describing the use of GSO register method (position register command used in the program). Compare the TWO illustrations!
The setup of the CNC lathe is identical in both cases, except for the method and purpose of the posicion measuring.
All illustrations in the applications also match the reasonable data entered In the too! geometry and the tool wear offset screens of the control.
Typical values along the X axis are always negative (as
shown in illustrations), lypical values along the Z axis are
usually negative. A positive value is also possible, but thaI
means the tool is above work and tool changing can be very
dangerous. Watch OUf for such situations'!
The actual selling procedures are subject of a CNC machine operation training and not practical to cover in a
programming handbook. There are additional methods,
also part of machine training, that allow faster tool setting,
using one tool as a master and setting all the remaining
tools relative to the mas/er tool.
•
Center line Tools
Tools that work on the spindle center line are tools that
have their tool tip located on the center line during machining. This area covers all center drills, spot drills, various
drills, reamers, laps, even end mills used for flat bottom
holes. At the same time, it disqualifies all boring bars, since
their tool tip does not normally lie on the spindle center line
during machining. Center line tools are always measured
from the center tine of the tool to the center I ine of the spindle along the X axis and from the tool tip to the program
zero along the Z axis. Figure 18-11 illustrates a typical setting for center line tools.
TURRET AT
TOOL CHANGE POSITION
T01
GEOM (Z)
~
o
~
~
o
LU
(!)
-
,,
--- - --<;
Figure 18-1 7
Typical geometry offset setting for CENTER liNE tools
130
Chapter 18
• Turning Tools
• Boring Tools
Turning tools - or
program zero,
imaginary tool tip to
a negative diameter) and along the Z
ative
as well. Keep in
if the culling tool
sen (for turning or boring) is changed from one radius to
another radius in the same Lool holder, the
setup
change
marginal,
change is enough to cause a scrap, so a
good care is
For turning, be extra careful for a tool
nose
thaLchanges from a larger
to a smaller
for example, from 3/64 (RO.0469) to lJ32 (RO.03l
TURRET AT
CHANGE POSITION
Figure 18·12
geometry offset setting for EXTERNAL tools
Boring tools - or
tools - are
measured
the imaginary
tip to program zero, along the X
axis (typically as a
diameter)
along the Z axis,
typically as a
value as well. In majority of cases.
the X value of a boring tool will
that for a turning or other
boring operations, same as for turning operations,
also be extra
for a lool nose
that changes
from a larger
to a smaller
It is (he same as
a
turning 1001. The scrap can be made very easily.
• Command Point and Tool Work Offset
various reasons, it is quite common to
ting insert in the
of work. primarily to
favorable CULLing conditions and to keep dimensional tolerances within drawing specifications. Cutting inserts are
(0 very high
but a certain
anee devialion should be expected between inserts obtained from different sources. If changing an
it is
to adjust the wear
for precision work. in order
to prevem
the part.
Tool
inserlS of
same shape and
but
with a different nose radius. Always
cautious when rean insert with an
that has a
tool nose radius.
to be
by the proper amount.
-1~- 0.0016
··0.0016
Figure 18-12
a typical geometry
for a
turning (external) tool and Figure 18-13 illustrates a typical
geometry setting
a boring (internal) tool.
RO.0156
RO.0313
TOOL
b
I
GEOM (2)
0.0136
0.01
J
Figure 18·14
Setting error caused by a different insert radius in the same holder
example in Figure
for a
1/32 ( .0313) nose radius (middle). and the
error for
a radius that is
(left) and one that is larger (right).
The dimensions
the amount
in the example.
ular
Figure 18·13
Typica/g8ometry offset setting for INTERNAL tools
for the partic-
TOOL LENGTH OFFSET
far. we have looked at two methods of compensation
for the actual position of the cutting tool in relation to the
machine reference point. One method was the
type,
position compensation, the other was the contemporary work coordinate system method (work offset). In both
cases, the emphasis was only on the X and Y axes, not on
the Z axis. Although the Z axis could have been included
with
method,
would not have been very
practical.
main reason is the nature of
CNC work.
decides on
setup of a part in
the fixture
appropriate location of
XYZ
program z.ero (part reference point or part zero). When
usIng work offsets, XY axes are always measured from the
machine reference point to the
zero position. By a
The
strict definition, the same rule applies (0 the Z
is that the measured
values will remajor
main unchanged for all tools, whether there is one tool used
or one hundred tools. That is not the case with the Z
The reason?
tool has a different length.
GENERAL PRINCIPLES
The length of
cutting tool has to be accounted for in
every program for a CNC machinIng center. Since (he
earliest applications of numerical control, various tech~
niques of programming tool length have
They
belong into one of two basic groups:
o
Actual tool length is known
a
Actual tool length is unknown
out, the rest is hidden in the holder.
tool holder is
mounted in
by means of a standardized tooling
Tool designations. such as the common sizes
HSK63, HSKlOO, BT40 and
are examples of established European
Any tool
within its category will fit any machine tool designed for that category. This isjust one more precision feature built inlo the CNC machine.
length of a tool for the purposes CNC programming must always be associated wilh the tool holder and in
relation to
machine design. For that purpose, manufacturers build a precision reference position into the spindle,
called the gauge line.
• Gauge Une
When the 1001 holder with the cutting lool is mounted in
the spindle of a CNC machine,
own taper is mounted
against an opposite taper in the spindle and held in tightly
by a pullbar. The precision manufacturing allows for a
constant location of the tool holder (any tool holder) in
spindle.
position is used for reference and is comthe name
it is an
called the gauge line.
line
for
Figure 19-1.
GAUGE LINE
AT MACHINE
«
I.L
t
Needless to say, each group requires its own unique programming technique. To understand
concept of tool
length in CNC programming, it is important to understand
length. This length is
meaning of the phrase actual
known as the physical tool length or just tool
length and has a very specific meaning in CNC programming and setup.
• Actual T001 length
tool
By holding a typical
physical length with a measuring
drill, we can
device. In human terms, a six inch long drill has a length of
to the other. In CNC
inches, measured from one
programming that is still true, but not quite as relevant. A
of her cutting 1001 - is normally mounted in a
drill - or
tool holder and only a portion of the actual tool projects
w
()
W
.
SPINDLE
MOTION
.J
co
«
I-;I
Fjgure 19-1
Typical front view
CNC vertical machining center
We use the gauge line for accurate measuring of lOa!
length and
tool mali on along the Z axis. Gauge
is
by
machine manufacturer
is closely related to another precision face, called the machine rabIe,
actually, the table top face. The gauge Ii ne is one
of a
that is
with another plane table
131.
132
Chapter 19
• labia lop Face
is also a convenient block to add coolant function
Every
machining center
a built-in machine taon which the fixture and part are mounted. Top of the
table is precision
to
flatness and
for
located
In addition, the table is located a certain fixed distance
from the gauge line.
like the position of
tool holder
in the spindle cannot be changed, the position of
table
for a removable table using a palette system) cannot
be
of the table creates another
line and parallel
reference plane that is related to the
to il as well. This arrangement allows to accurately program a tool motion along the Z
The tool length offset (compensation) can be defined:
in CNC
The most significant benefit of tool length
programmer to design a
programming is that it enables
complete program. using as many tools as necessary. without actually knowing the actual length of any
TOOL lENGTH OFFSET COMMANDS
Fanuc systems and several other machine controls offer
three commands relating to the tool length offset - all are
G commands:
All three commands are only applicable to the Z
Unlike the work offset commands G54-G59, G43 or G44
cannot
without a further specification. They can
only be used wilh an offset number designated by the
dress
The address H mUSI be followed by up 10 three
digits,
on the number of offsets available within
the
G43
G44
offset
G49
HOD
offset cancel
H..
Tool length offset number selection
MOS for the current tool:
N66 043 Zl.O H04 MUS
The resulting motion in the example will be to 1.0 inch
above
part zero. The control system will calculate the
distance to go, based on the value of H offset stored by the
operator during setup.
/9-2 shows a Lypical screen for the tool length
TOOL OFFSET (LENGTH)
No.
GEOMETRY
WEAR
001
002
003
004
005
006
-6.7430
8970
-7.4700
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
Figure 79·2
Typical too/length offset entry screen
set entry. Note that the actual display will vary from one
and the wear offset may not be
control to
on some controls. The wear offset (if available) is only used
adjustments to
tMllength as a separate screen entry.
044 command is hardly ever used in a program - in
fact. it has the dubious distinction of being the least used
commands of all Fanuc G codes. Its comparison with G43
is described later in this chapter.
Many CNC programmers and operators may not reaJize
that the Z axis setting in a work offset (054-G59) is
vel)' important for the tool
offset. The reason why
will be clear in the coming descriptions of different methods of 1001 length
setting.
programming manuals suggest the
or
G46 commands can also used for tool length offset. Although this is still (rue Loday and may have had some
in the early days, il is best to avoid them. First, the
position commands are not used very much anymore and,
second. they can
be used with the X and Y axes and do
not truly represent the Z axis
• Distance-lo-Go in Z Axis
Tool length offset should always
programmed in the
absolute mode G90. A typical program entry will be the
043 or 044 command, followed by the Z axis
number:
tion and the H
N66 G43 Zl.O H04
In order to interpret how the CNC system uses
tool
length command, the programmer or operator should
able 10 calculate
distance-fo-go the cutting tool. The
logic behind the tool length
is simple:
TOOL LENGTH
1
The value of the H offset will be added \0 the target Z position
if G43 is used, because G43 is defined as the positive tool
length offset
a
o The value of the Hoffset will
subtracted from the target
Z position if G44 is used,
negative tool length offset
G44 is defined as the
G43 z-O. 625 H07 .....
054 along Z is set to 0.0500, Z axis target is -0.625
the H07 is -8.28. The distance-to-go calculation uses the
same fonnula. but with
values:
Za
cases is the absolute Z
target position in
COOirQulate in the prognun.
Z
setting of the
(G54-G59), the H value,
the Z axis target are all
,_ ....distance-to-go. can
accurately calculated.
control system will use
Zd :::: Wz +
+H
z
..... where:
G54 Z is set to lO, Z axis
'"''"'"..........'... is 0.1 and HO 1
is set to
then the distance-to-go
will
==
:::::
0 + (+0.1) + (-6.743)
o + 0.1 - 6.743
-6.643
The
distance-lo-go will be
In
options require involvement of two people, or at
least two professional skills - the CNe programmer and the
CNe operator. The question narrows down to who is going
to do what
when. To be fair, both
have to do
something.
programmer has to •__ ~~,
tools
their number (the T address)
the H adoffset
for
G43 or
dress
operator
to physically set the
register the measured values of H
CNC system memory,
sure the fomru1a is always correct, try to
T
e Example Wr = 0.0200:
In this ,,"'..... i}, ....., the program contains
• On-Machine Tool length Setting
G43 Zl. 0 H03 ..... where:
Z is set to 0.0200, Z axis
value of H03 is
~
is
=
=
(+0.02) + (+1.0) + (-7.41)
0 . 02 + 1.0 - 7.47
"'"
-6.45
the bulk: of on-machine
.0 and the
CNe operator. Typically,
a negative target IJU"......'-,.u is
e Example - W
0.0500:
The program
contalns a negative Z coordinate:
z
re-
places a tool
spindle and measures the d1S~t.an(~e
tool travels from machine zero to part 'Zero (nf',nor~m
This work can only
done between jobs
definItely
nonproductive. It can
justified under
stances,
jobbing shops and
jobs
or for
with very few people. Although the
number of tools will take
longer
setting of a
than setting a
tools, there are setup methods available to the CNe
that allow reasonably speedy
on-mach ine tool
setup, namely using the master tool
method, descnbed
in this section. The one major benefit of this
it does not require
additional
a skilled person to op.:!ralte
The result is ",.., ...."""l"1t the tool will travel
towards the
distance-to-go will
In the last
and can be used
of a tool used for
(consisting of the
and the tool holder), can be set directly on the
U"\.,~1.J.J.L'" or away from it. These setup options are ofon-machine or off-machine tool length setups.
an advantage and it
corresponding
relationship to the
disadvantage. They both share a
as it applies to the
tool or its proto
two setup options are
and often cause
(or at
progrnmsome friendly disagreements)
each setup option
its advandisadvantages. Which one appears to be
will depend on many
factors as well.
e Example - W = 0:
~
-8.855
TOOL lENGTH SETUP
Work coordinate value
position in Z
(Z coordinate)
of the applied H offset number
G43 ZO.l H01
==
Again., the fonnula works
= Distance-to-go along Zaxis
H
(+0.05) + (-0.
+ (-8.28)
0 . 05 - O. 625 - 8 ~ 28
=
any distance-to-go calculation along the Z axis. '"'yr.....n_
mentmlg with other settings may
be useful.
S' where ...
~
==
-'
\
1
Chapter 19
• Off-Machine Tool length Setting
In technical terms~ the off-machine
requires the
work of a skilled tool setter or a CNC operator. Since the
seltln o is done away from the machine, a special equipment
is req~ired, adding to
overall cost of manufacturing.
This equipment can
a simple fixture with a height gage
(even made
or a more expensive, commercially
available digital display device.
• Tool Length Offset Value Register
Whichever method
the tool length setting is used, it
U\JI., ....... '" a
value that represents the length the
selected lOol. This value is
by
and must be
somehow supplied to the program, before the job is machined. The
must register
meusured value into
the system,
the
heading on the control panel.
The figure
a common setup a CNC vertical
machining center, looking from the front of the machine, a
typical operator's viewpoint.
column is located
a1
machine zero position. This
limit switch
tion
positive Z axis travel and is necessary for the autotool change on vil1ually all machining centers. All
four illustrated dimensions are either known, can
found
in various instruction or service manuals, or can be physically
They are always considered as known
or
dimensions and used as
critical
for uceurate machine
Distance between the tool gauge line and
Q
the tool cutting point
... dimension A in the illustration
Distance between the tool cutting point and the ZO
Q
(program zero of the part)
The control syslem contains a special registry for the tool
usually under
of tool
setlength o.{fset, toollenglh compensation
off
of the exact heading, the sellmg procedure
measured length is entered into Ihe control, so it can
by the program. The
is always well within
Z aXIs travel limits of the machine. yet still allows for
clearances for the part
and the tool Chan2,f:S.
To
the tool length offset, try to fully
stand theZ
motion
geometry orthe
machine
first. On vertical and horizontal machining centers, look at
1he XZ plane, which is the top
part for both. The
will be on the
pies are identical, but
chining center layout.
Z AXIS RELATIONSHIPS
To understand the general principles of tool length
let's look at the schematic illustration of a typical
a vertical machining center - Figure
'i
1-
r
LINE
MACHINE ZERO
A
0
I
B
for
'" dimension B in the illustration
of the part (distance between
the table
and ZO of
part)
Q
... dimension C in fhe iJlustration
Q
Total of all three previous dimensions
(distance between the tool gauge line and the table top}
... dimension Din the illustration
It is rather rare that the programmer or the operator would
always know all four dimensions. Even If that were possible, some calculations would not be worthwhile
The
reality is that only some dimensions are known or can be
found out relatively easily.
In the illustration, the dimension D is
known,
cause it is
distance determined by the machme manufacturer. It
not
possible to know the C
(height of
part with clearances), but with planning
common setup, this dimension can be known as well.
That leaves
A - the
between the (001
gauge line and the tool cutting point. There is no ~ther
method to find this dimension, but to actually measure It. In
earller
of numerical control, this
A had to
always known
embedded in the program. D<;;;""a'J"""
of the inconvenIences involved in finding this dimension,
Olher methods have
later.
Today, three methods are considered in programming
length setup, including the original method:
Preset tool method is the original method
Q
... it is based on an external tool setting device
Touch-off method is the most common method
Q
"-..Y'
Figure 19-3
Z axis relationships of the machine, cutting tool, table top
and the
height
o
it is
on the measurement at the ma,r.mfle
Master tool method is the most efficient method
... it is based
to the length of the longest tool
OFFSET
TOOL
1
benefits. The CNC programmer conand chooses one method over
these methods and operations do not
process directly - they are methsetup on the machine only. For proper unsubject
CNC programmers, they DIe
of which setting method
t",...,,,,v,,,, to the selected setting in the
a comment or message .
the tool length measurement "" ..",,..,,,,,0"
cutting tip of the Lool to the gauge line is accudetermined - Figure 19-4. Preset tools will
the
by
already mounted in a tool holder,
number of the tool and with the list of measured
to do, is to set
retool lengths. All the CNC operator
tools into the magazine and register each tool length
offset register, using the proper offset number.
• Preset Tool length
to preset the length of cutting tools
rather than during the machine
setup. This
the
method of setting tool
lengths. There are some
in this approach - the most
notable is the elimination of nonproductive time spenl durapplies to horizontal machining
ing setup. Another
to the center of
centers, where
zero is
the rotary or
table.
are disadvantages as
well.
tool length
external
04
05
06
8.5000
.. T001 length by Touch Off
cutting
are set at the exmachine runs a production
machine when jobs do
IS no
change. All the operator
values into the offset
setup can be done
tional G I 0 command
is to enter the measured
that portion of the
by using the op-
This melhod also
a
person responsible
number of small and
for presetting the cutting tools, A
medium users with vertical laClnmln~ centers cannot afford the additional
of the culting tools during the part
Ihe louch-off
when
method. This method may
IS
small job runs are machined.
scribed in the next secnon.
The tool length that uses the touch-off method is very
common, jn spite some
loss during setup. As the illustration in Figure
each tool is assigned an H
number (similar to
example), called the tool
length offset number:
GAUGE
UNE-
GAUGE
UNE- Figure 19·5
Touch-off method of the too/length offset
T___- - -,
PART
19-4
Tool len pleset away from the machine
WOlk
at (G54-G59) must be used
is to
machine zero poThis distance
corresponding H
menu of the
system, The important notion
is that the Z axis
settings for any work offset
and the common offset are normally set to ZO.oooo.
•
Using a Master Tool length
Using the touch-off method to measure tool length can be
a
significantly speeded up by using a special method
I1Ulster tool, usually the longest tool. This tool can
a real
or just a long bar with a
tip, permanently
mounted in a tool holder. Within the Z
travel, this new
'(001'
usually extend out more
anticipated
too) that
be used.
and the
work
norcontain theZ
set to 0.0, when the part touch-off
is used. This setting will change for
master tool
length
The master tool length measurement is very
efficient
requires the following setup
It
vides suggested steps
may need some modification:
Figure 19-8
the master tool
with setting of
the master tool and place it in the spindle.
2. lero the l axis and make sure the read-out on the
relative screen is lO.OOO or lO.OOOO.
3. Measure the tool length
the master tool, using the
touch-off method described previously. After touching
the measured
the tool in that position!
The greatest benefit of this seuing method is shortened
setup
If certain tools are
for
of jobs, only
the length of the master tool needs to be redefined for any
new pan height while all other tools
unchanged.
They are related to the master tool
4. Instead of registering the measured value to the tool
length offset number, register it into the common work
offset or one of the G54-G59 work offsets under the
1 setting! It will be 8 negative value,
5. While the master
set the relative l
is touching the measured face,
read-out to zero!
'6, Measure every other tool, using the touch-off method.
The
will be from
machine zero.
master tool tip, not from
7. Enter the measured
under the H
number,
in the tool length offset screen. It will always be
a negative value for any tool shorter than the master tool.
e Note:
•
643-G44 Difference
Initial
a.t the beginning of
chapter indicates that Fanuc and similar CNC systems offer two
commands that activate the tool
offset.
two
are
and G44. Most programmers use
G43 command exclusively in the program and may
have some I.Hlliculty to interpret the meaning of G44 command,
they have never used it.
is a good reason why G44 IS a dormant command - not quite dead but
would
to know how barely breathing.
and when - or even
to use one over the other.
is an
attempt at explanation.
First,
a look at the definitions found in various CNC
reference books and manufacturers' specifications
In different versions of these publications, the following
are
- all are quoted literally and all
typical
are correct:
Choosing
tool as master tool, the procedure is
logically same, except (he H offset entries will be positive
for any tool that is
than the master and they will
neRative
any tool
is shorter
master. In
rare case where the measured tool will have exactly the
offset entry for that tool
same length as
master too),
will be zero. Illustration in
19-6 shows the concept
of master tool setting.
Arter
master tool
into
axis of work offset, enter
distance
the tool
new tool to the tool tip of the master tool, and
in
appropriate H offset
If the
tool is an
actual tool, rather
a plain
used for
H offset value must be always set to 0.0.
G43
Plus offset
G44
Minus offset
G43
G44
Tool length offset
Tool
offset ~:I""_"""
G43
G44
Minus direction
Plus direction
These definitions are correct only if
within the context their meaning into consideration, That context is not
clear from
of these
Plus to where?
of what?
(he context, think about
use of
the toollenglh
on a CNC machine. What is the purpose of the tool length
LENGTH
1
main and most important purpose of any tool length
is to allow a CNC program to be
away
from the machine, away from tooling and fix\uring, and
without knowing the
cutting tool length
prodevelopment.
process has two
- one is in
the
at the machine.
program, either
together with
or 044 command is
the programmer. Al
number - that lS done
tool length offset can be set on or off the
is measured and
ther way. the tool
is entered into
control - that is the job the operalor. It is the
machine that has a number of
variations of only two G
LINE
exactly the same
not the
tool length
ming method). Program will
command (043 or 044), followed by the target position
along the Z axis and the H
number:
043 Z1.0 H06
or
044 Zl.O H06
The
system cannot
any benefits, until
the offset registers.
measured value for H06 is
if the H06 has been
as 7.6385, it will
as a negative value,
is used, and as a positive
value, ifG44 is used (1001 motions will be identical):
G43 Zl.O H06 .....• H06 = 7.6385
G44 Zl.O H06 ...... H06
+7.6385
{hat the
It is
actual Z axis
is
culated. USing G43, the H
value will be added (+) in
the calculation. Using 044, the H offset value will
The a~avel motion will be:
"'/U"bn (-).
043:
044:
Figure 19-7
Less common method of
Work offset (typically
Z + H06
Z - H06 :
+ (-7.6385) :::: -6.6385
(1.0) - (+7.6385) = -6.6385
(1.0)
(oollenglh
machine
with negative
(touch-off) will result in
The
selup process can automatically input all
the offset
as negative. That is
reason why
043 is the standard command to program tool length offset. G44 is just flOt practical for everyday work.
the tool length offset
must be set as well.
Figure 19-7 illustrates one of two ITlF'.r"v" to sel a
length command - 054 or other work
must be used.
GAUGE
LINE
f
PROGRAMMING fORMATS
Programming format for 1001 length
is very
and has been illustrated many times.
the following examples are some general applications of various methods.
The fLfst one will show programming method if no tool
length offset is available. Understanding the development
of tool length
over the years
it easier to apply
it in the
Other example
a comparison of
for the
programming
mru1p1m G54 to 059
The last example
shows the
to
method appl1ed (Q a simple program
using three tools, a typical way of programming today .
• Tool length Offset not Available
Figure 19-8
More common method of using the tool length offset.
No work offset setting is required and 643 is the preferred choice.
illustrates the other, and much more comIn this case, all work offset com.!lli!nds
will normally have a Z value set to 0.0.
In the early days of programming, tool length offset and
work
were not available. G92 position register command was
G
the current tool
position.
programmer had to
every
mension specifled by the machine manufacturer
and
dimension of (he job
specifically
ZfJ to the tool
distance
138
Chapter 19
--i""iII----
G45X.. H31 _ _ _--'.!.,
Block N3
......I - -_ _
G45X .. H31 _ _ _~..;.,
Block N3
G92X3.4Y2.8
G92X3.4Y2.8
Y2.8
Y2.8
GAUGE
GAUGE
LINE
LINE
G92Z9.0 (Block N6)
Figure 19·9
Setting too/length without too/length offset· program 01901
This early program reqUIred the position compensation
in XY axes and the position register
command G45 or
command G92 in XYZ axes. Each
must start at machine zero - Figure 19-9:
01901
m G20
(meR MODE SEL.ECI'ED)
N2 G92 XO YO ZO
(MAonNE ZERO POSITION)
N3 a90 GOO G4S Xl.4 H31
(X POSITION COMP)
N4 G45 Y2. B H32
(Y POSITION COMP)
N5 a92 X3. 4 Y2. 8
No G92 Z9. 0
N7 S850 MOl
N8 GOl ZO.l F1S.0 M08
N9 Z-O.89 F7.0
GOO ZO.l M09
Nll Z9. 0
mo
(TOOL pas REGISTER
(TOOL POS REGISTER Z)
(SPINDLE COMMANDS)
(Z APPROACH MOTION)
(Z CUTTING MOTION)
RAPID "-"' .• ......,.'"
(Ml\.CHDl'E ZIi:RO RBTORN z)
Nl2 X-.2 • 0 Yl0. 0
N13 M30
%
POSITION
(END OF PROGRAM)
• T001 length Offset and G92
When the tool length
became available, programming became
The position compensation G45JG46
was SliH in use at the
and
had (0 be set for both X
Y axes. However, G92 setting for the Z axis was replaced by
or 044 command, with an assi~led H offset
number - Figure
10.
Today, this method
position
tian G45/G46
tool
offset G43JG44 is
obsolete, or alleast quile old-fa<;hionecL Only (he
in
programming, with the
position.
Setting tool length with G43 tZl and G92 (XYj • mnr''''ITn
In an improved program. the tool
plied 10 Ihe firs! mOl ion command of
IS
01902
Nl G20
(INCH MODE SE:'.LECTED)
N2 G92 XO YO ZO
(MACHINE ZERO POSITION)
N3 G90 GOO G45 JO.4 101
(x POSITION COMP)
N4 G45 Y2.8 832
N5 G92 X3. 4 Y2. 8
(Y POSITION COMP)
(TOOL POSITION R.:IOOIIS~rER
N6 G43 Zl.0 HOI
LENGTH COMP Z)
N7 S850 MO)
CClMMANDS)
N8 GOI ZO.l F1S.0 MOS
N9 Z-O.89 F7.0
NlO GOO ZO.l M09
Nll G28 X3. 4 Y2. 8 Zl.O
N12 G49 DOO HOO
Nl3 M3 0
(Z APPROACH MOTION)
(Z CUTTING MOTION)
RAPID RETRACT)
(MAC.HJliIB ZERO R.E'I'lJlm)
(OFFSETS CANCELLATI~
(END OF PROGRAM)
%
When a program is developed using
blocks N6 and
N7 can be joined together for convenience. if
N6 G43 Zl.0 S850 MOl HOI
NI
method has no effect on the tool length offset, only
on the moment at which the spindle starts rotating. Position
and the 1001 length
cannot
programmed in the same block.
Note that
position compensation is still in effect in
due to the lack work coordinate
of
139
• Tool length Offset and G54-G59
most
programming has many
and functions available and G54-G59 series is one
The
has been replaced with work offset sysand, optionally, more. Normally, 092 is not
same program that contains any work offset sethrough 059 or the extended series.
example of using the tool length
work
environment:
.... rr..."."fTI
01903
N1 G20
N2 G90 GOO G54 Xl.4 Y2.S
N3 G43 Zl.0 H01
N4 saso M03
N5 G01 ZO.l F15.0 Moa
N6 Z-0.89 F7.0
N7 GOO ZO.l M09
N8 G28 Xl.4 Y2.S Zl.0
N9 G49 DOD HOO
NlO M30
%
(meR MODE "''''''"....'''' ..........
(XY TARGET LOCATION)
(TOOL LENGTH COMP Z)
(SPINDLE caaM1iNDS)
(Z APPROACH MO'lr:r:Ol~l
(Z ClJI'TmG MOTION)
(z RAPID
(MACHINE ZERO
(OFFSETS crua:LLl~TION)
(END OF Iff.N..NIU!<.to.W}
• Tool length Offset and Multiple Tools
of CNC programs include more than one
most jobs will require many different tools.
(independent of the previous drawings)
enters
a common method how the
three tools.
holes need to
spot-drilled, drilled and tapped.
or explanation of the
is not
. just concentrate on
now It is the program structure that is
note
is no change in the program structure
tool, only in the programmed
01904
Nl G20
N2 G17 G40 GBO TOl
N3 M06
N4 G90 GOO G54 Xl.O Yl.5 S1800 MOl T02
NS G43 ZO.S HOl MOB
(TOOL LG OFFSET FOR
N6 G99 G82 RO.l Z-O.145 P200 FS.O
N7 X2.0 Y2.S
N8 Xl.O Yl.5
N9 GSO
zo.s M09
NlO G2B ZO.S MOS
Nl1 MOl
G54X ..
Block N2
X3.4
N12 T02
Nl3 M06
Nl4 G90 GOO G54 Xl.O Yl.5 S1600 Mal TOl
Nl5 G43 ZO.S H02 MOB
LG OFFSET FOR T02)
Nl6 G99 G81 RO.l Z-O.89 F7.0
Nl? JU.O Y2. 5
Nl8 Xl-O Yl. S
Nl9 GSO ZO.S M09
N20 G28 ZO.S M05
N2l MOl
GAUGE
LlNE
N22 T03
N23 M06
N24 G90 GOO GS4 Xl.a Yl.5 S740 MOl TOl
N2S G43 Zl.O H03 MOB (TOOL LG OFFSET FOR T03)
N26 G99 GB4 RQ.S Z-l.O F37.0
N27 X2. 0 Y2. S
N28 Xl.O Yl.S
N29 GBO Zl.O M09
mo G2B Zl.O 14'05
N31 M30
%
Figure 19-11
Setting too/length with 643 (Zl and 1.:1'!)~f-U~" (XY) • program 01903
In this example. Figure 19through 059, (he blocks N2, N3
gether without a problem,
N2 G90 GOO
work offsets G54
can be joined toup processing:
G54 G43 Xl.4 Y2.B Zl.0 S850 M3 HOl
N3 ...
The command
will affect only the Z
axes, 043 with HO I
must move in the clear.
Also note that
is no tool
offset cancellation.
Cancellation will also explained later in this chapter.
140
Chapter 19
CHANGING TOOL lENGTH OFFSET
vast majority of programming
only a
tool
offset command
tool. Based
we have identified
1) with tool
offset H02,
I , Tool 2 (T02) with tool
the tool
some special
may
to be
the same tooL In
two or more tool length
applications, there
for one tool.
. 0.1
L
C
!
007
H07 H27
I
An example of a single tool length
that uses two or more
axis. Figure /9-/2 '11"Nr~.!"'("
groove dimensioned by its depth location
bottom (groove width of .220 is implied).
Figure 19· 13
- 4.0
of two length offsets for a single tool. The dIftS"8ni~8
between H07 and H27 offsets is the widih of slot (.125
r
Note
words - the boltom edge versus
fOP edge of
the slot milL Which edge is programmed as a reference for
the tool length? The one at the bottom or the top?
/3 ~hows that two ...",f.o.,..".,,,,..,, position~ are used
two
4.0
LOa I
/
•"",,, . .
007 is
cutter radius offset, and .125 is the un.., .....' ... mill width.
~- 1213.5
,.
,H.,,VH.
methods of programming can
calculating the difference manually,
multiple tool length offsets is
Lo allow fine groove width
example - program
for exammethod usduring maIt is shown
I
01905
(TWO TOOL LENGTH OFFSETS FOR ONE TOOL)
Figure 19·12
Example of programming more than one tool length offset for a
single tool· program 01905
Based on the illustration, we
to decide on the l..UlIllIl)t:.
method flISl (premachiril~g
the 03.000 hole is assumed). A .125 wide slot mill will be a good choice to
file the circle,
milling method for a fuJI
(see Chapter 29).
program can be shortened by
subprogram method
Chapter 39). Because the
groove width is
caner, more than one cut is
needed - two in
the first cut, the tool is
lioned at the
per drawing) and
first cut at the bottom
groove. The bottom
tool will
depth.
For the <>"'....'v.. u cut, the top edge of the slotting mill is
and the tool
profile for the second groove
first groove) at the depth of
ally, it will
(again. as
Nl G20
N2 G17 G40 G80
N3 G90 GOO G54 XO YO S600 M03
JOB CY...EARANCE)
N4 G43 Zl.0 HO? MOS
~~~ EDGE - BOTTOM)
NS G01 Z-0.65 F20.0
N6 M98 P7000
"""""""""'"IY"I GROOVE AT Z- 0.65)
EDGE - TOP)
N7 G43 Z-O.43 827
NS M98 P7000
GROOVE AT Z-O.43)
N9 GOO Zl. 0 Ma9
NlO G28 Zl.O MOS
Nll M30
%
07000
(SUBPROORAM FOR GROOVE IN 0190
Nl G01 041 XO.875 Y-O.B75 D07 F1S.0
N2 G03 Xl.75 YO RO.S75 FlO.O
N3 I-1. 7S
N4 XO.875 YO.a7S RO.875 F1S.O
N5 G01 G40 XO YO
N6 M99
%
TOOL LENGTH
1
R1.750
f4- G54Z(NEGATIVE)-
..
G43H ..
N3
N2
(
Figure 19·14
Full circle milling - subprogram 07000.
Start and finish of cutting is at the center of the groove.
H07 is used
botmill and H27 is
the ~,~ ..'''' ... mill. D07 is
for
cutter radius only. Figure
14 shows the tool motions
in subprogram 07000.
Figure 19-16
Typical tool length offset setting fOf a
Program zero is at the face 0/ the
tool.
example, tool
tom reference edge of the
The two
illustrations show typIcal setup of the
tool length offset for preseltools on a horizontal machining
zero at the cen ter
cen (er. Fig lire ) 9- J5 shows the
of the table.
19-16 shows
program zero at the
face of the
HORIZONTAL MACHINE APPLICATION
TOOL lENGTH OFFSET CANCEL
were aimed towards a
cenler. Although the logic of
applies equally to any machining center, reof the Z axis orientation, there are some noticeable
in (he practical applications on horizontal macenters (Chapter 46).
A
machining cenler allows programming of a
lool
on several faces of
each
has a
different distance from the tool
(along the Z axis), the
for each
It is common to
tool
work
different tool
face.
In programming. a well organized approach is always
important. That means, a program
that is turned
on when
should also be turned
not needed
anymore. Tool length offset commands are no exception.
cancellation
The tool
program. There is a special preparatory
available
lha( cancels
method of the 1001 length offset,
command to
Ihe 1001 length
either G43 or
offset in the program (or via MDl) is G49:
One method of
a single block -
G54Z(N
ison
returning to the
zerom
Z
..
10
Nl76 G49
Nl77 G91 G28 ZO
',:
A
method
the offset
N53 G9l G28 ZO HOD
Figure 19-15
offset setting lor a
(he center of the
tool.
In this case, the
is coupled with an H offset number zero - Hoo. Note, Ihere is no G49 in the block
for
and HOG does the job of cancellation. There is no
Hoo on the control. It
means cancellation
tool
length offset.
.
142
A program
command
safety line
Chapter 19
also be started with the
length offset
(under program contra!), usually In the
block or initial
The
is simple programmer
take advantage
of this rule and does not need to specifically
the tool
if the machi ne returns to the tool change posilength
is
all
with an automatic
examples
This approach is illustrated in
eluded in this handbook.
N1 G20 G17 040 GSO 049
.. , or a variaf;on of the same block:
N1 G20
N2 G17 040 Gao 049
is one more way to
tlot program it at all.
the tool
rule is quite explicit - any 028 or 030 com{both execute the tool return to the
will cancel the tool length automatically.
The
offset -do
A strange suggestion, perhaps, but
founded.
command at
examples in this handbook do not use
Why
What happens at the end of each tool?
Anyone of the methods will
that
active tool
will
canceled.
may be some differlength
manufacturers and consulting
ences between
ma:crlme manual will
be the
approach.
RAPID POSITIONING
• GOO Command
A CNC machine tool does not
chips. From the moment the
in a
program. it goes through a
(lons - some are productive (cutting),
(positioning).
""I"'I,p...,/
Positioning motions are necessary but nonproductive.
Unfortunately, these motions cannol be
eliminated
to be managed as efficiently as
For this
the CNC system provides a
called the
traverse motion. Its main objective is to shorten the
time between
operations. where
tool is not in contact with
Rapid motion
operations usually involve four
motion:
Q
From the tool change position towards
Q
From the part towards the tool
o
Motions to bypass obstacles
Q
Motions between different positions on the part
part
Preparatory command
is required in CNC program
to initiate the
Peed rate function P is not
required
if programmed, will be ignored
during the
GOO
Such a feed rate
will be
effective beginning
with the first occurrence of any
motion (G01. G02,
G03, etc.), unless 11 new P function is
cutting motion:
o Example A:
N21 GOO X24.5 F30.0
N22 Y12.0
N23 GOl X30.0
RAPID TRAVERSE MOTION
Rapid traverse mOlion,
called a positioning
is a method of
the cutting tool from one
position to another position at a
rQle of the machine.
The maximum rapid rate is
by the CNC mawithin the travel limits
common rapid rate
CNC machines IS
about 450 in/min (I 1430
modem
offer a rapid motion up to !
(38100
even more, particularly
machines. The
rale rapid molion
manufacturer determines
of the machine axes.
motion rate can be the same for
each axis or it can be
A different rapid rate is usually assigned to the Z axis, while the X and Y axes have the
same rapid motion rate.
Rapid molion can
as a single axis motion. or
as a compound motion of (wo or more axes simultaneously.
It can be programmed in the absolute or incremental mode
of dimensioning
11 can
used whether the
IS
rotating or stationary. During program execution,
operator
interrupt the rapid motion
pressing the
on the control panel, or even set~
ting the feedrate
switch to zero or a
rate.
Another kind
rate control can be achieved by
dry nm function,
during setup.
o
B:
N21 GOO X24.5 FlO.O
N22 Y12.0
N23 G01 X30.0 F20.0
N21, the GOO command
mains in
until it is canceled
same group. In the example
N23
The rapid traverse motion is
modal and reanother command of
the GOl command in
changes the
feed rate is reproat block N23.
used. It is
in
current units traveled ill one minute
in in/min or
mmlmin). The maximum rate is
set by the machine
manufacturer, never by the control
or the program.
A typical limit set by the machine
is a rate between
300 and 1500 in/min (7620 and
[00 mm/min), and even
Since motion per
is independent of the spindJe
rotation, it can be applied at
regardless of the last
spindle rotation function
M04. M05).
143
144
Depending on the
machine design,
motion
rale can be the same for a[l axes, or each axis can have its
maximum rapId rates for a typical
1181 inlmin (30000 mrnlmin) for
in/min (24000 mm/min)
lathe, the rates are somewhat
for example I in/min (5000 mm/min)
the X
and 394 in/min (10000 mm/min)
the Z
The
rapid rates can be
for modern
Every motion in the GOO mode is a, rapid non-circular
motion cannot normally be
made at the
actual linear mOlion of the tool
between two points is not ne(:es~;an the
path
in the form of a
Programmed tool
and the
resulting actual
will be different,
on
several factors:
o
The number of axes programmed simultaneously
o
The actual
o
The rapid traverse rate of each axis
• Single Axis Motion
Any
motion programmed specifically for only one
at a time is always a straight line along the selected
In
words,
motion that is parallel to
one
available axes, must
progTammed In a
rale block, The resulting
is
equivalent 10
distance between
start and end
- Figure 20-1.
Since the
of the rapid
is saving the
unproductive
(motion from the current tool position to
the targellool
the tool path
is irrelevant to
the shape of
parl. Always aware of the actual rapid motion (001 path for reasons
safelY, particulnrly when lWO or more axes are
at the same
No
must
in the way of the tool
If there is an
path, the obslacle
control for one
of detecting
an obstacle. It is
programmer's
responsibility to assure that any lool mali on (rapid motion
included) occurs without any obstacles in its way.
"--
examples of physical obstacles that can intool motion are:
o FOR MACHINING CENTERS:
o
cycles G81 to 089,073, G74
During a rapid motion, the tool path is much less predictable than during cutting motions. Keep in mind that
only purpose of rapid
from one part
to another location
motion is to
fast - but not necessarily straight.
of motion for each axis
Clamps,
fixtures, rotary or
machine
part itself, etc.
on a lathe),
during rapid motions GOO,
In
to bypass obstacles
still assure a safe
motion in the program at all limes. let's (ake a closer look at
(he
options while
a rapid
RAPID MOTION TOOL PATH
Some
terfere
lions in
towards a
table.
FOR LA THES :
Tailstock quill and body, chuck, steadyrest,
face plate, fix1ure, other tool, part itself, etc.
x
POSITIVE
1
!
e
e
X axis NEGATIVE
y
N
POSITION
Single axis motion for a ma,r:mllina center application (XY shown)
Several consecutive program blocks. each containing
to
only a single axis motion, can be included in the
obstacles to machining. This method
programis preferable in cases where only the exact or approximate position of
(such as
or fixtures) is known during
program preparation.
• Multiaxis Motion
We have already
that the cuning tool is moved at
a rapid rale using the GOO command. If this molion is a motion of two or more axes simultaneously, the programmed
path
the
rapid palh of the tool are not always the same.
resulting compound motion can be from
theoretical proand often is
grammed motion
RAPID POSITIONING
145
In theory,
two axes is equivalent to a
straight diagonal motion.
real mOlion, however, may
diagonal tool path at all. Consider
in Figure 20-2.
'8-
-------..,....:
9.452
o
both axes,
quired to
the ._ .. ,"' __ _
position. After
target position
! .02 seconds left to
The target must be rcacm~a
continues along
to reach the final
Another example,
Figure 20-2,
different for
coordinates in
with the rapid rate
11.812
0.91
1...-_ _ _ _ _ _ _ _ _ _ _ _.:.../
_ _ _ _--1
sketch for rapid motion examples
current tool position (the start point) is at X2.36
coordinate location. The tool motion terminates at
1.812
location. In the terms of i IIcremental IIlOtool has to travel 9.452 inches along (he X
along the Y axis.
If
rate for both axes is the same (XY rapid mosuch as 394 in/min, il will take
rates usually
PROGRAMMED
MOTION
ACTUAL
MOTION
x ::: 394 in/m in
Y::: 315 in/min
(9.452 x 60) / 394 = 1.44 seconds
to complete the X axis motion - but only
(2.753 x 60) / 394 = 0.42 seconds
is required to complete (he Y axis motion. Since
motion is not completed until both axes reach (he end point, it
.
that the actual tool path will be different from
tool path.
1-0.425
1.025
.-,-
.-, . .-
deviation· different rapid rate for each axis
not so common example, the X axis rate is set to
(10000 mm/min) and tbe Y axis rate is set to
(8000 mm/min). It will than take
(9.452 x 60) / 394 = 1.44 seconds
to complete the X axis motion - but only
.753 x 60) / 315 = 0.525 seconds
to complete the Y axis motion. In this case, the resulting
motion will also include an angular departure, but not at
• because of the different rating of rapid traverse rate
axis. During the 0.525 seconds (which is the common
time to both axes), the X axis motion will travel
0.525 / 60 x 394 = 3.448 inches
MOTION
ACTUAL
MOTION
x
y
Figure 20-3
Rapid motion deviation - same rapid rate for each axes
Figure 20-3 shows a combination of an
a
straight motion as the actual tool path.
at
the rate of 394 in/min (10000 mm/min) simultaneously in
but the Y axis motion will be only
.525 / 60 x 315 = 2.753 inches
resulting motion is at 38.605" and a slight rounding
applied. The actual departure angle is not always
to be known, but it helps to calculate it for rapid
some very tight areas of the part. It only
trigonometric
to make sure of
path,
the
rate is known.
Chapter 20
""""<~""""<----~~~««««««<
Both of
above examples illustrate an angular motion
along two axes, followed by a straight single axis motion in
the remaining
graphical expression of
motions is a bent
resembling a hockey stick or a dog leg
which are also very common terms applied to
a
Calculation of the actua! motion shape, as we
done
is only seldom
Taking some
prewithcautions, the rapid motion can be
out any calculations. If no
is within the work area
imaginary rectangle
by the diagonally posiis no danger of collision
tioned slar! and end point),
to the diverted rapid tool path. On CNC milling sysrectangly"of
tems, the third axis can also used.
above example will
enhanced by the third difnension
and a three dimensional space must be considered. In this
case, no
should be
chis
same rules apply
a rapid motion along three axes as
a two-axis simultaneous
motion. Note that the rapid
rale for
Z axis on
machining centers is usually
lower than the rapid rate for the X and Y axes.
This consideration is more important In turning appJ
lions than in
. due to the nature of programming for
(wo
In turning,
approach motion
may be
first, to avoid a collision with the
tailstock, and then along the X
The reverse motion
axis first, then along
Z axis moshould along
tion, in order to
the same safety
when returnto the tool
A typical application of this programming technique may
be useful after using a machining
(such as turning.
the
starting
facing,
elc.),
also its
point.
• Straight Angular Motion
In some uncommon circumstances, the theoretical rapid
tool path
correspond to the actual tool path (with no
bent line as a result). This will
If the simultaneous
tool motion has the same length in each axis and the rapid
rales all axes are identical Such an occurrence is
rare, although not impossible. Some
manufactur~
ers provide this feature as a standard and
machining center does
should know
situation
the resulting
feature or not.
is a straight angle, is when the rapid rating
for each
axis, but the required length of motion just 'falls' into the
that results in a straight angular ml'llflf'ln
Both of these occurrences are rare
or less a case of
good luck)
in actual programming will seldom happen.
To be on
safe side, never take any chances - it is always
more practical to program the rapid motion without the accalculation the tool path but with safety as a primary
consideration.
Figure 20-5
Typical
of a reversed rapid motion on a eNC lathe,
used to bypass
for example, a tai/stock
As Figure
than programming a
motion fTOm the turret
to the cutting position
be fTOm point A to point
the tool motion
(which
was spliL
approach towards the
will be in the order
of A to B Lo C, at a
rate.
point C to poillt D, the
cutting takes
When
cutting is completed,
will rapid the reverse order, back to the
Rapid motion will
from D to C (0 B to A.
a necessary precaution to bypass a potential obstacle, for
example, the tllilstock.
TYPE OF MOTION & TIME COMPARISON
• Reverse Rapid Motion
Any rapid motion must be considered in terms of approach towards a
and the return
to the tool changing position.
is the way a cutting
is normally
programmed - we start at a certain position and then return
cUlling activity for the tool is completed. It
there, when
is not a mandatory method, but it is an organized method, it
is consislent, and it makes programming much
lechnique of programming each
separately in
individual blocks of the program, is recommended only for
the
possible
during {he (001
path strictly
This method of programming
requires a Slightly longer cycle
than the simultaneous
multiaxis rapid motion. To
the
cona three
motion,
as a typical tool
proach in milling.
a rapid molion
an actual
the 1001
position.
a rapid
is required to
position,
As an example, the rapid rate is at 394 in/min (10000
mmJmin) for each
The motion takes place between
the coordinate
of X2.36 YO.787 ZO.2 (slart poinL)
XI1.812
ZI.O(endpoint).
So
we have
cut, starting from the tool
cutting
.
return
RAPID POSITIONING
The required lime for
easily calculated:
I:l
X
along each
time:
«11.812 - 2.36) x 60) / 394
I:l
can
1.440 sec.
Y axis time:
«3.54 - .7B7) x 60) / 394 ~ 0.420 sec.
I:l
Z axis time:
Figure 20·6
Rapid motion override switch set to 100% of rapid rate
«1.0 - .2) x 60) / 394 - 0.121 sec.
If all three axes are
simultaneously, the total
for positioning is 1.44 "...'-,...1,,1..1<>. which is the longest time
required
any
to reach
end point. The program
U be:
GOO X11.812 Y3.S4 Zl.0
actual production, after the program
been
and optimized
the
tool performance
productivity, the override switch should be set to the ! 00%
pointer, to shorten the cycle
this motion were to be
into
program blocks, the total time would be
vidual
added together:
RAPID MOTION FORMULAS
1.44 + 0.42 + 0.121 = 1.991 seconds
which is about 37.5% longer.
percentage will vary,
depending on the rapid motion rale and
rapid travel
length, measured
each machine
The program
blocks will be written separately:
GOO Xl1.812
Y3.54
Zl.O
The configuration of
rapid override switch varies
tween machines from
On some
machines,
rapid motion may stopped altogether, on
others, the tool will move at the slowest percentage and
cannot stopped
the override switch alone.
calculations relating to the rapid tool motion can be
expressed as
used quickJy at any time by
stituting the known parameters. Relationships between the
rapid traverse ra1e, length
the motion and the elapsed
time can be
in the following three formulas:
\
Note that the modality of GOO rapid motion command
does nol require repetition in the subsequent
REDUCTION OF RAPID MOTION RATE
a part setup or while proving a new program on
the CNC operator has an option to
a
slower rapid traverse rate than the
established
by the machine manufacturer. ~is adjustment is done by
means of a special
override switch, located on
control
panel.
switch has typically four selectable positions, depending on the machine brand and the
type of control
- Figure
The second, third and fourth positions on the rapid motion override
are
as
oj the acrapid rate - 25%, 50%,100% respectively.
are set
by the machine manufacturer.
first setting, typically
identified by FO (or FI) is a
motion rate set through a
control system parameter.
FO (FI) setting should always be Slower than any other setting, typically
than
lowest setting of25%.
T == Required time in seconds
R == Rapid traverse rate per minute
for the selected axis - in/min or mm/min
L = Length of motion - inches or mm
applied to the formulas must always be
within the selected system of measurement in the program.
Inches and inches per minute (in/min) must
used with
(he English
Millimeters
millimeters per minute
(mmlmin) must be
in the
system.
any calculation relatmg to
rapid traverse time, the measuring
units cannot be
1
Chapter 20
APPROACH TO THE PART
it might be a reasonable compromise to split
motion into two separate motions:
20-5 had an illustration
to a CNC lathe. For CNC
of part approach should be
with equal care.
in mind that the general
motion have (0 be considered for any machine.
at a rapid rate, the cycle time can
by keeping the part clearances to
minimum. Let's have a look at some po-
NJ14 G90 GS4 GOO XlO.O YS.O 51200 M03
NJ15 G43 ZO.S HOI
NGl6 GOl ZO.05 FIOO.O
N317 Z-l.S F12.0
In this method, the rapid motion has
first
to a much more comfortable position
above the part (N315). Then, the motion continued
LO
cutting start point. using the linear
I
in block N316. Since this is still a .-n""""
not productive, a relatively heavy
As may be expected in
is a
In the following example, an approach to the part is made
along the Z
with a clearance of .05 inches (1.27 mm)
in block N315:
was slightly increased, at the
has been given an opportuoverride switch for testing the first
in a
block mode). Once the prodebugged, the heavy feedrale in the
will speed up the operation and at the
an extra safety clearance. The program
motion can always be optimized
not be the besl approach for repetitive
is always 'new' for any repctition at a
it
be very useful when
thousands, for example).
N314 G90 G54 GO 0 X10. 0 Y8. 0 S1200 M03
N31S G43 ZO.OS Hal
NG16 GOl Z-l.S F12.0
a melhoel of "'r"r,<1-Y,n"'L
set and
part
as it should he.
allows very little
On the other hand, an inmay not
quite comfortable
particularly during the early
operator's convenience is considered
to the overall productiv-
(
\
,
Zaxis
MACHINE ZERO RETURN
a control system to return a cutting tool
machine
position is a
all modern CNC systems. Programmers
term mLlchine reference posiwith
home posi(ion or machine
is the position all machine slides at
extreme
limits of each axis. The exact posiby the machine manufacturer and is not
h'.lrH'rt'>rI during the machine working life. Return
is automatic, on request from the control
or via the program.
LlV~"""''-'H to
Z:::: UP (TOP)
I XV:;;;
RIGHT
i y-
WORK
,,~
MACHINE REfERENCE POSITION
rpt,3r?lnrp position is for referIn order
the CNC machine is accuwe need more than just the high quality components,
some unique location (hat can be considered the
point of
machine - a zero position - a home
tion. Machine
position is exactly such a
21·1
Machine zero
of a CNC vert}
to the Z axis in the description was
machine zero position for a
The Z
center is always where the Automatic
place. This is a built-in location,
distance from the machine table and
most machines, the standard machine
centers is at the extreme travel
in the positive direction, There are excepexpected,
t",r,""'/""'"
Machine zero is a fixed position on a CNC machine that
can
reached repeatedly, on request, through the control
panel, MOL or program code execution,
•
Machining Centers
Although the design of CNC machining centers
models, there are only four possible locations for
zero, within the XY view:
o
Lower left corner of the machine
o
Upper left corner of the machine
o
lower right corner of the machine
o
comer ot the machine
i
MACHINE
ZERO
POSITION
The most common and standard machine r",t''',,''''nr.,.
tion for vertical machining centers is at
ner of the machine, looking
XY plane - Figure 21-1.
~j
<'
Z:::: UP (TOP)
Z-
- X + .........
XV '" UPPER LEFT
I~
y- '
~ ! WORKAREA
It is
a new
from
also necessary to make a
lion and return there
pleted. So. several of the
convenient for setup of the part on
removal when the machining is
n located at the upper right XY comer
ma,cnlflma center
,
Figure 21-2
Machine lero position located at the upper left XY comer
CNC vertical machining center
21-2 illustrates. someCNC vertical machining
the machine zero position at the upper left corXY plane.
1
150
Chapter 21
In both illustrations, the arrows indicate the tool motion
direction towards the work area. Moving the tool from machine zero into the opposite direction will result in a condition known as overtravel - compare the two possibilities:
o
Tool motion from machine zero, if machine zero is located
at the upper right corner:
x + Y+ Z+
... tool motion will overtravel
o Tool motion from machine zero, if machine zero is located
at the upper left corner:
x- y+ Z+
... tool motion will overtravel
The other two comers (lower left and lower right of the
XY view) are not used as machine zero.
o
Tool motion from machine zero of a typicalrear lathe:
x+ Z+
... tool motion. will overtravel
• Setting the Machine Axes
From the previous sections, remember that there is a direet relationship between the CNC machine, the cutting
tool and the part itself. The work reference point (program
zero or part zero) is always determined by the CNC programmer, the tool reference point is determined by the tool
length at the cutting edge. also by the programmer.
Only the machine reference point (home position) is determined by the manufacturer of the machine and is located
at afixed position. This is a very important consideration.
• lathes
Fixed machine zero means that all other
references are dependent on this location.
The machine reference position for two axis CNC lathes
is logically no different from the reference position of the
machining centers. An easy access by the CNC operator 10
the mounted part is the main detennining factor. Both, the
X and the Z axes have their machine reference position at
the furthest distance from the rotating part, which means
away from the headstock area, consisting of the chuck, collet, face plate, etc.
For the X axis. the machine zero reference position is always at the extreme limit of the travel away from the spindle center line. For the Z axis. the machine reference position is always at the extreme travel away from the machine
headstock. In both cases, it normally means a positive direction towards the machine zero, the same as for the machining centers. The illustration in Figure 21-3 shows a
machine zero for a typical CNC lathe.
In order to physically reach the machine reference position (home) and set the machine axes, for example, during
the parlor fixture setup, there are three methods available
to the CNC operator:
o
The machine operator will use the XYZ (machining centers)
or the XZ (lathes) switches or buttons available for that
purpose. One or more machine axes can be activated
Simultaneously, depending on the control unit.
o
I
X-
l
figure 21-3
Machine zero position for a typical eNC lathe (rear type)
In the illustration. the arrows indicate the lool motion direction towards the work area. Moving the tool from the
machine zero into the opposite direction will result in overtravel in the particular axis:
Using the MDt- Manual Data Input mode
This method also uses the control panel. tn this case, the
machine operator sets the MOl mode and actually
programs the tool motion, using the suitable program
commands (G28, G30).
o
MACHINE ZERO POSITION
Manually - using the control panel of the system
In the CNC program - during a cycle operation
Using the same program commands as for the
MOl operation, the CNC programmer, n.ot the machine
operator, includes machine zero return command (or
commands) in the program, at desired places.
When the operator has performed the actual machine
zero return, it is always a good idea to set the relative and
absolute positions to zero on the display screen. Keep in
mind that the relative display can only be set to zero from
the control panel and the absolute display can only be
changed through a work offset, MDI mode, or the part program. This topic normally a parI of CNC machine operation training, directly at the machine.
For the last two methods of a machine zero return, the
CNC system offers specific preparatory commands.
MACHINE ZERO RETURN
151
• Program Commands
are four preparatory commands relating to
chine zero
position:
For
ma-
N67 1328
shows G28 programmed by itself in
G27
Machine zero reference position return check
G28
Return 10 the primary machine zero
reference position
G29
Return/rom the machine zero reference position
G30
reference pOSii
Return to
secondary machine zero
(more than one is possible)
the
listed
G28 is used almost
sively in two and three axis CNC programming. Its only
purpose is to return the current tool to the machine zero position and do it along the one or more axes
in
G28 program block.
• Command Group
All four preparatory commands
to G30 belong to the
group 00 of the standard Fanuc designation that describes
the non modal or one-shot G codes. In
designation,
each G code of the 00 group must be repeated in every
example, when G28 command is
block it is used in.
used in one block
the Z axis and then it is
in the
next block for the and Y axes, it has to be repeated in
each block as "pp,rjpr!
N230 1328 Z..
N231 1328 X •• Y.-.
(MACH:INE ZERO R.E'I'ORN Z AXIS)
ZERO REI'URN XY AXES)
The G28
in block N23! must be
If
the command is omitted,
last motion command programmed will be effective, for example, GOO or GO]!
RETURN TO PRIMARY MACHINE ZERO
Any CNC machine may have more
one machine
zero reference point (home position), depending on its design. For example, many
centers with a pallet
changer have a secondary machine reference position. that
is often used to align both the left and right pallets during
pallet
most common machine tool design is
the one that uses ~ly a
position.
reach this
primary home p6s[lion, the preparatory command G28 is
used in the program and can also be used during the MDI
control
The
command moves the specified axis or axes LO
the home position, always at a rapid traverse rale. That
means GOO command is assumed and
not have to
programmed. The
or axes of the desired motion (with a
be programmed. Only the
value) must
axes will
affected.
block - this is an
incomplete instruction. At least one axis must be specified
with the G28 command, for example,
No7 1328 Y ••
which
only send the Y axis to the machine zero reference position, or ...
N67 G28 Z •.
will only send the Z axis to the machine zerO reference
position, and ...
N67 G28
x .. Y •• Z ..
will send alJ three specified axes to the machtne zero
erence position.
multiaxis
requires caution watch for the infamous 'hockey stick' motion.
• Intermediate Point
One of the elementary requirements of programming is
the alpha numerical composition of a word. In the program,
followed by one or more digits. The
every letter must
question is what values will the axes in G28 have? They
will be the intermediate point for machine zero return motion.
concepl the intermediate motion in G28 or G30
is one of the most misunderstood programming features.
Commands G28 and G30 must always contain the interpoint (tool position). By Fanuc design and
tion, the G28/G30 commands have a built-in motion to an
intermediate point, on the way to machine zero. An
ogy can
made to an airplane flight from Los Angeles,
USA to Paris, France, thallemporarily stops over in New
York City. It may not be the most direct route, but it serves a
certain specific purpose,
example, to refuel
",prHII'"
The coordinate values of the axes associated with G28 and
G30 commands always indicate an intermediate point.
of the intermediate
or pOSitIon, is to
shorten the program, normally by one block.
reduction is so marginal that the philosophy behind the
may debated.
is how
concept the
ate point (position) works.
When the
or G30
IS used in the program,
at least one axis must be specified in the block. The value of
that axis is the intermediate point, as interpreted by the eonsystem. Absolute and incremental modes G90 and
I
make a great difference in interpretation the G28 or G10
behavior, and will be described shortly.
1
Chapter 21
MACHINE
/
/
I
!
/
make the
equal to zero and move
cutting 1001 to the
zero directly. This is done by
specifying (he errne<jlaile point as identical to the current
(001 position in
absolute mode - or - by specifying a
zero lool motion in
incremental mode.
• Absolute and Incremental Mode
I
/
........ -
, Y4.0
There is a
in programming the
zero return command
or G30 in the absolute
incremental
Remember the b<lsic di fference between
two
statements:
POINT
G90 GOO XO YO ZO
27-4
Intermediate puifll lor machine zero return· XY axes shown
G9l GOO XO YO ZO
Each
statement XOYOZO is
control
differently. To review, an
'v;>.>
a zero, for example XC, means position at the
point, if the mode is absolute,
command. If the mode is incremental,
the XO word means no motion for the
L ..... ' ..
The tool motion in Figure 2J-4 is from the central hole of
During sueh a motion, the tool can collide with the
upper right clamp on its way to
zero, if the motion
to the home position were
directly. Only the
X and Y axes are
An intermediate point can be
location, without
making the program any
program without an
intermediate point can be
lathes use (he U and Waxes
incremental
on absolute X and Z axes respectively), with
same
applications. Absolute axes coordinates
interpreted as the programmed
indicate the nrt:HIT,rlmFIlP'n
G90
GOO xs.o Y4.0
G2B X5.0 Y4.0
(MACHINED HOLE)
1t"la1...rL\.N,c, ZERO MOTION)
The same program with an intermediate point at a safe 10will change slightly:
G90
GOO X5.0 Y4.0
G28 Xl2.0 Y4.0
(MACHINED HOLE)
(MACHINE ZERO MOTION)
Comp,are the two program
are identical in terms
( -,. G28 USED IN THE ABSOLUTE
G90
Nl2 GOl Z-O.7S F4.0 MOS
N25 GOl X9.5 Y4.874
N26 G28 Z-O.7S Ma9
(-
Earlier examples
shown
reason behind this
ble motion. It is
- only to save a single program
block - that is all.
purpose is to use onc block
program to achieve two motions. that would otherwise require two blocks. A
could also be:
- they are the
tool motion:
~>
IN ABSOLUTE MODE)
G28 USED IN THE INCR:EMENTAL MODE)
G90
Nl2 GOl Z-O.75 F4.0 M08
N25 GOl X9.S Y4.874
N26 G9l G2B ZO M09
(G2a IN INC:REMENTAL MODE)
G90
GOO XS.O
Y4.0
X12.0
G28 Xl2.0 Y4.0
La produce
same
(MACHINED
(SAFE LOCATION)
(MACHmE ZERO RE'lL'URlN'1
result, but with an extra
For example,
the intermediate position, the tool can
be programmed to
an obstacle on the
to
chine zero.
rnn,,.,.,.·t1 whh care, the
tion may be
useful. Normally, it is more
Which method is better?
both methods produce
on a given situation or
identical results, the choice is
personal preference. To switch to the incremental mode has
its benefit, because the current tool location may not always
known. The disadvantage this method is that G91 is
most likely a temporary setting only and must be reset back
(0 G90 mode, used by the majority of the program.
A failure to reinstate the "mS;(]IU'IB mode may result
in an expensive and
serious error.
MACHINE
RETURN
Absolute mode of programming speci ties the currenltool
at all times.
position from program zero - always
Many examples
use the absolute
ming mode - after all, this is - or it should - the
programming mode, for the majority of
1
above example can be
so the intermediate
as the current tool posimotion is eliminated or intermediate motion can never eliminated, but
tioll.
it can
programmed as a physical zero distance.
090
There is one
incremental mode of mazero return
some very
It
happens in those cases when the current tool position is not
known to the programmer. Such a situation typically happens when using subprograms. where
mode is
used repeatedly to move the
incrementally (0 different
locations. For instance - where exactly is the cutting
tool
when
drilling cycle is completed in the N35
block the following example?
G90
N32 G99 GSl Xl.S Y2.25 RO.l Z-O.163 F12.0
(REPEAT 7 TIMES)
N33 G9l XO.3874 YO.6482 L7
(CANCEL
N34 G90 GSO Zl.O M09
(UNKNOWN ~n~T'~Tf~T\
N35 G2S (X???? Y????) Zl.0
Is it worth the extra effort to find the absolute location at
Probably no!. Let's look at some other examples.
coordinate
While in the absolute mode 090,
the intermediate point locatioll. When incremental
the
mode 091 is programmed, the coordinate values
actual
and direction the intermediate motion. In
both cases,
intermediate tool motion
be performed
first. Then - and only
final return to the machine
zero reference position will take
Y 1.0
the current lOol position as
position).
the program,
XY values of
G28 command that follows the position block are
important:
G90
N12 GOO X5.0 Yl.O
Nl3 G28 XO YO
Nl2 GOO XS.O Yl.O
Nl3 G28 XS.O Yl.O
By this
the imermediate poinl
in direct motion to the
machine zero.
reason is that
intermediate tool posiwith the current tool position. This r'\r("\, ..... r~....,.'has
to do with
values axes.
In the part program,
1.0 in the block N 13 must
repeated, while the absolute
090 is
in effect
current tool position, which
In cases when
current tool position is not known, the
zero return
to be
in incremental mode. in
this case, change temporarily to
mode
gram a zero length motion for each
axis:
G90
Nl2 GOO XS.O Yl.O
Nl3 G91 G2B xo YO
Nl4 G90
Again, an important
is in place here - always
remember to
back to
absolute
as soon as
in order to avoid misinterpreting the consecutive
program data.
[n a brief
the imermediate point cannot be
minated from the G28/G30 block. If situation demands a
zero without going
a separate
return to
termediale point, use a zero tool motion towards the
n"I"'';'''''' point.
method
on the
090 or
G91 mode at the
o
In
example, the G28 command
that the CUlting tool should
the machine zero position· identified
as XOYO in the
N 13. Since
G28 command relates
to the
zero only, it ~ould
to assume
that the XOYO relates to lhe~machine zero, rather than the
part zero. That is 110t con·eel.
XOYO
to the point through which
tool will
the machine zero positioll. That is the detined point
already known to be the intermediate position for the machine zero return command. This intermediate point is assigned
coordinates relating to
pan (in absolute
In the example, the cuuing tool will move \0
program zero
to the mach i ne zero, resu Itin a single
definition of two 1001 motions. This, of
the intended motion.
course, is not likely to
C
In G90 absolute mode motion to machine zero, the current
tool coordinate location must be repeated for each axis
specified with G28 command.
o In G9l
motion to machine zero, the current tool
motion must be equal to zero for each axis ·specified with
the G28 command.
• Return from the Z Depth Position
One common example of
the intermediate tool
in a program hlock, is the return from a
cavity to the machine zero. In the following
solely
the purpose of better explanation,
motions are used rather than a drilling
to retract
tool from the hole depth. In the example, the current XY
position is X9.5Y 4.874. and a
drilling operation will
simulated in
1
21
N24 GOO Z-0.43
N25 GOl Z-O.75
N26 GOO ZO.l M09
N27 a28 ZO.l MOS
N2Q G29 X9.5 Y4.B?4
N29 Mal
N2l G90 GOO GS4 X9.S Y4.B74 S900 MOl
N22 G43 ZO.l HOl MOB
N23 GOl Z-O.4S F10.O
N24 GOO Z-0.43
N2S GOl Z-O.75
In block N25, the tool is at
current tool position of X9.5
absolute COOfthe cutting is done and the tool has to be returned home in
axes.
reasons, the Z axis
must retract first Several
but three
of them are the most common:
o
Retract the Z axis above work in one block,
then return XYZ axes to machine zero
o
Retract the Z axis all the way to machine zero,
then return the XV axes in the next block
Q
2
To retract the Z axis all (he way \0
then return the XY axes in the next
Option 1.
return the Z axis to
zero:
N26 G28 Z-O.7S M09
return the XY axes to
zero as weJl:
N27 G28 X9.S Y4.9?4
complete program for Option 2
o Return XYZ axes to machine zero directly
from the current tool position
The Figure 21-5 shows the
the depth)
options.
xv
MACHINE
ZERO
POSITION
r-------+
~I
zi
0,
~t
~I
/'
/'
NI
J
Hole location
in XY axes is
X9.5 Y4.874
/'
/'
/'
INTERMEDIATE POINT
CURRENT POSITION
N26 G28 X9.5 Y4.874 ZO.l M09
Hole location jn XY axes is X9.5 Y4.B74
Figure 21-5
Machine zero return from a hole depth - milling
This is the intended method of programming, as Faouc
controls are
Some programmers may
with Fanuc on
but that is how it works.
Here is
Q Option 1
To retract the Z
work in one block
return the XYZ axes to the machine zero position,
commonly used:
the 'normal'
N26 GOO ZO.l MOS
This block must
lion, along the Z
e Option 3
To return all three axes
from the current tool position
the tool is still aL the
hole full depth), only one zero return block will be needed:
/'
/'
N2l G90 GOO G54 X9.S Y4.B?4 S900 MOl
N22 G43 ZO.l Hal MOS
N23 GOl Z-O.4S F10.D
N24 GOO Z-O.43
N25 GOl Z-O.7S
N26 G2B Z-O.7S M09
N27 G2B X9.5 Y4.874 MOS
N28 MOl
followed by a return LO the
N27 G28 ZO.l MaS
The complete program for Option J will
N2l G90 GOO GS4 X9.S Y4.874 S900 MOl
N22 G43 ZO.l HOl MOS
N23 Gal Z 0.45 F10.O
posi-
for Option 3:
N2l G90 GOO GS4 X9.S Y4.874 S900 M03
N22 G43 ZO. 1 HOl MOS
N23 GOl Z-O.45 F10.O
N24 GOO Z-O.43
N25 GOl Z-O.75 M09
N26 G28 X9.5 Y4.874 ZO.l MOS
N27 MOl
The molion La
1<1'-"11:'<;;
zero will take LWO
Step 1:
Z axis will rapid to ZO.l position
Step 2:
All axes will return to machine zero
Also note
rearrangements ofM09
neous
Turning the coolant
tical than stopping the spindle.
miscella-
MACHINE ZERO RETURN
5
Although this is a matter of opinion, the choice of many
is to move the tool out of a cavity or hole first,
caB the machine zero return command. If there is any
,',-,'A",-'" for this preference, it is the perceived safety the
programmer puts into the program design. To be
there is nbsolutely nothing wrong with the alternate
memoo, if it is
with care. Comparing'
opwith
other does
some valuable
o OPTION 1 ...
... is only reasonably safe,
of cycle time.
may
within the ,nrla",_,."",
o OPTION 2 ...
cffil'i"!nt than the previa us option, but
one of all
Return for CNC lathes
•
work,
setup.
zero return is also
ends at the machine zero
true the X axis but not of the
away on some
lathe
Typically, a CNC lathe program will
a way, thaI machining of the
will start
machine zero, but any subsequent pan will
from a safe tool change position. This
tical if the program uses geometry offset,
older 050 setting. The most common method of
zero return on the lathes is the direct method, without an
termcdiate point, because no G91 i s '
an
error is more difficult LO make:
N78 G28 UO
N79 G28 wo
is the most
any error in
in terms of program cycle time,
could result in a collision.
• Axes Return Required for the ATC
that purpose.
a
axis is required to
zero return is to make an
axes must be moved for
only the Z
G91 G28 ZO M06
Horizontal machining centers
reach its reference position
For safety
extra
grarruned as well, along Wilh
sian with an adjo.cent tool in the
These two blocks win return the cutting tool to
chine zero in incremental mode. there is no
motion applied. It is safer La move the
incremental mode U, then the Z
using the incremental
mode W. If the work area is clear (watch for [he tailslock),
both X and Z axes can be returned to the machine zero at
the same time:
N78 G28 UO wo
Figure 21-6 illustrates a typical withdrawal
a
from a hole, when the machining is completed.
MACHINE
ZERO
POSITION
G91 G28 YO ZO MOo
In both examples, the tool cn.an~:e
he effective, until the
been physically reached.
grammed in a separate
·
(\
I ndexmg onrotary axes
point and are used with
ear axes. For example, a B
will return to the
zero reference position in the following
G91 G28 BO
If it is safe, the B axis may be programmed
ously with another axis:
G91 G28 xo BO
Absolute mode designation follows the same rules for a
rotary or indexing axis, as for the linear axes.
21·6
Machine zero return (rom a hole depth. turning application
When using position register command G50, the XZ
must always be known for this command. In this
rules for machine zero return are
Assuming that the machine zero position is at
the coordinate position XlO.O Z3.0, the program for the
tool can be wriuen in two ways - one without using
command, the other one with the 028 command.
156
Q Example 1 :
The first example does not use 028 machine zero return
command at all:
Chapter 21
The format for G27 command is:
G27 x .. Y .. Z ..
where al least one axis must be specified.
N1
G20 (EXAMPLE 1) -
N58 G50 X10. 0 Z3. 0 S1000
(OLDER METHOD ONLY)
N59 GOO T0300 M42
N60 G96 5400 M03
N61 GOO G41 X4.0 ZO.lS T0303 MOS
N62 GOl Z-2.45 FO.012
N63 X3.8 M09
N64 GOO G40 X3.5 ZO.lS MOS
N65 X10.0 Z3.0 T0300
N66 MOl
Q Example 2:
The second example will use 028 machine zero reference command. to achieve the same target position:
N1 G20 (EXAMPLE 2)
N58 GSO XIO.O Z3.0 SlOOO
(OLDER METHOD ONLY)
N59 GOO T0300 M42
N60 G96 S400 M03
N61 GOO G4l X4.0 ZO.l5 T0303 MOS
N62 GOl Z-2.45 FO.012
N63 G40 X3.S M09
N64 G28 X3.S ZO.15 MOS T0300
N65 MOl
When used in the program. the cutling tool will automatically rapid (no GOO necessary) to the position as specified
by the axes in the 027 block. The motion can be either in
the absolute or incremental mode. Note that no G28 command is used.
Nl G20
N2 GSO r7. 85 Z2. 0
N3 GOO T0400 M42
N4 G96 S350 M03
(OLDER METHOD ONLY)
N5 GOO G42 X4.l25 ZO.! T0404 MOa
N6 GOl Z-1.75 FO.012
N7 UO. 2 FO. 04
NS G27 G40 X7.85 Z2.0 T0400 M09
N9 MOl
In the example. block N8 contains G27, but no GOO or
G28. This block instructs the CNC machine to return to the
position X7.85 Z2,0 and check, upon arrival to the target
position, if that position is the machine zero in all specified
axes (two axes in the example). A confirmation light will
turn on, if the machine zero position is confirmed. If the position is not confirmed, the program will not proceed any
further until the cause (misposition) is eliminated.
Most CNC programmers will likely feel more comfortable with the ftrst example and saving one program block
program will not likely be compelling enough to change
their programming style. The second example (Example 2)
can be programmed in the incremental mode as well, using
the U and W addresses. but it would not be too practical.
Compare the starting position in block N2 and the return
position in block N8. Assuming that this position is at machine zero reference point in both the X and Z axes, the
above example will confirm OK position in the N8 block.
Now, suppose that a small error has been made while writing block N8, and the X value was entered as X7.58 rather
than the expected X7.85:
RETURN POSITION CHECK COMMAND
N8 G27 G40 X7.58 Z2.0 T0400 M09
The less common preparalory command G27 performs a
checking function - and nothing else. Its only purpose is to
check (which means to ~lIfirm)\ if the programmed position in the block cO'1taining G27 is at the machine zero reference point or noL H it is. the control panel indicator light
for each axis that has reached the position will go on. If the
reached position is not at the machme zero, the program
processing is interrupted by an error condition displayed on
the screen as an alarm.
In this case, the control system will return an error condition. The error is displayed automatically on the control
screen (as an alarm). The system will no! process the remainder of the program, until the error is corrected. The
light indicating Cycle Scarr condition will turn off and the
source of the problem has to be found, When looking for
the source of the problem, always check both positions, the
start position block, as well as the end position block. The
error is quite easy to make in either block. Also note that
any axis not specified in the block will not be checked for
its actual position.
If the tool starling position is programmed at the machine
zcro reference (home), it is il good practice to return there
as well, when Ihe machining with that CUlling tool is completed. This is quite commonly done for CNC lathes, where
the tool change (indexing) normally takes place in the same
position, although this position does not always have [0 be
the machine zero. Usually, it is a safe position near the machined pan.
Another important poim is the cancellation of the cutter
radius offset and the tool offset The G27 preparatory com·
mand should always be programmed with the G40 command and the TuOO in effect (G49 or HOO). If the tool offset or the culler radius offset is still in effect. the checking
CarlllOI be dOlle properly, because the 1001 reference point is
displaced by the offset value.
MACHINE ZERO RETURN
157
Here is how the FLTst
(Example J) listed
G27 command. Note that the
can be modified to accept
will only move to the coordinates specified, 1101 La any
or
point. Block
will become the aci
tual check block. The control system will move the machine axes to X 10.0 Y3.0 and checks
this position is in fact
machine zero reference point
This is the reason Example J could modified, but not the
seciond Example 2.
N1 G20
N58 GSO XlO. 0 Z3. 0 91000
(OLDER METHOD ONLY)
N59 GOO TOlOO M42
N60 G96 9400 M03
(LATHE EXAMPLE)
T0303
G2S U5.0 W3.0
G29 U-4.0 ~.l75
command should always be
In
of both
cutter radius
(G40)
cycles (080), jf either is employed in the program.
(he standard cancellation 0 codes - G40 to cancel CUlter radius offset
GSO to
a fixed
before the
G29 command is issued in the program.
The
celed
A schematic sketch
the tool rnc,,,rm is illustrated in
N61 GOO G4l X4.0 ZO.15 T0303 MaS
N62 GOI Z-2.4S FO.012
N63 X3.0 Ma9
N64 GOO G40 X3.5 ZO.lS MaS
N65 G27 X10.0 Zl.O TOlOO
N66 MOl
machine
point return check can be
in
either the absolute or incremental mode. The absolute sta·
tement in block N65 (in the
example) can
replaced
with the
version:
,
I
/
I
/
N65 G27 U6.5 ~.85 TOlOO
IS a
Lo this command. A small price Lo
pay when
this checking command is a slight cycle
the deceleration of tool motion is built
time loss.
into the command by the control system, about one to
G27 command is
seconds
be lost
number of tools use
This
be a significant loss if a
check in every program.
The G27 command tp seldom used with geometry offset
setting of the tools, wl1ich is the current modern method.
The G50 command i:0llder and not
anymore on
newest
lathes, but many lathes are slill used in
try that do need the
setting.
RETURN FROM MACHINE ZERO POINT
The preparatory command G29 is
exact opposite
G28 or
command. While G28 will automatically reto machine zero position,
comturn the cuning
mand will return the tool to its original position - again, via
an intermediate point.
In normal programming usage, the command 029 usualJy follows G28 or 030 cOIllmanu. The rules relating to
the absolute and
are
for
in exactly
same respect as to the G28
All
programmed axes are moved at the rapid traverse rate to the
by the preceding G28 or
intermediate position firsl,
030 command block. An example for a
application
lustrates the concept:
6.80--'-- 7.62
G28
G29
Figure 21-7
AutDmatic return from machine lero position
The illustration shows a tool motion from point A to
point B first, then to point C, back to point B,
to
point D.
point A is the starting point of the motion,
point B is the intermediate point, point C is the machine
zero
point, and point D is the final point to
the
target position.
curequivalent program commands, starting at
rent [001 pOSition, which is point
and resulting in the A
to B to C (0 B to D lool path are quite simple:
G28 018.6 W6.8
G29 U-14.86 W7.62
Of course, there would be some appropriate action programmed
the two blocks. for
a tool
activity.
change or some other
Similar to G27 command, there is only a weak support
comamong CNC programmers. It is one of
virtumands that can be very useful in some rare cases,
ally unnecessary for everyday work. However, it is always
to know
'tools of trade' are available in
1'\"",<n""~.M"Irnlno- They
come
158
21
RETURN TO SECONDARY MACHINE ZERO
G28 machine zero command, specific
machines also have the G30 command. In
ler, and
handbook generally. many examples apply
equally to G28 and G30 commands and were sometimes
tn
identified as G28/G30 to cover both. So what is
G30 and why is this command needed it in the first
i& where ...
G30
In addition to
By definition,
preparatory command is a machine
zero return cummand tu the
machine zero posilion. That position must
available on the machine at the
lime of purchase. Note the descriptive word is secondary,
not second. In virtually all
G30 is identical to the
G28, except thaI it refers to a secondary program zero.
zero can be the physical
third, or even
point, as specified by the mamanufacturer. Not every CNC machine
a secondmachine zero
position, and not every
mflchine
machine even
one. Thi~
ence point serves only some very special purposes, mainly
for horiwntal machining centers.
programming format for G30 command is similar to
the G28 command, with an addition of the P address:
P
:::: indicates the selection of a
secondary reference position
:::: can be P2, P3 and P4 to identify
XVZ
:::: is the
the
(2-4)
point definition
(one axis minimum must be specified)
The most common use of a secondary machine zero
erence point in CNe programming is for pallet
In the control unit parameter
distance of
secondary reference point is set from
primary reference
point and is not normally changed during the working life
of the machine and the pallet
To distinguish between multiple secondary machine zero
positions, address P is added in the G30 block (there is no P
"t1rl .... '~'" used
If the
machine has only a sinsecondary machine
position, the
Pis
not required in the program,
PI is assumed in
G30
IS
x.. Y ..
same as
G30 Pl x .. Y ••
In this case, the selling of the second
point is
within the
of the control system. In
to
other programming considerations, the G30 command is
in exactly the same way as the much more common
machine zero return command.
)
LINEAR INTERPOLATION
Linear interpolation is closely related to the rapid positioning motion. Wbile the rapid tool motion is meant to be
used from one position of the work area to
withour curling,
linear interpolation
is u ....... "" .........
for actual material removal. such as contouring, pOj:Ke~ung,
face milling
cutLing motions.
is used in part programming to
from the start position 0 f the cut LO
uses the shortest
cutmotion programmed in
is
a straight line,
the
points. this mode, the cutter moves
contour start
from one position to another by the shortest distance between the
is a very important nrr\OT~~m_
ming feature,
in contouring and
angular motion (such as chamfers, bevels, angles,
in this mode to be accurate.
etc.) must be
can be generated in the linear
Three types
polation mode:
Cl
Horizontal motion
• Start and End of the linear Motion
Linear motion,
other motion in CNC
ming, is a motion
two end points of the conLour. It
position. Any start position
has a start position
is often called
position, rhe end position is
often called the target
The start of a linear motion
is defined by the current
position, the end is defined by
the target coordinates
current block. It is easy to see
!.hat the end position one motion will become the start
position of the next motion, as the tool moves along
part, through all contour
points.
• Single Axis linear Interpolation
The programmed tool motion along
single axis is ala motion parallel ta that
of the motion
or
mode will result
Programming in
in the same nrF~H'T"",
but at different feedFigure 22-1 for
... single axis only
o Vertical motion
o
Angular
y
Motian from
XOYO
axes
means that the control
thousands of intermediate coordinate points between
start point and end point of the
cut. The result of this calculation is rhe shortest path
tween the two p~nts. All calculations are automatic - the
control system constantly
and adjusts the feedrate for all cutt~axes, normally two or three.
LINEAR COMMAND
to
X7.0 Y4.0
5
4 -+--'--+--+3
2 ~~~~~~~-i~ -~~--,.f-
1
a
x
1
:nml1;!f1<:l'lfl
In GOl mode, the
function F must be in effect.
linear interpolation
first program block that starts
mode must have a feed rate in
otherwise an alarm
will occur during the first run,
power on. Command
Gal and feedrate F are modal, which means they may be
omiued in all subsequent I
blocks, once
they have been designated and
the feedrate reunchanged. Only a
location is
required for the axis designation in a
along two or
dition to a single axis motion, a
simultaneously.
three axes
be also
2
3
4
5
6
7
8
of the rapid mode and the linear irrt8rpo/ation mode
machmmg centers and the
tool motions (hat are parallel to
table
motions. On the CNC lathes.
as facing,
drilling, tapping
are
In all cases, a single
or the ho.rizonral
within the
current (working) plane. A singJe axis motion can never be
motion, which requires two, three, or more axes.
axis
name for a motion rhat is parallel to a
horizontaf or vertical only.
159
1
22
y
Motion from
X2.0 Y1.0
to
X2.0 Y3.0
and to
5
4
X6.0 Y3.0
3
2
1
O~·~--·--~···~·····~·····~-·~·········~-·X
gramming method is not
enough. Such n ..
ming projects more
an investment into a
computer based
system, such as
powerful and
Mastercam TM, that IS based
on modern computer
combined with machinknow-how. This
programming is using desktop
by virtually all machine shops.
and is
Computer based programming is not a subject of this handbook, btl[ its genera! concepts are discussed briefly in
chapter of the handbook
53).
F' ......" .......
o 1 234 567 8
three-axis (XYZ) '''" ..... " ....
in Figure 22·4,
22-2
(
Single lJxis linear interpolation motion
j nterpolation
linear motion is
4
the Y axis.
•
Axes linear Interpolation
A
motion can also be
along two axes
simultaoeously. This is a very common situation when lhe
start pOint of the linear motion and
point have at
least (WO coordinates [hal are
each other,
while in
linear interpolation mode GO I.
result of
two-axis motion is a straighltool
at an angle.
The
will always be the shortest
between
in a slraightline
the end point and
at an
by the control
y
Motion from
j.
X2.0 Y1.0
to
X6.0 Y3.0
5
Figure 22·4
Three axes
4
3
linear interpolation motion
PROGRAMMING FORMAT
2
1
x
a
o 1 234 5 6 7 8
In order to
a lool motion in the
interpolacommand GOI along with one,
Lool maLian, as well as a
feed-
two, or
axes
rate (F address) suitable for the job at hand:
Figure 22-3
Two axes simultaneous linear interpolation motion
GOI x .. Y.. Z.. F •.
• Three
All enLncs in the linear motion block are
to be
only if they are new or
the block instruction (word) that is affected by
needs to be included in the program block,
Interpolation
A linear
that takes place along
axis linear
same time, IS
simultaneous linear motion along three axes is possible on
virtually all CNC machining centers. Programming a linear
is not always easy, particularly when
motion of this
working with complex parts. Due to many difficult
lions involved in this type of tool motion, the manual pro-
Depending on which programming melhod is """ . . "'I.vU.
motion may be
absolute or n".·"''''''''
lory commands for milling
and W for
the linear·
LINEAR
161
• Individual Axis feed rate
LINEAR fEEDRATE
The actual
be programmed In two
a defined tool motion can
o ... per time
mm/min or in/min
o
mm/rev or in/rev
... per spindle revolution
machine type and dimenThe selection depends on
,,,,,,,,,,,,,,,~centers, drills,
£lanaI units used. Typically,
protilers, wire EDM, etc.,
mms, routers, flame
lathes and turning centers lypiuse feed rate per time.
cally use feed rate per
• Feedrate Range
only within
in milling applicais 0.0001 \
as in/min,
typical
" ..""un,,,, or deglmin. The lowest
for linear interpoin turning is dependent on the minimum increment
of the coordinate axes XZ. The following two tables point
out typical ranges a normal CNC system can support. The
is for
All
first table is for milling, the second
units used in pan programming are rpXlrp.<:PfI
tf>P,rlr<ltp
a certain
Minimum motion increment
MILLING
0.001 mm
0.0001 ·240000.00 mm/min
0.001 degree
deg/min
subject of actual cutting feed rate per
is not eruin programming al all, It is included here for
matically oriented and interested individuals only. There is
no
to know the following calculations at all
system will do them every time. all the
automatically. On the other hand. here it is
as
motion
unit must always calculate
individually. Depending on the
motion (its angular value), the cornup' one
and 'hold back' the other ax is
and it will do it constantly during the cut
The result is a
between !.he start and end points
of (he linear contour. Strictly speaking, it is not a straight
I
with edges so diminutive in
that
hne but a
they are
Iy Impossible to see, even under magnification. For all practical
the result is a straight line.
The calculations are
to the following
the CNC system, according
in Figure 22-5.
END
POINT
/"--r
,
END
POINT
.0001 inch
,-.
'-
Minimum motion increment
TURNING
0.001 mm
.==.
0.00001 - 500.00000 mm/min
0.001 degree
0.00001 - 500.00000 deg/min
.0001 inch
.000001 - 50.000000 in/min
lhall!!t: maximum feeurate thaI can
high. For actual cutting, that is true.
that
ranges are
to the control
The
will
feed rate, according to the macapabilities. Control system only prorange, that is more for the benefit or
than the actual user.
in
case is to allow the machine manufacturers flexibilIty within current technological advances. As technology
control system manufacturers will have to rechanges as well, by increasing the ranges.
Figure 22-5
Oal8 fDr the calculation of individual axis linear feedrate
GOO XlO.O Y6.0
GOl X14.S Yi.25 F12.0
linear motion takes place between two end points,
point at X 10.0 Y 6.0 to the end
at
Y7.25 - the feed rate is programmed at 12 in/min as
That means the actual travel motion
is either known or it can be calculated:
Xc
14.5
= 7.25 -
Zt
10.0 = 4.5
6~O
= 1.25
0
tool total mali on (as illustrated) is
motion, and can be calculated by
Theorem:
162
22
y
above formula is
root of the total sum
value of 4.6703854 as
5 ~~+.~...~~...+-.-.~~~~~~~.+
common, based on the square
sides, that win
travel length in the
+
4
3
2
1
control system will internally apply the
and
calculate the actual motion along we X axis (4.25), as well
the Y
(1
plus the length of
motion il(4.6703854).
values, the
system
will calculate the X
feed rate - there no motion
that takes place
0 -.... X
o 1 2 3 4 5 6 7 8
Figure 22-6
Example illustration for a simple linear interpolation
I-V<l, ...... "Jo
1.
(CLOOK.WJ:SE DIRECTION FROM
Fx = 4.5
I 4.6703854 x l2 = 11.562215
Fx = 1.25 I 4.6703854 x 12
3.2117263
G90 •••
G01 Xl.O Y3.0 F •••
X3.0 Y4.0
X4.5
X6.S Y'3.0
X7.5
Yl.S
X4.5 YO.S
Xl.O
n.o
e
Fx = 0
I 4.6703854 x 12 = 0.0
(ABSOL'!J'TE MODE)
(Pl TO
(P2 TO (3)
(P3 TO P4)
(P4 TO !;IS)
(PS TO (6)
(P6 TO P7)
(P7 TO (8)
(pa TO
2:
(COUNTERCLOCKWISE DIRECTION FROM PI)
G90 •••
In this example, there is no Z axis motion. If
Z axis
were part of the lool motion, for
a simultaneous three dimensional linear motion,
procedure will
be logically identical, with the inclusion of Z axis in the
calculations.
PROGRAMMING EXAMPLE
In order to illustrate the .... ~._ .. _~, use of
interpolation mode a CNC program,
is a simple example,
shown in
22-6.
For even more comprehensive understanding, we example will
presented twice. One tool motion will start and
end at the P I location and will programmed in the c1ockthe other
will start at
will
in the counterclockwise
direction.
GOl X4.S YO.S F ...
X7.S Yl.S
Y3.0
X6.5
X4.5 Y4.Q
X3.0
X1.0 Y3. 0
Y1.0
(ABSOLUTE MODE)
(P1 TO
TO P7)
TO PO)
TO P5)
\,
TO
TO
TO (2)
TO (1)
Linear interpolation
means of programming all
orthogonal (i.e.,
horizontal) molions, as well as
angular tool motions as the shortest Hnear distance between
two points. CUlling
must be
in this
mode, for proper m~lal
Note
coordinate
location that has not changed from one point to the next one block to the next is not repeated in
subsequent
block or blocks.
BLO-CK SKIP FUNCTION
In many control manuals, the block skip function is also
called the block delete function. The expression 'block delete' offers rather a misleading description, since no progTam blocks will actually be deleted but only skipped during progTam processing. For this good reason, the more
accurate description of the function is the block skip function, a term used in the handbook. This function is a standard feature of virtually all CNC controls. Its main purpose
is to offer the programmer some additionaJ flexibility in designing a program for no more than nvo conflicting possibilities. In the absence of a block skip function, the only alternative is to develop two individual part progTams, each
covering one unique possibility.
TYPICAL APPLICATIONS
To understand the idea of two connicting possibilities,
consider this programming application. The assignment is
to write a program for a facing cut. The problem is that the
blank material for parts delivered to the CNC machine is
not consistent in size. Some blanks are slightly smaller in
size and can be faced with a single cut. Others are larger
and will require two facing cuts. This is not nn uncommon
occurrence in CNC shops and is not always handled efficiently. Making two inefficient programs is always an option, but a single program that covers both options is a
better choice - but only if the block skip function is used in
such a program.
BLOCK SKIP SYMBOL
To identify the block skip function in a program, a special
programming symbol is required. This block skip function
symbol is represented by a forward slash [ / ]. The system
will recognize the slash as a code for the block skip. For
most of CNC programming applications, the slash symbol
is placed as the first character in a block:
~ Example 1 :
Nl
N2
N3
(ALWAYS PROCESSED)
(ALWAYS PROCESSED)
(ALWAYS PROCESSED)
(PROCESSED IF BLOCK SKIP IS OFF)
(PROCESSED IF BLOCK SKIP IS OFF)
(PROCESSED IF BLOCK SKIP IS OFF)
(ALWAYS PROCESSED)
(ALWAYS PROCESSED)
/ N4
I N5 •••
I N6 •••
N7 .•.
N8 •••
On some control systems, the block skip code can also be
used selectively for certain addresses within a block, rather
Ihan at its beginning. Check the manual if such a technique
can be used - it can be very powerful:
Q Example 2:
N6
N7 GOO XSO.O
N8 GOl ••.
I MOB
-"
This challenge illustrates a situation, where two connicting options are required in a program at the same time. The
In those cases, when the control system does allow the
most obvious solution would be to prepare two separate
block skip within a programmed block, aJl instructions beprograms, each properly identified as to its purpose. Such a
fore the slash code will be executed, regardless of the block
skip toggle setting. If the block skip function is turned ON
task can be done quite easily, but it will be a tedious, time
consuming and definitely an inefficient process. The only
(block skip function is active), only the instructionsfollowother solution is to write a single program, with tool mo- / ' ing the slash code, will be skipped. In the Example 2, the
tions covering facing cuts for both possibilities. To avoid
coolant function M08 (block N7) will be skipped. If the
block skip function is turned OFF (block skip function is
air cutting for those parts that require only one cut, a block
not active), the whole block will be executed in Example 2,
skip function will be provided in the program and applied
to all blocks relating to the first facing cut. The 'second' cut
including the coolant function.
will always be needed!
Other common applications of the block skip function indude a selt!Clive ON/OFF sLalus LOggle, sUl:h illi the coolant
function, optional program stop, pfOgTam reset, etc. Also
useful are applications for bypassing a certain program operation, applying or not applying a selected tool 10 a part
contour and others. Any programming deciSion that requires a choice from two predetermined options is a good
candidate for the block skip function.
CONTROL UNIT SETTING
Regardless of the slash code position within a block, the
program will be processed in two ways. Either in its entirety, or the instruction foHowing the slash will be skipped
(ignored). The final decision whether or not to use the
block skip function is made during actuaJ machining, by
164
Chapter 23
the operator, depending on the
of
this
purpose, a push button key, a
switch, or a menu item .
control panel the CNC unit.
selection is provided on
Selection of the
mode can be either as
(ON) - or inactive (OFF).
programs will not require any
skip codes. In
such cases, the setting mode for the block skip function on
the control panel is irrelevant, but OFF mode is strongly
switch setting
important,
recommended.
if the program contains even a single block containing the
slash symboL
active
ON will cause
instruccode to be ignored durtions in a block following the
ing
The
setting
will
cause
contralto ignore the
code and process all instructions written in the program.
A simple programming solution to
this potential
problem is available. Just repeat all modal commands in
the program
thal will not
affected by
block
skip function.
=
two
Example A - Modal commands are not repeated:
NS GOO XlO.O YS.O Z2.0
/ N6 GOl ZO.l F30.0 MaS
N7 Z-l.O Fl2.0
(GOl AND Moa
N8 •••
C Example B - Modal commands are repeated:
NS GOO X10.0 YS.O Z2.0
/ N6 Gal ZO.l F30.0 M08
N7 Gal Z-l.O Fl2.0 M08
N8 •••
""u",; llisled earlier, the contents of
N4,
be
if
block
function is ON.
They will be processed, if the swilch
IS
The
2, also listed
a slash in
block
slqsh symbol is preceding
miscellaneous function M08 (coolant ON). If
skip funcrion switch is ON,
the coolant wi!! be
if it is OFF, the coolant funclion
will
application may be useful in <I dry
run mode, to bypass the coolant flood during
verification, if no manual override is available.
....o\, ...
LJ",,""fHUlI"
BLOCK SKIP AND MODAL COMMANDS
In
examples A
B. the program block containing
position as
slash code indicates an intermediate Z
I. This position may
only certain cases
during machining
will decide whether to
use it or not, and also when to use it.
The
block, identified in the
as N6, contai ns several modal functions. The commands GO 1, ZO.1.
F30.0 and MOS will all remain in effect, unless they are
canceled or changed in
following block. From block
N7 it is apparent that
Z coordinate position and the cutling [eedrale value
changed. However. the
I
M08 commands are not repeated in the example A
will
not
in effect, if the block skip switch is set ON.
Both examples A and B will
identical results, but
only if
block skip function i~ in the
(OFF)
mode. The control
will then execute the instructions
in all blocks, in the
of ....,.n"',.""n'\
The processing result
To understand the way how modal values work with
skipped blocks,
that modal commands can be
tied only once in the program, in the block
they occur first. Modal commands are nol repeated in
quent
as long as they
unchanged.
In programs where the block skip function is not
at
all. there is nothing to do. When the block
function is
used, watch carefully all modal commands. Remember that
a command established in a block using the slash code will
not always be in effect. It
on the setting block
skip switch. Any modal
that
to be carried
over from a section with slash codes to the section without
codes may
lost if the block skip funclion is
Overlooking modal
when programming block
in a program with serious errors.
skip function can
be different
each programexample shown. If the block skip function is active
(ON) block instructions following the
will
not be
next example A yields an unacceptable result, with a fairly possible collision. The example B
uses careful
thoughtful approach with very
extra
work.
are the
when block N6 is skipped:
C Example A - Modal commands are nat repeated:
NS GOO X10.O YS.O Z2.0
, ............."" MOTION)
N7 Z-l. 0 F12. 0
N8 •••
(RAPID MOTION)
C Example B Modal commands are ron,""'Tl'"
NS GOO X10.0 YS.O Z2.0
N7 GOl Z-l.O F12.0 MOS
N8 ...
(RAPID MOTION)
(FEEDRATE MOTION)
BLOCK SKIP FUNCTION
Note that the
motion
I, the
F30.0 and
the
M08 are all skipped in the example
The X
and Y axes have not
updated in either example and
will remain unchanged.
conclusion is that the example
motion in two consecutive
A will result a Z axis
In the
blocks, causing a potemially dangerous
correct version, listed as
B, the programmed repetilion all commands - GO 1, F 12.0 and M08 - assures the
nrr' .... "'''""' will be run as intended. In
next section this
chapter we will look at
principles of program design for
different practical applications.
In the summary, there is one basic
developing
programs with blocks using the block skip function:
Always program a/l the instructions. even if it means repeating
some program values and commands that have to be preserved.
slash symbol can be
into the nT"e,r"n.
nrr,""'"rn has been designed for bOfh options.
in those blocks that define the optional skip
lected
blocks. Always check program!
a way that there is only
If the program is designed in
cut, problems may oceur during
Programming TWO cuts
all
parts
a
program, but will be inefficient
parts with a minimum stock. There will
too many tool
motions
as 'cutting
, when the
is minimal.
c:> Example - Variable stock face:
A
cutting a
that
in sIze is a common
problem in CNC work. A suitable solution is
for
turning
milling - the
should include tool motions for two cuts and the
skip function will be
on all blocks relating to theftrs1 cut
is a lathe
face cut,
the
facing siock varies
mill) and .275 (7 mm).
After considering several machining options, the programdY~'" that the
maximum stock that can
CUI will
(3.5 mm) Figure 23-J.
'-' .......
CHANGE
Any eNC program containing block skip
function should be checked at least twice.
X3.35
I
result of this double check must be always satisfactory, whether
the block skip in
or
without it. an error is
even a very minor error.
correct it
After the correction. check the program at
twice again, covering both types of processing. The
check is that a correction made for
reason for the
one type of processing may cause a different error for the
other type of processing.
N9
I
0
I
I
~. co h~
I z
I
N111
I
I
N7 I
X-O.OS
PROGRAMMING EXAMPLES
block skip function is
simple, often neglected,
yet, it is a powerful programming tool. Many programs can
benefit
a creative use of this
The type of
and some thinking ingenuity are the only criteria for successful implementation. In the following examples, some
of the
skip function are shown.
the examples as start points for a general program design or when covering similar machining applications.
• Variable Stock R'moval
Removal of
excessive
material is
during
a rough cutting. When machining irregular
(castbe difforgings, etc.) or rough facing on lathes, it
ficult to determine
number of cuts.
example, some
castings
a given job may have only the minimum excessuffimaterial, so one roughing or facing cut will
Other
for
same job may
larger and
two roughing or
cuts arc nceded.
Figure 23-1
Variable stock for fBcing in 8 turning I!JOfJ'ilCOtion - program 02301
02301 (TURNING)
(v:ARIABLE FACE STOCK)
N1. G20 G40 G99
N2 GSQ S2000
N1 GOO TQ200 M42
N4 G96 S400 M03
NS G41 X3.35 ZO.135 T0202 MOS
I N6 GOl X-O.OS FO.Ol
I N7 GOO ZO • .25
I NS X3.35
N9 GOl ZO FO.OS
N1.0 X-O.OS FO.Ol
N1.1 GOO ZO.l
N12 X3.S
N13 G40 Xl2.0 Z2.0 T0200
N1.4 MJO
%
166
...........••• ~----------~
NS contains
initiallool approach motion.
tool
next three blocks are preceded by a slash. In N6,
front
at ZD.l
N7 moves the tool away
cuts off
to
initial
face, block N8 is a rapid
diameter. There are no other blocks to
skipped after
to the fronl
block N8. N9
contains a
cutting motion, Nil is the
N lOis the front
motion, followed by standard final blocks.
Evaluate the example not once
least twice - it shows
what exactly happens. During the first evaluation, read all
blocks and
the block skip function.
the second time, ignore all blocks containing
slash
will be identical results when compared with the first
the number of actual
uation. The only difference will
is very
cuts - one, not two. In miiling,lhe
An
for a milling application uses a
inch face
material
to
faced varies bemill. The
(ween .120 and .3! 5.
largest reasonable depth
cut
selected will be .177 (4.5 mm) - Figure 23-2.
FIRST
X-3.0
Y4.0
CUT
X11.0
Y4.0
Chapter 23
........------.-------~~.........~~~----...:...
Block
does not need a
for a
reason - it will
be either FIS.O or FIS.O, depending on whether blocks N6
to N8 were skipped or not. The
is very important
block 10. Such a repetition guarantees the required
rate in the
block, when actual cutting takes
Both lathe and mill examples should offer at least some
logic used in program developbasic understanding of
menl, using the block
function. Exactly the same logical approach can be
for more than two cuts and can
also be applied to operations other Ihan face cutting.
• Machining Pattern Change
Another application. where the block
function may
be
efficiently. is a simple
programming. The
term family programming means a programming situation
bewhere there
a slight difference in
tween two or more parts. Such a
variation between
similar
is often a
prospect for block skip function. A minor deviation in a machining pattern
one
adapted in a single program usdrawing to another can
ing the block skip function. Following two examples show
typical possibilities of programming a change of the
path. In one
the emphasis is on a skipped machini ng location. In the other example, the emphasis is on the
pattern change itself. Both
are In
illustrate a simple
operation. the lathe example,
Figure 23-3 is related to program 02303.
23-2
Variable stock for facing in 8 ml1ling application· program 02302
02302 (MILLING)
(VARIABLE FACE STOCK)
N1 G20
N2 GI? G40 G49 Geo
N3 GSO GOO GS4 XlI.0 Y4.0
N4 G43 Zl.O S550 MO) Hal
N5 GOl ZO.1?7 F15.0 Mn8
/ N6 X-3.0 FIB.O
/ N7 ZO.375
/ N'8 GOO Xl!. 0
N9 GOl ZO
NlO x-J.a F1B.O
Nll GOO Zl.O M09
Nl2 G2S X-l.O Y4.0 Zl.O
M13 M30
%
Block N5 in the example contains the Z axis approach to
the first cut, at
177 level. The next
blocks can be
if necessary. In the N6 block, the
mill actually
cuts at ZOo I position, N7 is the tool
motion after
cut, and N8 returns the tool to
initial X position.
There are no other blocks to be skipped
block N8.
X43.0
-"L-;.I---X35.0
Figure 23-3
Variable maj:/If~lina pattern - turning application
upper picture shows
result with block skip
lion set ON. the lower picture shows the result with block
the -"arne
skip function set OFF,
02303
Nl G21
Nl2 GSO SleOO
Nl3 GOO T0600 M42
Nl4 G96 S100 MD3
BLOCK SKIP FUNCTION
167
N15 X43.0 Z-20.0 T0606 MOS
N16 G01 XJS.O FO.13
N17 GOO X43.0
/ Nle Z-50.0
/ Nl9 GOl X3S.0
/ mo GOO X43.0
ml X400.0 Z4S.0 T0600 MOl
Both variations of program 02304 machine a hole pattern with 6 or 4 holes. Block skip function has been used to
make a single program covering both patterns. The top of
Figure 23-4 shows the hole pattern when block skip function is set OFF, the bottom shows the hole pattern when
block skip mode is set ON.
Program 02303 demonstrates a single program for two
parts with similar characteristics. One part requires a single
groove, the other requires two grooves on the same diameler. In the example, both grooves are identical - they have
the same width and depth and are machined with the same
tool. The only difference between the two examples is the
number of grooves and the second groove position. Machining the part will require the block skip function set ON
or OFF, depending on the grove to be machined.
02304 (MI.LL.ING EXAMPLE)
Evaluate the more important blocks in the program example. The N15 block is the initial tool motion to the start
of the first groove at Z-20.0. In the next two blocks. Nl6
and N 17, the groove will be cut and the tool returns to the
clearance diameter. The foHowing three blocks will cut the
second groove, if it is required. That is the reason for the
block skip code. In the block N 18, the tool moves to the initial position of groove 2 at Z-50.0, in N19 the groove is cut
In the block N20, the tool retracts from the groove to a
clearance position.
N24 GSO G28 X30.0 Y7S.0 Z2S.0
The milling example shown in Figure 23-4, also in metric, is represented in program 02304. The program handles
two similar patterns that have four identical holes for both
parts and two missjng holes in the second pari only. This is
a good example of similar parts program, using block skip.
a
a
M
LO
ci
uj
N1 G21
N16 G90 GOO G54 X30.0 Y2S.0 MOS
N17 G43 Z2S.0 S1200 M03 H04
N18 G99 GS1 R2.5 Z-4.0 F100.0
N19 XI05.0
mo Y75.0
I N21 XSO.O Y50.0
/ m2 X55.0
m3 G98 X30.0 Y7S.0
0
X X X ><
><
$
I
I $-+- Y75.0
I"'i"'\
.
0
r....:
<0
uj
X
J
I
I
<it
I
-$-
4
$- I - Y75.0
3
t
Y54.0
-
Y25.0
47 447 -$
3
Y75.0
-$.
Y25.0
f!1
2
0
a
......
X
5-
3
w -$ - + - Y50.0
5 4
<B- '-- -$ - I - Y25.0
1
--"""""~~~""""
a
0C"')
X
$
6
-$1
a
0
I.()
0
0
X
X
......
M
$-
Y75.0
$- -
Y25.0
I-
3
0
r....:
<0
X
a
..0
0
.....
><
5'
2
Figure 23-4
Program 02304 - variable machining pattem for a milling
application - result with block skip OFF (top) and ON (bottom)
6)
A variation of this application is in the program 02305.
There arefive hole positions. but the block skip function is
used within a block, to control only the Y position of the
hole. Top of Figure 23-5 shows the pattern when block skip
function is OFF, the bottom shows the pattern when skip
function has been set ON. The middle hole will have a different Y axis position, depending on the setting of the block
skip function at the machine.
a
(")
6
5)
Blocks NI8 to N20 will drill holes 1,2 and 3. Hole 4 in
N2! and hole 5 in N22 will be drilled only if the block skip
function is set to inactive mode (OFF), but neither one will
not be drilled when the block skip setting is active (ON).
Block N23 will always drill hole number 6.
a
I
1)
2)
3)
4)
N25 MOl
a Lri
0 a
co ......
I
(HOLE
(HOLE
(HOLE
(HOLE
(HOLE
(HOLE
1
t
-
Figure 23-5
Program ()2305 - variable machining pattern for a milling
application . result with block skip OFF (top) and ON (borlom)
168
Chapter 23
02305 (MILLING EXAMPLE)
Nl G21
N16 G90 GOO G54 X30.0 Y25.0 MOS
N17 G43 Z25.0 S1200 M03 H04
N1e G99 Gal R2.5 Z-4.0 F100.O
N19 n05. a
mo Y7S.0
N2l X67.0 / YS4.0
m2 G98 X30.0 Y7S.0
N23 GSO G28 X30.0 Y75.0 Z25.0
j--X3.0
(HOLE l)
(HOLE 2)
(HOLE 3)
(HOLE
(HOLE 5)
/'
,/
,/
I
~~~=t~- X2.0
N24 MOl
X1.67S
hole 4 In block N21 will
drilled at the location of
X67.0 Y7S.0, if the block skip mode is
The address
Y54.0 in
N21, will not processed. If the block
the hole 4 will
drilted at coordinate
mode is
.0 position from
tion of X67.0 Y54.0. that case, the
the block N20 will
overridden.
to
the
proper drilling at position 5, the
block
N22 must written. If it is omitted. the Y54.0 from block
N22 will
precedence in block skip
mode.
Using the block skip feature is the simplest way of dea family of
parts.
applications arc
the
function
but they
the
fundamentals of a powerful programming technique and an
example of logical thinking. Many detailed explanations
and examples of programming complex families of parts
can be found in a special Custom Macro option Fanuc
fers on most control
• Trial Cut for Measuring
Another
application of the block
is to
the machine operator with means of measuring the part before any final machining on the part
been done. Due to
dimensional
the cutting tool comwith other factors, the
part may slightly
outside of the required tolerance range.
following method of programming is very useful for
parts
very
tolerances. It is
a
method
lhose parts,
part
is
difficult to measure after allinachining is
for
The same me.tho?
ex.ample
shapes, such as
is also quite
for parts
cycle
Indlviduallool is relatively long and all the
offsets have to
be fine
be/ore
machining.
approach to part programming is more efficient. as it
a recut. increases
finish, and can even
prevent a scrap. In either case, a trial cut programming
method that employs the
skip
is used Setting the
skip mode
the machine operator checks
the trial dimension,
the individual offset, if necessary,
with block
set ON.
general
equally applicable to
X2.0563
described in example
are
and milling - Figure 23-6.
Figure 23-6
Application of 8 trial cut for ml!l;~~lJ,rm{'J on a lathe - program 02305
02306
(TRIAL COT -
N1 G20
NlO GSO SHOO
Nll GOO T0600 M43
Nl2 G96 SoOO M03
/ Nl3 Gt2 X2.0563 ZO.l T0606 MOS
/ Nl4 GOl Z-O.4 FO.OOS
/ Nl5 X2.3 FO.03
/ N16 GOO G40 X).O Z2.0 T0600 MOO
/
(TRIAL Dn IS :2.0563 DlCHES)
/ N17 G96 S600 M03
NlB GOO G42 Xl.67S ZO.l T0606 MOS
N19 GOl Xl.O Z-O.062S FO.007
mo Z-l. 75
ml X3.5 FO.Ol
N22 GOO Gto XlO.O Z2.0 TOSOO
m3 MOL
When program 02306 is processed
the block
set
all blocks will executed, including the trial cut
and finish profile. With the block
set ON, the only op.....""lIn" executed will be the
to size,
the
cut. In this case, significant instructions are retained
by repetition the key commands (NI8 and NI9). Such a
repetition is very crucial
successful
in both
modes of
block skip function. MOO
in N16
stops the machine and enables a dimensional
Selecting trial
of
in the example may be
questioned. What is the logic
it? The trial diameter can
be other
size,
That would leave a .025
stock per
for the
cut. It is true
a different
diameter could have
selected.
four decimal numwas only selected for one reason - to psychologically
",n'Y"",.."e,.. the
to maintain accurate offset settings.
- programmers may
a three or
aeC:lmal number
- the
BLOCK SKIP FUNCTION
169
In the next
trial cut will also
the actual machining, but for a di
reason - Figure
7.
..-
ci
N
02308
(TRIAL CUT FOR TAPER.
/
X4.37S·
(T02 TR.IAI.. COT DIA IS 4.46 INCHES)
GSO S1750 T0400 M43
/ N9 G96 S550 M03
/ NlO GOO G42 X4.428 ZO.I T0404 MOa
/ N1l GOl Z-O.4 FO.OOa
/ Nl2 UO.2 FO.03
/ N13 GOO G40 X10.0 Z5.0 T0400 MOO
/ NS
- X3.87S
/
23-7
Trial cut for 8 taper cutting on a lathe program 02307
In program 02307. the
a feature difficult to measure
the tool offset in a
error
is not the right
a
an area of the solid
a straight
enables the operator to
trial dimension comfortably and to adjust the offset before cutting the finished
02307
(TRIAL CUT FOR TAPER. - ONE
Nl G20 G99 G40
N2 G50 S1750 T0200 M42
N3 G96 S500 M03
/ N4 GOO G42 X4.428 ZO.l T0202 MOB
/ NS G01 Z-0.4 FO.OOB
/ N6 UO.2 FO.03
/ N7 GOO G40 X10.0 Z5.0 T0200 MOO
/
'!WO TOOLS)
N1 G20 G99 G40
N2 GSa 51750 T0200 M42
N3 G96 S500 Mal
/ N4 GOO G42 X4.46 ZO.l T0202 MOB
/ N5 GOl Z-0.4 FO.OOa
/ N6 UO.2 FO.03
/ N7 GOO GtO XIO.O Z5.0 T0200 MnO
(TRIAL CUT DIA IS 4. 428 m:::H:E~S
/ NS G96 5500 M03
N9 GOO G42 X4.6 ZO.l T0202 MOS,-NlO G7l Pl1 Q13 UO.06 WO.OOS D1500 FO.Ol
Nll GOO X-J.875
N12 GOl X4.375 Z-0.73 FO.008
Nl3 X4.6 FO.012
Nl4 S550 M43
Nl5 G70 PH
Nl6 GOO G40 XlO.O Z5.0 T0200 MOl
a common
where a
cutting tool is used for both roughing and finishing
operations. It
a logical way of
the block skip
function,
a
form. In most applications, <'''' ....,''y"t'''
tools for roughing and finishing may be
depending
on the
of required accuracy. When
two cutting
for
tools, the trial cut dimension is usually more
the finishing
than for the roughing
02308, the block skip function is illustrated
is for roughing, T04 is
ting (ools ous
is used.
TRIAL COT DIA IS 4..428
/ N14 GSO 51750 T0200 M42
/ Nl5 G96 S500 M03
N16 GOO G42 X4.6 ZO.l T0202 MOB
N17 G71 PIS Q20 UO.06 WO.OOS D1500 FO.Ol
N18 GOO XJ.B75
N19 GOl X4.375 Z-0.73 FO.OOS
N20 X4.6 FO.012
N21 GOO G40 XlO.O Z5.0 T0200 Mal
N22 GSa 51750 T0400 M43
N23 G96 5550 M03
N24 GOO G42 Xl22.0 Z3.0 T0404 MOB
N25 G70 P18 Q20
N26 GOO G40 XlO.O Z5.0 T0400 M09
N27 M30
%
02308 can be improved further by includcontrol of taper on the width, for example. Programming a trial cut is useful but often a neglected technique, although it does present many
applications.
•
Program Proving
can
to check it
limited experience
easy to run a
for the first time.
common concerns of operators is the
towards a
particularly when the
The rapid motion rate of many modern
be very high.
over 1500 in/min. At
the rapid approach to the cutting position on
not add to the operator's confidence,
approach is
\0 the close
lenal.
most controls, the operator can set
ride rate to 100%,
and slower. On
the
rate
cannot be done.
The next two
02309 and 02310, show a typical
method to eliminate the problem during
mosetup and program proving, yet maintain the full
tion rate during
operations for productivity.
170
Chapter 23
Block
function in
examples
a less usual
- it is used for a section of a block, rather than the
block itself, if the control supports such a method.
For machining, the block
ON or
position and
function is set to
the
in this mode
the whole
program. If the ON seuing is required for one section of the
02309 (TURNING EXAMPLE)
Nl G20 G40 G9S
N2 GSO S2000
N3 GOO T0200 M42
N4 G96 S400 MOl
NS G41 X2.75 ZO T0202 M08
N6 GOl X .. FO.004
• Numbered Block Skip
but not for another, the operator
to be
usually in
program comments. This
changing block
mode in
of a program can
unsafe and
create problems.
r" ................
FO.l
N7 •••
02310
Nl G20 G17 G40 GSo
N2 G90 GOO G54 X219.0 Y7S.0 MOS
Nl G4l Z-1.0 8600 M03 H01
FlO.O
N4 GOl X.. F12.0
NS ...
[n both examples, the block skip is used within a single
of two
block.
design of both programs lakes
conflicting commands within the same block. If two conflicting commands
in a single block, the falter command used in
block will become effective.
In both examples. the first command is GOO,
second
L Normally, the GOI motion will
a pnonty.
the slash
the control will accept GOO. if
block skip is set ON, but it will
GOI, if the block
mode is
both
skip is set OFF. When the block
motion commands will be read
second
in
that block
effective (GOI overrides GOO). Watch
for one possibility, already emphasized:
An optional feature on some controls is a selective or a
numbered block skip function. This option allows the operator to select which portions of the
required the
ON setting and wbich portions
OFF setting.
the Cycle SIart key to
seuings can be done before
initialize the program. This
also uses
slash
symbol, but followed by an
within the range of I to
9. The
selection
mode is
on the control
screen (Setrings), LInder
matching switch number,
example. a program may
tmee groups, each
expecting a different setting of
skip function.
the switch
the
symbol,
are
clearly
and all
operator must do is to match the
control seuings with the
activity.
Nl •.•
N2 ..
Nl
n N4
N16 •••
N1?
/2 Nl8
12 N19
During the firs! machine run l the operator should set the
block skip
making
GO I command
The
tool
will be slower
in the rapid
but much
Also, the feedrate
switch
control system will become effective, offering additional flexibility.
When the program proving is
and the
tool
approach is confirmed, the block skip can be set ON, to prevent the GO I motion from
processed. Both 02309
and
10 are typical
of breaking with tradition
to
a specific result.
• Barfeeder Application
On a
lathe, the block skip function can
in
barfeeding, for a continuously running machining. If the
n'>rr.,,"nPT allows it, tbe techniques is quite
The typiprogram will actually have n.vo ends one will use
M99 function. the
end will use
M30 function.
block will
preceded by
block skip symbol and
will be placed before the M30 code in the part program.
This
technique is
in
44.
SKIP GROUP 1)
(BLOCK. SKIP GROUP 1)
(BLOCK SKIP GROUP 2)
\"""-"'-"-'" SKIP GROUP 2)
(BI,ocK SKIP GROUP .:2)
N29 •••
NlO
/3 Nll
(BLOCK SKIP GROUP 3)
(BLOCK SKIP GROUP 3)
N4S ...
rules apply
skip function as
for
normal version. Incidentally, the II selection is
same as a plam slash only, so blocks N3 and N4 above,
could have also
writte~ (his
INl
I N4
Numbered block skip function is not i:lVCllll:lDle on all controls.
Programs
the selective
skip function can be
very clever and even efficient, but they may place quite a
on the machine
For the majority of jobs,
be a plenty of programming
available by
the standard block skip function.
DWELL COMMAND
Dwell is another name
a pause in
program - It IS an
intentional
delay applied during program ....l"rl('''''~c
In this period of
specified in a CNC
- any
motion is
while all
program commands
functions
unaffected. When
time expires, the control
resumes processing the
program with the block immediately following the block
that contains the dwell.
•
Applications for Accessories
quite useful
second common application the dwell command
certain miscellaneous functions - M functions. Several such functions are
to control a
of CNC
as a barfeeder,·tailstock, quill,
machine accessories,
part catcher, custom features, and others.
programmed
dwell time will allow
full completion of a certain
as the operation of a tailstock. The machine
spindle may be
stationary or rotating in
cases.
Since there will
no contact of the
tool with part
category, It IS not important
the mamaterial in
chine spindle rotates or not.
Each application is equally important to programmers,
although the two are not used simultaneously.
On some CNC
the
command may also
be required when
spindle speed, usually after a
range
This is used mainly on CNC lathes. In
cases,
guidance as to how and
to program a dwell time is to follow the recommendation of the
CNC machine manufacturer. Typical examples of a dwell
lathe
are described in Chaprer44, covsubject.
PROGRAMMING APPLICATIONS
Programming a dwell is
in two
applications:
o
o
and can
During actual
when the tool is in contact with material
For operation of machine accl~sso
when no cutting takes
•
Applications for Cutting
is
DWEll COMMAND
When cutting tool is removing material, it is contact
with the machined part. A dwell can be applied during machining
a number reasons. If
spindle is
the spindle rotation is very important
a cut is
practice. the application of a dwell
mainly used
breaking chips while drilling, counterboring. grooving or parting-off. Dwell may al.so be used while
turning or boring, in order to eliminate
physical
left on the
by end
of the
1001. This,
IS
attributed to the tool
during cutting.
many other applications, the dwell function is useful to
control deceleration of the cutting feed on a corner during
feedrales.
example. This use of dwell could be parfor older
systems. both cases,
ticularly
machining operation to
dwell command 'forces'
fu.lly completed in one block, before the next block,can be
I'>"<,!""t,,,r/ The
still
to supply the exact peof time
for the
This time
to be sufficient - neither too short nor too long.
common preparatory command for dwell is G04.
other G commands, G04 used by itself only will do
nothing, It must always
another address, in
this case specifying the amount of time to dwell (pause).
The correct addresses
dwell are X, P or U (address U
can only used for a
lathe). The
time
specified by the
address is either in milliseconds,
or in seconds, depending on
address. Some
control systems use a different address for
purpose as
dwell
but the
gramming methods remain identical.
fixed eycles
machining centers also use dwell.
dwell is programmed together with the cycle
not
in a separate block. Only fixed
that
a dwell
time can use it in the same
all
applications,
the dwell command must programmed as an independelll block. It will remain
for that block only and does
over to the next block.
is a only one block
uO(~tlOin and is not modal.
dwell execution,
curis unchanged. but the
rent status of
cycle
171
172
Chapter
• Dwell Command Structure
The structure - or format - for the
function is:
X5 • 3
AU machines, excludingJlXed cycles
us . 3
l£JJhes
... Allmtlchines. illcludingjix.edcyc/es
P53
In any case,
typical representation is five digits before
and three digits after
decimal point, although that
vary on different control systems.
Since milliseconds or seconds can be used as units of
dwell, the relationship can be established:
The control unit interprets such a command as a dwell,
of the
preparatory command 004, which establishes meaning of
the address that follows it. If using the X or U address for
dwell
not feel comfortable, use the third alternative the address P. Keep in mind,
the address P dues nat accept lhe decimal point, so the dwel1 is programmed directly
as the number of milliseconds to control the pause duration.
One millisecond is l/lOOOlh of a second, therefore one second is equivalent to 1000 milliseconds.
not as a axis mOlion. This is because of the
aU,"IlC~'i:>"',) X and U can also
seconds, without a decimal point -
1304 X2.0
1s = 1000ms
lms = O.OOls
s =
ms
pl0
POOIO
second
millisecond
Ploa
P01DO
G04 X2. 0
1304 P2 000
1304 U2. 0
POOOl
..
Examples of practical application of the dwell fonnat are:
pYt[ferredfor long dwells
n. pnd"erred for short or memwn dwells
... l(jJhe
in seconds
p'
In
example, the dwell is 2 seconds or 2000 milliseconds. All
are shown. The nexi example is
similar:
1304 XO.S
G04 P500
1304 UO.5
... I m.iJ.Jisecond
.. 10 milliseconds
.•. TOO milliseconds
Depending on the programming
for dwell. the
format using
range of programmable time varies. For
digits in front of a decimal point and three oigils follOWing it, the
is
0.001 of a
and up to
mInI99999.999
presents a range from
mum of l/lOOOth of a second, up to
hours, 46 minutes
and 39.999
'''TI''lIH-
Dwell programming applications are identical to both
machining centers and lathes, but
U address can only
of either
or
used in lathe programs. The
English dimensional units has no effect on the dwell funcis not dimensional.
tion whatsoever, as
DWELL TIME SELECTION
example illustrates a dwell of 500 milliseconds, or
one half of a
Again, all three formats are shown.
a CNC program, the dwell function may appear in the
dwell as a separate block:
following way - note
N21 1301 Z-l. 5 F12.0
N22 1304 XO.3
N23 Z-2.7 F8.0
1304 DODO
Leading zero suppression is assumed in the format withpoinl (trailing zeros are
out the
Pl
II:~ where
is equal to
(DWELL COMMAND O. 3 SEC)
Programs using X or U addresses may cause a possible
The X and U
confusion, particularly to new
may incorrectly be interpreted as an
motion.
This will never be the case. By definition, the X axis and its
is the dwelling axis. X axis is
lathe application, the U
common to all CNC machines.
the only
Seldom ever the dwell lime will exceed more than just a
seconds, most often much less than only one second.
Dwell is
a nonproductive lime
it should
selected as the shortest time needed to accomplish the required action. The time delay for completion of a particular
machine operation or a special machine accessory is usually
by
machine manufacturer. Selecting
redwell time for CUlling purposes is al ways
sponsibility. Unfortunately, some programmers often overthe dwell duration. After all. one second seems
short
but think about this example:
In one block of
program. a dwell function is assigned
The
speed is set to
for the duration of one
480 rlmin and the dwell is applied at
locatjons on the
part. perhaps during a
operation. That means the
dwell,
cycle lime for each part 50 seconds longer with
without
dwell. Fifty seconds may not
then it would
DWELL COMMAND
173
~ee~ too unreasonable, but are they really necessary? Give
Jl a Itnle thought or - even better calculate it If the dweU·
must
used at all,
sure to calculate
mlllllnum
dwell that can do the job. It is easy to
the dwell arbiby
and without much thinking. In
example, the minimum dwell required is only 0.125 seconds:
60 I 480
= 0.125
This minimum dwell is eight
less than
programmed dwell of one second. If
minimum dwell is
used rather
estimated dwelL the
wlll
crease by only 6.25 seconds,
than
50 sec- a significant improvement in programming effion the machine.
and productivity
Minimum dwell calculation and other issues related to it
are
shortly.
MINIMUM DWEll
During a cut,
is for operations where cuttino tool is
contact with the machined part,
tion is important, but
selting
or number of revolutions).
minimum d:ell definiis unimportant (time
Minimum dwell is the time
to complete one revolution of the spindle,
Minimum dwell, programmed
lated,
a simple
Minimum dwell (sec)
seconds, can
=
calcu-
60
r /min
C Example:
SETTING MODE AND DWEll
Most programs
machining centers will use feedrate
per lime (programmed in inches per minute - in/min - or
millimeters
minute - mrn/min).
applications are
normally programmed in
per revolution, as
revolution - in/rev - or millimeters per revolution mmlrev. On many Fanuc controls. a parameter setting allows programming a
in
the elapsed
in seconds or milliseconds - or the number ofspindle revolutions.
Each
has
practical uses and benefits.
pending on
parameter setting, the dwell comwill assume a different meaning with
setting:
• Time Setting
To calculate minimum dwell in seconds for spindle rotarlmin into sixty (there are 60
tion of 420 r/min, divide
in one minute):
60 I 420 = 0.143 seconds dwell
The format selection of dwell block in the program will
depending on the machine type used and a
programming
All following examples represent
same dwell time of 0.143 of a ;)",,",'uuu
G04 XO.143
G04 P143
G04 UO.143
Regardless which formal is used, all dwell values in
specify dwell time of 143
which is
a second. It is allowed to
m
one program, but such a practice
not represent consistent
slyle.
G04 PlOOO
... represents
mi lliseconds.
\
dwell of one second,
to 1000
• Number of Revolutions Setting
For the
of spindle revolutions
the dwell is
expressed as the number of
the spindle rotates, within
the
of()'OOI to 99999.999 revolutions, for example:
G04 P1000
... represents the dwell
of the spindle.
the duration
one revolution
practical dwell applications in a
program,
calculated minimum dwell is only mathematically correct
not be
most practical value to use. It is always
and
better to round off the calculated value of the minimum
example. the G04 XO.I may
dwell slightly upwards.
become 004 XO.2, or - if a double value is used - then G04
XO.143 wlll
G04 XO.286, or even G04 XO.3 LO
round off the
reasoning for this
takes inlO considerIt is quite normal that the
ation some machining
CNC
may be running 11 certain job with the
perhaps even set at its
speed in an override
at 50%. Since 50% spindle speed override is
minimum on most CNC controls, the double mini·
mum
will
at least one complete
of production lime.
revolution, without
174
24
NUMBER Of REVOLUTIONS
In the other dwell mode (selected
the
format
only
to
the same,
but
be much different. In some appJicafor a certain
desirable to program a
revolutions, rather than
for a
In a lathe
tion programmed to
groov i ng tool to
to clean up
time in secomlS
~ where ...
60
: : : Number of minutes (translation factor)
n
:::: Required number of spindle revolutions
r/min:::: Current spindle speed (revolutions per minute)
C) Example:
To calculate
die revolutions, at
can be applied:
Dwell~
in seconds for full three
of 420 rfmin, the formula
= 60 x 3 / 420 = 0.429
The program block
die revolutions in terms of
following forms:
• System Setting
G04 XO.429
If the control
G04 P429
G04 UO.429
is set to accept the dwell as the number of spindle revolutions, rather than as time in
or
is very straightforward. All
milliseconds, the
that is needed is to
the dwell command 004, followed
by the number of "-u"'''
I
"U
G04 >3.0
the required three spintime will take one of
It
a good
to
backwards and ca1cuthe equivalent ofdwell time, represented as the number
of spindle revolutions. Usually,
result will not be an innumber and will
rounding to the nearest value
upwards. The above formula can easily reversed:
G04 P3000
G04 m.o
Each format
same result - adwell in the durevolutions. How can we tell from
ration of three
means time or revolutions?
the program whether the
We cannol. We have to know the control settings. The only
input values of the dwell input.
clue may be the rather
3.0 revolutions are
shorter than 3.0 secon(]s
of dwell. Note that the
point is still written, to allow fractions of a
such as one half or one quarter of a revolution, for
• Time Equivalent
The two modes cannot
in one program deliberately and even between
the mix is difficult.
system parameter can
set to only one dwell mode
at a time. Since control
are normally set for the
rather than the dwell exdwell in seconds or mil
spindle revolutions, the equivapressed by the number
lenllime must be calculated.
spindle speed (in rlmin)
must always be known in
a case.
"<>''''''"'''1'1 number
formula:
to be equal to
the follow-
Example:
confirm that the formula is t'f\MrPI"I use the value of
of the previous example
the number of
revolutions for a d well of 0.429 "".rny",." at 420 rfmin:
""""=....",,,,,, = 420 x 0.429 / 60
3 . 003 revoluJions
confirms the formula is correct. It is more than
that the calculation will start with a dwell that js alrounded, for example, to one half of a
""W''''''''"rev '" 420 x 0.5 /
60 .. 3.5 re\l()f.UIj'IJ11S
based on a
revoluCNC
especially
slow spindle
A slow spindle
nOl have the latitude
and does
a
error in the dwell
Keep in
not allow
mind that the goal is to get ar least one complete part rotation in order to achieve desired
Otherwhy program dwell at all? Consider
DWELL COMMAND
Dwell is programmed for one half of a second duration,
with
spindle rotation set to 80 r/min. The
for one half a second
ao x 0.5 I 60 = 0.6666667
which is less than one complete spindle revolution. The
reason for programming the dwell function in
place is not honored
and the
lime has to
creased.
of 0.5 seconds is therefore not sufficient.
The
dwell has La
calculated,
the formula presented earlier:
60 x 1
I 80 = 0.75 seconds
Generally, there is not much use
type of calculations - most programming assignments can be handled very
well with the standard dwell per time calculations.
LONG DWELL TIME
For machining purposes on CNC machines, an unusually
long dwell
is neither
Does that
mean long dwell times are not
is the programmed time that is well
A long dwell
above the established average for most normal
Lions. Seldom ever there is a need to
dwell time
during a part machining in excess of one, two, three, or four
seconds. The
range available on the
system
(over 27 hours) more important to the nl(lintl'nat1a pnthan to
programmer. A~ an example of a
typical application when a long dwel1 may,be beneficial, is
a program developed by
maintenance technicians
testing the spindle functionality.
carefully the following actual situation common to machine
- a spindle of the CNC machine
has
repaired
must be
before the machine
can
baqk to production. The
will
consist of running the
at various
for a certain period time of
selection.
In a typical
the maintenance department rea small
program, In
the machine "'1.1' II,,","..
will rotate
10 minutes aL 100 r/min, then for
minutes at
r/min. followed by the spindle rotalion at
highest rate of 1500 r/min
additional 30 minutes.
program development is not an absolute
since the
maintenance technician may do the test by manual methmanual approach will not be very
but it
serve the purpose of the maintenance test.
cases is to Slore
testing proceA better choice in
dure as a
program, directly into
CNC memory.
maintenance (service) program wi)) be a little different
for machining centers than for
but the
objectives will remain the same.
175
e:> Example - Machining Centers Spindle test:
S100 'M03
G04 X600.0
SSOO
G04 X1200.0
S1S00
G04 X1800.0
MOS
(100 R/MIN mITIAL SPEED)
(600 SECONDS IS 10 MINUTES)
(SPEED INCREASED TO 500 R/MIN)
(1200 SECONDS IS 20 MINUTES)
(SPEED INCREASED TO 1500 R/MIN)
(1800 SECONDS IS 30
(SPINDI..:E:
The example for machining centers starts with the initial
spindle rotation of 100 rim in. That selection is followed by
the dwell of 600 seconds,
guarantees a 10 minute
constant run.
spindle speed is then increased to 500
r/min
the dwell lime to 1200
for
minutes.
last selection is 1500
spindle speed running far 1800 seconds. or
30 minutes, before the
spindle
stops.
e:> Example - lathes - Spindle test:
M43
G97 S100 M03
G04 X600.0
SSOO
G04 X1200.0
S1S00
004 X1800.0
(GEAR RANGE SELECTION)
(100 R/MIN mITIAL
(600 SECONDS IS ~o MINUTES)
(SPEED DlCREASED TO 500 R/MIN)
(1200 SECONDS IS 20 MINUTES)
(SPEED DlCREASED TO 1500 R/MIN)
(1800 SECONDS IS 30 MINUTES)
MOS
(SPlNDLE
is very similar to
one for a mafirst
The initial spindle speed
range
for example. M43.
spindle
been set to 100 r/min. The
of
follows,leaving the spindle rotating for full Ja
minutes. Then the speed is increased to 500 r/min and remains that
for another minutes (1200 seconds).
fore the
is stopped, one more
is done - the
spindle speed increases to 1500 r/min and remains at that
for another 30 minutes (1800 seconds).
• Machine WarmaUp
A similar program (typically a subprogram) that uses a
long dwell time is favored by many CNC programmers and
CNC
operators, to 'warm-up' the machine before
running a critical job. This
warming activity takes
place typically at the start of a morning shift during winter
months or in a cold shop. This
aImachine to
a
ambient t",n'lT\Pr",tl
before any precisian components are machined.
same
approach can also be used to gradually
the maximum
spindle speed for high-speed machining (5000 r/min and
up). As usually, all safety considerations must have a high
priority in all cases.
1
24
• X Axis is the Dwelling Axis
control display screen shows how much time is still
the dwell time expires.
can
by
lV'-'!·'.H,,o:. at the X display of the
(position) screen of a typical
will
be
as X.
regardless of
P or are programmed. Why the
,,"',,_ ......._u as the dwelling axis and not any
is a
reason - because the X axis is the only
common to all
machine tools - i.e.,
machines,
mills, machining centers. flame cutters,
and so on. They all use XYZ axes.
(there is no Y axis) and wire EDM uses
no Z
machines are similar.
• Safety and Dwell
reminders have
a great degree of caution
dwell limes. particularly
or
'1"1""""''''''' The CNC machine should never be
unattended. In case of long
for
warning signs should be prominently
posted to prevent a potentially unsafe situation. If
are not
someone else should
chine serviced,
,,"YPTr''''''''
fiXED CYCLES AND DWELL
Chapter
of
handbook covers the subject of fixed
cycles for CNC mach in i ng centers and dri lis in a
detail. In-deplh descriptions of all cycles can
this
For
purpose of the current topic,
are
just some comments relative to the subject of dwell, this
time, as the dwell
to fixed cycles.
Several fixed
o
Normally,
o
Also cycles
program control!
GSB,GS9
and G84, only by parameter setting
cycles is always P, to avoid duin the same block. The address U
and the command
are never programmed in a
cycle - the dwell function is 'built' into all fixed cycles thal allow the dwell
(technically all cycles do).
dwell time remain the same
rules for
fixed cycles, as for any
machining application.
The dwell
Q Example.
N9 GB2 Xl.2 YO.o RO.2 Z-O.7 P300 F12.0
live upon
motion), but
tool or
sel1
inspection, lubrication, etc.,
must
if absolutely necessary
gram execution ~ as a manual operation, never
can be programmed with a
- 0.3
dwell will become
motion along the Z axis (actual
rapid return motion.
If a 004 P.. is programmed as a separate block in a fixed
cycle mode, for example between the G82 block and the
in that block and the
block, no cycle will be
definition is not updated. On
value of P in the fixed
the/latest controls, a system
setting enables or
disables this usage. If this
is used, the command
G04 P.. will be active
tool rapid motion from
location just completed.
function will always
is out of a hole, in the clear
executed while the cutting
This feature is seldom Y~""'lIr~'fl
FIXED CYCLES
Machining holes is probably the most common
tion, mainly done on CNC milling machines and
iog centers. Even in the
traditionaJly known for
their complex parts,
and aerospace components manufacturing,
instrumentation, optical
holes is a vital part
or mold making industries,
of the manufacturing nr-r,rp.,~<.:
When we think of what machining holes means, we
probably think first of such operations as center drilling,
spot drilling and standard drilling, using common tools.
However, this category is
wider. Other related
tions also belong to the category of machining holes.
standard center drilling, spot drilling and drilling are
together with related
as
tapping.
point boring.
tools, countersinking
even backboring.
Machimng one simple hole may
only one tool but
and complex hole
several tools to be
Number of holes
a given job is important for selection of proper ,..,,.,..,. . . rJ:l'mnnl approach.
holes machined with
having the same
they may even be at
combinations are
Illd'lUlIl~ one hole may be a ::.111111111;;'
many different hole
a well planned anu
In
of programming applications. hole operaa great number of similarities from one job to
another. Hole machining is a reasonably predictable operation and
operation that is
is an ideal subject
to be
very efficiently by a
For this reason, virtually aU CNC control manufacturers have incorpoingenious
for
in their control
use so the
or - morecnmmnnly - Ihefixed cycles.
POINT-TO-POINT MACHINING
method of point-to-point machining for holes is a
method of controlling the
of a cutting tool in
X
Y axes at a rapid
rate, and in the Z
at a
cutting feed rate. Some motions along Z axis may also include rapid motions. All this means is that there is no cutting along XY axes for
operations. When the
tool completes al [ motions
the Z axis and returns
from the hole to the
position, motions
to a new
X
Y axes resume and
the Z
are repeated. Usually, this
of motions occurs at
locations. The hole
and
is
by
cutting tool
Ihe cutting depth is controlled by the part program.
method of machining is Iypical to fixed cycles for
reaming, tapping, boring and related operations.
elementary
structure for point-topoint machining can
four general
(typical drilling sequence shown in
example):
Rapid motion to the hole location
... along the Xand/or Yaxis
a
Step 1:
a
2:
Rapid motion to
... along the Z axis
o
3:
Feedrate motion to the spe:ClTIl90 depth
... along the Zaxis
o
4:
Return to a clear position
... along the Zaxis
point of the cut
four
also I'pn,r.,<:"nr
required to program a
programming method, without
is only one or two holes a
is
more
a
program length is of no
imporis not the common case - normally, there are
in a part and several tools
to be used to
hole to engineering specifications. Such a
difficult Lo inLerprogram could be extremely loug and
pret and
In fact, it may even
too long to fit into
the
memory.
Machining holes is generally not a very sophisticated
procedure. There is no contouring required and there is no
multi axis
motion. The only
when actual
is along a single
- virtually always
cutting
lype of machining is commonly known as
the Z axis.
point-to-point machining.
177
178
25
• Single Tool Motions VS. Fixed Cycles
following two
compare
programming a hole pattern in individual
where each
of the tool
must be
as a
~ingle motion
and
same pattern
using a
cycle (02502). No explanations lO the programs are
at this stage
comparison is only a visual
Lration between two distinct programming methods, It
shows an application of a 03116 standard drill Ihat is used
inches. Only
holes are
to cut a full blind depth of
lf1
programmed in the example,
NS G99 GS2 RO.I Z-O.6813 P200 F4.5
N6 X3. S7 Y3. 4
N7 X2. 047
N8 GSa G28 X2.047 Y3.4 ZI.O M09
N9 M30
%
02501 required the total of 18 blocks, even
cycles,
three
only. In program 02502,
only nine blocks were needed.
shorter program 02502
is also easier to
there are no repetitious blocks. The
moditications, updates and olher changes can be
much
whenever required.
use
cymachining holes, even if a single
is machined.
FIXED CYCLE SELECTION
Y3.40
->-1--+----'
25·1
Simple hale
Y1.89
- programs 02501 and 02502
02501 (EXAMPLE 1)
(PROGRAM USES INDIVIDUAL BLOCKS)
Nl G20
N2 Gl'7 G40 GSa
N3 G90 G54 GOO X5.9 Yi.89 S900 M03
N4 G43 Zl.0 HOl MOB
N5 ZO.l MOB
N6 GOl Z-O.6S13 F4.5
N7 G04 P200 ,_
NS GOO ZO.l
N9 X3. 8'7 Y3.4
NlO GOl Z-O.6B13
Nll G04 P200
Nl2 GOO ZO.l
Nl3 X2.047
Nl4 GOl Z-O.6813
Nl5 G04 P200
Nl6 GOO ZO.l MOg
Nl7 G28 X2.04'7 Y3.4 Zl.0
NlS IDO
fixed cycles
by control
turers to eliminate
in manual programming
and allow an easy program data changes at
machine.
For
a number of identical holes
same starling point, the same depth, the same
same dwell. etc.
X and Y axes locations are
ent
each hole of
pattern. The
the
des is to
for programming
once - for (he first hole of the pattern. The
become modal for the duration of the cycle
Lo
repeated,
and until one or more
change. This
is usually for
location
new
but other
may be
for any hole at
lime,
for more complex holes.
A fixed
is called in
program
a
ratory G command. Fanuc and similar control
the following fixed cycles:
High speed peck drilling cycle
G74
Left-hand tapping cycle
G76
cycle)
GSO
Gal
G82
Drilling cycle with dwell
G83
Peck drilling cycle
G87
Back boring cycle
GSB
Boring cycle
Ga9
Boring
%
The second
hole pattern, but
uses
same
efficiency.
, , L. " J L
02502 (EXAMPLE 2)
(PROGRAM USES FIXED CYCLE)
Nl G20
N2 Gl1 G40 GSO
N3 G90 Gs4 GOO XS.9 Yl.89 S900 M03
N4 G43 Zl.O HOl MOB
FIXED CYCLES
179
The list is only generaJ and indicates the most common
use of each cycle, not always the only use. For example, certain boring cycles may be quite suitable for reaming, although there is no reaming cycle directly specified. The
next section describes programming format and details of
each cyde and uffers suggesliuns fur their proper applications. Think of fixed cycles in terms of their built-in capabilities, not their general description.
PROGRAMMING fORMAT
Z = Z axis end position = Z depth
o Position at which the reedrate ends
The Z depth position can have an absolute value ot an incrementaJ value.
P = Dwell time
o
General format for a fixed cycle is a series of parameter
values specified by a unique address (not all parameters are
available for every available cycle):
IN .. G.. G.. X.. Y.. R.o Z.. P.. Q.. 1.. J.. F.. L.. (or K.. )
The dwell time is practically applicable only to G76,
G82, G88 and G89 fixed cycles. It may also apply to G74,
G84 and other fixed cycles, depending on the control parameter setting.
o
Dwell time can be in the range of 0.001 to 99999.999
seconds, programmed as Pl to P99999999
Explanation of the addresses used in fixed cycles (in the
order of the usual block appearance):
___________N
__=__
BI_o_ck__n_um
__b_e_r__________~
.
'-
I
Within the range of Nl to N9999 or Nl to N99999, depending on the control system
G (first G command) = G98 or G99
o
G9a returns tool to the initial Z position
o
G99 returns tool to the point specified by the address R
o
Q= Address Q has two meanings
I'----------------------------------~
0
When used with cycles G73 or G83,
it means a depth of each peck
o
When used with cycles G76 or G87,
it means the amou nt of shift for bo ring
The addresses I and J may be used instead of address Q.
depending on the control parameter setting.
I = Shift amount
G (second G command) = Cycle number
o
0.9IY one of the following G commands can be selected:
The I shift may be used instead of Q ~ see above.
G73
Ge4
G74
Gas
G76
Gel
G86~. GS7
Ge2
GSS
Must include the X axis shift direction for
boring cycles G76 or G87
Ge3
Gag
J
x = Hole position in X axis
'--________
Y_=__H_O_le__
p_OS_j_tio_n__in__
Y_a_X_is________
= Shift amount
Must include the Y axis shift direction for
o
boring cycles G76 or G87
The J shift may be used instead of the Q - see above.
X value can be an absolute or incremental value
~1 1~
Y value can be an absolute or incremental value
R = Z axis start position = R level
o
Programmed in milliseconds (1 second = 1000 ms)
________
o
Applies to the cutting motion only
ThiS value is expressed in in/min or mmlmin, depending
on the dimensional input selection.
Position at which the cuning feedrate is activated
The R level position can have an absolute value or an incremental value.
s_pe_c_if_i~__t_io_n________~
F_=__F_ee_d_r_a_te__
L (or K) = Number of cycle repetitions
Q
Must be within the range of LO - L9999 (KO - K9999)
II (Kl) is the default condition
180
Chapter 25
GENERAL
tions,
discipline - it means
there are jimitaprogramming is not a
a lot with it. We talk
are
language programming but
about a Fanuc or
gramming, a Milsubishi or
example. Fixed cycles are
a
GOO Gal x .. Y.. R .. Z .. P .. Q.. L •• F ..
fixed cycle is processed, while in
Gal GOO X.. Y.. R.. Z.. P .. Q.. L .• F ••
fixed cycle is JIot processed, but
be performed; other values will
tion of the F feedrate value, which is
Consider fixed cycles as a set
ules - modules that contain a
grammed machining instructions.
'fixed" because their internal format cannot
These program instructions relate LO
predictable tool motion that rpn,""'lc
sic rules and restrictions
to
summed up in the following items:
a
Caution: In case of
command
.and a motion command of Group in
same block, the
order of programming those commands is
important
Absolute or incremental mode of
established before a fixed cycle is
anytime within the fixed cycle
uations at all costs!
In this chapter, lhe individua1 fixed cycles are
in detail and each cycle has an illustration of
can
or
structure.
illustrations use shorthand graphic symbols. each with
meaning. In Figure 25-2, the meaning of all symused in the illustrations is described.
---"l>
Rapid motion and direction
Cutting motion and direction
G90 must be programmed to select the absolute
G91 command is required to select the incremental
Manual motion and direction
a
Both G9D and G91 modes are modal!
Boring bar shift and direction
a
If one of the X and Yaxes is omitted in the
mode, the cycle will be executed at the .",,,,,,,tu.1'I 1/'lI~l'Il'I/'n
of one axis and the current location of the
o If both X and Y axes are omitted in the fixed cycle
the cycle will be executed at the current tool position.
a
If neither G98 nor G99 command is programmed for a fixed
cycle, the control system will select the default command
as set by a system parameter (usually the G98 command).
o
Address P for Ule dwell time designation cannot use a
decimal point (G04 is not used) - dwell is always
programmed in millisecon~s.
SymbOts and abbreviations used in fixed cvcles illustrations
\
o
a
If LO is programmed in a fix'ed cycle block, the control
system will store the data of the block for a later use, but
will not execute them at the current coordinate location.
ABSOLUTE AND
VALUES
The command GaO will always cancel any active fixed
cycle and will cause a rapid motion tor any subsequent
tool motion command. No fixed cycle will be processed
in a block containing GSO.
~ Example:
GSO Z1.125
Gao GOO Zl.125
is the SOJ11eGS
or
GOO Zl.12S
01, namely GOO, G01,
are the main motion comany
fix.ed cycle.
method
lated to the point of origin program zero,
menIal method, the XY position of one hole is
from the XY position of the previous
the distance from {he last Z value, one established
calling the cycle, to the position where
vated. The Z depth value is the
and the termination of feed rate motion. At
fixed cycle, [001 motion 10 the R
will
rapid mode,
FIXED CYCLES
181
INITIAL
LEVEL
INITIAL
LEVEL
/--/
--->t
R
- R LEVEL
lO--+-
From the practical point of view. always select this posilion as the safe level - not just anywhere and not without
some prior thoughts. It is important that the level to which
the tool retracts when G98 command is in effect is physically above all obstacles. Use the initial level with other
precautions. to prevent n collision of the cutting tool during
rapid motions. A collision occurs when the cutting tool is in
an undesirable contact with the part, the holding fixture, or
the machine itself.
~ Example of the initial level programming:
Figure 25-3
Absolute and incremental input values for fixed cycles
The following program segment is a typical example of
programming the initiaJ level position:
NQl G90 G54 GOO XlO.O Y4.S Sl200 M03
NQ2 G43 Z2. 0 HO 1 MO B (INITIAL LEVEL AT Z2. 0)
Nl3 G98 GBl XlO.O Y4.S RO.1 Z-O.82 F5.0
INITIAL LEVEL SELECTION
Nl4
There are two preparatory commands controlling the Z
axis tool return (retract) when a fixed cycle is completed.
G98
.. , will cause the cUlling 1001 10 retract to
the inilial position = Z address designation
G99
... will cause the cUlling tool to retract to
the R level position R address designatioll
=
G98 and G99 codes are used for fixed cycles only. Their
main function is to bypass obstacles between holes within a
machined pattern. Obstacles may include clamps. holding
fixtures. protruding sections of the part, unmachined areas,
accessories, etc. Without these commands, the cycle would
have to be canceled and the tool moved to a safe positIon.
The cycle could then be resumed. With the G98 and G99
comm\1nds, such obstacles can be bypassed without canceling the1ixed cycle, for more efficient programming.
InitiaJ level is, by definition~e absolute value of the last
Z axis coordinate in the program - before a fixed cycle is
called· Figure 25-4.
INITIAL LEVEL
R LEVEL
---++--'-- lO
(Z DEPTH)
Figure 25-4
Initial level selection for fixed cycles
N20 GBO
The fixed cycle (G8! in the example) is called in block
N 13. The last Z axis value preceding this block is programmed in block NI2 as Z2.0. This is setting of the initial
position - lwO inches above ZO level of the part. The Z level
can be selected at a standard general height, if the programs
are consistent, or it may be different from one program to
another. Safety is the determining issue here.
Once a fixed cycle is applied, the initial Z level cannot be
changed, unless the cycle is canceled first with G80. Then,
the initial Z level can be changed and the required cycle be
called. The initial Z level is programmed as an absolute
value, in the G90 mode.
R LEVEL SELECTION
The cutting Lool position from which the feed rate begins
is also specified along the Z axis. That means a fixed cycle
block requires two positions relating to lhe Z axis - one for
the start point at which the cutting begins, and another for
the end point indicating the hole depth. Basic programming
rules do not allow the same axis to be programmed more
than once in a single block. Therefore, some adjustment in
the control design must be made to accommodate both Z
values required for a fixed cycle. The obvious solution is
that one of them must be replaced with a different address.
Since the Z axis is closely associated with depth, it retains
this meaning in all cycles. The replacement address is used
for the 1001 Z position from which the cutting feed rate is
applied. This address uses the letter R. A simplified term of
reference to this position is the R level. Think of the R level
in terms of 'Rapid to star! point', where the emphasis is Of!
the phrase 'Rapid to' and the letter 'R' - see Figure 25-5.
182
Chapter 25
Z DEPTH CALCULATIONS
fixed cycle must include a depth of cut.
is the
at which the cutting tool stops feeding into the maleDepth is programmed by the Z address in the
block. The
point for the depth cut is programmed as a Z
value, normally lower
the R level
the initial level.
Again,
087 cycle is an exception.
(Z DEPTH)
Figure 25-5
R level selection for fixed
of cutting .£>"",... .. ".'"
it is also the Z
to which
cutting tool will retract
upon cycle completion, if preparatory command G99 was
programmed. If G98 was programmed,
retract will
to the
level. Later, the G87 back boring cycle will
described as an exception, due to its purpose, This cycle
not use G99 retract mode, only G98! However,
all
the R level
must be selected carefully. The
most common values are .04-.20 of an inch (I mm) above
the part ZOo Part setnp has 10 considered as well, and
justments to the setting
if necessary.
L.VL..u."I.
or four
R level usually increases about
tapping operations
cycles G74
G84, to
feedrate acceleration 10 reach
maximum.
To achieve a
of a high quality, always make a
cffort to program the calculated Zdepth accuratelyexactly, without guessing its value or even rounding it
off. It may tempting to round-off the
depth
.6979 to .6980 or even to
- avoid it! It is not a question
of triviality or whether one can
away with it. It is a malter of principle
programming consislem.:y. With this apand
it will be so
easier to retrace the
cause of a problem, should one develop later.
.:>vv........
for
the
c::> Example of Alevel programming:
N29 G90 GOO GS4 X6. 7 YB. a S850 M03
N30 G43 Z1.0 H04 MOB
(INITIAL LEVEL IS 1. a)
N31 G99 G8S RO.l Z-1.6 F9.0 ® LEVEL IS 0.1)
N32
N45 Gao
initial level in the example is in
N30, set to
.0. The R
is set in block N3) (cycle
block) as
,100 inches.
same block, the G99 command is programmed
during the
That means
the tool
will
above pan zero at the stall and
end of
When the tool moves from one hole to the
next, it moves along the XY axes only at this Z height level
.100 above work.
pO.'\ilion is normally lnwPr
Ihe initial
The R
level position. If these two levels coincide, the start and end
points are equivalent to
initial position. The R
is
commonly programmed as an
value, in
but
into an incremental mode
I. if the
application
from such a change.
Z depth calculation is
Q
Dimension of
on the following criteria:
hole in the drawing (diameter and depth)
o Absolute or incremental programming method
o Type of cutting tool used + Added tool point length
Q
Material thickness or full
depth of the hole
o Selected clearances above and below material
(below material clearance for through holes)
On
machining
the ZfJ is
programmed as
top of finished part face. In
case, the
of Z address will always be programmed as
absolute
a negative value, Recall
the absence of a sign in an axis
address means a positive value of that
This
has one strong advantage. In case
programmer
to write the
!l.lgn, the depth value will automatically
.--'·".....'A a positive value. In that case, the
tool will
the part,
area. The
move away
easily corpart program win not be
rected, with only a loss
c::>
of Z depth calculation:
illustrate a practical example Z depth
We will use a 0.75
consider the hole detail in Figure
inch drill to
a hole, with a full depth
a standard
drill is
the tuullip
consideration. Its design has a typical 1
to 1200 point
and we have (0 add an additional .225 inches 10 the
depth:
.3 x .75
.225
2.25 + .225 = 2.475
total Z depth of 2.475
G99 G83
can
X9.0 Y-4.0 RO.1 Z-2.47S Q1.125 F12.0
FIXED
81
RO.1
Z0
"""""'7"777"7i--t7:'177""'7'7'7 -
_.."J~<,~~~-,;'-- Z-2.25
~</7"/,fnL/C:/c","-
ABSOLUTE
INCREMENTAL
Figure 25-6
Z depth calculation for a drilling fixed cycle
A peck drilling cycle
machining, although
for G81, G82 or G73
tion is described in
--++--i-- 20
z- 2.4 75
25-7
G81 fixed
is used in the example for best
Z
would be the same
tool point length calculain Chapter 26.
lVVII~I:IIIV used for drilling
• Ga2· Spot-Drilling Cycle
DESCRIPTION- OF FIXED CYCLES
Description of Ga2 cycle
motion to XY position
In order to understand how each fixed cycle works, it is
structure of each cycle
important to understand the
and details of its programming format. In the following
descriptions. each fixed
will be evaluated in detail.
The cycle heading'
programming format
of the cycle, followed by the explanation the exact operaof each cycle will
tional sequences. Common
also be described.
All these details are important
a help in understanding the nature of each
as well as
cycle
to select for the best machining
As a bonus, the
knowledge of the internal
structure wiB help in deIn
area of cussigning any unique cycles,
tom macro programming.
• G81 - Drilling Cycle
WHEN TO
Drilling with a dwell tool pauses at the hole bottom. Used for
center drilling, spot drilling, spotfacing, countersinking, etc. anytime a smooth
is
at
bottom of hole. Often
used when slow spindle
needs to be programmed.
If used for boring, the G82 cycle will produce a scratch mark
on the hole cylinder during retract.
-<~
G98 (G99) G81 X.. Y.. R..
Step!
5
. ,
G82
Description of GBl Cycle
"C"",,'"''''
1
I Rapid motion LO XV position
2
I Rapid motion to R Level
3
I reedrate motion to Z depth
4
I Rapid retract to initial level (with G98)
or Rapjd retract to R level (with G99)
DWELL
WHEN TO USE 681 CYCLE - Figure 25-7 .
Mainly for drilling and center
Z depth is not
If used for
produce a
on the hole
a dwell at
the G81 cycle will
during retract.
Figure 25-8
G82 fixed cycle - typically used for spot drilling
184
Chapter 25
• GSJ - Deep Hole Drilling Cycle - Standard
Step
1
2
Rapid motion to R level
3
Feedrale motion \0 Z deplh
by the amount of Q value
4
retract by a clearance value
(clearance value is set by a system parameter)
5
Feedrate motion in Z axis by
the Q amount plus clearance
6
Items 4, and 5 repeal until the
programmed Z depth is reached
7
Rapid retract to iniliallevel (with 098)
or Rapid retract to R level (with 099)
WHEN TO USE G73 CYCLE· Figure
Rapid motion to the
depth less a clearance
(clearance is set by a system parameter)
6
Items 3, 4, and 5 repeat until the
Z depth is reached
7
Rapid retract to initial level (with 098)
or Rapid retract 10 R level (with G99)
WHEN TO
10:
For deep hole drilling, also known as peck drilling, where the
chip breaking is more important than the
retract of the drill
from the hole. The G73 cycle is often used for a long series
drills, when a
retract is not very important.
The G73 fixed cycle is slightly faster than the
cycle,
the name 'high speed', because at the time saved by not
retracting to the R level after
peck. Compare this cycle
with the standard deep hole drilling cycle G83,
G83 CYCLE - Figure 25-9 :
For deep hole drilling, also known as peck drilling, where the
drill has to be retracted above the part (to a clearance position)
after drilling to a certain depth. Compare this cycle with the
high speed deep hole drilling cycle G73.
G99
G83
Q
G98
Q
Q
- - - - - - - - - " -.. . .- .....~ Z DEPTH
·:::=d
Figure 25-10
G73 fixed cycle - typically used far deep hole driJling
(this cycle does not retract to R level after each peck)
-,0--- Z'DEPTH
Number of pecks calculation
Figure 25-9
G83 fixed cycle - typically used for deep hole drilling
(this cycle retracts to R level after each
• 613 - Deep Hole Drilling Cycle· High-Speed
Description of G73
motion to XY position
2
Rapid motion to R level
3
Feedrate mOlion to Z depth
by the amount of Q value
When using
G83 and G73 in the
always
have at least a reasonable idea about how many pecks will
the tool
in each hole. Unnecessary
drilling of
will accumulate
total
hundreds or thousands of
can very significant. Try 10 avoid
lost time. which can
too many pecks
hole. For predictable results,
the number of
number of pecks calculation applies equally to both
fixed cycles. Calculation
the number of
in
G83 and G73 is
on the
of the Q
<>/""I,.lrp"", and the
distance between the R level and Z
depth not from the top of part! Dividing this distance
the
Q value will
a number of
tool will make at
hole location. The number of
in a cycle must
an integer and fractional calculamust always rounded upwards:
G83 and
FIXED
185
Q Example 1 - English data:
G90 G98 GS3
x .. Y •. RO.1 Z-L4567 QO.45 F .•
In the example,
depth is 1.5567
of pecks can be
between the R
the Q value is .450, so the
and Z
1.5567 I .45 = 3.4593333
The result has too
used as is, because most
places for English units
units. The result must
The result of the
must be rounded to
18.667 or 18.666. Although it looks that only on.e
(0.00] mm) is at
it will make a big difference
way the rounding is
If only three pecks are
round off upwards, (0 Q I
CUt 1
CUt :2
CUt 3
l8.667
18.667
lS.666
Total
56 mm
If the result is rounded
to Q I 8.666, the numof pecks will be four and practically no cutting will take
during the last peck:
is four, so each hole will reThe nearest higher
quire four pecks. The
cannot be changed, so
only other available
to change the number of
is to change the R level
the depth of each peck. The
to
top face of part as is practiR level is usually as
cal, so there is not much
can be done there. That leaves
peck. By increasmg this
the Q value, the depth of
the total number of
will be fewer, by
ing the Q value, the total number of pecks will be higher.
CUt 1
CUt 2
CUt 3
18.666
18.666
18.666
CUt 4
0.002
Total
56 mm
4 • English
In this example, the distance
is
inches and four
Q Example 2 - Metric
G90 G99 G73 x.. Y.. R2,S Z-42.S Q15.0 F ..
Q : 2.5 I 4 = .625
example, the
between the R level and Z
depth is exactly 45 mm and the Q value is ]5 mm. The
suit jn exactly four pecks. each of
number of pecks will be 45
exact value of 3. No
of pecks executed per
by 15, which equals to
and the num-
In order to increase
change the current Q
R level and Z
are required:
case, no rounding is uO;;;.... O;;;:>:><11
QO.625 will redepth.
drilling value of Q
hole - all pecks in a
cannot be changed
will have an equal
the possible exception
peck. If the
amount is greater than the remaining distance to
Zdepth. only that
will be drilled.
In order to decrease the number of pecks.
change the current Q value to a
number.
if it is actually cala precise numthe R level
The result
:><;;,l\:; .... L~~U number of
Q value can be manipUlated in
(he Q value skillfully,
as an exact position of
penetration, This method is
IS necessary,
the number of pecks may nc','",,,,,P
any cycle time benefits.
Q Example 3 the distance between
R level and Z
IS
mm. and exactly three pecks are required. The
calculation of each peck depth is simple:
56 / 3
= 18.666667
part fixturing,
of material and other
tool can withstand.
depth of peck~ consider the overfor the job. The setup rigidity, the
of cutting tool, the machinability
contribute to what the
The goal in
gram under
That means n .. (\l'f"'~1"n
deepest Q amoum thal is reasonable and practical
Always jeep in mind that
particular job and its
are two fixed
the standard G84 and the
ten neglected
186
• 684 - Tapping Cycle - Standard
Description of G74 cycle
G98 (G99)
motion to XV position
The sequence of G84 fixed
is based on the normal
initial spindle rotation <>1-", ........."'.... by M03.
The tap design must be
G84 cycle with M03 "'1-'''-'->\......"
Step
motion to R level
hand design for the
in effect.
Description of G84 cycle
1
Rapid motion to XV !JV~'l"\.'ll
2
Rapid motion to R
6
7
eedrate motion to Z
pindle rotation stop
Spindle rotation reverse (M04)
and retract to initial level (with 098)
or remain at the R level (with G99)
WHEN TO
5
Spindle reverse
(M04) and
feedrate back to R level
6
Spindle rotation stop
7
Spindle rotation
(M03) and
retract to initial level (with
or remain at the R level (with 099)
WHEN TO USE 684 CYCI£ -
Figure 25-12 :
hand thread. At the start of
die Irotation M04 must be in effect.
various techniques of hole macnrnH""lUn'u""
notes cover only the most important tapand apply equally to both
11 :
Only for tapping a right hand thread. At the start of cycle,
the normal spindle rotation M03 must be in
G84
Q
Q
Feedrate selection for the tap is very important.
In tappinIL there is a
relationship between the
spindle speed and the lead of the tap - this relationship
must be maintained at all timas.
Q
The override switches on the control panel used for
spindle speed and feedrate, are ineffective
G84 or G74 cycle prol:ess.mg.
o
Tapping motion
even if the feSll:lMla
is ", ..",s,.. ,
processing, for safety reasons.
G98
?
SPIN
Rlevel should
in the tapping cycle than in the
other cycles to allow for the stabilization of the feedrate,
due to acceleration.
cw
- - - i - f - - - t - - ZO
G74
25-11
G84fixed
eXC./USII'IBIV used for right hand tapping
G98
ccw
•
The
initial
The
cycle
- Tapping Cycle - Reverse
of G7 4 fixed cycle is based on
rotation - M04.
must be of the left hand design for the
rotation in effect
.:>1-'111 .....""
cw
Figure 25-12
G74 fixed cycle - exclusiveJy used for left hand tapping
CYCLES
•
- Boring Cycle
WHEN TO USE 686 CYCLE
boring rough holes or
machining operations. This
cycle GB 1. The difference is
Step
USE G85 CYCLE· Figure
that require additional
cycle is very similar to the
spindle stop at the hole bottom.
NOTE - Although this cycle is somewhat similar to the G81
cycle, it has characteristics of own. In the standard drilling
cycle Gal, the tool retracts while the spindle ofthe machine
tool is rotating, but the
is stationary in the G86 cycle.
Never use the GaS fixed cycle for drilling - for example, to save
. since any deposits of
material on the drill flutes may
damage the drilled surface of the
or the drill itself.
Rapid motion to XV
WHEN
14 :
13:
INDLE CW
boring cycle is typically used for boring and rPRmlfifi
operations. This cycle is used in cases
the tool motion
into and out of holes should
finish, its
dimensional tolerances and/or concentricity, roundness, etc.
If
for boring, keep in
that on some parts
amount of stock may be removed while the cutting tool
This physical
is due to the
tool pressure during retract If the
finish gets
worse rather than improves, try
another boring cycle.
20
G8S
- typically used for rough and semifinish
• G81- Backboring Cycle
There are two programming r",..,m!;!t<:: available for the
backboIing fixed cycle G87 - the
one (using Q) is
more common than the
I and J):
Figure 25-13
G85
- typically used
and lBi1rlllllU
Step
• G8G· Boring Cycle
2
Spindle rOlation SLOp
Rapid molion to R level
4
Spindle rmarion stop
5
Rapid retract to initial level (with 098)
or Rapid retract to R level (with G99)
6
Shift in by the Q value
or shift back in the opposite direction of! and J
7
Spindle rotation on (M03)
8
Feedrate motion to Z
188
Chapter 25
9
Spindle rotation stop
10
Spindle orientation
11
Shift out by
Q value
or shift by the amount and direction of I and J
12
Rapid retract to iniliallevel
13
or shift
14
Spindle rotation on
Spindle rotation stop (feedhold condition is
and the CNC operator switches 10
manual operation mode and
a manual
then
10 memory mode).
CYCLE START will return to normal cycle
5
Shift ill by the Q value
WHEN TO
e rotation on
in the opposite direction of I and J
WHEN TO
G87 CYCLE Figure 25-15 :
is a special cycle. It can only be used for some (not all)
backboring operations Its practical usage is limited, due to the
~pecial tooling and
Use the G87 cycle only
If the
costs can be
economically. In most cases,
reversal of the part in a secondary operation is an option.
CYCLE -
25-16 :
T~e GSS cycle is rare. Its u~e is limited to boring operations
With speCial tools that require manual interference at the
bott~m of a hole. When such a operation is completed, the
tool IS moved out of the hole for
reasons. This
may be used by some tool manufactures for certain operations.
.I
I G88
NOTE - The boring bar must be set very carefully. It must
preset to match the diameter required for backboring. Its
bit must
set in the spindle oriented mode, facing
the opposite direction than the shift direction.
ON
G99
--~-:~zo
-~ Q ~--
_----.1.-4-_,(_
Z DEPTH
G98 ONLY
---~-zo
25-16
G88 fixed
. used when manual ""'Il>"""'~" is 'HHlI""'"
. Z DEPTH
,
•...SPINDLE START
• Ga9· Boring Cycle
-- R
figure 25-15
G87
cycle - t:}(GIUSI'VBIV used for backboring
• GSS - Boring Cycle
Step
Description of GSB cycle
Rapid motion (Q XY position
Rapid mOlion to R level
3
Feedrate motion to Z depth
4
Dwell at the depth - in milliseconds (P .. )
5
6
etract to initial level (with G98)
in at R level (with
WHEN TO USE G89 CYCLE Figure 25-17 :
boring operations, when
feedrate is required for the in
and the out directions of the machined hole, with a specified
dwell at the hole bottom. The dwell is the only value that
distinguishes the
cycle from
G85 cycle.
FIXED CYCLES
189
I G89
---l Q r--
.. ~ G98
[
G99
----+-~--+---zo
DWELL
z
~--->--- Z DEPTH
25-17
689 fixed cycle - 'typically used for boring or reaming
figure 25-18
676 fixed cycle typically used (Dr high quality boring
fiXED CYCLE CANCELLATION
• G16 ~ Precision Boring Cycle
is a very useful cycle for high quality holes. There
are two programming formats available for the precision
fixed cycle G76 the first one
Q) is much
I and 1):
more common than the second one
Any fixed cycle
is active can be canceled with the
GSO command.
is automatically transferred to a rapid mOltlon
GOO:
N34 GSO
N3S XS.O Y-S.75
Block N35 does not
plies it. This is a
the rapid motion, it only improgramming practice, but speci-
fied GOO as well may be a personal choice, although not
necessary:
N34 GSO
N3S GOO XS.O Y-S.75
milliseconds (P~) (ifused)
N34 GBO GOO XS.O Y-S.7S
6
cases,
7
8
Both of the examples will prOiaU(~e identical results.
even be a
choice.
second version of the
A combination of the two
is
a
choice:
I and J
retract to initial level (with
or remain at R level (with G99)
rather small, but
cycles. Althe cycle, it is a
though GOO without G80 would
poor programming practice that should be avoided.
are very important to
------------------~
FIXED CYCLE REPETITION
10
WHEN
When a selected frxed cycle is pro,granmrled
676 CYCLE - Figure 25-18 :
cycle is processed
once at
vvJ.J,......... u:v.......
tion within a part. This is the
the assumption that most holes
In the CNC program, there
f'r.rnn"\'''nr1 that would indicate
cycle. That is true, the cornmana
it
In fact. the """"'11".,..,,,1"11"'' '
is to be done just once LLVLJLLL<U
Boring operations, usually those for hole finishing, where the
quality of the completed hole is very important The quality
may be determined by the hole dimensional accuracy, its
high surface finish, or both.
The G16
parallel to
is also
axes.
to
holes cylindrical and
190
Normally, the control system will execute a
cycle
only once at a given location - it this case, there is no need
to program the number of executions, since the system defaults to one automatically. To repeat the fixed cycle
limes (more than once), program a special command that
'tells'
CNC system how many times you want the fixed
cycle to be executed.
• The L or K Address
The command that specifies the number of repetitions
(sometimes called loops) is programmed with the address
Lor K
some controls. The L or K
the fixed
cycle repetition is
to have a value
which is
equivalent to a program statement LI or
LI or Kl
address does not have to be specified in the program
For example. the
sequence,
call of the following drilling
N33 G90 G99
NJ4 G81 X17.0 Y20.0 RO.1S
IDS X22.0
N36 X27.0
N37 X32.0
N38 GBO •••
z-2.4 F12.0
is equivalent to:
N33
N34
N3S
N36
N37
N38
G90 G99 ••.
G81 X17.0 Y20.0 RO.15 Z-2.4 F12.0 Ll (Kl)
X22.0 Ll (Kl)
X27. 0 Ll (Kl)
X32.0 Ll
)
G80 ..•
examples will provide the control system with instructions for drilling four holes in a straight row - one at
the location of X 17.0 Y20.0, the other holes at locations
X22.0 Y20.0 and X27.0 Y20.0, and X32.0 Y20.0 respectively - all to the depth of 2.4 Inches.
If the L or K
in
is increased
rather added to the first example), for instance. from L I to
(or KILO K5). the fixed cycle will be repeated
times
at
hole location!
is no need
this type ma.chining. By changing the formal only a Htlie, the fixed cycle repetition can be used as a benefit - to make the
more powerful
N33 G90 G99 ...
N34 Gal X17.0 Y20.0 RO.l Z-2.4 F12.0
N35 G91 XS.O L3 (K3)
N36 G90 GSO GOO •..
With that change, the advantage of a feature 'hidden' in
the first example is emphasized equal increment
(ween holes being exactJy
inches. By using
incremental mode, on a temporary basis in block N35 and employing the power of the repetitive count L or K, the CNC
can be shortened dramatically. This method
a large number of hole
programming is very efficient
patterns in a single program. A fwther enhancement is (0
combine the L or K count with
or macros.
• LO or KO in a Cycle
In previous discussions,
default for a fixed cycle repetition was specified as Ll or Kl, that does not have to be
specified in the program. Any L or K value other than L 1 or
K] must always be specified, within the allowable
of
the Lor K address. Thllt
is between LO and
or
KO and K9999.
lowest
word is LO or KO - not
or KI! Why would we ever program a fixed cycle and then
say 'do not do iT>. The address LO or KO means exactly thaL
- 'do not execute this cycle '.
full benefit of the LOIKO
word will apparent in the examples listed under the section for subprograms, in Chapter 39.
By programming the LO or
in a fixed
what we
are really saying is not 'do not execute this cycle', but 'do
not execute the cycle yet, just remember the cycle
las for future use '.
most machining, fixed cycles are quite simple to
They do, however, have some complex
to be
in an efficient manner a single hole.
,.MACHINING HOLES
good chance that the majority of programs
machining centers
machining of at
least one hole, probably more. From a
spot drill to
reamIng,
and a complex backboring, the field of
hole
very large. In
we
at
many available
machining, and learn a
drilling
and
.
and sinThe most common type of hole
chining centers is in the area of drilling,
A typical
and single point
may bc to centcr drill or spot drill a
drill them, then
or bore them. Machining even a single
I to 089,
hole will
the fixed
G73, G74 and
all described in
Ltll.U"'"
SINGLE HOLE EVALUATION
even a
hole on a
aJ I reto be programmed. Before that, cutselected, speeds and
applied, the
best setup
and many other
must
be resolved. Regardless of
exact
start
with a thorough evaluation
relates to the drawing data.
will usudefine the material to
machined, the hole location
its dimensional
Holes are often described,
rather than dimensioned
the programmer has to
lhe missing details.
26-} shows a medium cornDlexity hole that can be
using a CNC machine.
,
/
1"", . ., . . . . . . . ."
How many tools will be needed? What about center drilling to maintain exact location
Is the spot drill a
What about
drilled hole for
lapping? What about the hole trdtl'r"'"I'J>(O
What about ... ?
• Tooling Selection and Applications
on the drawing information alone, it may seem
only two tools will be needed to program this hole. In reality, the implied information must
interpreted - it is not
the
the drawing to
how to machine the
hole - only the hole requirements related to functionality
and
A
CNC machinist will most likely
four tools
machining
are
selected,
tool could be a 90° spot drill, followed up
by the tap drill.
the through-the-hole drill and finally,
tap. A
center drill may
instead of the
spot drill, but an additional tool will be
to chamfer
the hole
at the top. All choices
to be sorted.
For this example, the following four
o
Tool 1 • TO 1 • 90 0 spot drill (+ chamfer)
o
Toal2· T02 -
o
Tool 3 - T03
LJ
Tool 4 - T04 - 7/16·14 UNC tap
Utap drill
are used:
,VJ .•>UUI
5/16 drill (through the 1'TI,n.,,,',,,,,
Tool f - 90 0 Spot Drill
Xy
1020
26·1
Evaluation of a single hole -
All the relevant information is in the
but some
is needed.
details and
hole location X3.SYS.0 was
in the drawing, as
-mild
program will
La
top face of part.
and tapping operaare obvious, but is that all there ta know?
L
The fust tool will be a 90° spot drill. Its
is duaJ - it
will act as a
drill and starts up
at a highly
A center drill or a
drill are
accurate XY
more rigid tools than a twist drill and either one
the hole, so the drill lhat follows
not
path (basic
are
purpose of the spot drill is its
chamfering capabilities. The design of this
allows a
at the top of the hole,
the
chamfer to
spot drill diameter is larger than the chamfer
qulred. In this case, a 05/8 spot drill will be
to chamfer the 07/16 hole.
IJU"~l1""1II1U example 02801
191
192
26
is selected, its cutling
calculated, not
to
chamfer for a tap size 07/16 (0.4375),
to be enlarged by .015
(.03 on
diameter), to the .4675 chamfer diameter.
shows the relationships of the hole to the tool
ters and
26-2
what purpose is the tap
Not all
done the same way. Some jobs
a loose fit, others a
fit. The fit for the tap is
by Ihe
of the tap drill. Mosl tapping applications
into the 72-77% full thread depth category. In this case,
T02 (letter U drill) will yield approximately
full
thread depth.
of the thread
found in catalogues all tap manufacturers.
for the 7/16-14 tap:
these are the
......~ -.....,,....... 00.625 SPOT
0.015x45"
0.2338
or
Z-O. 2338
Drill point length is
3/8
.3750
67%
v
.3770
65%
stock, 75 to 80%
the bolt
by only
for
the depth of cut will
diameter (0 x
programmed Z depth
the tap drill has to be deep
to guarantee the
full thread depth of .875.
means the full diameter of
drill has to reach a little
deeper, for example, to
That allows the end
c.hamfer length of the tap (0
the full lap depth of
specified in the
shows the lap
drill values graphically.
.4675 I 2
.4675 x .5
75%
thread depth is recommended, for
100%. A thread (hat
Figure 26-2
Spot drill operation detail TD 1 in program 02601
or
.3680
In genera] terms, for thin
00.4375 TAP
:--....,. .~ 00.4675 CHAMFER
ii-"--<-'l······
Note, that for a 90°
one half of the
u
.23375
later in this chapter.
Tool 2 • Tap Drill
(U)
will have to be a drill. In the exused
the job - one
the
the other one for
lap
is - which one first?
f
I
0.975
II certainly does matter
drill is programmed first.
The key here is the
the two drill diameters. It is a very small
only .0555 measured
on diameter, in fact.
a machining point of view, it
makes sense to use the larger drill first, than the smaller
drill. The tap drill is larger than the through hole drill, so the
will be the lap drill If
drill is programmed
firs!, the larger drill that
produce an inaccurate
hole, due to a very small amount material to remove.
1.5
26·3
drill
Now comes the question of
question is called a tap
It is
hole of proper size
the lap that
machining operation
detail- T02 in program 02601
In
will create a
depth) that can be
of operations.
tapping, it makes a
actual programmed depth for the tap drill will have to
into consideration one more factor ~
drill poim
lenRth.
drill or - 1001- point length is
abbreviated as
or just by the letter P. This Cmlp[(~r
MACHINING
table showing "" ... r"'1:" mathematical constants to calculate
drill point
most common constant uses the drill
diameter
by .300,
a 1180 drill point angle:
(.975+.111), will provide the
1.086.
Adding the two
pro.grammed Z
TODIJ -
most through-hole applications, this value will not be
- some extra clearance has to be added, applied to
the tool penetration (breakthrough), say fifty
(.050). The programmed value for the Lotal drill
(absolute Z value in the program) is the sum of
nominal hole length, plus the tool point angle length,
the
clearance. In the program
amount
the through drill depth will be:
UJVIUi)<1'
1.5 + .094 + .05
DrjJJ
L 644 or Z-l. 644 iJ!fiJeprognJm
The next tool is a tool that drills the hole through the mao
teriaJ. In the example, it is
1'03 (tool 3), a 05116 standard drill.
As for the cutting depth of
through drill. some simple
calculations are needed.
do the calculations, Ine required hole depth
known, which is 1.5 inches in
example. Then, the calculated drill
can be
added to the
drill
clearance.
to be made. Re~
been used to predrill an
means a smaller tool of 0.3125 is
hole. The drilling can start from
than from a clearance above the part.
R value is used and selected at R-0.986,
100
above the bottom of the
ing hole.
10014·
drilling operation are il-
The '-.;<lII.,.UIC.ll
6
There is one more tool left to complete this example. It
will be
for
7/16-14 thread. The thread
as specified in
is 7116 nominal diameter with
14 threads
(1114::::: .0714 pitch). Anytime a tapping tool is
in the program, watch the programmed
depth along the Z
particularly in a blind or semi-blind
hole. The
a semi-blind hole, because the
the tapped hole. If there were
through-hole is
no through-hole, we would have a blind hole (solid bottom). and if
were the same size as the tap
drill, we would
through hole.
=
THRU
1.086
1
for the Z depth calA through-hole is
culation, closely
hy
semi-through hole. A
blind hole has very little latitude, if any, and has to be programmed with a maximum care.
~. P = 0.094
Figure 26-4
drill operation detail- T03 in program 02601
First, evaluflte the drill point length P It is
relationship of two given values - the drill
drill pOint angie. For a standard 05116
that has 118 0 drill point angle, the 0.300 constant is used
length of the drill point Pis:
P
.3125 x .300
= .09375 = .0938
the through hole in the example,
1.5 inches
calculated depth
to
the
.094
The example drawing for the hole
for the tap depth
of .875 inches. This is the full depth
the thread. Full
depth of a thread is the actual distance a screw or a nut must
travel before stopping (before
programmed
depth is, if fact, an exteruled depth, which must be greater
than the theoretical depth, in
to
calculate the length of the
chamfer design (its type
in the tapping
Zdepth is
and can be optimized
not
a calculation but an 'intelligent
nOI much
that can be done and
This completes the section on tooling
a typical hole and provides enough data to
Some of the procedures used in the
now be explained in more detail.
• Program Data
In the example, only one hole is machined. If more holes
the following
are needed, they can be added by
the program inprogram. For one hole llsed in the
cludes all considerations for
spindle should be empty at the
02601 <SlNGLE HOLE EXAMPLE)
DIA - 90 DEGREE SPOT
Nl G20
N:2 G17 G40 GSO '1'01
N3 1406
N4 G90 G54 GOO X3.5 Y5.0 S900 M03 '1'02
N5 G43 ZO.l HOl MOB
N6 G99 GS2 RO.l Z-0.2338 P300 F4.0
N7 GSa ZLO M09
N8 G28 ZL 0 MOS
N9 MOl
ma
drilling is a removal
of
same
material removal is
(on milling systems) or by
turning sysu~rns). In either case, a
a
application is possible.
loose sense
word. drilling operations also cover the
extended areas of reaming, tapping and single point
Many programming principles that apply to drilling
lions, can be equally applied to all the related operations.
• Types of DriUing Operations
The drilling {",\"'~'r':lrl{"'\n is determined by either the
By the type of
- LE'TTER U DRILL - 0.368 DIA - .... ~~J
NlO '1'02
Nll M06
Nl2 G90 G54 GOO X3.5 YS.O S1100 M03 T03
Nl3 G43 ZO.l H02 MOS
Nl4 G99 G83 RO.l Z-1.086 00.5 F8.0
Nl5 G80 Zl.O M09
Nl6 G28 Zl.O M05
Nl7 MOl
(Tal Nl8 '1'03
By the type of hole:
Center drill
Through hole
Spot drill
Chamfered hole
Twist drill (HSS, cobalt, etc,)
Semi-blind hole
Spade drill
Carbide indexable drill
Special drill
DRILL THROUGH - 0.3125
i
"
.....=
Blind hole
Premachined hole
II
...
• Types of Drills
N19 M06
N:20 G90 GS4 GOO X3.S YS.O 81150 MO]
N:21 G43 ZO.l H03 MOS
N:22 G98 G81 R-O.9B6 Z-1.644 FB.O
N:23 GBO Zl.O MOg
N:24 G28 Zl.O MOS
N:2S MOl
('1'04 TAP)
N:26 '1'04
N:27 M06
N:28 a90 G54 GOO X3.S Y5.0 S750 MOl '1'01
N:29 G43 ZO.4 H04 M08
NlO G99 G84 RO.4 Z-0.9 F53.57
(F = S x LEAD)
Nll GSO GOO Zl.O M09
Nl2 G28 Zl.O M05
N33 GOO X-l.O Y10.O
(PART CHANGE POSITION)
Nl4 mo
and by their
oldest
most common
is aJwist drill,
usually made of high
Twist drill can also be
of cobalt, carbide
materials. Other drill deinclude spade drills, center drills, spot drills and indexable insert drills.
distinction in size is not only between metric and English drills. but also a finer distinction
within the category using English
All
drills
are designated in millimeters. Since the
(imperial)
dimensioning is based on inches (which is
dimensional unit), finer distinctions are
dimensions of standard drills in English units are divided
groups:
Drills are
o FRACTIONAL SIZES:
%
This rather "'.... '''.un,''"'
single hole
gramming
of
hole or the rype
shows that even a simple
and a great deal of
DRILLING OPERATIONS
1/64 minimum, in diameter increments of
o NUMBER SIZES:
Drill
o
SIZES:
Drill
a good lIlustration of what
The example 02601
kind of programming
machining conditions are neceslook at the details of drillsary for a Iypical hole.
ing operations in t:Tpnpr"" as they relate 10 various lools.
number 80 to drill size number 1
letter A to drill size letter Z
Metric
do not need any special U''''Ll' ",LJ'U" ,,,,.
English
a listing of the standard drills and
mal equivalents is available from many sources.
MACHINING HOLES
•
195
Programming Considerations
-.
A standard drill has, regardless of size, two important
features - the diameter and the point angle. The diameter is
selected according to the requirements of the drawing, the
tool point angle relates to the material hardness. They are
both closely connected; since the diameter determines the
size of the drilled hole, the tool point angle detennines its
depth. A smaller consideration is the number of flutes,
which is normally two.
•
Nominal Drill Diameter
The major consideration for a drill is always its diameter.
Normally, the drill diameter is selected based on the information in the drawing. If the drawing calls for a hole that
needs only drilling and does not need any additional machining, the drill is a standard drill. Its diameter is equivalent to the size specified in the drawing. A drill size of this
kind is called a nominaL or 'off-the-shelf' size.
Most applications involve holes that require other specifications in addition to their diameter - they include tolerances, surface finish, chamfer, concentricity, etc. In those
cases, a single regular drill cannot be used alone and still
satisfy all requirements. A nominal drill alone, even if the
size is available. will not guarantee a high quality bole, due
to machining conditions. Choosing a multitool technique to
machine such a hole is a better choice. The normal practice
in those cases is to use a drill size a bit smaller than the final
hole diameter. then use one or more additional tools, which
are capable of finishing the hole to the drawing specifications. These tools cover boring bars, reamers, chamfering
tools, end mills and others. Using these tools does mean
more work is involved, but the quality of the finished part
should never be traded for personal conveniences.
During the cut, the drill angular end will be gradually
entered into the part, creating an increasingly larger hole
diameter, yet still smaller than the drill diameter. At the
end, (he largest machined diameter will be equivalent to the
effective diameter of the drill used. The effective drill diameter defines the actual bole diameter created within the zone
of the drill end point. Typical use of this kind of machining
is a spot drilling operation for chamfering. The spindle
speed and feed must be calculated according to the effective
drill diameter. not the full diameter. The rlmin for the effective diameter will be higher and the feedrate lower than the
corresponding values for the nominal drill size. For this
kind of jobs, selection of a short drill for rigidity is advised.
Drill Point length
•
The second important consideration is the length of the
drill point. This length is very important to establish the
cutter depth for the full diameter. With the exception of a
flat bottom drill, all twist drills have an angular point whose
angle and length must be known in programming. The angles are considerably standard and the length must be calculated rather than estimated. because of its importance to
the accurate hole depth - Figure 26-6.
--j
00
r-
<ttj> j
1
Y
QJO ::: Drill
diameter
A :;;: Tool point
angle
p
~I
p ::: Tool point
length
Figure 26·6
Tool point length data for a standard twist drill
•
Effective Drill Diameter
In many cases, a drill is used to penetrate its/ull diameter
through the part. In many other cases, only a small portion
of the drill end point is used - a portion of the angular drill
tip - Figure 26-5.
NOMINAL
DRILL DIAMETER
On indexable insert drills this length is different, due to
the drill construction. The indexable drill is not flat and its
drill point length must also be considered in programming.
A tooling catalogue shows the dimensions.
The drill poinllength can be found quite easily. providing
the diameter of the drill (nominal or effective) and the drill
point angle are known. From the following fonnula and the
table of constants, the required drill point length for standard drills can be calculated. Basic fonnula is:
I
J
PROGRAMMED
DEPTH (P)
tan ( 90 -
J
EFFECTIVE
DRILL DIAMETER
Figure 26·5
Nominal and effective drill diameters (tvvist drill shown)
p ==
-
A
2
2
~ where ...
p
A
0
=
=
=
Length of the drill point
Included angle of the drill point
Diameter of the drill
)
x
D
1
same formula can be
mathematical constant (fixed
and used with a
drill point angle):
P
:::::
Drill point length
K
=
Constant (see the following table)
o = Drill diameter
most common constants are listed in this table:
Tool Point Angle
(degrees~
Constant
60
,866025404
82
,575184204
.575
90
,500000000
.500
118
30310
.300
120
75135
.289
125
83525
.260
130
53829
135
,207106781
.207
140
.181985117
.180
145
.157649394
.158
150
133974596
.134
The constant in
is
value is sufficient
all programming
value of the constant K
value is .300430310.
constant value
advantage
of being easy to memorize and there is no formula to solve.
For most johs, only three constants are
For 90°
(spot drilling
materials), 118 0 (standard materials),
They are easy to memorize:
and 135 0 (hard
o
0.500
o
0.300...
o
0.200
for a 90 0 drill angle
a 118 • 120 drill angle
0
0
for a 135° drill angle
• Center Drilling
Center drilling is a machining
that provides a
small, concentric opening for a tailstock
or a pilot
drill. Chamfering is not recommended
hole for a
a center
11. because of the 60°
of the tool.
The most common tool
center drilling is a
center drill (often called a combined drill and countersink),
producing a 60° angle.
North American
trial standards use a numbering system from #00 to
(plain type) or #11 to # 18 (bell type) for center drills. In
metric system, center
are defined by the pilot
for example, a 4 mm center
will have the pilot
meter of 4 mm. In
cases, the higher the number, the
the center drill
For some
at ions. such as
a tool with a
called a spot drill, is a
choice.
Many programmers
estimate the depth of a center
drill, rather than calculate it. Perhaps a calculation is not
necessary for a
operation. What is a ......"VJJ,.v .....
compromise
guessing and calculating is a
in Figure 26-7.
similar to
D
D1
Figure 26-7
Standard cemer drill cutting depth table· #1 to #8 plain type
L is the
of cut for an arbitrary effective diameter D
are all
dimensions for
size center drills.
most important of
them is
cutting depth L. Its calculation
been
D.
on an arbitrary selection of the
#5 center drill has the depth value L that is
based on an arbitrarily
chamfer dia·
meter D
inches. These values can be modified as
or a different table can be
A similar table can
for metric center
• Through Hole Drilling
a hole through the
common oprequires the Zdepth to
materia] thickness,
drill poiot length and an extra clearance beyond
the drill penetration point, also known as the breakthrough
amount.
MACHINING HOLES
197
1.25 + (.750 x .300) = 1.4750
part program, the block will
F
C
P
N93 GOl Z-1.475 Fo.O
or - in case of a fixed
N93 G99 GS5 XS.75 Y8.125 RO.1 Z-1.47S F6.0
1
I
F
I
T
p
Metric holes are treated exactly the same way.
example, a 16 mm drill is
to
full diameter
depth of 40 nun. The calculation uses the same constant as
the
In
units:
40 + (16 x .300) = 44.8
The depth
Figure 26-8
Drill depth calculation data
Through hole (top) and Blind hate (bottom)
in the drawing will have to
ex-
tended by the calculated drill point length.
programmed block will have the Z axis value equal to the total
of the 40 mm specified depth, plus
4.8 mm calculated
point length:
In Figure
is shown {hat the programmed
for a
through hole is the stun of the material thickness that is
equivalent to
full diameter depth F, plus the breakthrough clearance C, plu~
tool point length P
N56 GOl Z-44.8 F150.0
example, if
material thickness is one inch and
standard dril1 diameter D is
of an inch,
programmed
including a .050 clearance, will be:
NS6 G99 GSl X21S.0 Y175.0 R2.5 Z-44.8 FlS0.0
1 + .050 +
x •
1. 2375
Pay attention to
table, vise,
leis, fixture, machine table,
when programming the
tool breakthrough clearance. There is usually a very
space below
bottom face of
parI.
• Blind Hole Drilling
major difference between drilling a blind hole and a
drill does not penetrate the material.
through hole is that
Blind hole drilling
not present any more problems
than a through hoJe drilling, but use a peck drilling method
for
holes. Also a choice of a different drill geometry
may
the
and the hole cleanup may often be necessary as well.
In a
shop
depth of a blind hole is
given as thefull diameter depth. The drill point length is not
normally considered to be part of the depth - it is in addi·
rion to
specified depth. In Figure 26-8, the programmed
depth a blind hole will
the sum of
full diameter
depth P, plus the
point length P.
an example, if a
drill (0.750) is used to
drill a full diameter hole depth of ] .25 of an inch, the prodepth
be:
If the depth appears in a fixed
the same depth value
will be used, although in a different format:
When machining blind holes, the cutting chips may clog
the holes. This may cause a problem, especially if
is a
operation on the hole, for example, reaming or
tapping. Make sure you include a
slop code MOO
or MO I before this operation.
if
the program is
hole will have to be cleaned every
·-executed. Otherwise,
more efficient optionaJ program
Slop MOl is sufficient.
• flat Bottom Drilling
bottom hole is a blind hole
a bottom at 90° to
drill centerline.
are two common methods of programming
a hole. A good practice is to use a standard
drill to start the hole,
use a flat bottom drill of
same
diameter and
the hole to
full depth. Also a good
choice is to use a slot drill (also known as the center cutting
mill), without predrilling. This is
best method, but
some tool
may not be
To program a flat bottom hole using a slot drill is quite
simple. For example - a 10 mm hole should be
mm
deep (with a flat bottom). Using a 010 mm slot drill, the
program is quite short (tool in spindle is assumed):
02602 (FLAT ~ - 1)
N1 G21
N2 G17 G40 GBO
N3 G90 G54 GOO X.• Y.. 5850 M03
N4 G43 Z2.5 HOl ~e
198
N5 GOI Z-25.0 F200.0
N6 G04 XO.S
N7 GOO Z2.5 M09
NB G28 Z3.0 MOS
N9 M30
%
A fixed cycle could be used instead and other improvethe
is correct as is.
ments added as well.
next example shows a program for two tools a 112
standard drillllnd a 112 inch flat bottom drill. The required finished depth is Z-0.95 at the flat bottom:
02603 (FLAT BOTTOM - 2)
('1'01 - ~ INCH STANDARD DRILL)
Nl. 020
N2 017 G40 G80 '1'01
N3 M06
N4 G90 G54 GOO X .. Y•• S700 M03 T02
N5 043 ZO.1 HOI M08
N6 G01 Z-O.94 F9.0
N7 GOO ZO.l M09
N8 G28 ZO.l
N9 MOl
('1'02 - ~ INCH FLAT BOTTC'IM DRILL I END MILL)
Nl.0 '1'02
NIl M06
Nll G90 G54 GOO X.. Y.. S700 M03 '1'01
Nl.3 G43 ZO.l HO.2 MOS
Nl4 GOl Z-0.74 F15.0
Nl.5 Z-0.95 '1!7.0
NI6 004 XO.S
Nl.7 GOO ZO.l Ma9
Nl.B G2B ZO.1 MOS
Nl9 mo
%
are three blocks
special
in program
02603.
first block is N6, indicating the depth of
standard
The drill stops short the full depth by .010
an inch. Z-0.94 is programmed
of the
A little experiment as to how short may be worth it.
A reason for not drilling to
full depth with the standard
is to prevent possible
mark at the hole center.
The other two blocks appear in the second tool of the
gram - blocks N] 4 and N 15. In block N 14, the flat bottom
drill
at a heavier
to
depth of only .740
inches. That makes sense, as
is nothing to cut for the
flat bottom drill for almost
of an inch. Follow the calculation of the 0.740 intermediate depth from this procedure:
From the total depth of .94 cut by the standard drill (TO 1),
su blracl the length of the tool point P. That is
for a 118 0
drill point angle
0.5 drill. The
is .79.
the
result. subtract .05 for clearance, and the
is the Z
value of Z-0.74. In the block N15, the flat bottom drill removes the
material left by TO I, at a suitable CUIting feedraLe, usually programmed at a slower rate.
Chapter 26
From the machining viewpoint, programming a center
drill or a spot drill first to open up the hole may be a better
choice. This extra operation will guarantee concentricily
for both the standard drill and the flat bottom drill. Another
possible improvement would
to use a suitable end mill
instead of a flat bottom drill. An end mill is usually more
rigid and can do the job much better.
• Indexabla Insert Drilling
of
great productivity improvement tools in muLlem machining is an indexable insert drill.
drill uses
carbide inserts,
like many
tools for milling or
It is
to drill holes in a solid material. It
does not
center drilling or spot drilling, it is
with high spindle speeds and relatively slow feedrales and
is available in a variety of sizes (English and metric). In
blind
most cases, it is used for through holes,
holes can be drilled as well. This type of a drill can even be
used
some light to medium boring or facing.
The
of the indexable
driB is very precise,
assuring constant rool length, as well as elimination of
regrinding dull tools. Figure 26-9 sbows the cutting portion
of a typical indexable drill.
r,
D = DRILL DIAMETER
H = DRILL POINT LENGTH
Figure 26-9
CUffing end of a typical indexable insert drifJ
In the illustration,
D of
drill is the hole
produced by the drill. The
point length H is defined
by the drill manufacturer and amount is listed in the toolcatalogue.
example. an indexable drill with the D
of 1.25, may have the H tip length .055. The
indexable drill can be used for rotary and stationary applications, vertically or horizonlally, on machining centers or
lathes. For
penormance,
coolant should be
through the drill, particularly for tough materials,
sure
The coolant not only
long
and horizontal
disperses the generated heat, it also helps flush out the
chips. When using an indexable insen drill, make sure
is
power at the machine
The power requirements at the spindle increase proportionally with indrill diameters.
On a machining center, the indexable drill is mounted in
the machine spindJe, therefore it becomes a rotating tool. In
used in a
spindle
this
the drill should
MACHINING HOLES
runs true - no more than .0 J0 inch (0.25 mm)
(Total Indicator Reading). On spindles that have a quill, try t6
work with the quill
spindle, or extend it as little as
possible. Coolant provisions may
an internal
ant, and special adapters are available for through the hole
cooling, when
drill is
on machining centers.
On a CNC lathe, the indexable drilling tool is always stationary.
correct
requires
(he drill is
tioned on the center and concentric with the spindle centerline.
concentricity should nol exceecl JlO') inch
(0.127 rom) T.l.R.
exercise care when
operation starts
on a ""rl'",..,. that is not flat. For
use 1IIU't;)I.<l.UU::;
drills on surfaces that are 90" to the drill axis (flat
Within
the drill can
be used to enter or exit an
inclined, uneven, concave, or convex
quite successfully. The
may
to be reduced
the duration
of
interrupted cut. The
26-/0 shows the areas
the feed rate should be slower.
199
PECK DRilLING
Peck drilling is aJso
interrupted cut drilling. It is a
drilling operation, using the fixed cycles G83 (standard
peck drilling cycle) or G73
speed peck drilling cycle). The difference between
two cycles is
tool retract method. In
the retract
each peck will be to
the R
(usually
the hole), in
there will only
be a
relract (between .02 and .04 inches).
Peck drilling IS often used for holes that are too deep to
drilled with a single tool
Peck
methods
standard
several opportunities to improve
techniques as well. Here are some possible uses of
drilling methods for machining holes:
o Oeep
drilling
o Chip
- also used
short holes in
materials
o Cleanup of chips accumulated on the flutes of the drill
o
Frequent cooling and lubricating of the drill cutting
o
Controlling the drill penetration through the material
In all cases, the drilling motions of the
an
cut
can be nrf'l,n .. ",rrlT1nt>t1
by specifying the Q address value In the
peck.
value specifies the actual depth
the Q
the more pecks will
generated
vice
versa.
most deep hole dril1ingjobs, the exact number
pecks is not important,
are cases when the pecking cycle needs to be
• Typical Peck Drilling Application
Uneven entry or exit surface for indexable drills feedrate:
F :::: normal feedrate, F/2 reduced feedrate (Dne half Df F)
For
majority of
drilling applications, the peck
drilling depth Q needs to be only a reasonable depth. For
a
hole (with
depth at
1 inches at
the tool tip) is drilled with a .250 diameter drill and
depth.
cycle may
programmed like this:
Nl37 G99 GS3 x .. Y.. RO.l Z·2.125 QO.6 F8.0
In the illustration, the
F identifies
area that is cut
with the
feedrate (normal entry/exit), and the
indicates the area that requires a reduced
For the
feed rate , programming one haJf
normal
is sufficient
In
illustration, the
a shows a lilted surface
(inclined
the b
shows an uneven surface,
the
c and d show convex and concave
respectively.
These programming values are reasonable for the
hand - and that is that matters. For most jobs, the
is
not too
• Calculating the Number of Pecks
If the number of pecks the G83/G73 cycle will
is
knowledge of how
important, it has to be calculated.
Q
a given tomany pecks will result with a
depth is usually not important. If the program is running
efficiently. there is no need for a modification.
find out
how
pecks the G83/G73
will generate, it is
important to know
total distance the drill travels
tween the R level and the Zdepth (as an incrementa! value).
It is equally imponant to know the peck depth Q value.
Q divided into the travel
is the number of pecks:
200
26
result 1.339/3 is
-a
that
to
be rounded to the maximum of four decimal places (English units). Mathematically correct rounding to four decimal places will be
Follow individual peck depths to
see what will happen:
Ilir' where ...
Pq
Td
a
Peck 1
Peck 2
Peck 3
Peck 4
Number of pecks
::::: Total tool travel distance
= Programmed peck depth
For example. in
following GR1
N73 G99 Ga3 x .. Y•. RO.12S Z-1.225 00.5 F12.0
divided by .$00,
distance is 1
pecks can onty
Since the
which yields
positive, the nearest higher integer will be the actual
number of pecks, in this case 3.
• Selecting the Number of Pecks
Much more common is the programming of a
If only a certain number of pecks will do
number of
the job in the most efficient way.
Q value has to be calculated
Since the Q value specifies·the depth
each peck
not
number
pecks, some simple
math will be nccd~d to select the depth Q. so it corresponds
to the
number of
For example - we require 3 pecks in the following cyclewhat will the Q depth
N14 G99 G83 x •• Y.• RO.l Z-1.238 0 •• F12.0
The total drill travel from the R
to the Z depth is
1.338. To calculate the
depth Q value, the new
one:
mula is similar to the
.4463
.4463
.4463
.0001
accumulated depth
accumulated depth
accumulated depth .. .
accumulated depth .. .
.4463
.8926
1.3389
1.3390
will be four pecks and the last one
only cut
.0001 - or practically nothing at alL
those cases, where
the last cut is very small and inefficient, always round the
calculated Q
upwards, in this case to the minimum of
.4464 or even to .447:
N14 G99 Gsa x.. Y.. RO.l Z-1.239 00.441 F12.0
Always remember,
cutting tool will never go past
depth in a very
programmed Z depth, but it could reach
inefficient way that should be corrected.
• Controlfing Breakthrough Depth
Less frequent programming method, also very powerful,
the breakthrough
is to use the peck drilling cycle to
of tbe drilllhrough the material, regardless of the drill size
or material thickness. Here is some background. In many
the
tough materials, when the drill starts
tom of the part (for a through hole), creates potentially
the tendency
difficult machining conditions. The drill
to push the materia! out rather than cut it This is most common when the drill is a little dull, the material is tough. or
the feed rate is fairly
adverse conditions are also
the lack luthe result of heat generated at the drill
brication reaching the drill cutting edge, worn-off flutes
and several other factors.
The
solution to
problem is to relieve the
pressure when it is about halfway through the hole, but not
completely through 26- J I,
r-
IGi' where
a =: Programmed peck depth
Td
p.
:::::
Total tool travel distance
Number ofrequ ired pecks
Using the above formula, the result
I
QO.446:
Therefore, G83 block Q depth will
RO.1
is .446.
N14 G99 G83 x .. Y•. RO.l Z-1.238 QO.446 F12.0
No rounding is necessary in this case. Now,
look at another situation, where
has
very slightly:
have a
distance
N14 G99 Gal x .. Y•. RO.l Z-1.239 Q.. F12.0
00.925
0.75
I
I
0.05
J .~
. ::::::~¥~~. ;::~ Z-0.825
P =0.15
Figure 26-11
Controlled breakthrough of 8 hole using 683 peck drilling cycle
MACHINING
Peck drilling cycle G83 is great for it, but the Q depth
eulalion is extremely important. The total number of peeks
is not important, only the last two are
for this
with the drill
pose. To control the problem
tration, only two peck motions are needed.
illustration
sllOws tile two positions
a 0112 dril1 drill through 113/4
thick plate.
most jobs,
a hole requires no special treatment.
Just one ctrt through (using G81 cycle) and no
drillLet'S/evaluate Ihe solution to
situation. The
has
point length of .300 x .500 = .1
Take one
half (.075) of the drill point length as the first
amount, which will bring the drjl\ .075 below the 3/4
thickness, to (he Z depth of Z-0.825. This depth has to be
reached with
value of{he Q depth.
in mind that the
from the R
Q depth is an incremental value,
level, in this case RO. J. That specifies the Q depth as
QO.925 (.100 above
.825 below ZO). The
Z depth is the final drill depth. If .05
added
below the plate, the Z depth will be the sum of the plate
(.05) and tbe drill point
thickness (.75), the
(.150),
the program value of
G99 Ga3 x .. Y.. RO.1 Z-O.9S QO.925 F •.
does not only solve a particular job related problem, it also shows how creativity and programming are complementary terms.
REAMING
The ream
operations are very
to the drilling operations, at least as far as the programming method is concerned. While a drill is used to make a hole (to open up the
hole), D reamer is used to enLarge an existing hole,
Reamers are either cylindrical or tapered, usually deof different configurawith more than two
tions.
of
cobalt, carbide
with brazed carbide lips.
reamer design has its advantages and
Carbide reamer, for example,
has a
resistance to wear,
may be not economically justified
every hole. A high speed steel reamer is
economical, but wears out much
that a carbide
reamer. Many jobs do nol accept any compromise in the
tooling selection and
cuning 100\ has to selected correedy for a given job. Sizing and finishing
such as a
reamer, have to be
even more carefully.
Reamer is a sizing tool and is not designed for removal of
heavy stock. During a reaming operation, an existing hole
will be
- reamer will
an existing hole to close
erances
add a high quality
finish. Reaming will
not guarantee concentricity of a hole.
holes requiring
both high concentricity and tight
center drill or
spot drill the hole firsl, then drill it the normal
then
rough bore it and only then finish it with a reamer.
201
A reaming operation will require a coolant to help make a
during cutbetter quality
finish and to remove
ling. Standard coolants are quite suitable, since there is not
very much heat generated during reaming. The coolant also
serves in an additional role, to flush away
chips from
the part and to maintain
surface finish quality.
• Reamer DeSign
In terms of design, there are two
of a reamer that
have a direct relationship to the CNC machining and programming. The
consideration is the flute design.
Most reamers are designed with a left-hand nute
tion. This design is suitable to ream rhrough holes. During
the
the left-hand flute
the
to the
bottom of the
an empty space.
holes
that have to be reamed, the len-hand type of a reamer may
not
suitable.
other factor of the reamer design is the end chamfer.
to enter an existing hole that i5> ~till without a
reamer end
chamfer, a
allowance is required.
provides that allowance. Some reamers also have a short
the same purpose. The chamfered
taper at their
is sometimes
a 'beveUead'and its chamfer an 'attack
angle'. Both have to he considered in programming.
In
• Spindle Speeds for Reaming
Just like for standard drilling and other operations, the
spindle speed
for
must closely
of material being
Olher factors, such
to the
as the part setup, its rigidity, its
and surface finish of the
completed hole, etc., each contributes to
spindle
rule, thc spindJe speed for
will reasonable
use a modifying factor
.660 (213), based on the speed used for drilllng of the same
material.
example, if a speed of 500 r/min produced
drilling conditions, the two thirds (.660) of that
reasonable for r",,,,rn,,..,,,·
500 x .660 = 330 r/min
Do not program a reaming motion in the reversed spindle
rotation - the cutting
may
or
dull.
• Feedrates for Reaming
The reaming
are programmed higher than those
used for drilling. Double or triple
are not unusual.
The purpose of the high feedrales is to force the reamer to
cut, rather than to rub the material. If the
is too
slow, the reamer wears out rapidly.
slow feedrates
reamer actually tries to encause heavy pressures as
the hole, rather than remove
stock.
202
Chapter 26
• Stock Allowance
SINGLE POINT BORING
material left for
must be smaller (undersize) than
pre~drillcd or pre-bored hole - a logical requirement.
Programmer decides how
smaJler. A stock too small
reaming causes the premature reamer wear. Too much
stock for reaming
the
and the
reamer may break.
A hole to be
A good
is to
about 3% of
reamer
diameter as the stock allowance. This applies to the
diameter· not per side. For example, a 3/8 reamer (0.375),
will
well in most conditions if the hole to be
has a diameter close to .364 inches:
.375 -
(.375 )( 3 / 100)
.36375 '" .364
Most often, a drill that can machine the required hole diameter exactly will not be available. That means using a
boring
to
the hole
reaming. It also mean
an extra cutting tool, more setup
program and
other disadvantages, but the hole quality will be worth the
In
cases, for
materials
some of the
the
allowance left in the hole
is usuaJly decreased.
• Other Reaming Considerations
general approach for
is no different than for
other operations. When drilling a blind hole,
reaming
it, it is inevitable that some chips from
drilling remain in
the hole and
a smooth reaming operation.
Using the program stop function MOO before the reaming
operation allows the operator to remove all the chips first,
for a dear entry of
reamer.
Another sizing operation on holes is called boring.
jng, in the sense of machining
is a point-to-point operation along the Z
only, typical to CNC milling maand machining centers. It is also known as a 'single
"
the most common lool is a boring
bar that
only one CUlling edge. Boring on
lathes is
considered a contouring operation and is nol covered in
""""'V<~' (see Chapters 34-35).
Many jobs requiring precision holes that have previously
done on a special jig boring
cannow done
on a
machining center, using a
point boring
(001.
modern CNC machine tools are manufactured to
very high accuracy, particularly for the positionmg
repeatability - a proper
tool and its application can
produce very high quality holes.
• Single Point Boring Tool
As for practical purpose, a
point
ishing, or at
a semijinisi1il1g, operation.
is
to enlarge - or to size - a hole that
been drilled, punched
or otherwise cored.
boring 1001 works on the diameter
the hole
is to produce the desired hole diameter, within
often with a quality
surface finish as well.
Although
is a variety of
of boring tools on
the market, the single point boring lool is usually designed
the cartridge type inserts. These inserts are mounted at
end of the holder (i. e., a
bar) and
have a
built-in micro adjustment
fine
of
boring diameter Figure
12.
The reamer size is always important. Reamers are often
made to produce either a press fit or a slip fit. These terms
are nothing more than machine
expressions
certain tolerance ranges
to the reamed hole.
Programming a reamer
a fixed
Which cywill be the most suitable?
is no reaming cycle defined
Thinking about the traditional machining
plications, the most accepted reaming method is the feed-in
moandfeed-out method. This method requires a
lion to remove the material from the hole, but it
rea
motion back to the starting position, [0
maintain the hole quality - its
and surface finish. It may
be tempting to program a rapid motion out of a reamed hole
to save cycle lime, but often at the cost of quality. For the
best
the feed-out of
reamed hole is necesSuitable
cycle available for the
is
which permitsJeed-in and feed-out mOlions.
cutti ng feedrate of the cycle will the same for both motions.
Any feedrate
will
both motions - in. and out.
D ::: EFFECTIVE
Figure 26-12
Effective diameter of a single polflt boring too/
same programming techniques are applied to the
boring bars of other designs, for example, a block tool. A
block (001 is a boring bar with two cutting
J 80°
If
adjusting mechanism for the diameter is not
available on the tool holder, the effective boring diameter
must
preset, using
a special equipment, or
slow but true
tried trial-and-error method.
trial
and error selup is not that unusual, considering the setup
methods that are available for a single
boring bar.
MACHINING HOLES
Just
any other cutting tool, a single point boring
achieves the best cutting results if it is short,
and run'S
concentric with spindle centerline. One of the main causes
of
bored holes is the boring bar deflection, applying
equally to milling and turning. TIle 1001 tip (usually a carbide bil), should be properly ground, with suitable cutting
CfPr'rnF'I ...... ' and
position of the
in the spindle or its orientation - is very important
many boring operations on machining centers.
• Spindle Orientation
Any round tool, such as a drill or an end mill, can enter or
exit a hole along the Z
with IiUle programming considerations for the hole quality. Neither of the tools is
holes that
high quality
finish
close
tolerances. \Vith boring, the hole surface integrity is very
important. Many boring operations
that the cutting
tool
not
the hole
during retract.
retracting from a
almost always leaves some marks in
the hole, special methods retract must be
There is
one such method - it uses cycle G76 or G87 with the
dIe orientation feature of the
a shift
boring tool away from the finished surface.
feature was
already described in Chapter 12, so just a reminder now.
The sale purpose of spindJe orientation is (0 replace
tool holder in exactly the same position after each tool
change. Without
orientation, the tool tip will stop at
a random position of circumference. Orienting
spindle
boring purposes is only one half of the solution. The
other is
setting position of the boring
is
a responsibility of the operator, since it has to be done
setup at the machine. The boring bar cutting must
set in such a way that when
shift
place in fixed cycle
or
it will into
direction away from the
finished hole
ideally by the
vector relative to the
angle of the
orientation 26-13.
When
machine
is oriented, it must be in a
slopped
The
cannot rotate during any machining operation that requires a spindle shift. Review descriptions of the fine boring fixed cycle G76
the
boring cycle G87
Chapter 25. Machine operator must
alwnys know which way the spindle
and into
direction
lool shift actually moves.
Programming a bored hole that will
later
and
straightness of
finished hole.
surface finish
the
bored
is not too important If the boring is the last machinmg operation in the hole, the
are that the surfinish
be very important It is difficult to retract the
boring lool without leaving drag marks on the hole cylindrical
that case, select a suitable fixed
probably the precision boring cycle G76 is the
r~"'""';"e the boring bar only to assure the
• Block Tools
When using a single point boring bar for roughing or
semi finishing operations, there is an oplion lhat is more efficient. This option also uses a boring tool,
one that has
two cutting
(180 0 opposite) instead of one - it is
called a block tool. Block tools cannot be used
fine finishing operations,
they cannot shifted. The only
way of programming a block lool is within the 'in-and-out'
tool motion. Several fixed cycles support this kind motion. All
'in
at a specified
On
way
'out', some motions are feed rates,
are rapid, depending on
cycle selection.
cycles that can used with
block tools are G81
G82 (feed-in~rapid-out), as well as
and
that
in and feeds oul while the machine
spindle is rotating and another one, G86, when the tool retracts while
is not
The greatest advantage of a block lool is
that can programmed for this tool.
jf the feed rate for a single point tool is .007 per flute,
a
block tool it will be at least double .. 014 inches per flute or
more. Block tools are generally available in
from
about 0.750 inch and
CUTIING
BIT
A
BORING WITH A TOOL SHifT
There are two fixed cycles that require the tool shift away
from the centerline of current bole. These cycles are boring
G76 and G87. G76 is by far
most useful
both
are illustrated
in
02604.
• Precision Boring Cycle G76
Figure 26-13
Single point boring bar and the spindle orientation angle
Spindle orientation is factory designed
fixed.
grammer considers its length and, usually, its direction.
The G76 cycle is used for
requiring a high quality
of the size and surface finish. The boring itself is normal,
nn'"JP'lIpr the retract from the hole is special. The
bar
stops at the bottom of the hole an oriented position,
away by the Q value in
cycle and retracts back to the
starting position,
it shifts back to normal position.
204
26
G76 cycle has been described in detail in the previous chapter. In (his chapter is an actual programming exshown as a single hole in Figure 26-/4 mm.
12'27 '\
- - - - + - - CUTTING DIAMETER
BODY DIAMETER
BACK CLEARANCE
- ««<-- Initial level
.- 025
r
I
30
~:"""':"~::-==r=:=~~~~«<~. . . .~ R level
Figure 26·15
Setup considerations lor a backboring roo/
Figure 26·14
Drawing for 676 and 687 programming example - program 02604
From the drawing. only the
mm hole is considered,
and the program input will quile simple:
N .. G99 G76 xo YO R2.0 Z-31.0 QO.3 F12S.0
A hole bored with G76 cycle will have a high quality.
• Backboring Cycle G81
• Programming Example
In order to show a complete program. four tools will be
used - spot drill (TO I). drill (T02) , standard boring bar
(T03) and a back boring
(T04). Program is 02604.
02604 (G76 AND GS7 BORING)
(TOl
15 MM DIA SPOT DRILL - 90 DEG)
Nl G2l
N2 Gl? G40 GSO TOl
Although
backboring cycle
some applications, it
is not a common fixed cycle.
the name suggests, it is a
boring cycle that works in the reverse direction than other
cycles· from the back oflhe part. Typically, the backboring
operation starts at the bottom the hole, which is the 'back
of the part', and the boring proceeds from the bottom upwards, in the Z positive direction.
N3 MaG
The
cycle has
described in the previous chapter. The Figure
also shows a diameter of 27 mm,
which will be
during the same setup as the
mm
hole. This larger diameter is at the 'back side of the part' )
and it will be backbored, using the G87
mo TOJ
Figure
shows the setup of
tool that will bore
the 27 mm hole, from (he bottom of the hole, upwards.
a
attention to the descriptions.
the diameter of
In the illustration, the 01
smaller hole. and 02
the diameter of (he hole to
be backbored.
is always
than 01. Always make
sure there is enough clearance
the body of the boring
bar within
hole
at the hole bottom.
N4 G90 G54 GOO XO YO 51200 M03 T02
NS G43 ZlO.O H01 MOS
No G99 G82 R2.0 Z-S.O PlOO FI00.0
N7 GBO Z10.0 M09
N8 G28 Z10.0 MOS
N9 MOl.
(T02 - 24 MM DIA DRILL)
Nll. M06
NlJ G90 G54 GOO XO YO 5650 M03 T03
N13 G43 ZlO.O H02 MOS
Nl4 G99 GBl R2.0 Z-39.2 F200.0
Nl5 GSO ZlO.O M09
N16 G28 Zl.O.O MOS
Nl7 MOl
(T03 - 2S MM DIA STANDARD BORING BAR)
NlB T03
Nl9 M06
N20 G90 G54 GOO XO YO S900 M03 T04
N21 G43 ZlO.O H03 MaS
N22 G99 G76 R2.0 Z-31.0 QO.3 F125.0
N23 GSO ZlO.O M09
N24 G28 ZlO.O MOS
N25 MOl
(25 DIA)
MACHINING HOLES
205
(T04 - 27 MM DIA BACK BORING BAR)
N26 T04
N27 M06
N28 G90 G54 GOO XO YO 5900 MOl Tal
~9
part to
accurately seated in
hole by
a bolt
that has to
on a
nat surrace will require countersinking or spotfacing
emtlon. All three operations require a perfect alignment
with the
hole (concentricity). Programming technique is
the same for all three operations, except
for the lOa I used.
and feeds for these tools are usually
than for drills of equivalent
Any hole to
enlarged must
prior to these operations,
,'"p'T""''''' For
G43 ZlO.O H04 MOS
N30 G98 G87 R-32.0 Z-14.0 Ql.3 F12S.0 {27 DIA}
N31 Gao Z10.0 M09
N32 G28 ZlO.O MaS
N33 G28 XO YO
N34 M30
%
Make sure to follow all rules and
gramming or setting ajob with
or 087
in the
'Many of them are safely nru'nrF'f1
•
Precautions in Programming and Setup
The precautions for boring with a tool shift relate La a few
special considerations thaI are
realization the two cycles G76 and
The following list
sums up the mas! importam precautions:
o
The through boring must
o
The first boring cycle
must be programmed
all the way through the hole, never partially
o
For the G76 cycle, only a minimum Q value is required
0.3 mm or .012 inches}
o
For the
cycle, the Q value must be greater than one
half of the difference
the two diameters:
(D2·D1)12 ==
done
the backboring
== 1,
plus the standard minimum Q
(0.3 mm)
o
Always watch for the body of
boring bar, so it does
not hit the
surface during the shift. This can happen
with
boring bars, small holes, or a large shift amount.
o
Always watch the body of the boring bar, so it does not
hit an obstacle
the part. Remember that the tool
length o11set is measured to the cutting edge, not to the
actual bottom of the boring tool.
o
G87 is always programmed in G98
never in G99 mode I!!
o
Always know the shift rllTI',r:ttrln and set the tool properly
•
Countersinking
Countersinking is an operation that enlarges an existing
hole in a conical
to a
depth. Countersinking
for holes
have to accommodate a conical bolt
From all three similar operations, countersinking re,
quires the most calculations for precision depth. Typical
three
o
o
degrees· the most common angle
90 degrees
Other angles are also possible, but
frequent.
To
the programming
(lnd the required
calculations, the cutting tool used must known first Fig.
ure 26~J6 shows a typical countersinking
A
'-
I
L
26-16
Typical nomenclature of a countersinking tool
ENLARGING HOLES
An existing
can also
the top.
enlarge an existing hole at the top, we can use one of three
methods thal will
an existing hole. These methods
are common in every machine shop. They are:
o
o
Countersinking
C'SINK or CSINK on drawings
Counterboring
C'BORE or CaORE on drawings
o
Spotfacing
S.F., or
on drawings
Ai! three machining methods will enlarge an existing
hole, with one common purpose they will allow the fitting
In the illustration, d is the countersink body
A is
countersink angle, F is the diameter of the lool nat
(equal to z.ero for a sharp end), I is the body length.
requires certain data in the
Programming of a
drawing. This information is
provided through a de(leader/text) in the drawing, for
.78 DIA CSINK - 82 OEG
13/32 DRILL THRU
Chapter 26
is one challenge
a countersink.
countersink
accurate. That
0.78 in the description.
countersink angle is
diameter can
by carefully calculating lhe Z depth. That should not
too difficult, because we can use the constant
K for the tool poml
length (described earlier in
then calculate the
culli depth, similar to drills. The problem here is thallhe
constant K for a drill point always assumes a sharp poim at
tool tip. Counters!
tools do not always have a
(except for some
sizes). Instead, they
a diameter of the
F,
specified in toor
catalogues.
countersink diameter,
flat diameter, e is
of the sharp
Z-DEPTH is the programmed tool depth. In this case, the angle A is 82", the flat
is 3116 (.1875). The
diameter F as per
the sharp end e can be
Figure 26-17 illustrates an
quirement, shown in II Iypical
e .1875 x .575
e= 1
a
re-
process of calculation is
lhe heighl e, for a given flat
constants as applied to a
=
.866
.575
==
.500
In [he illustration, D is
A is the countersink
Zdepth
0,625
enough. First, deterF. Use the stanlength:
(K for 82" = .575)
a
a
Z depth = .78 x .575
end will be:
.4485
o
Since that depth
the height of
has to be done to find out the Z depth, is to subtract
from (he theoretical Z depth:
o
Z depth "" . 4485
o
o
0.000
0.750
Figure 28-17
Programming <JY"'TJ"'J> of a countersinking operation
Figure
known and unknown counterdepth
of a
sinking
countersinking
o -.....;
.1078 '" .3407
This is the programmed Z depth and the
for the countersink in
drawing may look
Ihis:
N35 G99 Ga2 XO.75 YO.625 RD.l Z-O.3407 P200 FS.O
could be lowered,
machined in the previous VIJ''''aUVlll_
Be careful
level will most likely
ways program the G98 command and a small
for example,
I:
N34 G43 ZO.1 HO) M08
(0.1 IS INITI.JU, LEVEL)
N3S G98 Ge2 XD.7S YO.625 R-O.2 Z-O.3407 P200 FB.O
A
•
e
Figure 26- 78
for calculating the Z depth of a countersink,
D and F and the
A
Counterboring
Counlerborlng is an operation
enlarges an existing
depth. Counterhole in a cylindrical shape to the
for holes that have to accommodate a round
It is often used on uneven or rough surfaces. or
are not at 90° to
boll assembly. As for the
selection, use a
tool specially defor this type of machining, or a suitable end mill
In either case, the
uses G82 fixed cycle.
is always given) there
depth of the
are no extra calculations
26-19
a
counterboring
MACHINING
DEEP
Handling this programming problem is not difficult, once
available options are evaluated. The options are two
,... ..""1"'\" .."1"'.... ' commands 099. used with fixed
exclusively. Recall that
command will cause
the culling tool to return to
initialleve!, the 099 comwill cause the cuuing tool to return to the R level. In
practical programming. the
command is used only in
cases
an obstacle between
to be
Figure 26-19
Programming example of a counterboring operation
N41 G99 G82 X.. y"
RO.l Z-O.2S P300 FS.O
In counlerboring, if a relatively slow spindle speed and
fairly heavy
are
make sure the dwell
P
in G82 cycle is sufficient. The rule of thumb is to program
the double value or higher of the
minimum
dwell. Minimum dwell Dm
For example. if
spindle speed is programmed as 600
rfmin, the minimum dwell will be 60/600=:0. J. and doubled
to 0.2 in the
as P200. Doubling the minimum
dwell value guarantees that even at 50%
override, there will
at least one full
spindle that cleans
the
Many programmers
to use a slightly
for more than one or two revolutions at the
REQUIRED
26·20
Tool motion direction between holes at rl.ffll"",.t heights
Figure
illustrates two programming possibilities,
in a symbolic representation. The front
of a stepped
holes. On
part shows
direction of tool motion
the left. the
from one hole to the next
cause a
collision with the wall and 098 is
safety. On
the right, with no
098 is not
and 099
the initial
is usually done
a clear
where the Z value must
tool location above all obstacles.
A practical example of this technique is illustrated in Figure 26·2 J nnd
02605.
• Spotiacing
Spotfacing is virtually identical to
(hat the depth of cut is
minimal. Often,
shallow
Its purpose is to
enough material to provide a nat surface for a
bolt, a washer. or a nul.
technique is
same as that for
I
I
--003/16
I
DRilL THR~
MULTILEVEL DRILLING
On many occasions, the same cutting tool will have to
down between di
to move
(steps on a part).
a drill will cut
the same depth. bul start at different
must be
two major
efficiently (no time
(no collision).
0.15
0.50
......,....,+.,-.,.Y-,.-,--:..~ --~----------
1.00
Figure 20-21
Multilevel drilling· nmi'lr;:lflr"lmii1fl example 02605
....... 0.00
0.40
208
Chapter 26
tools are
- TO I is a 90° spot drill, cutting to the
depth of .108 below each step
T02 is a 03/16 drill
Ihrough, programmed to the absolute depth of
1.106:
02605
EXAMPLE)
(TOl - 0.375 SPOT DRILL - 90 DEG)
Nl. G20
N2 GI7 G40 G80 TOI
NJ M06
N4 G90 GS4 GOO XO.25 YO.375 5900 M03 T02
NS G43 Zl.O HOI M08
N6 G99 G82 R-O.4 Z-0.60B P200 F8.0
N7 YO.75
NB Y1.12S
N9 Gge Yl. 625
NlO G99 XO.87S R-O.OS Z-O.2Sa
Nll Yl.125
Nl.2 Gge YO.375
Nl.3 G99 Xl.687S RO.I Z-0.10a
Nl.4 YO.7S
Nl.5 Yl. 625
Nl.6 X2.437S Yl.12S R-O.3 Z-O.508
Nl.7 YO.375
N1B GSO Zl.0 M09
N19 G28 Zl.0 MOS
N20 MOl
WEB DRILLING
Web drilling is a term for a drilling operation laking place
two or more parts, separated by an empty space.
The programming challenge is to make slich holes efficiently. It would be
La program one motion through all
the
parts as well as the empty spaces.
many
inefficjent.
holes, this approach would prove to be
Evaluate the front view of a web drilling example shown in
2r5-22,
Z-1
R-1.575
- . - - - - - Z-2.0
DRILL THRU)
N21 T02
N22 M06
N23 G90 G54 GOO X2.4375 YO.375 S1000 M03 TOl
N24 G43 Zl.O H02 MOS
N25 G99 Ga3 R-O.3 Z-1.106 QO.35 F10.0
N26 G9S Yl.125
N27 G99 Xl. 687S Yl.625 RO.l
N2e YO.7S
N29 YO.375
NJO XO.a7S R-O.OS
NJI Y1.12S
N32 Y1.625
N33 XO.25 R-O.4
N34 Y1.125
N3S YO.7S
N36 YO.375
N37 GSO ZI,Q M09
N3S G2B ZI.O MOS
NJ9 GOO X-2.0 YlO.O
N40 :teO
%
Study the program in detail. Walch the direction of toolsTO I slarts at the
left hole and
at the
right
hole
hole, in a zigzag motion. T02 starts at the lower
and ends at the lower left hole, also in a zigzag motion.
Note there are more G98 or G99 changes
the first tool
than the second tool. In
hole machining undersland three areas of program control, used in 02605:
o G98 and G99 control
o R level control
o Zdepth control
Tool point length == 0.075
Clearance :: 0.05
Figure 25-22
Web drifling eX8lnPIe (front view) program 02606
In
program, X I.OY 1.5 is
as the hole position.
Drawing will not show
R levels or Z depths, they have
to be calculated. In the example,
above and below each
are .05,
the first R level (RO.I). The
length of the 1/4 drill point is .3 x .25 ::::::
02606 (WEB DRILLING)
(T01 - 90-DEG SPOT DRILL - 0.5 DIA)
Nl. G20
N2 G17 G40 GBO TOI
N3 M06
N4 G90 G54 GOO Xl.O Yl.S 8900 M03 T02
NS G43 Zl.0 HOl MOS
N6 G99 Ga2 RO.l Z-O.14 P250 F7.0
N7 GBO Zl. 0 M09
N8 G2a Zl.O MaS
N9 MOl
(T02 - 1/4 OIA DRILL)
Nl.0 T02
N1l M06
N12 G90 G54 GOO Xl.O YI.S S1100 M03 Tal
N13 G43 ZI.O H02 MOB
N14 G99 GSl RO.l Z~O.375 F6 . 0
(TOP PLATE)
(MIDDLE PLATE)
NlS R-0.7 Z-1.25
Nl6 Gge R-1.S75 Z-2.0
(BOTTOM PLATE)
Nl7 GSO Zl,O M09
Nl8 G28 Zl.O MOS
ID9 :teO
%
MACHINING
209
Sjng~e
Note that a
program, rather than
only one plate in the
required three blocks of the
usual one.
.
Also note
in block N 16.
Only one hole is
in the example, so the 098 is not reneeded.
cancellation command G80 with a
take care of the tool rereturn motion in block N17
tract from
hole. However. if more holes are machined,
move
LoollO the new
080 is proIn this case,
098 is
when the drilts
penetrates the last plate of the parr.
example is nOI a
solution to
drilting cuts, as there is still some
wasted motion.
only efficient programming
is
to use the optional custom macro technique and develop a
unique
efficient web drilling cycle.
TAPPING
Tapping is
only to drilling as the most common
hole
operation on
machining centers.
it is
very common to tap on a CNC mill or a
center,
two tapping fixed cycles are avai lable for programming
are the G84
plications on most control systems.
for normal
(R/H), and
cycle for reverse
tapping (UH):
The higher clearance for the R level allows acceleration
of the feed rate
0 to 30 Inches
minute to
place
in the air.
the tap contacts the part, cutting feed rate
should at programmed value, 1101 less. A good rule of
thumb is to program the tapping clearance about two to
the normal clearance. This
will guarfour
antee the feedrate [0 be fully effective when the actual
ping begins. Try to
a slightly smaller number, to
the program more efficient. Another good
ojrlIe tap
method is to double, triple, or quadruple the
and use that value as the
above the
Whichever method is used, purpose is to eliminate the feedrate
associated with motion acceleration.
was the
amount. The
Another
high value 30 in/min (F30.0) has also been carefully calculated. Any cutting fecdratc
tapping must synchronized with the spindle
- the rlmin programmed as the
S
Keep in mind that the tap is basically aform tool
the thread size
shape are buill
it Later in
chapter, the
between the spindle speed and the
feed rate is explained in more detail. The cutting
F
in the program example was calculated by mUltiplying the
thread leod
the spindle
given as rlmin:
F
for righl hand threads
1 / 20 TPI x 600 r/min "" 30. a in/min
to calculale feedrate is to divide the spindle
the number
G74
hand threads
with M04 spindle rotation
Reverse tapping - for
following
shows that programming a
to other fixed
All
one hole is
motions, including spindle stop and
boltom are
in the
N64 G90 G54 GOO Xl.S Y7.125 S600 M03 T06
NoS G43 Zl.O HOS MOS
N66 G99 GB4 RO.4 Z-O.B4 F30.0
N67 GSO
Is it possible to tell the tap
used? It should
In the
example, the tap
20 TPI (twenty threads
per inch). plug tap.
coordinates are missing from
the
cycle,
current tool position has
established in block N64. The usual R level is the
starting pOSltlon
the Z depth is the absolute depth
thread. The
address in the block is feedrate in inches
per minute (in/min), programmed with the F
the R
ofRO.4 has a value that is somewhat
higher than might
used for
reaming, single
the programmed
point boring and similar operations.
feed rate
to be unreasonably high.
is a
values - (hey are bOlh correct
selected
reason for
intentionally.
threads per
(TPI):
F = 600 r/min / 20 TPI = 30.0
quality of the tapped hole is
important, but it is
not influenced solely by the correct
of
feeds, but by
other
as welL The
the tap. its coating, its
the flute
helix configuration, (he
the start-up
being cut tap holder itself all have a
final quality of
tapped hole.
profound effect on
is mandatory,
best results in tapping, a floating
unless the CNC machine supports
tapping.
ing tap holder design gives the tap a 'feel', similar to the
feel that is needed for manual tapping. A floating tap holder
has is
called the tension-compression holder and its
applications are the same for both milling and turning
tap to be pulled out
erations. This type of holder allows
of it or pushed
it, within
The only
of the tool (tool oriable difference is the mounting
entation) in the machine (either vertical or horizontal).
High end floating tap holders also have an adjustable
and even
which can
the feel of the
of the tension
Tapping applications on CNC
are similar to those
on machining centers. A
tapping
a lathe
control is not needed, as
one tap size can
used per
part
tapping
programmed
the 032
command and block-by-block method.
210
Chapter 26
I
lathe tapping is different but not mo~difficult than
tapping for CNC machimng centers. Because it does nol
make some common errors.
use fixed cycles,
This chapter llses examples for tapping on CNC lathes in a
_a
TAPERED
sufficient depth .
• Tap Geometry
are literally
of lap
used in
CNC programming applications. A
book would easily be filledjusr on the topic of tapping tools and their applicalions. For CNC
only the core
of tap
geometry are important.
are two considerations in
the programming and the
o
Tap
PLUG
a
BOTTOMING
Figure 26·23
Typical tap end - chamfer geometry configuI8lion
geometry
o Tap chamfer geometry
Flute Geometry
The flute geometry of a tap is described in tooling catalogues in terms such as 'low helix', 'high helix', 'spiral
flute', and
These terms basically
how the
cutting
are ground into
body of
When
programming a tapping operation, the effectiveness of (he
flute geometry is tied to the spindle
Experimenting
is limited by
tap lead (pitch),
with the tapping
but (here is a greater latitude with the spindle speed selection. The
material and
flute geometry of the lap
both influence
machine spindle speed.
almost all
designs (not limited to
only) are the
of
corporate policies, engineering decisions and philosophies,
various trade names and marketing
there is not a
one way
use
tool' or 'use
for a CNC
program.
tooling catalogue of a tool
is the best
source of technical data, but a catalogue from another supplier
provide a
solution to a particular
Information gathered from a catalogue is a very good starting
the data in (he CNC program. Keep in mind
that the
share some common characteristics.
Tap Chamfer Geometry
chamfer geometry relates to the end configuration of
the
For CNC programming, the most important
of
the tap end point geometry is the tap chamfer.
In order to program a
hole
tap must
hole being
selected according to the specifications
If tapping a blind hole, a different tap is required
tapping a
hote.
are three
of
taps, divided by their
geometry configuration:
o Bottoming tap
o
a
Plug tap
a Taper tap
The major
tap chamfer.
26·23 shows how the
of
the drilled hole wi 11 influence programmed depth of the selected
The tap
length c is measured as the number of
threads. A typical number of threads for a
is 8 to ! 0,
a
tap 3 to 5,
for a
I The angle
chamfer a
varies for
typically 4-5 0 for the
tap, 8-1
the plug tap and
25-35° for the bottoming tap.
will almost always require a bottoming tap,
A blind
in most cases and a taa through hole will require a
per
in some rarer cases.
in different words,
the greater depth allowance must
the
the lap
be
to each drilled hole.
• Tapping Speed and feedrate
The relationship of the
spindle
(r/min)
and
programmed cutting feedrate is extremely important when programming the cutting motion in feedrate per
time mode. Per time mode is programmed as in/min (inches
English
and mmlmin
minute) in programs
(millimeters
minute) for
metric units programming.
This per minute mode is typical to CNC milling machines
and machining
where virtually all work is done
For tapping operations,
ther in in/min or
less of the machine tool. Iltways program the cutting
rate as
distance
muSI
during one
spindle revolution. This
always equivalent to the
lead of the
which is the same as the tap pitch (for taponly),
taps are normally used to cut a
only.
the feedrate
revolution mode, mode tbat
is always equivalent to
1alhes, the
example,
the feed rate.
of .050 results in .050
feedrate. or FO.OS in the
MACHINING
211
""""I ......'" the typical
mode is
always per
in per minute
and thefeedrate is cruculated by one of the following formulas:
~ where ...
Pipe
are similar in design to
long to two groups:
A similar formula will produce an identical result:
Ft
::::
r I min x F,
F,
==
Feedrate per time (per minute)
=
Spindle speed
Feedrate per revolution
=
F,
a 20TPI
1 / 20
~
.0500 inches
feedrate has to
spindle speed,
F = 450 x
into considera450 r/min:
.os = 22.5 = F22.5 (in/min)
A metric tap on a lathe uses the same
(pitch) using 500
a tap of 1.5 mm
with the
750 mm/min:
F :
500 x 1.5 = 750.00
o
Straight
NPT and API
NPS
(parallel)
Programming
pipe taps follows the
considerations for standard threads. The only common difficulty is
how to calculate the Z depth position at least as a reasonable one, if not exactly. The finaJ depth may be a
of
some experimentation
a particular tap
typical materials.
A proper
II size is very important. It will be different for tap
that are only drilled and for lap holes that
are drilled and reamed (using a
per foot taper
The following is a table taper pipe thread
group and recommended tap drills, data that is
CNC programming:
F750.0 (mmVmin)
is to maintain
relationship of the
spindle speed. If the spindle
speed is changed, the feedrate
time (in/min or mm/min)
must be
as well. For
tension-compression
holders, adjustment of
downwards
underfeed) by about
percent may
This is
tension of the tapping holder is
more l1exible than
compression of
same holder.
in the above example is changed from
(tap size is
at 20 TPI), the
must be
a new tapping
F : 550 x .05 = 27.50 = F27.S
In the program, the new tapping tpop.,(1 ... ",tp will be:
F = 27.5 - 5% : 26.125
Taper taps
(I
lead for a mill will
nrr,al"",.rnrnprl
tion
o
taps. They
(nominal size), is not the size of
but
of the pipe
American National
'lfH1UllJ7L pipe taper (NPT)
a taper ratio of I to 16. or
inch per foot (1.7899
I per side) and the tap chamis 2 to 3-112
Ike where ...
r/min
to change the spindle speed of the tool in
proon the CNC machine,
forget to
modify the feedrate
the tapping tool
This mistake
can happen during program preparation the office or during
optimization at the machine. if the
is
small,
may be no
more due to luck than intent. If the change of spindle speed is major, the tap will
most likely break in
• Pipe Taps
Feedrate per time
minute)
Spindle speed
Number of threads per
=
=
TPI
actual feed rate value would be F26.1 or even
NPl Group
Pipe
Size
Drilled Only
TPI
1/16
11/16
.9062
57/64
1.1406
H/8
for NPT
for
212
straight pipe
drills are recommended:
the following
With modern CNC machines, the method of rigid lapis no need for "U'~'-l''''1
ping has become quite popular.
holders. such as the
Decimal Size
.2500
.3438
1/8
27
1/4
18
7/16
.4375
3/8
18
37/64
.5781
%
14
23/32
.7188
3/4
14
59/64
.9219
1.0
11-
1.1563
1-1/4
1.5000
1·1/2
1.7500
2.0
2.2188
The tapping feed rate maintains the same relationships
pipe taps as for standard
• Tapping Check
When programming a
operation,
sure
program data reflect the true machining conditions.
may vary between
majority of them are
cal to any tapping
on any type of CNC
Here is a short list
that relate directly to (he tapping
operations in CNC I"\r{"\ar!'\m,ml
u
Tap cutting
(have to be sharp and properly
u
Tap design
the hole being tapped)
u
Tap ;;,h.ronmi"nt
to be aligned with tapped hole)
the
o
Tap feed rate (has to be related to the
the machine
speed)
lead and
o
Part setup
(rigidity of the machine setup and the tool is important)
o
Drilled hole must be premachined correctly
(tap drill
is important)
o
Clearance for the tap start position
(allow clearance for acceleration)
o
Cutting fluid ;::'CIC;I"UU
U
Clearance at the hole bottom
(the
of thread must be
o
Tap holder torque adjustment
o
Program integrity (no errors)
compression type -
ular end mill holders or
collet chucks can be
the cost of tool
the CNC
control sys(em must suppan the rigid tapping
ture. To program
there is a special M
available - check the
The rigid tapping mode must be supported by
the eNC machine before it can be used in a progr
HOLE OPERATIONS ON A LATHE
point hole
on a CNC lathe are much
more
than
on a CNC machining center.
the number of
drilled or tapped in a
operation on a lathe is
one
part
(two are
rare). while the
holes (or a
may be in lens, hundreds and even thousands.
boring (internal
on a lathe is a LUlU..,.'"
lion, unlike boring on a milling machine, which is a pointto-point operation.
All the point-to-point machining operations on a CNC
lathe are limited to those that can be machined with the culting tool
spindle centerline. Typically,
these operations
center drilling,
drilling,
A variety of other cutting tools may
reaming and
also be
a center cutting
mill (slot
dri II) to open up a
or to make a flat bottom
An internaJ burnishing
may also be used for
such
as precise
a hote, etc. To a lesser
operations, such as counterboring and
may
lathe spindle centerline, with a special
programmed at
operations in
point-to-point
- not a contouring tool.
this
will have one common denominator - they are all
centerline and
with the X
program
for all
programmed in
(r/min), not in the constant
that reason,
is used - for
onaCNC
lathe must
G91 SS15 1403
will assure the required
100% spindle
of cutting)
of tap holders have their own special rewhich mayor may not
any effect on the
If in doubt, always
with the
for
operation.
r/min at the normal spindle
happen if
is used with G96 comthan the proper
command? The CNC
will use the given information, the spindle
in the program (given peripheraJ - or
per minute, asft/min).
will then calculate
required spindle speed in
for (he use by (he ma-
MACHINING
213
if
(surface) speed for a given
ftlmin. the r/min at a 03 inch (X3.0) for the
approximately:
I
S
3 = 573 rpm
ftlmin is applied to the diameter
formula does not change. but
x 3.82) I 0 = 0
S
(ERROR)
mIght be expected to stop (because
laws), it will do the exact opposite (bethe control design). Spindle speed will reach
rlmin that the current gear range will allow. Be
- make sure that the centerline operations
lathe are always done in the G97 (r/min) mode
on a
not in the G96 mode (CSS) mode.
''HHllU''''--
The first method may
when the tool motion area is
stacles in the way (do not count on
a
The
second method, and probably the most common in programming, will
move the Z
not 100
close) to the part, say .50 inch in
tion that follows is the X
centerline (XO). At this
drill) is far from
Z
will be to the Z
where thc actual
nates (or at
with obstacles along
way. The obstacles are - or alleast
could be - the lailstock, the
catcher, the steadyrest, the
etc.
example of this programthe
is the previous example, modified:
path
N36 T0200 M42
N37 G97 S700 M03
N38 GOO xo ZO.5 T0202 Moa
N39 ZO.1
N40
method
the tool approach along
two tool positions - one is the safe clearance
the other one is the safe clearance position for
start.
is a minor alternative to this motion Z
will be at a cutting feedrale, rather
motion rate:
• Tool Approach Motion
A typical geometry offset configuration setup (or
values) on a CNC lathe often have a relatively large X
small Z value. For example. the geometry
offset for a tool may be X-lI.8Z-1.0 (or G50XJ 1.8Z1.0).
location indicates a suitable tool change position
to a drilL What does it mean to the lOa] motion
a drilling operation?
It means that the rapid motion will complele the Z
motion long before completing the X axis motion (with
hockey-slick motion of the rapid command).
motion very close to the part
N36 T0200 M42
N37 G97 S700 M03
N3S GOO XO ZO.1 T0202 MOS
N39
To avoid a potential collision
wards the part, use one of the
o
o
Move the X axis first to the spindle ""..'t"'.·I1 ......
then the Z axis, directly to the start location
for the drilling
Move the Z axis first to a clear rlO~!ltlon
then the X axis to the spindle
then complete the Zaxis motion
the drilling start position
N36 T0200 M42
N37 G97 S700 M03
N3S GOO XO ZO.S T0202 MOS
N39 GOl ZO.l FO.OS
N40
approach motion, the Z axis motion has
to a linear motion, with a relatively high ","'" .. ",'"
in/rev (1.25 mm/rev). Feedrate override can be used
setup, to conlrolthe rate of the feed. During actual production, there will be no significant loss in the cycle time.
• Tool Return Motion
The same logical rules of motion in space thal apply to
the 1001 approach, apply also to the tool return motion. Remember that the firsl motion from a hole must always be
the Z axis:
N40 GOl z-o. a563 FO. 007
N41 GOO ZO.1
N40. the actual drill cutting motion
cut is completed. block N41 is
out of the hole to the same position it
It is not necessary to return to the same
the
style more
214
the cutting tool is safely out of the hole, it has to return to
tool changing position.
are two methods:
Q
Simultaneous motion of both axes
o Single axis at a time
Simultaneous motion of the
same problem as it
on
Z axis will complete
the part face. Also,
during a return motion if
,-,,-,,-.,,.ll .... and the programming
Z axes does not pres- on the conmotion first, moving
is no reason to fear a
approach motion was
was consistent:
mo GOl Z-O. 8563 FO. 007
ml GOO ZO.l
N'72 XU. 0 Z2. 0 T0200 M09
If in
or if an obstacle is
to in the way of
a tool
for example a
program a single
axis at a time. In most cases, that will move the positive X
axis first. as most obstacles would be to the right of the part:
N70 GOl Z-O.SS63 FO.007
N'71 GOO ZO.l
N72 X12.0
N73 Z2. a T0200 M09
The
example illustrates the return motion
with the
programmed first Tht!
that Lhe tuol is
.] 00 off the front face is irrelevant - after all, Ihe tool started
Culling
that distance without a .....1"1,1'\1,...,.,
Other,
wards and
traditional, methods for the tool motion tathe part are
• Drilling and Reaming on lathes
• Peck Drilling Cycle· G14
On Fanuc and compatible
pelitive cycle G74 available,
ent machining operations:
there is a multiple recan be used for two differ-
o Simple roughing with chip breaking
Peck drilling (deep hole drilling)
o
this section, the peck drilling usage of the G74 cycle is
The roughing
of the G74
is a
. operation
ordinary drilling.
first, then
starting position
finally. its depth position. In addition, establish (or even calculate) the depth of
each peck. The lathe cycle 074 is
limited in what it
can do, but it has its uses. Its format for peck-drilling is:
G74
xo Z •• K ••
IGi" where ...
G74
drilling cycle
XO
Indicates cutting on ....m'?"'.·lj""
Z
== Specifies the end point for drilling
K
Depth of each peck (always positive)
following program uses illustration in Figure 26-24,
and shows an exampk~ of
a
6 hole (0.1875)
with a
drill depth of .300
NBS T0400 M42
N86 G97 S1200 M03
N87 GOO XO ZO.2 T0404 MOS
N88 G74 XO Z-O.BS63 KO.3 FO.007
N89 GOO X12.0 Z2.0 T0400 M09
N90 MOl
is also quite common operation,
on a
a hole opening to be used with other
as means
There are three
tools, such as
lathe machining:
drilling, typical to a
o
Center drilling and spotfacing
o Drilling with a
o
6
drill
Indexable insert drilling
Each method
same programming
as those
section earlier.
of the mil1ing lype
there are no
lathe work. Keep in
that on a CNC lathe, the
rOlaling. whereby the
tool remains stationary.
keep in mind that most lathe operations take place in a
zontal orientation,
concerns about coolant
tion and chip removal.
Z-O.8563
Figure 26-24
Sample hole for the
lathe example
The peck
motion will start
the
position
in block N87
to the Z-0.8563 posmon in
block N88.
in a 1.0563 long cut Calculation
the number of pecks is the same as in milling.
MACHINING
215
each peck, there will be
total
and one partial length peck, at
Z-O.l
Z-O.4
Z-O.7
Z-O.SS63
first three pecks are .300 deep
one starts at ZO.2 and ends at 2-0. 1. That will result in two
cut being in the air. Programmer has to
thirds of
this approach is an advantage and when
method would be more suitable. At the end
the G74 cycle, the drill will make a
distance. This distance is set by a
tract by
control system and is typically about .020 inches (0.5
A full retraction after each peck out of the hole (simito the
cycle for milling controls) is not supported
G74 cycle.
thal
is no programmed
out
when the peck drilling cycle is completed.
lion is built-in within the G74 cycle. If a
GOOZO.2M05 follows block N8S, no
operator extra confidence when
the hole
• Tapping on lathes
Tapping on CNC lathes is a common
that follows the same machining principles as
ing centers. The major difference for
of a tapping cycle. There is no
on a lathe, since most of lathe
only one hole of the same type.
may preselH some
difficulties. Unfortuare more common among programmers with
these difficulties
Step 01
Step 02
Step 03
Step 04
Step 05
Step 06
Step 07
Step 08
Step 09
Step 10
Step 11
Set coordinate position
Select tool and
Select spindle speed
rotation
Rapid to the center line and clearance with offset
Feed-in to the
depth
Stop the spi ndle
Reverse the spindle rotation
Feed-out to clear of the part depth
Stop the spindle
Rapid to the starting position
Resume normal spindle rotation or end program
Translated into a
step
can
general guide to '",",,",,,,,,.,
careful1y. this step by
everyday programming as a
lathes.
layout of the part and (he 1001
example 02607. The examthe eleven steps
on a very solid foundation.
02607 is correct - but only
Are there possible problem
TOOL
HOLDER
012.0
9/16-12 TAP
Figure 26-25
Typical setup of a
fool on a
lathe - program examples 02607 and 02608
FLOATING TAP
216
02607
ON LATHES)
(ONLY THEORETICALLY CORRECT
is normally used for single
controls). The G32
point threading. Two major
will be achieved with
the
command - the spindle will be synchronized,
the feedrate override will be ineffective by default
will be solved If (he
matically). The second
die M functions are
the same block as
tool motion. That means
the
N46
with
is in the new program 02608.
(T02 - TAP DRILL 31/64)
N42 MOl
(T03 -12 PLUG TAP)
N43 T0300 M42
N44 G97 S450 M03
N45 GOO XO ZO. 5 M08 T0303
N46 GOI Z-O. 875 FO. 0833
N47 MOS
N48 M04
N49 ZO. 5
NSO MOS
NSl GOO X1.2. 0 Z2. 0 T0300 Ma9
N52 IDa
02608
TAP DRILL 31/64)
N42 MOl
%
A brief look at
02607
anything is wrong.
essary motions
therefore. correct.
contains major flaws!
ON
(PRAC'I'ICALLY CORRECT VERSION)
(T03
not show that
All earlier
have been carefully followed.
Conducting a more
study of the
will reveal two areas of
difficulty or even
The
first problem may
if the feed rate override setting
switch is not set to 100%. Remember, the
is always equal Lo
lead (FO.0833
for 12. TPI). If the
switch is set to any
but 100%, the
will be
at
at worst
damage.
other problem will become evident only in a
block mode run, during
or machining. Look at
N46 and N47. In the N46 hlock, tap reache~ the Z axis
- while the spindle is still rotating! True,
will be slopped in block N47, but in the
mode it will be lao late. A
situation will """"",,,.,,
(he feed-oul motion.
reverses in
but does not move until
N49 block is processed.
the program
is a very poor example of lapp! ng
lathes.
are some details usually not considered for a
application (such as
G84 tapping cycle),
used for milling programs.
milling, all tool mOlions are
built-in, so they are contained within the fixed
eli
the first potential problem of the
will 'd_'_~
programming the M481M49
disable the fecdrate
Even better
mOlion command
mode (G33 on some
N43
N44
N4S
N46
N47
N48
N49
N50
%
PLUG TAP)
T0300 M42
G97 S4S0 M03
GOO XO ZO. 5 MOB T0303
G32 Z-O.S75 FO.OB33 MOS
ZO.S M04
Ma5
GOO Xl2.0 Z2.0 T0300 M09
M30
The block (N48 in
example)
the spindle
is not required if the
is the last tool
stop
in the
although it does no harm in any other program. Compare
program 02608 with
02607.
Program 02608 is a
deal more stable
possibility of any
problem is virtually
• Other Operations
There are many other programming
reJating to
machining
on CNC machining centers
lathes.
This chaprer
some of the most important and
the most common possibilities.
Some less common applications, such as
operations using tools for backboring, or block boring tools.
tools with multiple
edges and other
for
machining
may quite infrequent in
However, programming
unusual
more difficult
the A"f'fF"~"'''
tool motions,
everyday tools.
a CNC programmer is
The real ability
terms of applying the
knowledge and
new problem. It requires a thinking process
a degree of ingenuity
work.
PATTERN OF HOLES
In
point-la-point
operations, consisting of
drilling, reaming, tapping,
etc., we are often require9 to machine either a single
or a series
holes
with Ihe same tool, usually followed by
tools. In
several holes are much more commOn than a
Machining
holes with the same loa I means
machining a pattern of holes or a hole pattern. An English
as a 'characterislic or
dictionary defines the word
consistent arrangement or
'. Translated to
hole
two or more holes machined with .
machinioao
same lool establish a
The
hole
IS
laid out in the pari
either randomly (characteristic
or design) or a certain
(consisTent arfolrangement or design). Dimensioning of a hole
lows standard dimensioning
laid out
some
part and the various methods
their programmake malLers
all programming e.xamples
related (0 Lhe hole panerns wi II assume a center drill ing operation, using a #2 center drill,
chamfer
.150,
to the depth of .163 (programmed as 2-0.163).
nrr\ar:"m reference point 20) is the top
10 be
in
~pindle.
the
of clarity, no hole diamelers or material
and
are specified in the examples.
From the dictionary definition above, we have to establish what makes a hole paHern characteristic or consistent.
Simply, any
that are machined with the same
tool, one hole after another, usually in
of COlwenience.
means all
within a single pattern have the
same
diameter. II also means that all machining
must start at
same R level and
at the same 2 depth.
Overall, i( means that all holes wllhm a pauern are machined the same
any
tool.
TYPICAL HOLE PATTERNS
Hole paHerns can be categorized
each group having the same character.
encountered in CNC programming
the following pattern groups:
o
o
pattern
Straight row pattern
o Angular row pattern
o Corner pattern
o
Grid pattern
o
Arc
o Bolt
pattern
Some groups
be divided
into smaller
groups. A thorough understanding
each pattern group
pattern.
should
you to
any similar
available that have a
are several control
built-in hole
a boll
for example
circle nlIll'prn
nrr\a ...'~m'm ng routines simplify the
hole pattern
quite substantially, but the prostructure is
unique to that panicular brand of
conlrols.
control and cannot applied to
RANDOM HOLE PATTERN
The most common pattern used in programming
a
pattern.
pattern
holes is a
where all holes share
same machining characteristics,
but the X and Y distances between them are inconsistent. In
other words, holes within a
pattem
the same
LaO!. the same nominal
usually the same depth,
but a variable distance from each other - Figure 27-/.
-
-
4.4
-.,..J
1.4
0-
o
•
l
,,
2
1B 20
. .4
~_ _ _ _ _ _ _ _ _ _..... O!~_J_._L_1.
figure 27·'
Random pattern of hotes· program example 02701
are no special lime saving
used in programming a random
- only a
fixed
used at individual hole locations. All XY coordinates
programmed manually;
within the hole pattern have to
control
features will
no help here at all:
217
218
Cha
02701 (RANDOM HOLE PATTERN)
Two
program 02702 should be
, In block N6, the di
mode was
absolute G90 (0 the incremental G91, to take
When all ten holes have
the equal pilch
to include return to
chined, the program
zero position motion, in the example, along all
axes.
However. without a calculation, we do not know the
lute position atlhe tenth
for the X axis (the Y
remains unchanged al
of .60 inches = YO.6).
solve this 'problem',
the cycle with G80,
G91 mode in
move (0 the machine zero position
in the Z axis first
Then - still in the incremental mode
I - return both X and Y axes to
machine zero simullaneously.
N1 G20
N2 G17 G40 GSO
N3 G90 G54 GOO Xl.4 YO.S S900 MOl
N4 G43 Zl.O HOI MOB
NS G99 Gal RO.l Z-O.163 F3.0
N6 X3.0 YJ.O
N7 X4.4 Y1. 6
N8 X5.2 Y2.4
N9 GBO M09
NlO G28 ZO.l MOS
Nll G28 XS.2 Y2.4
N12 IDO
%
STRAIGHT ROW HOLE PATTERN
to the X or Y axis with an equal
Figure 27-2 shows a 10 hole
with a pitch of .950 inch.
Hole
pitch ~s a
pattern
- 'I
• program example 02702
The programmi
takes advantage of a fixed
cycle repetition
Lor K address. It would
be inefficient to program
hole individually. As always,
(he tool wiJl be positioned at the first hole in G90 mode,
then the cycle will machine
hole in block N5.
the remaining holes,
mode must be changed to
incremental mode G91,
the controllo machine the olher nine
incrementally, along the X axis
only. The same logic would
for a vertical pallern
along the Y axis. In that case,
would be
programmed along the Y
Note lhallhe repetition
ofspaces, not the numcount is always equal to the
of holes. The reason?
hole h!ls already been
machined in the cycle call block.
02702 (STRAIGHT ROW HOLE PATTERN)
Nl G20
N2 G17 040 G80
N3 G90 G54 GOO Xl.lS YO.6 5900 MOl
N4 043 Zl.O Hal Moe
NS G99 Gal RO.l Z-0.16l Fl.O
N6 G9l XO.95 L9
N7 G80 1409
N8 G28 ZO MOS
N9 G28 XO YO
NlO MJO
%
Normally, this first tool of the example would be followed by other LOols to
the hole machining. To
protect the program and
from possible probute command is
lems, make sure that the G90
for every tool (hal
ANGULAR ROW HOLE PATTERN
TYP
0.6
row hole
27
in a row al an
is a variation of a
pattern. The
between the two is that
pitch applies 10 bulh X
Y axes. A hole
pattern of this type will be
on the part drawing
as one the two possible dimensioning methods:
o
X and Y coordinates are given for the first and the last hole
In this method, the pattern
and no pitch belween holes
is not speci-
o X and Y coordinates are given for the
hole only
In this method, paUern angular
the holes is
is specified and
In either case, all the necessary
Y dimensions are
to write the program. However, the programming
will be different for each method of drawin bo
• Pattern Defined by Coordinates
method of programming is
row
pitch between
increment between holes along
be
This axial distance is
as
X is measured
X axis.
along the Y axis). Such a calculation
in two equally accurate ways.
The lirs( calculation method can use a
method, but it is much casier (0 usc the ratio
stead. In the Figure 27-3, the pattern length
Ilxis is I
and along the Y axis it is 2.0:
(2.625 -
=2.0)
HOLES
219
N7 GBO M09
o
o o
N8 G28 ZO MOS
N9 G28 XO YO
NlO M30
%
Note that the program structure is idt:nlicallu- Lhe exam-
ple of the straight row
with L5 (KS)
+----10.82-----.... -
except the incremental move
two axes instead of one.
.. Pattern Defined by Angle
27·3
be defined in the drawing
hole, the number of
between holes and
Angular hole pattern with two sets of coordinates· program 02703
of this kind has all the holes
by equal distances along X and Y axes. As all holes are equally spaced,
ratio of the sides for individual holes is identical to the
of the whole pattern. When
mathematically,
f\('r'p'rn,pnl between holes along
to the
'l>la" ..", of I 0.82 divided by
of X axis
"IJ""''''''. the increment along the Y
to the overIstance of 2.0 divided by
Y axis spaces.
so the X
number of spaces for a six
(the delta X)
equally
holes,
angle of pattern inclination - Figure 27-4.
2.0
10.82 / 5 = 2.1640
and the Y axis increment (the
27-4
2.0 / 5 = .4
Angular
The other calculation method uses lTigonometric fllncwhich may also be
as a confirmation of the first
vice versa. Both
must be identical, or
is a mistake somewhere in the calculation. First, es-
In
to calculate the X and Y coordinate
trigonometric functions in this case:
- 02704
use
x = 4.0 x coa15 = 3.863703305
Y = 4.0 x sin15
1.03527618
10.47251349"
can be written after you round off the calculated
. program 02704:
C = 2.0 / sinA = 11.00329063
C1 = C / 5 = 2.20065813
with coordinates, pitch
02704
Raq 2)
m G20
Now, the actual increment along the two axes can
culated, using C I dimension as the distance between holes:
x increment = Cl x cosA = 2.1640
Y increment = Cl x sinA = .4000
The calculated mcreOlents match in both methods,
lalion is correct,
can now be used to write the program
(02703) - block
the vaJues:
02703 (AN'GOLAR Raq
m G20
N2 G17 G40 GBO
N3 G90 G54 GOO X1.0 YO.62S S900 M03
N4 G43 Zl.O HOl M08
NS G99 Gal RO.l Z-O.163 F3.0
N6 G91 X2.164 YO.4 L5 (K5)
N2 G17 G40 G80
N3 G90 G54 GOO X2.0 Y2.0 8900 M03
N4 G43 Zl.0 HOl MOB
N5 G99 GSl RO.l Z-0.163 Fl.O
N6 G91 X3.8637 Y1.0353 L6 (K6)
N7 GBO M09
N8 G28 ZO MOS
N9 G2B XO YO
mo M30
%
Since the calculated increments are rounded values, a certain
accumulative error is inevitable. In most cases, any error will
be well contained within the
drawing tolerances.
However, for the projects
highest precision, this
error may be important and must
taken into consideration.
220
Chapter 27
To make sure all calculations are correct, a simple checking method can be used (0 compare the calculated values:
~ Step 1
Find the absolute coordinates XY of the last hole:
x
Y
2.0 + (4.0 x 6 x coalS)
=
25.1B221983 = X25.1822
=
2.0 + (4.0 x 6 x sinl5)
=
8.211657082 = YB.2117
02705 (CORNER PA'I'TERN)
Nl G20
N2 G17 G40 GaO
N3 G90 G54 GOO X2.2 Yl.9 S900 M03
N4 G43 Zl.O H01 MOS
N5 G99 G8l RO.1 Z-0.163 F3.0
N6 G91 Xl.5 Yl.B L2 (K2)
~ Step 2
Compare these new XY coordinates with (he previously
calculated increments as they relate to the lasl hole of the
pattern (using rounded values):
x
Y
Note that both X and Y values are accurate. When rounding. particularly when a large number of holes is involved,
the accumulative error may cause the hole pattern out of
tolerance. In that case, the only correct way to handle the
programming is to calculate the coordinates of each hole as
absolute dimensions (that means from a common point
rather than a previous point). The programming process
will take a little longer, but it will be much more accurate.
CORNER PATTERN
Pattern of holes can be arranged as a corner - which is
nothing more than a pattern combining the straight and/or
angular hole patterns - Figure 27-5,
1,5---'
---
1.8
N7 Xl. 8 L6 (K6)
NB Y-l. B L2 (K2)
N9 GSO M09
mo G28 ZO MOS
Nll G2B XO YO
Nl2 1000
%
2.0 + 3.8637 x 6
25.1822
2.0 + 1.0353 x 6 = 8.2118
=
=
comer hole will be machined twice. Visualize the whole
process - the last hole of one row pattern is also the first
hole of the next pattern, duplicated. Creating a special custom macro is worth the time for many comer patterns. The
nonnal solution is to move the lool to the first position, call
(he required cycle and remain within that cycle:
l
i--
I
.
l1le program offers 00 special challenges. In block N6,
the angular row of holes is machined, starting from the
lower lefl hole, in N7 it is the horizontal row of holes, and
in N8 the vertical row of holes is machined. The order is
continuous. Just like in the earlier examples, keep in mind
that the repetition count Lor K is for the number of moves
(spaces), not the number of holes.
GRID PATTERN
Basic straIght grid pattern can also be defined as a set of
equally spaced vertical and horizontal holes, each row having equally spaced holes. If the spacing of all vertical holes
is the same as the spacing of all horizontal rows, the final
grid pattern will be a square. ff the spacing of all vertical
holes is not the same as the spacing of all horizontal rows,
the resulting grid pattem is a rectangle. A grid pattern is
someti mes called a rectangular hole pattern - Figure 27-6.
I
1 1.8
I I
-wED 0 0 0
--"'1
, GOO 0 0 (j)-e-~8
CD.
1--8I
,
1.9
(B---r
.
0
0000$--'..l
2.1
OOOOUJ--,
00000
00000
00000
I
I
I ,
-
2.2
figure 27-5
Corner pattern of holes· program example 02705
All rules mentioned for the straight and angular hole patterns apply for a corner pattern as well. The most important
difference is the corner hole. which is common to two rows.
A comer pattern can be programmed by calling a fixed cycle for each row. Soon, it will become apparent that each
I
0·0 0 0 (]j---.-L
2.4
'---1.7
-r
I
Figure 27-6
Rectangular grid hole pattern - program example 02706
PATTERN
HOLES
1
A grid pattern is very similar to a series of corner patterns,
similar programming methods. The
tion
a grid pattern programming is in its
Each
row can be programmed as a single row pattern, starling.
for example,
the left side of
IroW. Technically,
that is correct, although not very efficient duc to the loss of
the tool has to travel from
last hole of one
row, to the
hole the next row.
motion. To
a zIgzag motion, program
row or colwnn
at any corner bole. Complete that row (column),
then jump to the nearest hole the next row (column) and
repeat the process until aU rows and columns are
The
lime of the
motion is kept to the minimum.
000
More
02706 (STIlAIGm' GRID PAT'I'ERN)
Nl G20
N2 G17 G40 GaO
NO G90 G54 GOO Xl.7 Y2.4 S900 M03
N4 G43 Zl.O H01 MOS
N5 G99 GSl RO.1 Z-O.163 F3.0
N6 G91 Y2.1 L6 (K6)
N7 Xl.S
N9 Y-2.l L6 (K6)
NlO X1.8
Nl1 Y2.1 L6 (K6)
N12 X1. 8
N13 Y-2.l L6 (K6)
N14 Xl.8
Nl5 Y2.1 L6 (K6)
N16 GSO M09
Nl7 G2B ZO M05
NlB G28 XO YO
N19 IDO
%
Two features the
are worth noting - one is the
pattern to another - it has no repejump from one row of
tition address L or
because only one hole is being machined at
location. The
feature may not be so
obvious right away.
make the program shorter, stan
the
that
the larger
of
(the
in the program
02706).
example is a
variation on
previous examples and also adheres to all
the
established so
A special subprogram made for
a
pattern is also a common programming
and
can be used as well.
o
a
3.5
-14.0
27-7
Angular grid hole pattem - program example 02707
The unknown increment in the drawing is the distance
a hole in one
measured along the X axis,
row to the next hole in following horizontal row:
x ~ 4.6 x tan16 = 1.319028774 (Xl.3l9)
The program can be written in a similar
as for the
the extra 'jump' between rows will
straight row grid,
take place along both axes:
02707 (ANGULAR GRID)
Nl G20
m G17 G40 GBO
NJ G90 G54 GOO X4.0 YJ.5 S900 M03
N4 G43 Zl.0 HOl MUS
NS G99 GS1 RO.1 Z-O.163 Fl.O
N6 G91 X3.2 L5 (KS)
N7 Xl. 319 Y4. 6
NS X-3.2 LS
N9 Xl. 319 Y4, 6
mo X3.2 L5
)
N1l X1.319 Y4.6
N12 X-3.2 LS
Nl3 GBO M09
N14 G28 ZO MUS
NlS G2S xo YO
N16 M30
%
• Angular Grid Pattern
the straight grid pattern is the most common
a grid
pattern
square and rectangular hole
pattern may also be in the shape of a parallelogram, called
an angular grid pattem - Figure 27-7.
the programming approach
the same as
for
rectangular grid pattern, the ollly extra work required is the calculation of the
increments, similar
to previous methods:
Many
will consider even more
programs for grid patterns
efficient way approaching
by using subprograms or even User Macros. Subprograms
patterns con~isling of a large
are especially useful
number of rows or a large number of columns. The
subprograms, including a practical example a really
grid
is covered in Chapter
subject of
user macros is not
in this handbook.
Chapter 27
e STEP 1
ARC HOLE PATTERN
Another quite common
pattern is a set of equally
arranged
an arc (not a circle). Such an
equally spaced set of holes
portion of a circle
cumference creates an arc hole pattern.
approach to programming an ~rc hole pauern should
same as if programming any other hole pattern.
as the one that is most convenient. Is it the
or the last
arc that is easier to tind the
coordinates for?
at 0"
0' clock or
position) would be beBer?
In
27-8
shows a typical layout of an arc
that is nearest to 0° iodirection), then continue
direction of the arc.
e STEP 2
Use trigonometric
ordinates of the first
to calculate the X and
co-
Hole #1
x = 1.5 + 2.5 x cos20 == 3.849231552
Y = 1.0 + 2.5 x siDlO
e
1.855050358
3
Use the same
culate XY coordinates
included
hole in the pattern,
the second hole angle will be 40°, the third
Hole #2
x = 1.5+ 2.5 x <::os40 = 3.415111108
Y = 1.0+ 2.5 x sin40 = 2.606969024
1.0
1
I
Figure 27-8
Arc hole
4 EQSP
x == 1.5 + 2.5 x 00s60
Y c: 1.0 + 2.5 x sin60
program 02708
Hole #4
and
A number of
is needed to find
X
Y
coordinates
hole center location within the bolt
hole pattern.
procedure is similar to that an angular
but with several more calculations.
line in a grid
The calculation uses trigonometric functions applied to
each hole
- all necessary data and other information are
drawing.
holes, exactly the .... V~.Ul ...
required to get the 1"'-'1""1'1,.1"1
""-'...,"1"".... there are four holes,
eight
calculations will necessary. Initially, it may seem as a lot
of work. fn terms of calculations, it is a lot
work. but
keep in mind that only two trigonometric formulas are involved for any number of holes, so Ihecalculations will beobservation
come a lot more manageable. Incidentally,
to just about any other simi lar programming
can be
lo use
will be
Hole #3
1.5
arc center locations are known, so is the
programming, is
programming task
.4151)
.607)
2.750000000
3.165063509
x = 1.5 + 2.5 x cosSO = 1.934120444
Y == 1.0 + 2.5 x sinelO '" 3.462019383
e
Hole #1:
Hole #2:
Hole #3:
Hole #4:
Now,
.9341)
.462)
4
X3.8492
Xl.41S1
X2.7S00
X1.934l
Y1.B5S1
'l2.6070
Y3.16S1
Y3.4620
program for the hole arc pattern can be written,
XY coordinates for
hole location from the
calculations 02708:
02708 (ARC PATTERN)
Nl G20
N2 Gl'7 G40 GSO
N3 G90 GS4 GOO X3.B492 Yl.85S1 S900 M03
N4 G43 Zl.0 HOl M08
NS G99 G8l RO.l Z-O.163 F3.0
N6 Xl.4151 Y2.60'7
m X2. '75 Y'3.1651
N8 Xl.9341 Y3.462
PATTERN OF HOLES
223
N9 G80 M09
N10 G28 ZO.l MOS
N11 G2B Xl.9341 Y3.462
N12 MJO
%
There are two other methods (perhaps more efiicient) to
program an arc hole pattern. The first method will take an
advantage of the local coordinate system G52. described in
Chapter 40. The second method will use the polar coordinate system (optional on most controls), described later in
this chapter - In program 027 JO.
BOLT HOLE CIRCLE PATTERN
A pattcrn of equally spaced holes along the circumference of a circle is called a bolt circle pattern or a bolt hole
pattern. Since the circle diameter is actually pitch diameter
of the pattern, another name for the bolt circle pattern of
holes is a pitch circle pattern. The programming approach
is very similar to any other pattern, particularly to the arc
hole pattern and mainly depends on the way the bolt circle
pattern is oriented and how the drawing is dimensioned.
A typical bolt circle in a drawing is defined by XY coordinates of the circle center, its radius or diameter, the number of equally spaced holes along the circumference, and
the angular orientation of holes, usually in relation to the X
axis (that is to the zero degrees).
A bolt circle can be made up of any number of equally
spaced holes, although some numbers are much more common than others, for example,
4,5,6,8,10,12,16,18,20,24
First, select the machining location to start from, usually
at program zero. Then find the absolute XY coordinates for
the center of the given circle. In the illustration, the bolt pattern center coordinates are X7.5Y6,0 ..There will be no maChining at this location, but the center of the circle will be
the starting point for calculations of all holes on the bolt circle, When the circle center coordinates are known, write
them down. Each hole coordinate on the circumference
must be adjusted by one of these values. When all calculations for the first hole are done (based on the circle center),
continue to calculate the X and Y coordinates for the other
holes on the circle circumference, in an orderly manner.
In example 02709 are 6 equally spaced holes on the bolt
circle diameter of 10.0 inches. That means there is a 60° increment between holes (360/6=60). The most common
starting position for machining is at the boundary between
quadrants. That means the most likely start will be at a position that corresponds to the 3, 12,9 or 6 o'clock on the
face of an analog watch. In this example, the start will be at
the 3 o'clock position. There is no hole at the selected location, the nearest one will be at 30° in the counterclockwise
direction. A good idea is to identify this hole as a hole number I. C?ther holes may be identified in a similar way, preferably In the order of machining, relative to the first hole.
Note that each calculation uses exactly the same format.
Any other mathematical approach can be used as well, but
watch the consistency of all calculations:
Hole #1
x '" 7.5 + 5.0 x cos30 '" 11. 830127
y == 6.0 + 5.0 x sin30 '" 8.500000
Hole #2
In later examples, the 6-hoJe and the 8-hole patterns (and
their multiples) have two standard angular relationship to
the X axis at zero degrees.
x
Figure 27- 9 is a typical bolt circle drawing. The programming approach for a bolt circle is similar to arc paHern.
Hole #3
Y
7.5 + 5.0 x cos90
6.0 + 5.0 x sin90
7.5000000
11.0000000
==
::;;
C
(Xl1.8301)
8 s1
.
(X7 .5)
(Yl1. 0)
x '" 7.5 + 5.0 x cos150
3.1698729B (X3 .1699)
Y = 6.0 + 5.0 x sin150 '" 8.50000000 (Y8.S)
Hole #4
x :;: : 7.5 + 5.0 x cos210
010.0
3.16987298 (X3.1699)
3.50000000 (Y3.5)
y '" 6.0 -I- 5.0 x sin210
Hole #5
I
x == 7.5 -I- 5.0 x cos270 == 7.50000000 (X7 • 5)
Y == 6.0 + 5.0 x sin270
L
- 7. 5 - -t
I
Figure 27-9
Bolt circle hole pattern· program 02709
==
1.00000000 (Yl.O)
Hole #6
x == 7.5 + 5.0 x cos330 == 11.930127 (XU.8301)
Y '" 6.0 + 5.0 x sin330
:;:::
3.500000 (Y3.5)
224
Chapter 27
Once all
are calculated, the program is writpatterns:
ten in the same way as
the following explanation and [he
any hole in any bolt circle pattern can
The formula is similar for both axes:
02709 (BOLT CIRCLE
Nl G20
N2 017 040 080
X
cos«(n-l)x B+A)x R+X,
Y
«(n-l)x B+A)x R+Yc
N3 G90 G54 GOO Xll.8301 Y8.S S900 M03
N4 G43 Zl.O HOI MOe
N5 G99 G8l RO.l Z-O.163 F3.0
N6 X7. 5 Yll. 0
N7 D.1699 YB.S
N8 Y3.S
N9 X7.S Yl.O
NlO X11.830l Y3.S
Nll GBO M09
Nl2 G2S ZO.l MOS
Nl3 G91 G2B XO YO
Nl4 ICO
~ where ...
x
Y :::::
n ::::
H
B::::::
A :::::
%
R :::::
It would be more logical to
bolt circle center as
program zero, rather than the lower
comer of the part.
ThIS method would el"
of the boll circenter position for each
value and perhaps
reduce a possibility of an error. At
same time, it would
it more djfficult to set the
on the macoordinate
chine. The best solution is to use
offset method. This method is especially useful for those
jobs that require translation of
boll
(or any
paUern) to other locations
same part setup. For
details on the G52 command, see
40.
• Bolt Circle formula
In
calculations,
are
repetitious
The methods are the same, only
changes.
of calculation offers an
opportunity for
a common formula that can
used, for av"n-> ... '
of a computer program, calculator data input.
etc.
27-10 shows the basis for such a formula.
B
Xc :::
Yc :=;
X coordinate
Hole Y coordinate
Hole number counter - CCW from 0"
Number of equally spaced holes
between holes = 360 I H
First hole angle· from 0°
Bolt
radius or bolt circle diameter12
Bolt
center from the X origin
Bo It circle center from the Y orig in
• Pattern Orientation
The bolt
gle of the
orientation is specified by the anthe 0° of the bolt circle.
In daily
bolt circle patterns will have not
only different llUIIlVl"1 holes, but different orientations as
well.
bolt
most commonly affected are those
spaced holes is based on the mul...) and multiples of eight (4, 8,
16,24,32, ... ).
relationship is important, since the orientation of the first hole wlllinfluence the position of all the
pattern.
other holes in the bolt
I
Figure 27-1 J shows relationship of the first holt\position
to the 0° location
0" location is equivalent
to the 3 o'clock
or the
direction.
'j
I
\ R
~
._-,.....i
Figure 27·10
Basis for a formula to calculate bolt hale pattern coordinates
Figure 27-11
Typical orientations af a six and
hole boh circles
PATTERN
HOLES
2
POLAR COORDINATE SYSTEM
So
all mathematical calculations relating to the arc or
bolt circle pattern of holes have been using lengthytrigonometric formulas to calculate each coordinate. This seems to
a slow
for a
CNC system with a very
advanced computer. Indeed, there is a special programmethod
(usually as a control option) that
takes
all the
calculations
an arc or bolt
circle pattern It IS
the polar coordinate system.
There are two polar coordinate functions available, always
recommended to be written as a separate block:
cancel
Polar coordinate
27·12
Three basic characteristics of polar coordinates
OFF
Polar coordinate system
ON
for bolt hole or arc
may
programmed
polar
system commands.
Check
the options of the
before using this
method.
programming format is similar to that of programming flxed cycles. The format is,
identical- for
In addition to the X and Y data, polar coordinates also require tbe center of rotation. This is
point
grarnmed
G 16
Earlier,
in program
02708 and
27-8 were calculated using trigonometpolar
control
the
can be much simplified 10:
02710 (ARC PATTERN
N"
G9.. G8..
x.. Y.. R.. Z.. F ••
N2 G17 G40 G80
N3 G90 G54 GOO Xl.S Yl.O S900 M03
distinguish a standard
cycle
used in the polar coordinate mode.
StaIlaaJro cycle.
system
6 must be issued to acpolar mode (ON mode).
the polar coordinate mode is completed
no longer required in the
the command G 15 must be used to
it
mode). Both commands must in a separate block:
N.. G16
N •• G9 •• GS ..
N •.
N ••
N •.
N •• G15
(POLAR COORDINATES ON)
x .. Y .. R •• Z •• F ••
(MACHlN.ING HOLES)
u .....1•..........,.
CDORDlNA'l'ES OFF)
second factor is
meaning
X and words.
standard fIXed cycle, the XY words defIne'the
of a hole rectangular coordinates,
as an
solute location. In the polar mode and
effect (XY
both words take on a totally different meaning a radius and an angle:
a
The X word becomes radius of the bolt circle
a
The V word becomes
IO.INl')
N4 G43 Zl.O HOl MOS
U;"".",VJ..:>
same
POLAR)
N1 G20
N5 G16
(POLAR COORDlNA"l."BS ON)
N6 G99 Gal X2.S Y20.0 RO.l Z-O.163 F3.0
N7 X2.S Y40.0
N8 X2.5 Y60.0
N9 X2.S Y80.0
NlO GIS
COORDlNA'l'ES OFF)
Nll GSO M09
N12 G9l G28 ZO M5
N13 G28 XO YO
Nl4 mo
%
next program 02711,
are equally spaced on
the bolt circle circumference. Dimensions in Figure 27- J3
are
to the
coordinate prCignurururlg lTlemlOa.
120:O~-'
;'
,I
I
60°
R6.8
180°-8-
of the hole, measured from 0°
Figure
illustrates
ments for a polar coordinate system.
requrre-
Figure 27-13
Polar coordinate system applied to bolt hole circle - program 02711
226
Chapter 27
02711 (GI5-GI6 EXAMPLE)
N1 G20
N2 GI7 G40 GBO
N3 G90 GS4 GOO XO YO S900 N03
N4 G43 Zl.0 HOl MOB
N5 GIG
G 17 plane is known as the XY plane. Ifworking in another
plane, make double sure to adhere to the following rules:
(PIVOT POINT)
The first axis of the selected plane
is programmed with the arc radius value.
(POLAR ccx)RDmATES ON)
N6 G99 GSl X6.B YO RO.I Z-O.163 F3.0
m X6.B Y60.0
The second axis of the selected plane
is programmed as the angular position of the hole.
NB Xo.8 Y1.20.0
N9 X6.8 nao.o
NlO X6.8 Y240.0
Nl1 X6.8 Y300.0
Nl2 GIS
ID3 GBO M09
Nl4 G9l G28 ZO MOS
N1.5 G28 XO YO
(POLAR COORDINATES OFF)
In a table fannat, all three possibilities are illustrated
Note, that if no plane is selected in the program, the control
system defaults to G 17 - the XY plane.
ID6 M30
%
G-eode
Selected plane
First axis
Second axis
G17
'I:(
X = radius
Y = angle
G18
IX
Z = radius
X = angle
G19
YZ
Y = radius
Z = angle
I
Note that the center of polar coordinates (also called pivot
point) is defmed in block N3 - it is the last X and Ylocation
programmed be/ore the polar command G 16 is cal.led ill
the program example 02711, the center is at XOYO location (block N3) - compare it with program 02710.
Both, the radius and angle values, may be programmed in
either absolute mode 090 or incremental mode 091.
If a particular job requires many arc or bolt hole patterns,
polar coordinate system option will be worthy of purchase,
even at the cost of adding it later. If the Fanuc User Macro
option is installed, macro programs can be created withnut
having polar coordinates on the control and offer even
more programming flexibility.
•
Plane Selection
Chapter 29, and particularly Chapter 3 J, describe the
subject of planes. There are three mathematical planes,
used for variety of applications, such as polar coordinates.
G11
XY plane selection
GtB
ZX plane selection
619
YZ plane selection
Selection of a correct plane is extremely critical to the
proper use of polar coordinates. Always make it a habit to
program the necessary plane, even the default G17 plane.
Most polar coordinate applications take place in the default XY plane, programmed with the G 17 command.
•
Order of Machining
The order in which the holes are machined can be controned by changing the sign of the angular value, while the
polar coordinate command is in effect. If the angular value
is programmed as a positive number, the order of machining will be counterclockwise, based on. the 0° position. By
changing the val.ue to a negative number, the order of machining will be clockwise.
This feature is quite significant for efficient programming approach, particularly for a large number of various
bolt hole patterns. For example, a center drilling or spot
drilling operation can be programmed very efficiently with
positive angular values (counterclockwise order). The start
will be at the fust hole and, after the tool change, the drilling can continue in the reverse order, starting with the last
hole. All angular values will now be negative, for the
clockwise order of a subsequent tooL This approach
requires a lot more work in standard programming, ~hen
the polar coordinates are not used. The polar coordinate
application using the G 16 corrunand eliminates al.1 wmecessary rapid motions, therefore shortening the cycle time.
FACE MILLING
milling is a machining operation that controls
height
machined part. For most applications,
milling is a relatively simple operation, at least in the sense
it usually does not include any difficult "V'lLU'.'"
cuWng tool used for face milling is typically a
tooth cutter, called a face mill, although end
for certain face milling operations, usuaUy within smaJl areas. The top surfaces machined with a
mill are generally perpendicular to the
of the
cutter. In CNC programming, the face
are fairly simple, although two important .... v,'''' .....'''.
are
Q
Selection of the cutter diameter
Q
Initial starting position of the tool in
to
It
to have some experience
milling principles, such as the right cutter
tion, distribution of cuts, machine power
other technical considerations.
ones are covered in this chapter, but
catalogues and various technical ...""F,,,,...,, ... ,,.,,,.
in-depth source.
CUTTER SELECTION
all milling operations,
tool that rotates while the
that a
employs a cut~
stationary.
material be re-
a
cut or
milling is so effortless
not pay sufficient
milling cutter, proper
chine requirements and
A typical face mill is a multi
cutter with interchangeable carbide inserts.
face mills are
not recommended for
although an HSS end
mill can be a suitable
to
mill small areas or areas hard to get to in any other
Typical to a face milling
operation is the fact that not
of the milling cutter
are actually working at
same time. Each insert works
only within a part of one complete revolution. This observation may be an
consideration when trying to
establish an optimum
a face milling cutter. Face
milling does
power resources from the
machine tool.
in the cutter body. it is
properly mounted.
•
Selection Criteria
Based on the job to be
GUller has to Lake into account
mill
Q
Condition of the eNC machine
Q
Material oftha part
o
Setup method and work holding integrity
Q
Method of mounting
Q
Overall construction of the cutter
o
Face mill diameter
Q
Insert geometry
The last two items, cutter
will influence the actual
although other items are
geometry,
the most,
• face Min Diameter
a single 2.5 inches
mill as a suitable
a good formation of
For multiple cuts,
that can be used for
rigidity, depth and width
related factors.
of face milling is to machine
specified height. For this type of
.
a
mill diameter size, which
in
means to use relatively large diameter face mills.
2 12 inches (50 to 300 mm) are not unusual,
the job.
The
top of a part to
m
width
mill. All tooling ..........u.J.v'F.u•.".,
mill (5 inches in the ..."' ...... ,,1-"'"''
though
body
can be found in
well. The nominal diameter always refers to
of the cut. There is no way to tell the actual
tool
body from the nominal size alone, it
looked up in the tooling catalogue. Normally,
of the cutter body is not needed, except in
cases
227
Chapter 28
where the face milling
place close to walls or
obstacles. The size of the cutter body may prevent access to
some areas of the part and
interfere elsewhere as well.
28- J shows some typical configurations.
Negative bej'ml~rrv
Negative
face mills
the insert
usually require a
machine
and a robust
side effects are poor fonuation of
the
but not for some kinds of cast irons,
is hardly any curling
during chip forwhere
mation. Their main benefit is the
economy, since
are generally
sided, offering up to
for a single
inserted in
mill.
Double Negative Geometry
Fjgure 28-1
Nominal diameter of various face mill cutters
• Insert Geometry
and ,",pr'",..,.,,,,,
tenuino\ogy of
to
understand
tenus
m promilling cutters
the
tooling
companies
available
gramming. Most
booklets for the cutters
inserts
catalogues and
explain the cutter
as well as all
they manufacture
in mind that
tool technology
related terms.
rapidly and constant
are
does change
programming
chapter,
being made.
very basic items insert geometry for
we look
cutters.
face
Insert geometry and insert
is determined by a design I.hal
insert in the
during a cut.
strongly influence quality of the cutting. There are typically three general categories.
on the cutting rake
of the
mill (known as
rake angle):
o ;::rtive geometry
o Negative
o Combination of both
Double negative geometry can
only if the machine
sufficient power rating
both the cutting tool
and
part are finnly
within a
iron or certain hard
will usually
double negative
The chips do have
the
to concentrate
the machined
and
do not flyaway from
ease, possibJy
chip jamming against the
or wedging
confined areas. PositiVe/negative
this clogging problem.
~FI!.:mL'R
I Negative Geometry ,
Positive / Negative geometry is
most beneficial to
operations where chip clogging could ...."'r·A...''''
This dual
offers strength
'curling'
into
insert with the
a spiral shape, This design usually most suitable
full
widtb
milling.
Always consult
specifications
the
cutting tool manufacturers
compare several products
deciding on the most suitable choice for a particular
Facc mills and their inserts come literally in hunand
manufacturer claims superiority
CUTTING CONSIDERATIONS
... single or double
or double
... positive I npn'l'ITI'l.11>
Any
variations are too numerous to list, but a
short overview offers at least some
for further studies,
Positive Geometry
cutters require
machining power
cutters, so they may more suitable on CNC
machines
usually small machines. They
a good
are a
choice for machining
cutting load is not too heavy.
single
therefore less
To program a cutting motion for a face mill, it is impor(ant to understand how a
mill works best
different conditions.
example, unless a specially designed
milling cutter
insert geometry, shape and
are used, try to
milling a
width that is
to, or only a
larger than, the cutter diameter.
cut may cause the
edge to
width face
wear out prematurely
chip to 'weld'
to the insert Not only the
suffers in form of a wear out, the
surface finish
as well. In some more severe
cases, the insert may
to be discarded
Increasing the machining cost.
and undesirable relationship
part width during
milling.
FACE MILLING
229
Desirable
Undesirable
I
~
CI
28-2
Schematic relationship of the cutter diameter and. the pa.t! width.
Only the cutter size (a) is
although not Its posItIOn.
The illustration shows only relationship of
culler diameter to the
width - it does not suggest the actual
of culter
into the
The most
tant consideration
programming of a face
the angle the milling cutter enters inlO the
• Angle of Entry
mill
is
by position the
to the part
[f a part can
cutler cenler line
with a single cut, avoid situations where the cutter
center
position
the part center
This neutral position causes a chatter and poor finish.
[he cutter away from
center line, either for a negative cutter
angle, or a
cutter entry angle. Figure
both types
angles and their effects.
A
angle of entry (not shown)
culter center
Needless to
coincident with the part
enters material, a certain force is
angle,
cutting
Since insert
it is the
absorb most of the
of the insert, a positive entry
may cause a
un........ ' ..!"."" or at least some insert chipping. Normally,
entry method is not recommended.
Negative
of an
force
at the middle, at the strongest point of the insert.
is the
preferred method, as it increases the
It is always
a good
to keep the
mill center within [hepar! area,
rather
away from it.
way, the
will always
enter at the preferred negative
assume a solid part
mill has to travel over some
cut will
intenupted.
into and
exit from
part during imenupted cut will cause the cutter
entry angle to be variable, not constant As many other facconsidered in
milling, take these rectors have to
ommendations and suggested
only as guideAlways consult a tooling representative on the
method of handling a particular face
job,
\ar\y
materials that are difficult to
•
Milling Mode
In milling, the prograllUTIed cutting direction,
to
table motion direction is always
important. In face,
this
so important
it is discussed in several sections of this handbook
covers a subject called the
ing mode.
Traditionally, there are three milling mode possibilities
in milling operations;
o
milling mode
o Conventional milling mode
NEGATIVE
/
ENTRY ANGLE .~
a
"
--bl
Figure 28-3
Insert entry angle into the part. W:: width of cut
(a) at the strongest/nsert po.int - ne!!~tive entry angle
(b) at the weakest Insert pomt . positive entry angle
o
Climb milling mode
A neulral
mode is a situation where the cutter
or a face, climb milling on one
lows
center line of a
side and conventionally milling on the
side of center
conventional
mode is also called
'up'
line.
mode and the climb milling
is also called
'down'
mode, These are aU correct
although the terminolmay be a little confusing. The terms climb milling and
conventional milling are more often
with peripheral
milling than with face milling, although exactly the same
principles do apply for an milling. For most face milling
cuts, the climb milling mode is the best overall vHI... lv'....
In Figure
(a)
the neutral
example (b) shows the so called down cutting
(or climb milling mode) and example
shows the so
called up cutting
conventional
mode).
o
Chapter 28
As an overall general
a coarse density cutter is usually a suitable choice.
more cutting inserts are
in material simultaneously, the more
power will
required.
of the
density, it important
to have sufficient cutting
- the chips must not
clog the
but fly out freely.
......-- Programmed
direction
Table
direction .......
a
.......... Programmed
direction
At all
at least one cutting
must be in contact
with the
which will prevent heavy
cut.
the possible damage to the cutter and to [he machine.
face mill diameter is
situation
occur jf a
for a
narrow part width .
PROGRAMMING TECHNIQUES
Table
direction .......
b
......-- Programmed
direction
Although defined earlier as a
simple operation,
milling can programmed
better if some common sense points are
Since
milling often
cutting area, it is important to consider caretool path from the start position to
fully
position. Here is a list of some points that should evaluated
any face milling operation:
o
Always plunge-in to the required depth
away from the part (in the air)
o
If surface finish is important, change the cutter
direction away from the part (in the air)
o
the cutter center within
for better
conditions
Q
Table
direction .......
part area
Typically, select a cutter diameter that is about
1.5
larger than the intended width of cut
28-5 shows a simple plate
28-4
Face milJing modes:
(a) Neutral milling mode
(b) Climb or 'down'milling mode
(c) Conventional Dr 'up' milling mode
for
Width of cut
• Number of Cutting Inserts
Depending on the face mill size, the common tool is a
multi tooth cutter. A traditional tool called fly-cutter has
usually only a single cutting insert and is not a norrnallool
of choice in CNC. The relationship of
number of inserts
in the cutter to
cutter diameter is often called
cutter density or cutler pitch.
gories,
{InSUffiCient overlap
Width of cut
mills will belong into one of these three cateon the cutter density:
o
Coarse density
· .. coarse pitch of
o
Medium density
· .. medium pitch of Inserts
o
Fine density
· .. fine pitch of inserts
b
Figure 28-5
Width of cut in face milling -
diameter
is the recommended method
FACE MILLING
1
Figure 28-5a illustrates
incorrect and Figure
the correct width a face mill cut. In the example (a), lhe
cutter is
in the part with
full
causing
friction at
cutting
and
tool
The example (b) keeps only
2/3 of the cutter diameter in the
work, which causes a suitable chip
as well as favorable angle insert entry into the material
• Single face Mill Cut
For
first face
programming example, we will
use a 5x3
(1 inch thick) that has to be face milled
along the
top
to the final thickness of .800.
28-6 shows this simple drawing.
XOYO is at
lower left comer. To establish
position, consider the part length of
the cutter
(512=2.5) and the
(.25).
start
X axis position will be the sum of these values, X7.75. For
Y axis start position
the n,vp'f'hi'lnO'<.:
on
edges and select climb milling
(It the same
Actually, the climb milling
be combined with a
little of conventional
which is quite normal
face
milling operations. Figure
shows the cutter start position at X7.75Y 1.0, and
end position at X-2.75Y 1.0, as
well as the
of calculations.
---5.0--~
3.0
5)(3
PLATE
5)(3)(1
Figure 28-6
Example af a single (ace miff cllt - program 02801
From the drawing is apparent that the face milling will
part, so the X axis horizontal direction
place along
will be selected. Before the
can be started,
are two major decisions to
a
mill diameter
a Start and
28·7
Face mill positions for a single face mill cut example
The position YLO was based on the desire to have about
overhang at
one quarter to one third of the cutter
part edge,
best insert entry angle.
1.5 inch overis 30% of
cutter diameter, the programmed
position was established at a convenient YI.O.
Now, part program for the single
milling cut can be
as program zero (ZO). Only one
written, with the top
face cut is used - program example 02801.
position of the cut
There are
important decisions to make, but these
two are the most
The part i~ only 3 inches wide. so a face mill that is wider
than 3 inches should be selected. Allhough a
inch
mill seems like a natural choice, let's see if it conforms
to the conditions that
been established earlier.
diameter should be 1.3 to 1.6 larger than the width
cut. In this case, 3 x 1.3 = 3.90 and 3 x !.6 4.80. With a
04.0
mill, that means only I
times larger. Cooneed for
cutter to overlap both
of the
;)""I'<A-lIUU of afive
face mill diameter is
Once the
mill
has
trate on the sfart and end positions.
reasons,
plunging to the depth has to start away from the part, in
air. The decision to cut along the X axis (horizontally) has
is whether from the left to the
been
so the
left. It
does not
or from the right to
except for the direction of chip flow, so selection from [he
to the left is arbitrary.
02801
(SINGLE FACE MILLING COT)
N1 G20
N2 Gi? G40 G80
NJ G90 G54 GOO X7.75 Yl.O 5344 M03
N'4 G43 Zl.O HOi
N5 GOl Z-O.2 F50.0 MOS
N6 X-2.?S F21. 0
m GOO Zl. 0 M09
N8 G28 X-2.?S Yl.O Zl.0
N9 MJO
%
Spindle speed and
are based on 450 ftlmin surface speed, .006" per tooth and 8 cutting
used only
as
Note the Z axis approach in block N4.
Although the tool is well above an empty area,
rapid
motion is split between blocks N4 and N5, for safety reasons. With increased confidence, rapid to the
directly
be an option, if
This
shows the proZO at the top of the unmachined
not the more
customary finished face.
232
•
Chapter 28
Multiple face Min Cuts
general principles applying to a single
cut do apply equally to multiple face cuts. Since the face mil! diameter is often too small (0 remove aU material in a single
pass on a large material area, several passes must be programmed at the same
area to be
are several cutting
for a
milled and
may produce good machining
under certain circumstances. The most typical
ods are multiple unidireclion£ll cutting and nwltiple bidirectional cutting (caJled
at the same Z depth.
ROUGHING
FINISHING
Multiple unidirectional cuts start from the same position
in one
bUI
the position in the other axis,
mining,
it
the part. This is a common method
lacks efficiency, because of frequent rapid return motions.
Multiple bidirectional cuts, often called
cutting,
are
used frequently; they are more efficient then the
unidirectional method, but cause the face
and
milling
to the conventional
versa. This
may work for some jobs, but is not
erally recommended.
In the next two i1Iuslrations, Figure 28-8
cally a unidirectional face milling. Figure
bidirectional
milling.
Bidirectional approach to a
for rough and finish face milling
face cut
There is
fairly
method that cuts only in
one
normally in climb milling
This method
of a circular or a spiral motion (along the XY
may
axes) and is the most recommended method. It combines
the two previous methods and is illustrated in Figure 28- 10.
scnematishow~ a
Figure 28·10
Schematic tool path representation for the climb face milling made,
applied tD a unidirectional cutting
ROUGHING
FINISHING
FigUre28~
Unidirecti naf approach to a multiple face cut
for rough d finish face milling
illustration
the order and direction of
viduallooi motions.
is to make each cut approximately
same width,
only about 213 of
diameter
cutting at any time, and always in climb milling mode.
Compare the
motions of
two methods, In
a tool path difference (cutter position) between
irlg and finiShing is also showli. The
directi?n .may
be either
the X or
the Y
pnnclpIes
of the cutting motion will remain the same.
Note the start position (S) nod the end position (E) in the
two illustrations. They are indicated by the heavy dot at
face
center of cutter. Regardless of the cutting method,
start and
milling cutter is always in a clear position at
of cutting, mainly for safety reasons.
10'S
13
i
~
6
13 x 6
Figure 28-11
Example of a multiple face mill cut - program 028D2
FACE MILLING
233
The programming example
multiple face milling cuts
is based on the drawing shown in Figure 28-11. The previously discussed
are applied
should present no
difficulty in understanding the program.
02902
of the examples could
been done in a shorter
the X
resulting in a smaller program. Howpurpose of exampJe illustrations, using the Y
was more convenient.
USING POSITION COMPENSATION
(MULTIPLE FACE MILLmG CUTS)
Nl, G20
N2 G17 G40 GBO
N3 G90 G54 GOO XO.7S Y-2.75 8344 M03
N4 G43 Zl.O HOl
N5 GOl z-O.2 F50.0 MOa
1)
(POS 2)
(POS 3)
N6 Y'8. 75 F21. 0
N7 GOO X1.2. 25
4)
N8 GOl Y-2.7S
(POS 5)
N9 GOO X4.0
(POS
NlO GOl YB.7S
(POS 7 - 0.1 OVERLAP)
Nll GOO XS.9
(POS 8 - END)
Nl2 GOl Y-2.7S
Nl3 GOO Zl.O M09
Nl4 G28 XB.7S Y-2.75 Zl.O
Nl,S M30
%
In p'fOgram 02802. aH relevanr blocks are identified with
too] positions corresponding to the numbers in an earlier
Figure 28-10,
width was separated into four equal cuteach, which is a little
than 2/3 of a
cutter. its
width of cut.
of
the part are the same as for the single
cut example.
major deviation from the norm was the motion to position
number 7 in
and block Nl] in the program.
The last cutting motion is from position 7 to position 8. In
order to make the surface finish better, the expected cut was
overlapped at X9.0 by .100 to the
value of
In Figure
the schematics
02802 program
are shown, including block number references.
In both previous examples, the starting XY position of
the face
has
calculated,
its
a suitable
To use 0280 I program as an example, the starting position was X7 .75 Y 1.0.
part was
5.0 inches. plus a clearance of
plus the
inches cutter
total X7.75 absolute value of
cutter center.
disadvantage of this
is apparent when
using a
mill that has a different diameter than the one
expected by the
A last
change of the
mill at the
may cause problems. Either there will
be too much clearance (if the new tool is smaller) or worse
will be not enough clearance (if
tool is larger).
is another way to solve this problem.
As the title of
section
the solution is to use
<obsolete' Posirion Compensation feature of the control
system, already described in Chapter
It is probably
only
application of the position
on
modern CNC machining centers.
to
Figures
show that we have to face (with
cut) a 5>::3
using a 05 inch face mill. In
to the safety rules in machining, the
mill has
in an open area, away from the part. In ormill cutting
from
part
by one quarter
inch, the clearance of
inches has to
be incorporated with the
ofthe face mill, which is
inches, to achieve the actual tool starting position for
milling cutter.
In a
milling program, this situation will
of the following forms:
on one
mill radius is programmed using the actual values
o
The
o
Position compensation method is used
In the first case, the program 0280 I may be
with
following content:
result,
02801
(SmGLE FACE MILLING CUT - NO COMPENSATION)
Nl G20
N2 Gl? G40 GBO
N3 G90 G54 GOO X7.75 Yl.O 8344 MO)
N4 G43 Zl. 0 H01
N5 GOl Z-O.2 F50.0 MOe
05.0 CUTTER
Figure 28-12
Multiple face milling details for program example 02802
N6 X-2. 75 F21. 0
N7 GOO Zl. 0 M09
NB G28 X-2.7S Yl.O Zl.O
N9 M30
%
234
Chapter 28
Block N3 moves the face mill to the actual, calculated
start posllion the cut. In block N6, the cut is completed again. at
actual previously
position.
program 02803 using position compensation is similar. but it
some notable
does
02801 with the new proCompare the original
02803, program that uses the position compensation
5 x 3 PLATE
28-13
Example of the position con10eJr}sal[lOn as applied to face milling program 02803
02803
(SINGLE FACE MILI..ING CUT)
(USING POSITION C'OlMPllmlAT
Nl G20
N2 G17 G40 GSO
N3 G90 G54 GOO XS.O Yl.O 8344 MOl
N4 G43 Z1.0 HOl
N5 G46 XS. 25 DOl
N6 GOl Z-O.2 F50.0 MOS
N7 G47 X-O.2S F21.0
Ni GOO ZLO M09
N9 G91 a2B XO YO ZO
NlO teO
%
When comparing, note the major differences in
N3
. (new X value), in block N5 (compensation G46), and
in block N7 (compensation G47). The situation will benefit
from some more detailed evaluation.
The N3 block contains
X position with value of X8.0.
That is the initial position. Since the plan is to apply the
compensation G46 (single contraction), the tool has to be at
a position of a larger value than
one expected when
compensation is completed. Therefore, XS.O is an
value. Note that if the G45 compensation command were
the initial position would have to be a smaller
than the one
when
compensation is
completed. This is because the position compensation is always relative to the programmed direction.
The N5 block is added to program 02803. It contains the
position compensation G46, which is a single contraction
in
programmed direction by the compensation amount
contained in the register of DOl offset. Note that the prowhich is the total of
grammed coordinate value is
the part length (5.0) and the selected
(.250).
mill radius is totally disregarded in the program. The
main benefit this method is that, within reason, the
grammed coordinates will not change, even if the face mill
diameter is changed.
example, if a 03.5 inch
mill
is used. the job can
done very nicely, but the starting position may have to changed. In this case, the stored value
1.75, but
N5 will still conthe DO I offset will
CNC system will do its work.
tain
last block worth a further look is N7. It contai os G47
position compensation command. The X value is equivalent to the selected clearance of X-0.25.
G47 command
means a double elongation-of the offset value along the
of the
programmed direction.
is
need LO compensate at the start of cut, as well as at the end
of cut. Also note the initial position
the
the same,
no compensastart position cannot
milling
tion will take place. With some ingenuity, the
can be programmed very creative]y, using a rather obsolete
programming feature.
CIRCULAR INTERPOLATION
and
and many olher
machines, routers,
filers, wire EDM, and others.
applications. there
related 10 contouring.
the other
chapler.
along
a tool path
contouring is called
in proftling on
centers, as well as
such as simple
and laser pro-
Circular inlel polalion is used
complete circles ill such applications as
radii (blend and parlia}), circular IJV'~"'''''~ CI"\n"r1r'~ Or conIcal shapes, radial recesses,
corner
helical
even large counterbores, etc. The
terpolale a defined arc wilh a very
information is given in
/ - CENTER
QUADRANT
POINT
/
RADIUS
figure 29·1
Basic elements DI a circle
• Radius
MENTS OF A CIRCLE
understand the principles of programming various cirmotions, it helps to know something about
basic
As an
that is
entity known as the
common in everyday life, a circle
various properthat are slrletly mathematical. only considered in
disciplines, such as Computerized
mol ion control and aUlomation.
following definition ora circle and
that are related (0 a circle arc based on some common dictionary definitions - Figure 29· 1.
similar definitions of a circle that can
and mathematical books. The
a circle and its various properties as
handbook, provides a sufficienl knowledge
programming. Additional
will
for some specialized or complex
appl
At this time, become at leasl
miliar with the geometrical and trigonometric
for arcs and circles.
In the simplest
.~u,~"'_~, terms, a circle is defined by
ils c:enfer point and its
os. Two of the most important
in part programming are Ihe
elements of a circle
radius and the
center point location
circle is also important
of the word radius
CNC programming.
is radii, although the word
'has been accepled as
a colloquial term. In
programming, radii and diameters are used all the
on a daily basis for aJmost all
contouring machines.
in machine shops use
radius and diameter dimensions a lot, with an almost unlimited number of possible
Radii and diameters are also
tool insert designation, they are
gauging (inspections), as well as in
tions and various auxiliary
programming. the
actual application of an arc or
is not important, only
its mathematical ,..1'"I'::IT<:I,..tp·rl
235
236
•
Chapter 29
Circle Area and Circumference
The area of a circle is defined by this formula:
~ where ...
A
R
1t
Area of the circle
:=
= The circle radius
= ((lnstant (31415927)
The circumference of a circle is the length of a circle if it
were a sU"aight line:
1.& where ...
C
o
Circumference of the circle
The circle diameter
7L
Constant (3.1415927)
It is important 10 note that both the area and circumference of a circle (its actual length) are seldom used in CNC
programming, although understanding their concepts presents a rather useful knowledge.
QUADRANTS
A quadrant is a major properly
or a circle and can be de-
fined mathematically:
A quadrant is anyone of the four parts of the plane
formed by the system of rectangular coordinates.
It is 10 every programmer's benefit to understand the concept of quadrants and their applications for circular motions In milling and turning programs.
A circle is programmed in all four quadrants, due to its
nature, while most arcs are programmed within one or two
quadrants. When programming the arc vectors I, J and K
(described later), the angular difference between the arc
start and end points is irrelevant. The only purpose of arc
vectors is to den ne a unique arc radius between two poi nts.
For many arc programming projects, the direct radius can
be used wi lh the R address, avai lable for majority of control
systems. In this case, the angular difference between the
start and end pOints is vcry important, because the computer will do its own calculations to find the arc center. The
arc with the angular di ffcrenee of 1800 or less, measured
between the start ;:md end points, uses an R positive value.
The arc in which the angular difference is more than 180°,
uses an R negative value. There ru-e two possible choices
and the radius value alone cannot define a unique arc.
Also worth mentioning is a mirrored tool path and its relationship to the quadrants. Although it is not a subject of
Ihe current chapter, mirroring and quadrants must be considered together. What happens to the tool path when it is
mirrored is determined by the quadranl where the mirrored
tool palh is posilioned. rn the Chapter 41 are more details
abom mirror image as a programming subject. For now, it
should be adequate to cover a very brief overview only_
For example, if a programmed tool path in Quadrant I is
mirrored [0 Quadrants II or IV, the cutting method will be
reversed. That meanS a climb milling will become conventional milling and vice versa. The same rule applies to a
programmed tool path ill Quadram II as it relates to Quadmnts 1 and III. ThIS IS a very important consideration ror
many materials used in CNC machining, because climb
milling in Quadrant! will turn into conventional milling in
Quadmnts II and IV - a situation that is not always desirable. Similar changes will occur for other quadrants.
•
Quadrant Points
From [he earlier definition should be clear (hat quadrants
consist of two perpendicular lines that converge at the arc
center poi nt and an arc that is exactly one quarter of a circle
circumference. In order to understand the subject deeper,
draw a line from the center of an arc thai is paraHelto one of
the axes and is longer than the arc radius. The line created
an intersection point between the line and the arc. This
point has a special significance in programming. It is often
known as the QuadraJlt Point - or the CQldinal Point - although the lauer term is not used too oftcn, except in mathematical terminology. There are four quadrant points on a
given circle, or four intersections of the circle with its axes.
The quadrant points locations can be remembered easier by
associating them with the dial of a compass or a standard
watch with an analog dial:
Degrees
Compass
direction
Watch
located
direction
between quadrants
0
EAST
3 o'clock
IV and I
90
NORTH
12 o'clock
I and II
180
WEST
9 o'clock
II and III
270
SOUTH
6 o'clock
III and IV
At this point of learning, it may be a good idea to refresh
some fermI) of rhe ~ngle direction c1efinition The eSf("lb-
lished industry standard (mathematics, as well as CAD,
CAM and CNC) defines an absolute angular value as being
positive in the counterclockwise direction and always starling from zero degrees. From the above table, zero degrees
correspond to the East direction or three n 'e/()rk position of
an analog clock - Figure 29-2.
CIRCULAR INTERPOLATION
237
POSITIVE DIRECTION
/
I
•
1
Circular Interpolation Block
There afC two preparatory commands
programming an arc direction:
ANGLE
G02
Circul<Jr motion clockwise
G03
Circulm mOlion counterclockwise
DIRECTION
MatheJ7Iatlcal rU>1Jmlll1n 01 the arc direction
quadrant poinls arc im·
In some cases, the quadrant
,even If the cIrcular
is is particularly lrue
where crossing the quadmodern controls
block, wilh
PROGRAMMING FORMAT
The progrnmming format
path must i ncl ude
lask of cUlling an arc
parameters are defined as:
1001
(he
o
Arc cutting direction (CW or CCW)
o
Arc start and end points
o Arc center and radius value
The cutting
must
more detaillaler in this
used for circular molion . . . rr"'rr'........
ramelers related to the
•
"Y'I
Arc Cutting Direction
A cutting 1001 may move
clockwise (CW) or
lenns are assigned by convemion.
mol ion direction is determined hy
at the plane in which the circular mOlion
The motion from [he plane venical
horizontal axis is clockwise, reverse
is counterclockwise. This convention has rnalltematical
docs not always malch the machine axes
IeI' 31 describes machining in planes, this
take a brief look
Both the G02 and G03 commands are modal.
they remain In effect unLilthe end of program or until canceled by another command from the same G
usually by another mOlion command.
The preparatory commands G02 and
are
words used in programming 10 establish circular
tion mode. The coordinate words following
command are always designated within a
The plane is normally based on the available axes
lions ofXY, ZX and YZ for milling or
applications.
Normally, (here is no plane selection on a lathe, ahhough
some conLfol indicate it as G 18. (he ZX
The plane selection and the combination of circular motion
and the arc cutting direclion determine the
arc end point, and the R value specil'ies !hearc radius. Special arc center modifiers (known as vectors) are also availif
programmer requires (hem.
Wilen Iht!
or G03 command is aclivaled by a CNC
any
active 1001 motion command is automalically canceled. 111is canceling mOlion is Lypically
GOO, Gal or a cycle command, All circular 1001 path momust
programmed with a cUlling feedrate in dlecl,
applying the same basic rules as for linear interpolation.
That means the fcedrale F must be programmed before or
the cUlling mOlion block, Jf (he feedrate is not speciin the circular motion block, the control system will
aUlomatically look for the last programmed feed rate. If
in effecl al all. many controls usually rcturn an en'or
(an alarm) to lhat effect. The feed rate
tIed in one of two ways. Either directly, wilhin
block only or indirectly, by assuming Ihc lasl
motion in a rapid mode is not posnot possible is Ii simultaneous three axes circular molion.
more details on this subject, look up Chapler
helical mil
On
mllSI
majority of older conlrols, direct radius address R
specified and the arc center vectors I, J and K
238
Chapter
29
_
... _....................................................................... ...
G02 x .. Y .. I.. J ..
G02 X .. Z .. 1.. K ..
G03 X •. Y .. I.. J ..
G03 X .. z .. I.. K ..
Milling program - cw
Turning program - cw
Milling program - CCW
Turning program - CCW
Control systems supporling the arc radius designation by
address R will also accepllhe UK modifiers, bUi the reverse
is not (rue. If bOlh the arc modi fiers UK and the fad ius Rare
programmed in the same block, the radius value takes priority, regardless of the order:
G02
(GO))
• Arc Center and Radius
x.. Y .• R.o r .. J ..
G02 (G03) x" Y .. I .. J .. R ..
The controls [hat accept only the modifiers UK will reLurn an error message in case Ihe circular interpolation
block contains the R address (an unknown address).
•
Arc Start and End Points
The Slar! poim of an arc is the point where circular interpolalion begins, as determined by the cUlling direction.
This poinl must be located on the arc and it can be a tangency point or an Intersection, resulting in a blend radius or
a partial radius respectIvely. The instruclion contained in
the start roint block is sometimes called the departure
command - Figure 29-3.
CENTER
POINT
j,
START ,CENTER
POINT I POINT
START
POINT
CCW=+
~ ~
\.,
' . -, ' - R
.-.::'-,- ---.-.-,
--1-
-.- 1USED IN MILLING
~
K-
-
USED IN TURNING
Figure 29·3
Center point and start point of an arc
The arc start poilU is always relative to the cU!ling motion
direction and is represented in the program by coordinates
in the block preceding the circular molion. In terms of a
definition,
The start point of an arc is the last position of the cutting
tool before the circular interpolation command,
Here is an example:
N66
N67
N68
GOI XS.75 Y7.S
G03 XII.. 625 Y8. 625 R1.l25
GOl X .. Y ..
In Ihe example, block N66 represents the end of a contour, such as a linear motion. It also represents (he start of
the arc that follows next. III the following block N67, the
arc IS machined, so Ihe coordinales represent the end of arc
and slart point of the next elemen!. The last block of the exnmple is N68 and represents the end point of (he elemcnt
Ihat starred from the arc. The end point of the arc is the coordinate point of any two axes, where the circular mOlion
ends. This point is sometimes called the target position.
The. radius of an arc can be designated with the address R
or with arc center vectors r, J and K. The R address allows
programming the arc radius directly, the lJK arc center
vectors are used to actually define the physical (actual) arc
center position. Most modem control systems support the
R address input, older conlrols require {he arc center vecto.rs only. The basic programming format will vary only
slightly between the milling and turning systems, particularly for the R address version:
G02 x ..
G02 x..
G03 X ..
G03 X..
Y .. R ••
Z .. R .•
Y .. R ••
Z .. R •.
Milling program - CW
Turning program - cw
Milling program - CCW
Turning program - CCW
Why is [he arc center location or the arc radius needed at
all? It would seem that (he end pain! of an arc programmed
in combination with a circular interpolation mode should
be sufficient. This is never true. Always keep in mind lha!
numerical cOlltrol means control of the LOol path by nUn/ben', In this case, there is an infinite number of mathematical possibilities and all are corresponding to this incomplete definition. There is virtually an unlimited number of
arc radii thal will fit between the programmed stan and end
poinl~ ;mil ~till milinlrlin the cutting direction.
Another important concept to understand is that the CUlling direction CW or CCW has nothing to do with the arc
center or the radius. The control system needs more information than direction and target point in order to cut the desired arc. This additional information must contain a definition thaI defines a programmed arc with a unique radius.
This unique radius is achieved by programming the R address for the direct radius input, or using (he UK arc center
vectors. Address R is the actual mdius of the tool path, usually the radius taken from the part drawing.
•
Arc Center Vectors
Figure 29-4 shows the signs of arc vectors I and J in all
possible orientations. In different planes, different pairs of
vectors are used, but the logic of their usage remains ex·
actly the same.
Arc vectors 1. J and K are used according to the folloWlll l1
definitions (only I and J are shown in the illustration): e
CIRCULAR INTERPOLATION
239
G02
G03
Quadrant
Quadrant
II
1+ JO
1+ J-
1+
T
/
/
Quadrant
III
Quadrant
IV
J+
D
29·4
Arc vectors I and J (also known as arc modifiers) and
1+ J+
1- J+
10
1- J+
designation in different quadrants (XY plane!
error.
cases where both
There is JlO
and
Arc center vector K is the
with "n" ... ili"rl
measured
the start point or the arc,
to the center of the arc, parallel to the Z axis.
(he start point of lhe arc and the
arc (as specified by the DK vectors) is
most
as an incremenlal distance
the two points.
control systems. for example many
Cincinllati
use the absolute designation to
an arc center.
cases, the arc center is programmed
as an absolute value from the program zero, no! from
arc center.
sure how each of the cOnlrol
terns in the
shop handles these situations.
in this respect creates a major
format, so be careful 10 avoid a
io those
in the shop.
using absolute
arc center.
specified direction applies only to the incremental
of arc center. It is the
of relative posi·
tion oflhe arc center from the starl point, programmed with
a directional sign - absence of the
assumes a
positive direction, minus
direction
and must always be written. Arcs
center de·
finition follow standard
•
Arc in Planes
machining centers,
the three geometrical planes
correct arc vectors must be
G17 G02
G18 G02
G19 G02
(G03) x .. Y •• R •.
(G03) X •• z .. R ••
(G03) Y •• Z •• R •.
(or
I .. J .. )
1.. K •• )
J .. K .. )
o
Chapter 29
E
y
G18 - ZX PLANE
G19 - YZ PLANE
x
z
z
~------------~X
y
29-5
Arc
direction in three planes - the orientation of the axes is based on mathematical, not machinc, plancs
plane is no! aligned with the
axes used mlhe program a(e
[he circular molion will
rn,-n'T\f' to the axis selection ill the program.
modal
motion is omiued. The
Ihis potentially harmful problem is to follow a
In nonstandard planes. (he circular program
always contain specifications for both a..'(es, as
arc vectors or the R value. Such a block is
will always be executed on the
of axes
priority_ This mediod is preferable to the
vious!y defined plane. Even if the plane
correct, the resulting tool motion will
The simplest form of a blend radius is
pendicular lines that are parallelw (he
orthe start and end points
only a
I ions or subtraclions More complex cl'llcul/'llion is
when even one line is al an angle. In this case,
point,
functions are used to calculate the staft or
or both. Similar calculations are required for blends between other entities as well. A blend arc is
known as a
arc or afillet radius.
•
Partial Radius
The opposite of a blend arc is a
smooth blend between two conlour
RADIUS PROGRAMMING
an arc,
11 '" I', n
Progrrunming arc is very common.
is only a porlioll. of a circle and
are
gram an arc. If the arc is 360°, it must
the
start position bei the same as end position.
In
case, a full circle is Ihe resu 1t.1f only a portion of the
only 11
Two
".,-1 as a ra-
point is not tan-
il in two
for the arc start
a blend are, dehad
used in
III
o
Blend radius
o
Partial radius
Each radius may be nrr\OrMTIrrlJ'·rI
rection and each may
any orientation that the culti
•
Blend Radius
A point of tangency between an arc and
adjacent element creates a blend radius. Blend radius is defined as a radius tangent between a line
em arc, an arc and a line, or
between two arcs. A blend arc creates a smooth transition
point of tanbetween one conlour element and another.
gency is the only contact point between the two elements.
FUll CIRCLE PROGRAMMING
All Fanue
and many
controls support a full
circle programming. Full circle is an arc machined along
360°. Full circle
is
on the Jathes in theory
only, since the
not allow it. For the millfull
is fairly rouli ne and is reas:
o
Circular
o
Spotface milling
o
Helical milling (with linear
o
Milling a cylinder,
or cone
CIRCULAR INTERPOLATION
1
A full circle cutling is defined as a
tool motion
completes 3600 between the start
end points. resulting in identlcal coordinates for the start and end tool pos)([ons. This a typical application
one
programInl
of a full circle - Figure 29-6,
GOl Z 0.25 FlO.O
G02 X2.0 YO 7S 1-1.25 JO F12 0
G02 XO.7S Y2.0 IO Jl.25
G02 X2.0 YJ.25 11.25 JO
G02 X3.25 Y2.0 IO J-l.2S
GOO ZO.l
(BLOCK 1
(BLOCK 2
3
(BLOCK 4.
a four block programmi
/
\
The arc start and end pOints are
located al a quadrant poinl of the axis line, which is an
pol1anl programming consideration. The quadrant
the example is
to 3 o'clock position (0°),
thaI (he G02 is
block only for the
to be repealed in a
program.
to the occurrences of 10
Ihey do not
they change.
\
starting position
--2.00 -
rant points,
29-8
I1rl1f1rrnm entry
Full circle programming using one block
thaI COV-
cutli
"\
\
OF 4)
OF 4)
OF 4)
OF 4.)
G90 GS4 GOO X3.25 Y2.0 S800 MQ3
GOl Z-O 25 F10.0
G02 X3.2S Y2.0 1-1.25 JO F12.0
more difficult by establishing the
cut
from any of the four
are at
, 1800 and 270". For exam-
, there will be five circular
ple, if the
coordinates of the start poml of
blocks, notfour,
the arc (shown asxs
ys
willhavetobecalculated using trigonometric functions - Figure 29-8:
xs
(FULL CIRCLE)
GOO ZO.1
controls do nut allow a circular I 1"1 fj>rl"l," I
more than one quadrant per block. In this case,
to be divided among four or even
on the srarting tool position. Using the
the resulting program wlll be a
same resuiL') - Figu.re
START
POINT
"- -- R1.25
I,--2.00-~•
29-8
Full circle programming using five blocks
'.
I
I
2.00
R1
I
J_
Figure 29·7
Full circle nJ'f'lI,,::.n'fflUII'I
four blocks of program entry
G90 G54 GOO X3.25 Y2.0 seoo M03
code
G90 GS4 GOO X3.04B3 Y2.6808 SBOO MO)
G01 Z-O.25 FlO.O
1 OF 5)
G02 X3_25 Y2.0 I-1.0483 J-O.6808
G02 X2.0 YO.7S I-1.25 JO
2 OF
G02 XO.75 Y2.0 IO Jl.25
3 OF 5)
4 OF 5)
G02 X2.0 YJ.2S I1.25 JO
G02 X3.04S3 Y2.680B IO J-l.25
(BLOCK 5 OF 5)
GOO ZO.l
Values x~ and y, were calcu lated by the
functions:
~
1.25 x cos33
1.0483382
Ys = 1.25 x sin33 = .6807988
242
29
•
From the resuits, [he start poinl of the cut can be found:
X=2+Xs '" 3.0483382
Y = 2 + Ys
2.6807988
Boss Milling
As an example of a full circle
be used, as illustrated in Figure
X3.0483
Y2.6808
If the control
in one block,
quire the I
a
o
01.812
CilflnOI
G90 G54 GOO X3.0483 Y2.6808 S800 M03
GOl Z-O.2S F9.0
G02 X3.0483 Y2.6808 1-1.0483 J-0.680a
GOO ZO.l
J
"ri,-I""'M
R.
TOP
cannot be arbitrarily replaced with
next example is tlot correci'
L
,-
G90 G54 GOO X3.0483 Y2.680B 5800 M03
GOl Z-O.2S F9.0
(* WRONG *)
G02 X3.0483 Y2.6808 Rl. 25 F12. 0
GOO ZO.l
~",
····1
'lIIj
I
FRONT
.
I
. Mathematically, lhere are many options for a
full
programming. If an R value is programmed for a
360 0 arc, no circular motion will take place and slich a
block will be ignored by (he conlrol. This is a precaution
built into {he control software, to prevent from cutting an
incorrect arc because of the many existing possibilities. In
29-9, only a handful of the possible ares is shown.
The circles );hare the same cutting direction, start point. end
poinl, and radius. They do nOT share center points.
29-10
Boss milling eXiJ~mf)"e
lor program 02901
are terms used for external milling
is an
milling of a full
The cutler used will be
j/VI.-Fl. •• l.
at
deplh:
02901
(0.75 DIA END MILL)
Common
radius and
motion direction
--
Common
start and
end point
N1 G20
N2 G17 G40 GSO
N3 G90 G54 GOO X-l.O Yl.S S750 M03
N4 G43 ZO.l HOI
NS GOl Z-O.37S F40.0 MOS
N6 G4l YO.906 DOl F20.0
N7 XO F14.0
N8 G02 J-O.906
N9 GOl Xl.O F20.0 M09
NlO G40 Yl.5 F40.0 MOS
N11 G91 G28 XO YO Z2.0
Nl2 M30
%
In program 0290 I, the tool moves first to the
lion and depth, then the CUller radius
When reaching the cutting depth, the tool
a
climb milling motion to the top of boss. Then it
around the circle to the same point moved away
./
Figure 29-g
Manv mathematical possibilities exist lor a lull circle
withR
by revcrsing the initial motions, it returned to its Y
start poi nt - Figure 29- JJ shows Ihe block numbers.
CIRCULAR INTERPOLATION
243
N2
N9
N5
N8
N8 GOl G40 XO F20.0 M09
N9 G9l G28 XO YO Z2.0 MaS
mo M30
%
Program 02902 shows both
arc start
point at 90'" programmed at ] 2 0' clock position.
radius offset started during the motion from
arc center.
A cutter radius offset cannot start or end in a circular mode.
N7
This is true for almost any circular application,
very few that use a special cycle.
• Internal Circle Cutting ~ Circular Start
Figure 29-11
Boss miJling example - tool motions for program 02901
Alternate applications may include multiple
1."""""''', a semifmishing pass, wo cutting
related to machining.
• Internal Circle Cutting - linear Start
.LU""'Ll'Q' full circle cutting is common and has many
such as circular pockets or counterbores. In an
simple linear approach programming me:thcfd
last example will not be practical when smooth blend
l.vJeen the approach and the circular cut is required.
prove the surface finish, the start position of ,-",-".I..u,:u
tion can be reached on an arc. The usual startup is
ftrst at a 45° linear motion, to apply
cutter
then on an arc that blends with the full
29-13 illustrates the principle and
the complete program.
~"'''''U1J'~, a 01.25 circular cavity is to be machined to
tion will
.250 inch, 3n program 02902. A simple
moused for the startup. where the entry point blend
The cutting tool is a center """'.,"'"
as a slot drill) - Figure 29-12:
Figure 29·13
Internal circle cutting linear and
approach
02903
(0 . 5 DIA CEN"l'ER END
29·12
Internal circle cutting - linear approach only
02902
(0 . 5 DIA CENTER END MILL)
m G20
N2 G17 G40 GBO
N3 G90 G54 GOO XO YO 8900 M03
N4 G43 ZO.l HOl
N5 GOl Z-O.25 F10.O MOB
N6 G4l YO.625 DOl F12.0
N7 GO) J-O .625
Nl G20
N2 G17 G40 GSO
N3 G90 G54 GOO XO YO 9900 M03
N4 G43 ZO.l HOI
NS GOI Z-O.2S FlO.O MOS
N6 G41 XO.3125 YO.3125 001 F12.0
N7 GO) XO YO.62S RO.3l2S
NB J-O.625
N9 X-O.3l2S YO.3l2S RO.3125
NlO GOI G40 XO YO F20.0 M09
Nll G9l G28 XO YO Z2.0 MOS
Nl2 M30
%
244
Chapter
method is slightly
quality with a circular approach
than with the linear approach.
If a control systems has the User Macro option and many
circular
are required, the 02903
could
uu."JJ"'V to a macro. Some
cycle built-in.
• Circle Cutting Cycle
What is not true in
circular application, is true
in this situation. In normal programming of arcs
cles, a cutter radius
cannot start in an arc tool mr,nr,n
In Gl
13
mode, the start molion from
center position is circular to
compensated start
on the arc circumference.
all built into the control and [here no choice is offered.
sider this situation as a special case, definitely nol as a
On some
CNC models, there is an additional
rarne!er In the, G I
13 format - the rad illS
This indicates special
to reduce air cutting lime.
controls, for example some
but not Fanuc, have a built-in routine
circle using special preparatory
G 12 and G 13. These cycles are very rnn,\lpn
ming aid and to the surprise of many
dropped this feature many years
13 progranuning.
29-14, will
IS a logical relationship between G02 and G ]2, as
as between G03 and G 13:
Full circle cuning
cw
Full circle cutting
ccw
12
lhese two spe-
A typical programming
cial commands is quite simple:
I
r:r-----t---t"'J - - L
0.25
G12 I .. D .. F ..
G13 I .. D .. F .•
Full circle CW
Full circle CCW
13
start
3
or
the start pomt of the cuI
equivalent 10 the 9
command cannot be
is the radius of
as an incremental value
(plus sign is assumed), the
, wh icn is equivalentto the
If the sign is negative,
at 1800 position. which is
direction
Y
direction.
PrograrHJIlt;U D
is ule co 11 trol register number
the cutter radius offset
F is
address.
on some controls, but
are alternate versions of this
very similar in nature.
be (lcceptecl for successful usThe cutting tool must
a circular pocket, the
plane and (he arc starting
al 0 0 or J80" (Y axis start
is nol possible).
a
cutter radius
(G 12 to Uie right, G 13 to the left). Never program the commands G41 and
using G 12 or G 13 command. If
the culler
IS In
it will be overridden
the seleclion orGI2 orGl3.
approach is to
these two
mode (CUller radius
cded) al all
Full circle cutting using 612/613
• program 02904
02904
(0 . 5 DTh CENTER CTJT'I'ING END
N1 G20
N2 G17 G40 GSO
N3 G90 G54 GOO XO YO 8900 M03
N4 043 ZO.l HOl
NS GOl Z-O.25 Fl0.0 MOB
N6 G13 IO.62S DOl F12.0 M09
N7 G91 G28 XO YO Z2.0 MOS
AVAILABLE)
N8 M30
%
The program is only two
but it is
simpler to develop. The cutter
offset IS automatic
(built-in) and the editing at
is much easier.
is also an additional
since the start point on
circle is not a result of a
line, but a lead-in arc,
finish quality will
than using olher
method when
types of tool approach. This is a
the machined surface quality is impol1ant. There is also a
built-in lead-out arc in the
[0 (he lead-in arc,
Ihal is effective when the
is completed.
CIRCULAR INTERPOLATION
245
ARC PROGRAMMING
./
/
With a full arc cutting, which means the complete 360°
motion, the R address cannot be used at all. The arc center
vectors I and J have to be applied, even on latest controls.
What if the circle is 359.999°? Well, at first, circle must
have 360°, therefore the word 'circle' is Incorrect. Even i.l
small difference of 0.00 I ° does make a difference between
a circle and an arc. Although this difference IS much more
important mathematically than for practical programming,
the distinction is very important. In circular interpolation
terms, an incomplete circle is nothing more than an arc.
Look at this arc a little differently. If a 90° arc is made, Ihe
R address can be programmed. for example:
- R+
Start point /
"
I
j
./
I
\
End point
- - CONTOUR
Start point
./
j
GOl X2.0 YS.25 F12.0
G02 X3.75 Y7.0 Rl.7S
.// _ .._- CONTOUR
If an arc that covers exactly 1800 is programmed, {he program will no! he much different:
GOl X2.0 YS.25 F12.0
G02 XS.5 YS.25 Rl.75
Figure 29-15
Sign of R address for circular cutting - onlv the center is different
The following example is identical [Q the previous onc,
except for the R address sign.
Note that the Y coordinate is the same for the arc start and
end position. The Y value In the circular motion block does
not have to be repeated, it is used here only for illustration.
G01 X10.5 Y8.625 F17.0
G02 X13.125 Y6.0 R-2.625
Another example shows programming an arc of 270",
still using the R address. Are the following blocks correct?
180°, establish a particular programming style. If the style
GOl X10.5 Y8_625 F17.0
G02 X13.12S Y6.0 R2.625
The blocks appear to be correct The calculations, Ihe format, individual words. they all appear to be right. Yel, Ihe
program is wrong.! Its result Will be a 90° arc, not 270 0 .
Study the illustration in Figure 29-} 5. It shows that there
is not just one, but fHiO mathemaUcal possibilities when the
R address is used for arcs. The solid contour is the tool path,
the dashes identify the two possible radii.
Programmers do not normally think of these mathematical alternatives, unlil they program arcs larger than ISO"
(or scrap a part). This is a similar situation to U1at of a full
circle, described earlier. Although (he I and J vectors can be
used to relnedy the problem, a different remedy may be a
preferred choice. The R address can still be used in Ihe program, but with a negative sign for any arc thal is greater
than 180°. For arcs smaller than ]80 0 , the usual posili ve R
radius remains in effect. Recall from some earlier explanalions lhal if there is no sign with the R word (or any other
word), lhe word assumes a positive value. Compare the two
programming examples:
GOI XlO.5 Y8.625 F17.Q
G02 X13.12S Y6.0 R2.625
(90 DEGREES)
(270 DEGREES)
If frequently programming arcs that cover more than
is well thought out, it will avoid the costly mistakes associated with the R address sign error.
FEEDRATE fOR CIRCULAR MOTION
In most programs, the feedrate for circular interpolation
is determined the same way as feedrale for linear inlerpolalion. The cutting feed rate for arcs is based on established
machining conventions. 'TIley include the work setup, material machinabi1!ty, (001 diameter and its rigidity, programmer's expenence and other factor·s.
Many programmers do not consider the machined radius
when seiecring the cutting feedrate for the tool. Yet, If the
machined surface finish quality is really important, always
consider the size of every radius specified in the parr drawing. Perhaps the same feedrate for linear and circular motions programmed so far may have to be adjusted - either
upward or downward.
In lathe programming, there is no reason \0 distinguish
between linear and circular lool motions, regardless of the
radius size. The tool nose radius is usually small, only averaging .0313 inches (or 0.8 mm) and the equidistant tool
path IS close to the programmed tool path, taken from a
drawing. This is not the case for milling contour programming, where large tool radii are normal and common.
Chapter 29
The
arc feedrale is nol required in
gram. If
cutler center tool path is close LO
1
contour, no adjustment is needed. On the
band,
when a
diameter cutter is used to contour a small outradius, a problem that affects the
finish may
occur.
this case, the tool center path
a much
arc
one in the drawing. In a
is used
shorter
Two formulas provide
to find the adjusted arc
feedrate,
to the linear
Both formulas are recommended for external or
contouring only, nOT
rough machining of solid material.
•
Feedrate
Outside Arcs
For outside arcs,
,ildjusled feed rate will be higher than
the linear
calculated from Ihis formula:
In normal programming, the
arcs as well. as determined by
material. The formula for
~ where ...
F0
FI
iii? where ...
FI
r/min
F!
=
n
linear feedrate
Spindle speed
Feedrate per tooth
Number of cutting
A linear feedrate for 1000
A
ormm/min)
on
linear feed rate of J 4 in/ml n, an
requires an upward adjustment
a
.0045 initooth load and
Using a rela-
(WO culling edges, the r"""',.., ....,'" is 9
tively large cutrer diameter,
larger, the linear feedrate
motion may be 11:........."""':
The elementary rule of
Feedrate for outside arc
Lineadeedrate
radius on the part
radius
==
(\5.875 mm) or
or down for circugood finish.
Fe =
14 X (.375 + .25) / .375 = 23.333333
is a major incre<ls!!, to
in lhe program,
r\n',Hl~'r the same example with ,75 cutter
14 x (0.375 + 0.75) / 0.315
adjustmenl for arcs is that
the normally programmed
is increased for
outside arcs and decreased for inside arcs· Figure 29- 16.
TPPflrnlt" changed from 14
If1crease.
use prevIOus
adjustment is justified or not.
(01.5):
42.0
inimin - D 3
to determine
CUTTER
• Feedrate for inside Arcs
arcs, the adjusted
feed rate, calculated from
will
lower than
formula:
/
/
DECREASED - - . FEEDRATE
''''
"
NORMAL~
FEEDRATE
Figure 29·16
Feedrate adlil/stlTlel1lts for circular tool motion
F;
""
F,
R
0::
Feedrate for
arc
linear feed rate
Inside radius on the
Cutter radius
Based on lhe Jinear feed rate
inch inside radius with
downward:
Fi
'" 14 x (.8243 -
The result is a feedrate
will be Ihe applied fPpnrllfP
14 in/min, the feed rate for
I
must be ad/ .8243 = 3.384932
inimin, In the program,
F address.
CUTTER RADIUS OFFSET
known as a profile
IS
nOf-
MANUAL CALCULATIONS
milling applications by establishing
then movmg the cutting tool inX
Y
or both axes simultaapplications, either (he X axis or the Z
axes can be used 10
turn or bore a conof
contour elemenl
one block of culling molion. These mopomts can be programmed
in
or
they can use an absolute value
position or an incremental distance. In either case, keep in
uses the cemer line of
or X
tool movements. AIprogramming is a very convenient
development, it is also a method \.Jnaccomact with rhe material,
the cutting tool must touch the programmed
not its cen.ter line.
path for all contounng operations is always
to the
tool molion. Whether used on a
lY
machintn center or on a CNC lathe, the cutfing rool
'"
.
must always be tangent TO The conlOw; which means
the tool motion has to create a path where the cemer poinl
of the cutter is always at the same distance from the contour of lhe part. This is called the equidistant tool path.
Some realities should ,",/Or'nIT''''
30- J, The most noticeable nm"~r'J"
contour must always take
sated by its radius, which means
macated in positions shown in the
chining requirement is not
by the
ity of the
drawing.
a
all dimensions
to
the part contour, no! the contour
tool cenler. In fact,
the drawing is
to
tool positions illustrated
in the upper
The question is how do the tool center uv;,,,,,,,.
from a drawing 10 the
part contour'?
Actually, lhey
is equipped with an
cutler radius compenturning systems,
compensalion or
and common
to apply the offsel
drawing dimen(he necessary calculations
The illustration in Figure 30-1 shows two types of a tool
palh, Que is Iwi compensaled, the other is compensated.
Both are applied [0 a particular conlour, wiLh the culler dia~
meter shown as well, including its positions.
,I -
\'~
I
CUTTER 0 (TYP)
.....
Tool path with
.,... NO OFFSET
J.,.:..------~_)
PART PROFI
Figure 30·1
Tool path not compensated (above) and CDfnp8'nSI!Jil(;:a
by the cutter radius
to aULOmate something, we have to
how it works, If something is aulomated already. the
knowledge of how it works makes the job so much
particularly when encountering a difficulty that has to
resolved very quickly. To really understand cuuer
offset - many programmers and machine operators
nol
it is important to understand the principles built in the
tern, principles thal are very much based on basic mathematical calculations, including the often unpopular
nomclry calculations. A very simple drawing is shown in
30-2 for that purpose.
program zero will he selected at the lower left corner
of Ihe parl. Since lhe culling will be external, in a climb
milling mode, the tool will start along the Y direction
At
moment, the start and end 1001 position is not importanL only calculations of [he individual contour points at
and tangency points.
7
248
Chapter 30
All five points can be summed up in a small table:
Point No.
X coordinate
t
-,
1.125
I
J
'''-...-RO.625
2.25
Figure 30-2
Semple drawing for manual calculations {examples)
Note that there arc. five points on the drawing, one LIt each
contour change. These points are either intersections or
points of tangency. As eaeh point has two coordinates, lolal
of ten values will be required,
The drawing always offers some points thaI need no calculations. fl is a good idea 10 gel well organized and mark
the points from the drawing first Then, make a chart in the
order of tool path. Study Figure 30-3 carefully - it shows all
five points and all the values thaI need no calculation, perhaps some addilion or sublraClion only.
-._--X-AXIS I V-AXIS
P1-XO.OOOO. YO.OOOO
P2
pi x(fQ500. Y1 :1250
P3 X2.2500.
?
P4~2.2500 i YO.6250
-X1.6250 YO.oooo I
"-
P1
,
,
XOYO
Figure 30·3
ContDur change points required by the cutter path
Out of the len values required. nine of them are given.
The missing Y value for P3 is not expected on the drawing,
Reaardless of whether the cutter radius offset is used or nOI,
so~e calculations will always be necessary and this IS one
of Ihem. Afler ali, /nallual programming is done by hand.
Figure 30-4 shows the trigonometry method used.
:-
- 2.25
~-~
_"
18
l
0
_"W,_
a:::: 2.25 x tan18
a=07311
P3(Y)
P3(Y)
=1.125 + a
=1.8561
Figure 30-4
Trigonometric calculatiDns to find unknown YcODrdinate
Ycoordinate
i''''''''·
I
""""
Pl
XO
YO
P2
XO
Yl.125
P3
X2.25
Y1.8561
P4
X2.25
YO.625
P5
X1.625
YO
Once all the coordinates are completed, [here is enough
dala to start the tool path, but only if the cutter radius offset
feature is used. However, lilal is not the intention at the moment. To illustrate, a whole /lew set of points has 10 be
found - coordinates for the center of the clIlter.'
• Tool Path Center Points
The cutting lool for milling is always round. An end mill,
for example, has a diameter of a certain size. Even tools
used for turning and boring have a round end (called the
1001 nose radius), even if it is relatively small. Of course.
we all know that any round object has a center. Milling culter or a lathe tool lip are round objects, so they have a center. This evaluation may sound a bit too elementary and it
is, but it is also the basis, lhe key element, the whole concept, of cutter radius offset. Every control system takes il
into consideration.
Take, for example, an electric router \001 to cut a shape
out of wood - how is it used? Using a pencil oUlline of the
desired shape, the router bit is placed into the tool and starts
CUlling, Where? It starts clilling outside of the outlined
shape, otherwise the piece cui will be either too 1Q/~r<e or too
small! TIle same procedure is used when cUlting a board
wilh a saw - the saw width has to be compensated.
This activity is so simple, It might have been even done
automatically, without serious thinking. The radius of the
router bil (or the width of the saw) was compensated for before and during the cut. Just like Ihe outline of the shape in
wood is followed, [he outline of the machined part, outlille
that is offset by the culler radius is followed as ,.,vell.
The tool path generated by the cuttIng 1001 center always
keeps the same distance from the part contour (outline).
There is even a special name for [his type of tool path - 1\ IS
called the equidislom tool path, which means 'distant by
the same amount'. Figure 30-5 shows the sample drawing
with the applied equidistant lool path.
The question now is - what 10 do aboulthe point coordinmes that have just been calculated and stored in lhe above
table, Are lhey useful? Can they be used in a program? Yes
to the firsl question, but not yet to the second. A few addiiional conditions have 10 be taken into consideration.
RADIUS OffSET
--em,
PI X axis Y
P1' X-i5:3750 y-o.
P2
-
--
---
"
__ v
P3' X2.6250
?
P4
RO,375
30-5
taUI(JJsram tool path· cutter center coordinates
"''''r.", ..'. . ,......
Figure 30-6
rpm,rlCHU
the old sel of points wi II
ra calcupoints, Again, try to see which
are
establish them first.
point PI? It
the new PI has (he value
radius
also (he value of culler radius in
Y
Contour change
for the cutter center path
Figure 30-7
of point P2calculalion. The
trigonometry melhod
is a subject programmers have
10 know how \0 work wilh - il is part of mathematics, ~x­
lended to CNC program
A similar calculation is reqUIred for P3, shown in
sin18
.y= 1.-_
-- x
.
cos18
from the old P L The actual value
an)'
cak:ulaleri flI nil, wilhaUi kllowillg the cuf-
=1.125 +N
• Cutter Radius
P2(Y) = 1.3975
the culler is always
been phYSically
of the cutler must
I" (0,0025 mm =
reground tools, 10015 previ-
or
are undersize or oversize
some
this means that programming the cenlerl
the exacllool radius to be known althe
in all cases,
•
Y1.125
Figure 30-7
Calculation of P2 for the cutrer
N = 1 + sin~8 x 0.375
Center Points Calculation
Coordinate poinls illustrated in Figure 30-5 above,
sent the center or
cuuer radius al each con ram change
point. Now, another
can be brought inlo lhe
picture, Ihe cutter
A new coordinate set of five
poinls can be
example, (1 brund new CUller of 0.750 will
Which points can
withoul any trigonometric
lY=
,III
=
P3{Y) 1
P3(Y) =
Y1
the illustralion directly,
Look at and evalu-
ate Figure 30-6. OUI of len values requirt:d. only eight have
that Ihe previous lcn calcuas well, adding 10 the overall
been idenlified, but also
lalions had to be done
programming effort.
on programming of the
I n order to lin ish the d
and P3 have to be calcutter center, the two Y values ror
culaled. Let's start wilh point
30-8
Calculation of P3 lor the cutter center point
are known,
center
points are in the
. appear in that same ordcr II) Ihe
the pOlnt loc3tions hut
various G
and other dam.
contour.
250
Chapter 30
momenl, it is slill 100 soon to write the
new
closed with the table of
The Type C cutter radius offset lhe
ahead lype (also
called the illlersecrionollype) is
one
is used on all
modern CNC systems today.
is no need to call it Type
C anymore, as there are no olher
available.
0.750 cutter but none
Point No.
Pl
y
X
•
Y-O,375
X-O,375
Defini1ion and Applications
offset is a
of the control system [hal
a contour without knowing the exact
X-O,
P3
P4
X2,625
P5
X1.625
diameter
of the cutter.
ture performs all
points, based on
YO.625
digit I used in the calculations. It may
where it came In(o {he
It represents lhe value of sin 90°, which is I
in fronl of (he Y - il is a symbol for
Jitllclriangle
Specified direction of the cutter motion
o
Radius of the cutter stored in
control system
[a develop a program without
knowing the exact CUller diameter at the (ime of programming. It also
CNC operator to adjust, to fine
iunc, the WHer
in the control system (nominal. oversize or undersize), during actual machining, In practical
terms,
cutter
(and tool nose radius offset
on lathes)
for a number of reasons:
conhad no culler rawas developed in
had to be calcu-
lat(~d WiTh the cwfer radius in
This method of programming added a great amount of time to the part development process, greatly
rhe possibility of
programming errors and disallowed any Oexibility during
mach1l1ing. Even a small di
between the pracutter radius and the
culler radius required
and the creation
memory in those
control tcchnolcontrol syslem
melh-
Tvpes of Cutter Rad
o
- and machining - this feature
The previolls examples are Iypical to (he
•
Points of the drawing contour
a vec-
COMPENSATED CUTTER PATH
or
o
word 'delta',
in mathematics 10
101', or a distance.
methods useu 011 the early
trols (normally of the NC lype, not
dlUS offsel feature at aIL The lOol
such a way (hal the contour
sophisticated feaof contour change
Offset
o .. 5ln;nnpt'
o Unknown exact
of the cutter radius
o
Adjusting for the cutter wear
o
Adjusting
o
Roughing and finishing operations
the cutter I1pt'lpl:tlon
o Maintaining mJ'l,(,nlTlinn
Every
may not be LOa clear at
moment,
knowledge of this topic, it wjlJ
10 understand the subject. The suggestions are only some
the possibil
the automatic cutler radius offset
Now lei's look at
aClual use ill prognunmi
but wilh
PROGRAMMING TECHNIQUES
As the CNC technology developed, so dId the cutler radius on'set methods. This development has laken three
slages, Today, they arc known as the
types of a cuner
radius onsct - the Type A, thl.! Type B. and the Type C:
D
Type A offset - oldest uses special vectors in the program
to establish the cutting direction (039, G40, G41, G421.
o
Type 8
old uses only G40, G41 and G42
in the program, but it does not look ahead.
Overcutting is
for Type 8 offset.
o
Type C
- current uses only G40, G41 and G42
in the program, but with the look ahead feature.
Overcutting is
for Type C offset.
o
Points of the drawing contour
o
Specified direction at the cutter motion
o
of the cutter stored in the control
items are the actual data sources.
work wllh dnta and the data hilS to be
the purposes of this charier, we assume that
conlOur chnnge points are based on the
coordinates.
RADIUS OFFSET
•
1
Direction of Cutting Motion
an external or an
tool palh
there will always
a choice
now only, the directions can
the coantrm:/ockwise direction
the pffit contour.
by Ihe faci
(in milling), or the
(in turning). These are two very separate
to be clarified - which one 10
motion of (he [ahle or motion of Ihe lool?
u. ...., ... U'l,
IS
motion oflhe
that
follow one
of the CNC machine type, ir is ,"",,,,,,,,..,1
rule of CNC programming:
tool motion
statement is true for CNC lathes, where it is
but it is
CNC machining centers,
true for other lypes
l"Iser Clllling machines,
il is
Figure 30-9
ma-
Cutter path direction as ir relates to a stationary pM contour:
fa b) No motion direction shown - left and right is unknown
fe - d) Cutter positioned to the LEFT of the contour
(e - f) Cutter positioned to the RIGHT of the contour
etc. When it comes to the so
versus counlerciockwise, a closer look
IS
•
• left or Right - not CW or CCW
care of is to eliminate the
ing terms r l r l r F \ , l I l
reserved '-1"_11..1'::"
place in
and counterclockwise. These terms are
circular interpolation and have no
the cutter radius offset.
and Right are used
the left or to the right
the direccion oj
when faced with the
we determine the correct poto a certain previously esA moving objcct is said to be La
a stationary object, depending on
mowmem.
Offset Commands
In order to program one or
direction), there are two nrt>',","',r'l
to
the culter
I or G42 mode is canceled by
G40 command:
Cutter radius offset mode CANCEL
is no difference. The comto the left or to the
looking inLO the cutler
all three radius ofrser
30-9.
The illustration
a direction, a cutler with
to the left of the conlow;
fied and pOSItioned to the
Out of the two
ler? Compensation to
centers, because it
cutting, assuming that a
with M03 rotation. There
sation to the right. causing so
mode of cutting. This mode
cases, after consultallon with a
applies to milling systems, not to
G41
G40
E
of G41, G42 and G40, to the cutter path
252
30
terms of the milling method.
answer to
command is applied
is applied to the
conventional milling mode,
is true only if the spindle
rotates with M03 funclion
CW) and the culthe spindle must
ler is right hand. If the cutter is
rotate with MQ4 function aC!Ive (spindle CCW) and all
rules applying to cutter radius
are the exact opposite
discussed here.
is no cutler radius offset apG40 command is in
10 the climb milling mode,
30- J J shows
as a climb mi 11 ing
and the 042
as a conventional mill'
most common in
Climb milling mode is
millmg, particularly in contour milling.
area
last question is seltings. We are
areas (offset screens on the control
the Position
Tool Length
17 to 19 respectively).
earlier
to look at
their relaAlthough
of the CNC
the same prin-
offsets in more depth and
tionship to the compensation
cutter
this lopic
appear to be aimed at
the programmer has fa
equally well, if nol in even more deprh.
• Historv of Offset Types
have developed over (he
and because their
and
many of me older
in use
understand the
models are
and their application, it is
to know what
of offset the Fanuc control
IS as expected the lower level or
control is, the
lower [he nexibility, ano vit:e vt:rSl1.
the word
bility - il IS not the quality that is
or higher - just the
flexibility. DIfferences arc cal:eg,on:reo as Offset Memory
There are three
on Fanuc systems:
t
Conventional Milling
G42
Climb Milling
G41
...... Tool motion direction
Type A - lowest level of flexibility
o
Type B - medium level of
o Type C - highest level of 1'1"".1""1.1" ... ,
Figure 30-11
Climb milling and conventional milling mode for
a rigllr hllnd currer and The spindle rotarion mode M03
• Radius of the Cutter
of
gram Ihe Lool
culler path,
nOl mean
forgotten or ignored
question al this
speci fled in the nrr,or'lrn
First, look at
ferem CUHer radi
o
offset that allows to procontour were the required
cutrer
should be either
30- 12 - it illustrates the
SMALL
MEDIUM
LARGE
not confuse these
memory types with the
Culler radius offset
determine how
1001 length offset and the cutter
offset will be entered into the contTol
nothing else. Work offsets
054 to 059 are not
Tool Offset Memory Type A
The Type A tool offset IS the lowest level available. Its
Ilexibility is very lim
because Ih is offset
the
tool length
wlth
cutter radius
in a single
column. Because
sharing for two different offoffset- In
it means
IS
registry area as
clIn he used, with
wilh this Iype of
cal type in their
value.
covered later,
memory are the most economi-
Tool Offset Memorv Type B
Figure 30·12
Effect of
cutter radius on the actual tool path
values.
has only a single screen column.
Now - do not assume! The twO
columns for tool
values
at all. They are
for the
in one column and the Wear
this distinction. the
for both, tool length
program uses addresses
CUTTER
3
•
Tool Offset Memory Type C
Wilh Ihe Ihree lypes of Tool MemDlY
The Type C offset group offers the most
the only offset type available that
values from those of {he lool radius, It still
tinction of the Geometry Offset and the Wear
Type B docs. That means Ihe control display
columns - yes,jour columns in lOlal. In this
addresses Hand D will be used for their
BOlh the Type A and rhe Type Bare
with only a single register, where the lool
ues are stored along with the cUller
amounts.
Normally, the Type A and Type B are associated wirh the
H only. That means me H
is
with
command, as well as wilh the G41 or
cUfling tools do not require the cutler radius
but all CUlling lools require the tool
program. If a particular cutler requires both 1001
offset number and cutler radius offset number, two
offset numbers from the same offset range must be
in the program and stored in the control register,
is the reason these offsets are called shared offsets.
Offset
No.
01
02
03
0.0000
0.0000
0.0000
.................... ........ww
Offset
No.
01
02
03
_
Wear
0,0000
0,0000
0,0000
0.0000
0.0000
0,0000
..
...
...
,
H-offset
Geometry
Wear
0,0000
0,0000
0.0000
0.0000
0,0000
0,0000
example, programmed tool T05 requires both
which obviously cannol have the same offset number.
is to use Ihe tool number as the tool length offset
number
increase that number by 20, 30,40, or so, for
cutter radius offsel. The entry for the Type A in the offset screen
be similar to the one in Figure 30-/4:
_w
Geometry
Offset
05
D-offset
Geometry Wear
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
3()·14
Shared offset Mh;:~/M' PM'~~~ for tool offset memory Type A
[here are two columns avai table, but
entry in the offset screen will
shown in Figure 30- ] 5:
30-13
Fanuc (00/ offset memorv types A B, C from the top down
•
it is reasonmethods
able to expect somewhat different
for each type. Up to a point, this IS true.
It is relatively easy to [ell which offset type is
j list look at the conlrol display. Figure 30- /3
ieal appearance of each Offsef MeinDl))
with zero vaIues). The aClual appearance
different, depending on the control model.
Offset
Address H or D ?
Programming Format
No.
35
I Geometry .
10.0000
Figure 30-15
G41 x. .. D ••
01' ..
G42 X .. D ..
01' ..
G41 Y .. D ..
or ..
Shared offset
G4.2 Y .. D ..
many axes can
chapler as well,
address to usc and
of the tool motion and how
at a time will be discussed in this
the question of which
H address or the 0 address?
offset memory Tvpe B
The Type C
will
the 10(.)1 length and the tool
umns, the same offsel
no need for the 20, 30,
H address is r"'C'L"r,'''''''
the D address is
cutler
her Figure 3()~ J6 show~ an input
to the Type A and the
columns. Since
their own col-
both - there is
In
254
Chapter 30
The cardinal rule number two is also simple and is based
on the adherence to the first rule:
Always apply the cutter radius offset
-8,6640
0.0000
0.3750
Figure 30-76
Unique offset register screen for tool offset memory Type C
•
together with a tool motion
0.0000 I
Geometry and Wear Offsets
Similar to the application of geometry and wear offsets
for toollenglh offset, described in Chapter J9, the identical
general rules can be used for the cutter radius offset.
Offsets entered in the Geometry offset column should
only contain the nominal culler radius. In the examples, we
have used a 0.750 cutler, with the radius of 0.375, That is
the nominal value and that would also be the typical value
entered into thc Geomerry offset column. The Wear offset
column should only be used for adjustments, or fine tuning,
relative to the nomina! size, as required during setup andior
machining. There is no separate column for adjustment or
fine tuning for the Type A offset. Adjustments can still be
made, the only difference is that the value in the single column will always change with each adjustment even if it
represen ls the cutter rad ius.
These two rules are not arbitrary - rules can be broken.
The suggestion here IS to follow the rules until a better way
is found. When selecting a startup (001 position, a few questions are worth asking:
o
What is the intended cutter diameter?
o
What clearances are required?
o
Which direction will the toof take?
o
Is there no danger of collision?
o
Can other diameter cutter be used if needed?
o
How much stock is to be removed?
The same drawing used already will be used for this example as well and (he cutter radius offset will be appl ied to
Ihe contour. To turn the offset on, to make it effective, the
cutter will be away from the actual cutling area, in the clear.
The intended cutler is 0.750, the climb milling mode is desired, nnd .250 clearance is away fTom the contour. Wilh
these numbers, the start position is calculated at X-0.625
Y-O.625. Figure 30-17 shows the start position that satisfies
all rules and answers the questions established earlier.
APPLYING CUTTER RADIUS OFFSET
All programming aids required to apply the cutler radius
offset in an actual CNC program are now known. The actual application, the way 10 use the offset in a CNC program, as well as the methods of proper usage, will be discussed next. There are jour nwjor keys to a successfu I use
of lhe culler radius offset feature:
i . 0.25
:~
~I
I
L-yO
1. To know how to start the offset
3. To know how to end the offset
-iY-O.625!
./
2. To know how to change the offset
RO.375
J
XO
-
, ~-O,25
4. To know what to watch between the start and end
Each item is important and will be discussed in order.
100.75 CUTTER
0.25 CLEARANCE
Figure 30· 17
Slarr position of the cutter before radius affset is applied
• Startup Methods
Slarting up the cutler radius offset is much more than using the G4IX ..D .. in the program (or something similar).
Starting up the onset me(l.ns :1dherence to two cardinal rules
and several important considerations and decisions. The
cardinal rule number one is simple - it relates 10 the start position of the cutter:
Of course, the suggested location is not the only one suitable, but it is just as good as other possibilities. Note that
the cutter located at the position X-0.625Y-0.625 is lwr
compensated, the coordinates are to the cenTer of the cutter.
Once the start location is established, tJle first few blocks of
the program can be written:
03001 (DRAWING FIGURE 30-2)
Always select the start position of the cutter
away from the contour, in the clear area
N1 G20
N2 G17 G40 GSO
NO G90 G54 GOO X-0.625 Y-0.625 S920 M03
CUTTER RADIUS OFFSET
5
N4 G43 Zl. 0 HOl
N5 G01 Z-O.55 F2S.0 MOB
N6
(c)
(FOR 0.5 PLATE THICK)
extra safety, the approach to the depth of Z-0.55
on a V2 inch plate thickness) was split into two moalthough
cutter is safely above the clear area.
the
heen
the first motion can be
direction IS to the left the
Moving the
I command is
means
first target
location. Howbecause the
as well. That means
Next decision is
point. Normally,
Lead-in motion, or
all of them corlocation eventually.
are some possible options;
and re-
IS
N.. GOl G4l XO YO 001 Fl5.0
N .. Yl 125
(l?2)
N ..
In alllhree versions. the cutter radius
gether with the first motion, while still away
(he option
actually
part contour.
part, selecting the option (a) is the
method of the lead-in. A combination of (a)
good choice, wilh the Y axis target in
Once the offset has been lUrned on, the conlour
poims can be programmed along the part
lhe
computer will do ilS work by conswlltly
I.he c;uUer
properly offset at all limes. The program
I can now
be extended up [0 poim P5 in the original illustration:
03001 (DRAWING FIGURE 30-2)
Nl G20
N2 G17 G40 GSO
N3 G90 G54 GOO X-0.625 Y-0.625 5920 M03
N4 G4.3 21-0 HOl
N5 G01 2-0.55 F2S.0 MOS (FOR 0.5 PLATE THICK)
N6 G41 XO 001 F1S.0
(START OFFSET)
N7 Yl.125
N8 X2.25 Yl.8561
N9 YO.625
NlO G02 Xl.625 YO RO.625
Nll GOl X •.
At block N 10, the tool has reached Ihe end of the
radius. The contouring IS not yet finished, the bottom side
has to cut, along the X axis. The question is - how far to
cut and when to cancel the cutler radius offset?
c,
Figure 30-18
Possible lead·in molions ro apply rhe cutter radius offset
This is the last cut on the part, so it has (0 be machined
the offset is slill in effeCT! The cutter can end al XO,
butti1at is not a practical position - the tool should move a
bit farther, still along the X axis only. How far is further?
Why nm to the same X-O.625, the original start position?
is nOlthe only clearance posilion available, but is the
most reliable and consistent. The block N II will
The (a) option is
first and the cutter
lion, Then, the tool continues
(Y 1.1 25), already in the
These two motions will appear in
N .. GOl G41 XO DOl F15.0
N.. Yl.12S
as:
Nll GOI X-O.625
(P2)
N .•
The option (b) is
motions, whereas two
version will not be
for the
the progmm would stillue correct:
N .. GOl G41 YO 001 F1S.0
N .• XO
N .. Y1.12S
N ..
(P2)
cutter has len the pari contour area and the cutter
is not required anymore. It will be canceled
but a lillie review of the startup may help.
culter radius was known for th is job, which is not alcase. The programmer needs a suitable 100/. because the Culling values depend on it. WIthin reason, a
or 0.875 cutter are not far apart - except for clearp.:lrlH\{~(-, of .250 was selected for .375 cutler
means the program is still good for cutters up
to and including 01
. CNC operator has this freedom,
l)v".<\U;,,, the only change is [0 the DOl offset amount in the
256
Chapter 30
control
offset registry. The
may
have to be adjusted, if necessary. We will look
at what
when the culle.r radius offsel is applied,
rule to establish the start
selected with a
the largesT culler that
•
i ncreased for a
or for a
that is
complete the program, leI's
the cutter radius offsct, when it is no
•
Finally, the program 03001 is completed. There was no
need for any
tool
- such an change is
rarher a rare occurrence, at
contouring operations
using milling controls.
Ihe directional change may
needed in the
some comments may be useful.
Offset Cancellation
or
A lead-in mOllon has been used at the
the culler
radius offset. To cancellhe offset a
motion will be
length of Ihe lead-out (just as the length of the
Cutter Direction Change
During a normal mil
cui, Ihere will seldom be a
to change Ihe cutler offset direction from left to right or
from
10
. If it
become necessary. the normnl
one mode 10 the other withow
command. This practice is seldom
G41 [0 G42 would
10 the
has (0 be somewhat greater Ihan or at least equal [Q
cutter radius. The lead-in and the lead-out motions are
called ramp-in and ramp-out
'fhe safest place to cancel cutter
for any ma-
IS away from the contour
This should
be a clear area position.
end position, Figure
9
Lion In (he example.
now be written.
HOW THE RADIUS OFFSET WORKS
from given examples is
good way to
by a recipe or a
help in
cases, but it will not help much in cases where
there is no
no
and no example. In those
to really undersland all principles behind
cases, il is
such as principles of the cutter
thc
The
is a good beginning. Next
during the tool motion in
N6 G41 XO DOl F1S.O
I
0.25
,
YO
It is not as simple as illooks. We cannot
block,
as N6, and know exactly what
to understand what the
do not think. they only execute
inslruclions and follow these instructions
B
N6 IS an Instruclion: Move 10 XO,
the radius
Sf 0 red in DO! 10 lhe left, during a linear motion aT 15
j
RO.375
- ....
ill/mill. This is Ihe program
ion to the control
. Where does the too! SlOp?
Figure 30-19
Cutter radius offset cancellation· program 03001
-
ill Figure 30-20:
program
-
tool-.......--.- ......
--llIJli'-
tool
03001 (DRAWING FIGURE 30-2)
----"
Nl G20
N2 G17 G40 G80
N3 090 GS4 GOO X-O.62S Y-O.62S S920 M03
N4 G43 ZL 0 HOl
NS GOl Z-0.S5 F2S.0 MOS (FOR 0.5 PLATE
N6 G4l XO DOl F1S 0
(START 1"'1 C''C'<:!,""'"\
1
N7 Yl.125
N8 X2.25 Yl.856l
N9 YO.62S
NlO G02 Xl.625 YO RO.62S
Nll GOl x-o 625
N12 GOO 040 Y-O 625
NlJ Zl. 0 M09
Nl4 G28 X-0.62S Y-O.625 Zl,O
Nl5 M30
%
001
(CANCEL OFFSET)
001
- I
Figure 30-20
Ambiguous slartup for a curter motion in radius affsef mode
RADIUS OFFSET
7
there are fWO possibilities and they are both
compensate the culler to the left
conditions specified in block
the cUlling tool moves to
as eXT)eClea
is
on to the left of (he pari contour,
the motion, using the radius value stored in the
tef
what is the problem?
is ambiguous. There are IWO possible outcomes, while only one is required. Which one? For
lef! part of the illuslration, one where the 1001
Y + direction next, when Ihe radius offset
This is the key.' The mOL ion direction thaI
block must be known to the control.
does the control handle
culler radius offset Type C
a buill-in
the 'Iook-ahead'type of cutler radius
look· ahead feature is based on the principle known
as buffering or reading-ahead. Normally, the control processor executes one block at a time. There will never be a
,-aU.)",U by any huffered block (next block).
In a shari overview, lhis is the sequence of events:
C)
1 left :
position after N6 is Y positive direction:
next
N6)
o
control detects an ambiguous situation,
and does not process the block as yet
o
control advances the processing to the next block
(that is NJ), to find out into which direction
tool
be
next
ways Ihe program can be written:
Q Example 1 - Figure
The control will first read the block i":l"In,t;:urlinn
startup of the cutter radius offset (that is the
o
N3 G90 GS4 GOO X-0.o2S Y-O.62S S920 M03
N6 G41 XO DOl Fl5. 0
(START ,.....,."",."......
N7 Y1.l2S
''''',('-,-.,... ..... ".,. Y-MOTION FOLLOWS)
type of the cutler radius offset is
2next
Iy in the software, but makes the contour
lS Y negativedireClion:
mi
expected,
so much easier on a daily basis. As maybe
are some siluations Lo be aware of.
N3 G90 G54 GOO X-0.62S Y-0.625 5920 M03
N6 G41 XO 001 F1S.0
N7 Y-1.125
(START OFFSET)
Y-MOTION FOLLOWS)
In both cases,
content of block N6 is the same, but the
motion Ihat follows the N6 is nOI - Figure 30-21.
•
Rules for look-Ahead Cutter Radius Offset
Look at
following sample program selection, not re-
hued to any
examples;
NO MOTION block
N17 G90 GS4 GOO X-0.75 Y-0.7S S800 MO)
N20 GOl xo DOl F17.0
N21 MOS
N22 Y2.S
(START OFFSET)
(NO MOTION BLOCK)
(MOTION BLOCK)
in
program structure? Ignore
coolant ON function in block N21. H it
can
wrong with it. The fact rem.Olion
block N21 , wh ich is Ihe
same block Ihe. control
wi II look ahead 10 ror I he direction of the next too! mOlion, Look at one more program
selection - again, as a new
What is
-Figure 30-21
Importance af the next tool motion for curter radius offset.
Y+ next direction on the
y. next direction on the right
•
look-Ahead Offset Type
The block N6 alone does not contaln suflicient amount of
data 10 successfully apply the
nextlllolion
- in fact, thf' dirf't:/irm of the next motion - must
known \0
the control system at all times!
Q Example - two NO MOTION blocks:
N17 G90 G54 GOO X-0.75 Y-0,75 S800 M03
N20 GOl XO 001 F17.0
N21 MOS
N22 G04 PlOOO
N23
n.s
OFFSET)
MOTION BLOCK)
(NO MOTION BLOCK)
(MOTION BLOCK)
258
Chapter
"",,·h.,,",c - but not wrong - this lime there
following the CUller radius offblocks
do HOI include any molion.
a program Ihalll1ighl be line if the
radius
were nOl applied. With an offset In effect, such
a program structure can create problems. Controls with the
'look-ahead'
can look ahead only so many blocks.
If the
the
one block look-ahead is atare two or more look-ahead blocks availon the control features. and not all consuggestions:
o
If the control has a
type cutter radius
It:CltUI't:;. but the number of blocks that can be
UI"c:;;,;:,t;U ahead is not known, assume it is only one block
o Make a test program to find out how many blocks
the control can read ahead
o
the cutter
offset is started in the program,
hard not to include any non· motion blocks - restructure
jf necessary
in mind that the control subjects the program input
to lhe rules embedded m the software. The correct input
must
In the foml of an accurale program,
kind of a response can b~ expected If the culter rais programmed wrong? Prohably a scrap of the
If the conlrol syslem cannol calculate the offset culler
position, it will act as if the offset were not programmed at
all.
means, Ihe initial tool motion will be towards the
XO wllh the cUfter center. When Ihe necessary information
is passed on [0 the control, the offset will be applied, usually lao lale, after Ihe CLllIer has entered the parl. Scrap is
the most likely result in Ihis case. Such an incorreCT
gram is shown in Figure 30-22:
03002
(PROGRAM WITH RADIUS OFFSE.'T """"''''VJ~J
N1 G20
N2 G17 G40 GBO
N3 G90 G54 GOO X-O.S Y-O.S Sl100 M03
N4 G43 Zl.O HOi
NS GOI z-O.SS F20.0
(FOR O. 5 PLATE TKICK)
N6 G41 XO 001 F12.0
Nt MOS
N8 G04 PlOOO
N9 Y2.5
NlO X3.S
Nll YO
Nl2 G01 X-O.S
Nl3 GOO G40 y-o.s
Nl4 Zl. 0 M09
NlS G28 X-O.S Y-O.5 Zl.O
Nl6 M30
%
(NO MOTION BLOCK)
{NO MOTION '-'''-''-''-','',
(MOTION """""""-''-,
{MOTION ....'-"-,"-'"
(MOTION BLOCK)
(MOTION '-''-''-,''-'"
CAl)1CE:L OFFSE.'T)
A conlrolthaL can read only one or I1vo blacks ahead \'v'iII
nrr\nr,,,",,
03002
-Ihe next marion is in
(In
In
to avoid
program structure lhat
eonUIlns more
black,
• Radius
one hal f of lhal
very
- rule should help to make
cutter radius offset will nOl fail:
iQVERCUT,
AREAl
--+-;.. /
error due tD w(()ng program structure· program 03002
example. in Ihe program 0300 I, the lool
~iLion is at X-O.625, (he targel position is XO.
the programmed Ienglh of the tool travel is
selected was .375, which is smaller and adheres 10 the rule.
There are lwo other possibilities - one, where the CUller
is the same as the programmed length of the 1001
travel, and lWO, where the cutter radius is larger than
programmed length of the lool travel.
Figure 30-23 shows a stan position of a cuLLer thal
same programmed length of lravel as the culler
is ceJ1 a In Iy a! lowed, bu I def] ni tel y nOL
n'\'~nrl"'r1
reason is it limits the range of adjustmenls that can
10 the actual cutter radius during machini
l'\Y't1.
RADIUS OFFSET
9
N3 G90 G54 GOO X-O.25 Y-O.62S S920 M03
No G41 xO DOl F15.0
Y1.125
N7
RO.375
Y-O.625
o
X
30·23
Cutter start position is equal to the cutter radius
Tlte followillg example
in a .375 travel
programmed along the X
If the 001 amount
as
(han .375, there will be a motion toward XO. If the 001
amount is equal to
the difference between the
grammed length and
length is zero and there will
not be any molion along
X axis. In that case, the
of the radius takes
without a movement and the motion (0 the
Y I I will continue.
N3 G90 GOO G54 X-O.37S Y-O.62S S920 M03
N6 G41 XO 001 F1S.0
N7 Yl.12S
(START OFFSET)
(P2)
What will happen here?
Ihecontrol calculates
the
between the
travel length
and the culter radius .375.
the direction of
next travel as Y
thai because the
cutter is positioned to the
the intended motion, it
to move. 125 in the X
direction! That does not seem
to a problem.
is a plenty of free
there is a problem - (he control does not recognize the
Programmer knows it, but
that there is a free
control does not. The
who designed the
have taken a
actions; yet, they wisely
to play it safe.
decided to let the control
to rejeci
and issue an alarm.
pending on the
alarm 'Overcutting will
occur in cutter radius
or
ence' or a similar
will appear - the common alarm
04J on Fanuc
systems.
number for this error is
Many programmers, even with a long
perienced this alarm. If nOI, they were either
or have never used cutter radius offset in the
Anytime the cutler
interference alarm occurs, always look al
surrounding blocks as well, not just at the
onc
the
processing.
(START
Try to avoid
like this one - although
coo-eet, they do not provide any flexibili!y and can cause
serious difficulties at some lime in the future.
Figure 30-24 shows a start position where
partially on
of(he target position.
nirely not
system will
an alarm
In (he next
we look at the cutter
ence that occurs
a lool mot jon, not just at
or tennination of the cutter radius
•
Radius Offset interference
The last
illuslrated only one of
pOSSIbllines, when the cutter radius offset
occur. Another cause for this alarm is when a cutter radius is trying to
enter an area
is smaller than the cutter radius, stored as
the D
amount. To .
the next proin Figure 30-25.
gram
1: 1
t.--1.00
RO.20
RO.25
o
1.1
0.50
figure 30-24
' - - -_ _ _ _ _- - - - 1 _
Cutter start position is smaller then the cutter radius
program sample is
except the X axis start
if the cutter is
.3750:
similar to the pretion is (00 close
in the DO 1 regis-
30·25
Simple drawing lor program 03003
,
260
r 30
03003 (DRAWING FIGURE
Nl G20
N2 G17 G40 GSO
N3 G90 G54 GOO X-O.625 Y-0.62S S920 M03
N4 G43 Zl.0 HOi
NS GOl Z-O.SS F2S.0 Moe
0.5 PLATE THICK)
N6 G41 XO DOl FlS.O
(START OFFSET)
N7 YO.925
N8 G02 XO.2 Yl.125 RO.2
N9 GOl X1.0
NlO YO.75
Nll G03 Xl.25 YO.S RO.25
Nl2 GOl XL 75
N13 YO
Nl4 X-O.625
Nl5 GOO G40 Y-O.625
OFFSET)
Nl6 Zl.O M09
Nl7 G28 X-O.625 Y-O.625 Zl.O
drawing dimension can no! be changed,
of the cutter diameter must be changed, to a culler
that is
.500 inches. The
.200 is no problem, as external
not allow gouging in cutter rafeature is built-in and
is no
to see what would actually happen, if
were not
Nobody wanls to see the gouging on
the pan, but the
30-26 shows the same effect
cally. rn
was a real error in the earlier forms
ter radius
Type A and Type B.
I~
NlB M30
R0.25
program is quite simple, it is correct
it follows all
discussed so rae The key to succes<:; i <:; the selecl ion of
cutter diameter and the entry amount the address
into
control system. Let's see what will
- the
inch
mill. The
same culler is used as before, a
amount DOl stored in the control will
control unit will process the information from the
with the offset amounts to
Then, it executes the blocks as il moves
the par!. Suddenly, at block N7 alarm No. 041
occurs cutter radius inleJference problem.
What
happened? There [s nothing wrong with t'he
Most CNC operators would look at
gram
it. After careful study, if they fi nd it correct,
the cause or the problem must be somewhere
of
Try not [0 blame the computer and don't
more ti me once you are
that the
Check the offset input in 001. The amount
the tool in
there. That is also OK
drawing next. That [$
erything seems
and
is
a
the screen,
step.
!GOUGE
001 =0.375
=1:1
Figure 30·26
Effect 01 overcutting (gouging) in cutter
offset mode.
Tvpe Cradius offset (look ahead type) does not allow overcutting
• Single vs. Multiaxis Startup
There is another
stanup, particularly if
tion along twO axes,
look at
no problems. Now we look at
cutter radius
startup mo,.,,.,.~. __ single axis.
cutting, with
cutting.
in Figure 30-27, usEvaluate the two approach
ing a cutter radius offset startup towards an internal profile,
for example, a wall of a pockel or
in[ernal contour.
the relationships between:
o
dimensions
." alld '"
o
input
.. , and... Offset amounts
o
Offset amounts
Program input
... and... Drawing dimensions
may
a while
amount of experience a-; well, In
to. It
pro-
the problem is in the relationship
amount and [he drawing dimension.
Study
radius of
375. This
- there is an
is set to the cutter
is expected \0 tit into the
it cannot - hence ihe alarm.
Possible problem in cutter radius offset mode during a startup
with two axes simultaneously (intemal curting shown)
CUTTER RADIUS OFFSET
261
o Correct approach - single axis motion:
Here are the first few correct blocks of each method:
The correct programming approach shown on the left
side of the illustration contains the following blocks - only
the starting program blocks are listed:
N1 G20 (CORRECT APPROACH WITH A SINGLE AXIS)
N2 G17 G40 GSO
N3 G90 G54 GOO XO YO S1200 M03
N4 G43 ZO.l HOI Nne
NS G01 Z-O.25 F6.0
(FOR 0.25 POCKET DEPTH)
N6 G41 Y-0.7S DOl FIO.O
(START OFFSET)
N7 XO. 75
N8 YO. 75
There is no internal radius in the program 10 worry about,
so the amount smred in the offset register DOl does not
have [0 consider i[ and wi!J represents (he cuucr radius as is.
o Incorrect approach - multiaxis motion:
The incorrect mol ion approach shown on the right side of
the illustration contains the following initial blocks:
N1 G2 a (INCORRECT APPROACH WITH TWO AXES)
N2 G17 G40 GSO
N3 G90 G54 GOO XO YO S1200 M03
N4 G43 ZO.l HOI MOS
N5 GOI Z-0.25 F6.0
(FOR 0.25 POCKET DEPTH)
N6 G41 XO.7S Y-O.75 DOl F10.O
(START OFFSET)
N7 YO.75
There is no way the control system can detect the bottom
wall of the pocket at Y-O.7S. The startup for the offset is exactly (he same as for external cutting, but more damaging.
Compare the two possible startups for the drawing shown
in Figure 30-2, earlier in the chapter. If [he radius offset is
started with a single axis motion, (he result is shown at the
left side illustration in Figure 30-28.1f the offset is started
with a (wo-aJ(is motion, the result is shown at the right side
illustration in FiJ;ure 30-28.
xi
t
YO-'-
)
1./"):
N'
~
oj
wi
'--
~
D01
-j -- - D01
'W
'0
xl
o Correct approach - single axis motion:
G20 (CORRECT APPROACH WITH ONE AXIS)
N2 G17 040 GSO
N3 G90 G54 GOO X-O.625 Y-O.62S 8920 M03
ill.
N6 G41 XO DOL F1S.O
N7 Y1.125
o Correct approach - multiaxis motion:
N1 G20 (CORRECT APPROACH WITH TWO AXES)
N2 017 G40 Gao
N3 G90 G54 GOO X-O.625 Y-0.62S 5920 M03
N6 G41 XO YO DOl FlS.0
N7 Yl.125
There will always be a problem that cannot be solved in
any handbook, regardless of how comprehensive that book
may be. The subjects and examples included in this handbook present common basis for a better understanding of
the subjecl. With growing experience, the understanding
becomes much deeper. Before going any further, let's review some general rules of the cutter radius offset feature.
OVERVIEW Of GENERAL RULES
Reminders and rules are only important until a particular
subject is fully understood. Until then, a general overview
and some additional poinls of interest do come handy. Programming the cuuer radius offset is no differenl. The following items are marked [M] for milling, [T] for turning,
and [M-TJ for both types of control systems:
o
[M-T J Never start or cancel the radius offset in an
arc cutting mode (with G02 or G03 in effect\. Between
the startup block and the cancel block, arc commands
are allowed and normal, if the job requires them.
o
[M·T J Make sure the cutter radius is always smaller
than the smallest inside radiUS of the part contour.
o
I M-T lin the canceled mode G40, move the cutter to a
clear area. Always consider the cutter radius, as well as
all reasonable clearances.
o
I M-T I Apply the cutter radius offset with the G41 or
G42 command, along with a rapid or a linear motion
Y-O,625
o
X
-~~~-
Correct approach in X
Correct approach in XY
Figure 30·28
Startup of the cutter radius offset for external cutting:
Single axis approach, shown on the left
Two axis approach - shown on the right
(START OFFSET)
(P2)
Note that in cascs of the cutter radius offset for an external contour, both programs listed are correct, because there
appears LO be 110 interference with any section of the part. In
fact, there is the same interference as in the internal milling
example - the only difference is that Ihis type of 'interference' is of no consequence - it tokes place while in the air.
YO
'V:'O.62S·
(START OFFSET)
(P2)
to the first contour element (GOO or GOl in effect).
262
Chapter 30
-"""--"""-""""--"""'"
o
[M) Reach the Z axis milling
in the G40 mode
offset cancel mode).
-
the preference to a single axis approach
position.
o
I M I Do not
th e offset num ber 0,. for in the
program it is a sma!! error that can cost you a lot.
o I M·T J Make sure to know exactly where tbe tool
command point will be when the radius offset is applied
two axis.
o {M-T In the compensated mode (G41 or G42 in effect),
watch
blocks that do not contain an axis motion.
non-motion blocks it possible Imissing X, Y and Z).
o I M-T } Cancel cutter radius offset with the G4Q command,
with a
o 1M)
after
0.375 ---
from the depth (along the Z axis only)
radius offset has been canceled.
I..IIC1VVHlfJ
o [ M I Make sure the cutter radius offset corresponds
to the work plane selected (see Chapter 31).
o [ M·T ) G28 or G30 machine zero return commands will
not cancel the radius offset (but either one will
the tool length offset).
o
-
or a linear motion (GOO/G01) only,
axis motion only.
I M-T I G40 comlTland can be input through the MOl to
cancel the cutter radius offset (usually as a ""lIf 'II II,.,'
or an emergency measure).
to illustrate practical application of a cutter radius offset
will be on the specified lOlerance in the
as
+.002/- .000, for the dimensions of the I wo
meters - the
external and 02.0 internal. Note that
of all dimensional tolerances is the same for both
meters. This statement will be very important later.
•
Measured Part Size
machinist knows thal
the part depends on many factors,
setup, cutting depth, material
the selection of 1001, its exact
PRACTICAL EXAMPLE - MilLING
The following in-depth example
practical appltcalion of the cutler radjus
(0
CNC programmer and the CNC operator. It covers
ally all situations that can happen during
process and presents solutions to maintaining the
dimensions of the part. The tirSI subject that
(0
understood is the difference between the programmed and
the measured part size.
•
Part Tolerances
When a part is inspected, the measured
one of tile three possible oulcomes:
o night on size
o Oversize
o Undersize
can
only
... within specified ' ....I"'r"'''... '''''
... will be scrap for
... will
scrap
external cutting
The first outcome is always
the extemal or internal
In both cases, the
specified roleral1ce
IS outside of the
requires a look at
additional (wo items thai also have to be considered:
o
The next example
radius offset on the part
that reason, only a simple
simplest tool path. btlt not """t'I>~'~"'r'
method. Figure 30-29 shows
o
External cutting method
... known as Outside or 00
... known as Inside or 10
the machined canthe tenns oversize and WIto the type of cUlling. The folmost
results:
CUTTER RADI
263
,
No Action Required
Scrap Likely
Recut Possible
it is clear (hat no action is necessary
is within tolerances. regardless of
or the internal cutting took place. For
or
Y2.S
->~"'---«««««::«-.-««<- ........................
Tool path
motion
\
results, a recut may be possible or
Y 1<25
\
\
the likely result.
(02.500 inch OD in the exthaL is measured as larger than the allowed tolerance can likely be recul, but a size that is smaller Ihan the
range will result in a scrap.
internally (02.000 inch ID in the examas smaller than the allowed
recut, but a size that is larger then the allowed
range will
in a scrap.
•
3D-3D
Detail lor external tool path shown in example 03004
Programmed Offsets
most a1tractive feature of the cutter
it allows to change the actual tool sire right on
by means of the offset registerfunction D. In
example, only one lool is used - .750
mill - and one single cut for each contour
Toolpath
motion
Offset
position
.0
internal). The program XOYOZO is at the center
and the top of the part:
03004
(Tal - 0.75 DIA END FINISHING MILL)
(**** PART 1 - 2.S DIA EXTERNAL CUTTING **** )
Nl G2D
N2 G17 G40 GSO
N3 G90 G54 GOO XO Y2.5 S600 M03
POS.)
(CLE.AR+TOOL LG.)
N4 G43 ZO.l HOi MUS
FOR 2.5 DIA)
NS Gal Z-0.375 F20.0
MOTION)
N6 G41 Yl.2S 001 FlO.O
(EXT. CIRc:LE CUTTING)
N7 G02 J-L2S
MOTION)
NB GOl G40 Y2.S
ABOVE)
N9 GOO ZO.l
(**-- PART 2 - 2.0 DIA INTERNAL COTrING **** )
(START POS. AT XOYO)
NlO YO
FOR 2.0 DIA)
Nil G01 Z-O.8 F20.0
(APPROACH
Nl2 G41 Yl.O Dll FS.O
CIRCLE ,.....,..........'L'""",
Nl3 G03 J-LO
MOTION)
NJ.4 GOl G40 YO
(CLEAR
N15 GOO ZO.l M09
AXIS MACHINE ZERO)
NJ.6 G28 ZO.l MOS
(OPTION.1\L
N17 MOl
position
Figure 30-31
Detail for internal tool path shown in
As is customary in
program 03004, the tool path uses
programmer. This is
and the other positions defined by
not only the standard but also
most convenient method
Lo develop a CNC
is easy to understand by the machine
dimensions are
easy to trace (if
can be made, if
required. In plain
ignores (he
CUlfer radius and
as if the culter were a
a cutting
a zero diameter.
point - in
• D
The
Figure 30-30 shows
program - the external
30-3/ shows the lool path
gram - the internal d
half of the
03004
Setting
cutter is
work. The madiameters and the
- ifnot in the
264
Chapter 30
One critical fact to he established first is that the CNC
system always calculates a specified offset by its euUer radius, lIot by its diameter.l[ means the programmer provides
[he cutter radius offsel in the form of a D address. On the
machine, the programmed offset DO I will apply to the cutter radius registered in offset 1,002 \0 (he radius registered
in offsel 2, ecc. What actual amounts are in these registers?
Since no radius oflhc cutter is included anywhere in the
program, the offset register D mllst normally contain the
culler radius actual value. Be careful - some machine parameters may actually be set to accept the cutter diamefel;
although all internal calculations are sti II set by the radius.
Evaluate program 03004; what will be the stored amount
of DOl? A 0.750 inch end mill is used, so the DOl should
be set to .375. This is correct in theory, bUI factors such as
tool pressures, material resistance, tool defiecLion, actual
1001 size, tooltoJerances and other faclors do inlluence the
finished part size. TIle conclusion is that the DOl registered
amount can be .:'75, but only under idea! conditions.
Ideal conditions are rare. The same factors Ihat influence
machining will also have a significant effect on part dimensions. It is easy to see thal any measured size that is not
within tolerances can be only oversize or undersize and exrenwl and internal cutting method does make a difference
as to how the offset can be adjusted.
Regardless of the cUlling method, there is one major rule
applied to the cutter radius offset adjustment in any control
system - Ihe rule has two equal pans:
POSITIVE increment to the cutter radius offset will cause
the cutting tool to move AWAY from the machined contour.
NEGATIVE increment to the cutter radius offset will cause
the cutting tool to move CLOSER to the machined contour.
Note the word 'incremenr' - it means that the current radius offset amount will be changed or updated - but not replaced - with a new amount. The concept of 'moving away'
and 'moving closer lO' the part refers 10 the tool motion as
the CNC operator will see. TI1e measured size of the part
can be controlled by adjusting the culler radius offset value
in lhe control, programmed as the D address, according to
these two rules. The most useful rule that applies equally to
the external and internal adjustments has two alternatives:
dius offset commands G41 or G42 as well as the D address
offset number - with the appropriate cancellation by G40.
Evaluating what emc/I)' happens during the tool motion
for each cutting method (external or iJUernal) offers certain
options. In both cases, the cutling tool moves from the
starting position, within (he clear area, to the large! position of the machining contour. This is the motion where the
culler radius offset is applied, so Ihis motion is critical. In
fact, this is the motion that determines the final measured
size of the parl. Each method can be considered separately.
•
Offset Adjustment
Before any speciai details can be even considered. think
about how the offset amount can be changed. rn those cases
where the size of the part is to be adjusted, the incremental
change of the offset value is a good choice. Incremental
offset change means adding to or sublracTing/rom the current offset amount (using the +INPUf key on a Fanuc
screen) or sloring the adjustment in the Wear offset screen
column. Changes to the program data is never the option.
•
Offset for External Cutting
Evaluate the tolerance range for the outside circle 02.5.
The tolerance for this diameter is +.002/-0.0, so all sizes
between 2.500 and 2.502 are correct. Any sIze smaller than
2.5 is undersize and a size greater than 2.502 is oversize.
There are three possible results of the measured size for
external cutting. All examples are hased on the expected
middle size of 2.50 I and on DO 1 holding the amount of
375, which is the radius of a 0.750 milling culler.
o External measured dimension - Example 1
2. SOlO Ivilh DOl", 0.3750
This is the ideal result - no offset adjustment is necessary.
The tool culling edge touches the intended maChining surface exactly. All is working well and the offset setling is accurare. Only standard monitoring is required. This is not
such a rare situation as it seems - in fact, il is quite common
with a new CUller, rigid setup and common tolerances.
o External measured dimension - Example 2 :
2.5060 'Nilh DOl::: 0.3750
To ADD more material TO the measured size,
use LARGER setting amount of the 0 offset
To REMOVE material FROM the measured size.
use SMALLER setting amount of the 0 offset
Experienced CNC operators can change offset settings at
the machine, providing the program contains the culler ra-
The measured diameter is .005 oversize. TIle tool edge
has nOI reached the contour and has to move closer to it.
The radius offset amount has to decrease by one hal f of the
oversize amounl, which is on the diameter or width bUlthe
offset amount is entered as a radius, per one side. Offsel
DOl is adjusted incremenlally by .0025, to 001==0.3725.
o Externalrneasured dimension - Example 3:
CUTIER RADIUS
2.4930 wiill
DOl
5
• One Offset or Multiple Offsets?
0.3750
is .008 undersize.
cUlling
has reached beyond the programmed machil1ing
and
(() move away
it. The radius orf:::.et
amount has 10
by One half of the undersize
amounl. The
on the diameter (or
The
width)
and the goal was the middle tolerance of 2.50 I
ternZll diameter and 2.00 I for the internal
offsets in the program needed or a will a
Keep in mind that (he last few
possibilities that were independent
no common connection. Program 03004
mon connection bel ween the two
end mill, used for Culling both
dius,
mentally by
• Offset for Internal Cutting
results of the measured size for
are based on the expected
and on D II holding the amount or
culler.
Assume for a moment, thal only one
ample 001. with the stored amount of
~ured, the external diameter is 2.00 I After
nu
cutting (he internal diameter of 2.000 inches, when measured
again, its
is nol2.00 I as
but only 1.999. 111is
measurement is .002
the expected diruncter.
The reason is
bOlh
have a +.002/·0.000 tolerance, The
+.002 means
meter, +.002 means
set alone cannot
on bOfh
(hat if
Internal measured dimension - Example 4 :
2.2010 will!
The program 03004 used 001 for the
and Dll for the internal diameter. Only one
Dll = 0.3750
011
is the ideal result - no offset adjustment is ne.:essary.
The lool cutting
!Ouches the intended machining surAll is working well and the offset selling is accurate. Only normal monitoring is required.
o Internal measured dimension - Example 5 :
2.0060 ""'1111
programmer should alprogram and suggest (he
as a professional courtesy.
D11 = 0.3750
a Scrap
The measured diameter is .005 oversize. The tool
has reached beyond the intended machining
has 10 move away from it. The radius offset value
by onc halfoflhe oversize amount.
is 011 the diarllcter (or width), but (he offset amount is entered as a radius, pef side only. Tne Dll offset must
incremented by .0025, to D 11=0.3775.
o Internal measured dimension Example 6 .
can be used here. The goal is to use
a way that the pari will not likely be a
even with an unproven tool. A good operator can
SCfilpS
by wrong offsets, at least to some
key is to create some temporal)! orfset
goal IS 10 force a cut Ihat is oversize externally or
in.ternaily, measure II, adjust it. then recut to the right
Whether machining an external or internal tool path, even
the best setup will not guarantee that the part dimensions
will be within tolerances. When machining ,.In
contour, the diameter can be cut il1femionally
(han
required - in a controlled way. In this casc, the
diame[cr will be roo small is present
1.9930 witll Dll = 0.3750
measured diameter is .008 undersize.
[he intended maehini
move
creased
is on the
tered as a radius,
crcmcnred by .004, to 0 II
When iI comes 10 initial ol'fset amounts, some
In-
In internal contour machining, the diameter can
cut
leI/tiona")' smaller than required, in a cootrolled
this case, the risk chalthe diameter will be 100
is
ent. Either ease offers benefits but some drawbacks, 100.
266
r 30
solution is 1O move the tool
machined surface by a
pos;/ive
increment amount must be
greater than the '-I'IJ'-'-'l'-U error of the tool radius, as well as
being suitable
a recul.
away
In both cases, when
to
R
test cut is made, measure the
by one half of the di fference bediameters. If only one side is
meter and adjusllhe
tween measured and
CUl, the di
is not hal
pOint
point
o
X
to
.9
a
30-32
• Program Data ~ Nominal or Middle?
Tool reference point for turning and bon"ng - (a) turning, {bJ boring
Many coordinale locations in the
dimensions that are
is - what happens if the
are two
erance range?
• Radius Offset Commands
tions are
grammers. One
commands used in milling
contouring on CNC lathes - Figure
of tolerance
LO use the nominal size
ignore the
nions have some credibility and should not
. In lhis handbook, the
preference is to use the nominal dimensional sizes and let
the tolerances be handled by
llse of offsets - at the
is that a program using
machine. Two reasons prevail.
in case of drawnominal dimensions is easier [0
ing changes, they will affect
more often than
nominal sizes.
+
G42 - RIGHT
+
G41 - LEFT
TOOL NOSE RADIUS OffSET
Figure 30-33
Lathe application of the fool nose radius offset
All the principles and
radius offset for a lathe
mainly caused by the
In milling, the cutting tool is
is the cutting edge and its radius
most common is
tools have a di fferent
a
carbide insert. An Insen may
one or
more CUlling edges. For strength and longer insert Ii the
has a relalively small comer
raturmng and boring tools are:
1/64 ::: .0156 (English) or OAO mm (metric)
1/32 .0313 (English) or 0.80 mm ,metric)
3/64 .0469 (English) or 1.20 mm (metric)
JJ"'''''"J,)'' the too! cutting edge is often
a
n.ose radius offset became common.
Offset of the tool nose radi us
to the
of the contouring direction
G42
Offset of the tool nose radius
to the R!GHT of the
G40
lathes, G codes do not use
in (he
edges,
/lose,
• Tool Nose
corner of the lOa],
into allose 1ad ius.
corners of a lurning tool and a boring tool.
tool nose reference point in turning is often called
point, the imaginoly point and, lately, even
It is the poinl tn;i! is moverl along Ihe contour,
it is directly related to XOZO of the part.
G41
•
Orientation
center of a circle symbolizing an
to the conlour by its radius. In
are part of the 1001 radius. on lathes,
tools do have a radius but ""',... ",.,,,
nose
center is also equidistant from the contour,
the edges change their orientation, even for the same
Additional definitions are needed in a form
a vector
pointing towards the radius center.
vector is
tip orientation, numbered arbitrarily.
MH''''n,''' to eSLablish the nose radius center
shows two tools and their tip
CUTIER RADIUS OFFSET
267
single axis motions are part of a contour thal also includes
radii, chamfers and tapers. In this case, the tool nose radius
offset is needed, otherwise all radii, chamfers and tapers
will not be correct. The illustration in Figure 30-37 shows
what areas of the part would be undercut or overcut, if the
tool nose radius offset were 110t used during machining.
-.-~
/'
o
Reference point
X
a
......
to ZO.J
I
I
a
.......
Lbl
Figure 30·34
Relationship of the /00/ reference point and the nose radius center
The tip orientation is entered during the setup, according
to arbitrary rules. Fanuc controls require a fixed number for
each possible tool tip. This number hus [0 be entered into
the offset screen at the control, under the T heading. The
value of the [001 radius R must also be entered. If the tool
tip is 0 or 9, the control will compensate to the center. Figures 30-35 and 30-36 show the standard tool tip numbering
for CNC lathes with X+ up and Z+ [0 the right of origin.
a
- PROGRAMMED CONTOUR
T2
b.
Figure 30-37
T7
EHect 01 tool nose radius oHset . (a) oHset not used (b) oHset used
• Sample Program
T3
Figure 30-35
Arbitrary tOO/lip numbers for nose radius offset· rear lathe shown
2
.-
6
The following program example 03005 shows a simple
application of the lDOI nose radius offset all an external and
internal contour, based on the drawing in Figure 30-38.
Only the finishing cuts are shown - roughing is also necessary, but would most likely use the special G71 multiple
repetitive cycle, described in Chapter 35.
1
00
I'l.O
C'">N
C\lN
,
•
NN
.
NN
0
N
..90
NN
X4.750
X4.510
5
7
TLR
I.t) I.t)
NN
..- co
..- 0 ,
.-3
X3.250
X2.650
X2.410
- - X1.990
X1.750
XO.950
-- XO.750
-XO
I
8
4
TLR :;: Tool radius
Figure 3D-36
Schematic illustration of the too/ tip numbering (Fanuc controls)
•
Effect of Tool Nose Radius Offset
Some programmers do not bother using the tool nose rat!ius offset. ThaI is wrong.! TheorelicaJly, there is 110 need
for the offset if only a single axis is programmed. However.
l.O
I'
00
00
00
...-0
0
N,
NC\J
,
0
N
NN
.
C\J
...-
,
N
Figure 30-38
Simplified sample drawing for program exampfe 03005
2
30
03005
NGl T0300
{EXTERNAL Fnrr5EIDrG
NG2 G96 5450 M03
N33 GOO G42 X2.21 ZO.l T0303 MOB
N34 GOl X2.6S Z-O-12 FO_007
NG5 z-0.825 FO.Ol
N36 X3.2S Z-1.l2S
N37 Z-l. 85
Change of Motion Direction
CNC lathes, a change in
10 a turning cut(-s) with G42 in
problem is u,,,'''-U,,.,'.Al
N44 T0400
(INTERNAL FDrrSHING)
N45 G96 S400 M03
N46 GOO G4l X2.19 ZO.l T0404 MOS
N47 GOl Xl.75 Z-0.l2 FO.006
N48 Z-l.6 FO.OOS
N49 G03 XO.95 Z-2.0 RO.4
NSO GOl XO.75 Z-2.l
N5l Z-2.925
NS2 U-O.2
N53 GOO G40 xa.o Z2.0 T0400
NS4 MOl
Note that the contour start
positions are in the
clear area - away from the pan. Make sure there is enough
clearance. Cutter radius
inteJference alarm
(alarm #41) is always
clearance.
Minimum Clearance Required
>TLR x 2
•
much more often than on machining centers.
shows a facing cut On a solid
N38 G02 X4.0S Z-2.2S RO.4
N39 GOl X4.S1
N40 x4.8 Z-2.395
N41 £10.2
N42 GOO G40 X8.0 ZS.O T0300
N43 MOl
•
nose radius offset, programming the minimum
or at least.! 00 Inches per side (2.5
a
clearance for all three standard tool nose radii 1164, 1/32 and 3/64 (0.40, 0.80 and 1.20 mm
-
x2
X 1.70 I Correct
X 1AO
approach
····X1 ,00
XO
CLEARANCE
-,
X-0,07
Incorrect
approach
Figure 30-40
Tool nose radius offset change for the same tool
N2l T0100
(CORRECT APPROACH)
N22 G96 S400 M03
N23 GOO G4l Xl.7 ZO T010l MOa
(START)
(FACE OFF)
N24 Gal X-O 07 FO.D07
N25 GOO ZO.l
(ONE AXIS ONLY)
N26 G42 Xl 0
(THEN COMPENSATION)
N27 Gal Xl.4 Z-O.l FO.012
( CONTOURING)
N28 Z-O.65
N29 X ••.
Face CUlling is a single
for consistency. For sol id
the center line, X-0.07 in
ally larger than double tool
the tool leaves a small un
the face will not be flat.
>TLR x 4 i
on 0
correct tool motions on the
If the above program is
>TLR x 4
on 0
>TLR x 2
-- --.-
Figure 30-39
Millimum C/l;laI8I1CB lor loo/nose radius offset
Figure 30-39 shows minimum clearances
start and end of cut. Make sure the nose radius
jnlo
x 2 and x 4
twice or four
becomes a
N21 T0100
(INCORRECT VERSION)
N22 G96 S400 M03
(START)
N23 GOO G4l Xl.! ZO T010l MOS
(FACE OFF)
N24 GOl X-O.07 FO.007
N25 GOO G42 Xl_O ZO.l
(*** WRONG ***)
( CONTOURING)
N26 GOl Xl.4 Z-O.l FO.012
N27 Z-O.65
N28 X ..
... the face will never be completed!
PLANE SELECTION
From all available machining operations, contol/ring or
profiling is the single most common CNC application, perhaps along wilh hole making. During conlouring, Ihe 1001
mOlion IS programmed in at least three differenl way~:
o
Tool motion along a single axis only
o
Tool motion along two axes simultaneously
o
Tool motion along three axes simultaneously
Planes in the mathematical sense have their own properties. There is no need Lo know them all, bUllherc are imporlant properties relaling 10 planes lhat are useful in CNC
programming and in various phases or CAD/CAM work:
o Any three points that do not lie on a single line define
a plane (these points are called non-collinear points)
There are additional aXIS mOlions thaL can also be applied
(thefourllI andfifth axis, for example), but on a CNC machining cenler, we always work with at least three axes, although nol aiwa)'s simullaneously. This reflects the lhree
dimensional reality of our world.
That is notlhe case for the following lhree programming
procedures, where Ihe various consideralions change quite
signilicanlly:
o
Circular motion using the G02 or G03 command
o
Cutter radius offset using the G41 or G42 command
o
Fixed cycles using the G81 to G89 commands,
or G73, G74 and G76 commands
A plane is defined by two lines that intersect each other
o
A plane is defined by two lines that are
parallel to each other
o
A plane is defined by a single line
and a point that does not lie on that line
o A plane can be defined by an arc or a circle
This chaptcr applies only 10 CNC milling systems, since
turning systems normally usc only two axes, and planes are
therefore no! required or used. Live tooling on CNC lathes
does no! cnler lhls subject.
Any absolute point in the program is defined by lhree coordinates, specified along the X, Y and Z axes. A programmed rapid motion GOO or a linear mOlion GO I can use
allY number of axes simullaneously, as long as lhe resulling
(001 motion is safe wilhin the work area. No special considerations are required, no special programming is needed.
o
o
Two intersecting planes define a straight line
o
A straight line that intersect a plane
on which it does not lie, defines a point
These malhematical deflnitions are ol1ly Included for reference and as a source of addilional information. They are
!lot required Cor everyday CNC programming.
MACHINING IN PLANES
The path of a CUlling lool is a combination of straighl
lines and arcs. A too! mOllon in one or two axes always
lakes place in a plane designated by two axes. This type of
mOl ion is n·vo-dimellSional. In contrast, any tool mol ion
lhal takes place in lhree axes al the same time is a Ihreedimensional motion.
•
Mathematical Planes
In all three cases - and only ill these three cases - programmer has LO conSider a special selli ng of the control system - il is called a seleCTion of lhe rnachining plane.
In CNC machining, the only planes [hal can be defined
and used are planes consisting of a combination of any fwa
primary axes XYZ. Therefore, the circular CUlling morion,
curter radius offset and fixed cycles can Lake place only in
anyone of the three available planes:
WHAT IS A PLANE?
[
To look up a definition of a plane, research a slandard
textbook of malhematics or even a dictionary. From varioLiS
definitions, plane can be described in one sentence:
The actual order of ax is designarioJl for a plane delinition
is very imponant. For example, lhe XY plane awl the YX
plane are ph.vsically the same plane. However, for the purposes of defining a relative (001 motIon direction (clockwise vs. counrerclockwise or lefr vs. right), a clear standard
- must be established.
.
A plane is a surface in which a straight line joining any
two of its points will completely lie on that surface.
';('( plane
ZX plane
YZ plane
269
270
y
international standard is based on the mathematical
ru Ie that spec i fies Ihe ji rsr letter of the plane designation
ways refers to the /lO/'izonral
and the second
reLa the verlical axis when the plane is viewed. Both axes
are always orthogonal
and vertical) and
pendicular (aL 90°) La each
In CAD/CAM, this standard deiines (he
Ihe lap and baHam,
front and back, elc.
~O3
G;;;\ X
arc defined as:
G;;;\
z
RIGHT - YZ
STANDARD
malhemalical designation of
is to write the alphabetical order of
axes twice and
pair with a space:
In mathcmaticalterms. the
~O3
G;;;\ y
~O3
TOP - XY
A simple way to
Dxes for alllhree
all
X
OF PLANES
z
t ~G03
~y
t ~G03
~X
TOP-XY
----~-~------.--,..
..
-YZ
--.. ,-
----
PLANES ON A VERTICAL MACHINING CENTER
Plane
x
z
Xy
vz
I
y
x
z
y
NOle the emphasis on Ihe word ·mathematical'. The em-
is intenlional, and for a
soon
apparent, there is a
mathematical planes and the machine
the
direction of the
•
reason. As will
between the
as defined by
Machine Tool Planes
view
:J
front view
view
.. , YZ
3J-l
di
betwo definitions, caused by a viewpoints that are
both
planeon
ill us(ratioll.
The
and operators alike.
of 1001 motions
are
and machined in
all
machining centers,
pendicular to the XY plane.
m:e the same in this
main reason is that
for contounng)
XY plane.
is always perhorizolHal appli-
Program Commands for Planes Definition
The sekction of a plane for
related controls
adheres to the mathematical designation of planes, nOE the
actual
machine tool planes. In a
each
the
mathematical planes can
preparatory command - a
G
selection
III
II is
is extTemely Imyet often neglected and even misunderstood by
XV plane
o
The right
In programming, the selection
•
machining center
axes. Any two
a plane. A machine
be detlned by
machine from standard operating position.
machming center, (here are three standard
perpendicularly (straighl
o
of standard mathematical planes (above),
on a eNC machining center (below)
that the XY plane and lap view are Ihe same in
so is the YZ plane
side
mathematical plane is
front
machine. which is XZ. as
in the middle
where
plane
plane be- '
horizontal axis
G18
ZX plane selection
G19
YZ plane selection
motions (programmed with GOO) and all linear
(programmed with G01),
selection
command is
irrelevant and even
ThaI is
other motion modes, where
(ion in a
is extremely important
sidercd
For machining applications using the circular interpolation mode, with G02 or G03 commands, cutter
offset
mode with
1 or G42 commands and fixed
mode
with G81l0
commands, as well as
G76. the
plane selection is
ieal.
PLANE
271
• Default Control Status
.cIRCULAR INTERPOLATION IN PLANES
If the plane is nol
faults automatically to G 17
LX plane in turning. If the plane
grammcd, it should be induded at the
Since the three plnne commands only
La/" motions, cutter radius offsets and fixed
selection command G 17, G 18 or G 19 can
before any of these machining
Always program the aplprOI)riate p,lanle se~lec·tionl cOlmmland
Never rely on the control .. "'.... ,,,. . ,..'"
Any plane selection change is
prior Lo actual tool path change.
can
onen as necessary in a program, but only one
active at any time. Selection o[ one plane
plane, so the G 17/G 18/G 19 commands
Allhough true in an informative sense, it is most
the opportunities to mix all three plane
program arc remole. From all three available
only the circular motion is affected by plane "'-"~'-'''VI
look at the programming of a
as well, at least for comparison
STRAIGHT MOTION IN PLANES
rapid motions GOO and linear motions GOI arc constraight motions when compared with circular molions. Siraight molions Can be programmed for a SIngle
or as a simultaneous motion along two or three axes. The
following examples only show typical unrelated blocks:
~ Example - Rapid positioning - GOO
GOO X7. 5 Z-l. 5
GOO YIO.O Z-O.2S
GOO X2.0 Y4.0 Z-0.75
When we compare Ihe mathematical axes
Ihe actual orientation of the machine axes
machining cenLer). the XY plane (G J cmd the
plane (G 19) correspond to each olher. These two planes
normally present no problems to CNC programmers. The
plane (G 18) may cause a serious problem if not propunderstood. Mathematically, the horizontal axis in
G I plane is the Z axis and the X axis is the vertical axis.
a vertical machining center, the order of machine axes
is reversed. It is important to understan.d that the
and counterclockwise directions ollly appear La
but In reality, they are the same. If the mathemalical axes orientation is aligned with the machine axes,
they will indeed match. Figure 31-2 shows the
the mathematical planes with the machine planes:
x
GOl X8. 875 Z-O. 84 FlO. 0
GOI Y12. 34 ZO.l F12. 5
STAN
MATHEMA TICAL
ZX plane
,G03
G~\
;
x
STANDARD
ZX PLANE
MIRRORED
XY7-3D
interpolation - GOl :
GOI X-l. 5 Y4. 46 F15. 0
the COIlfrom the
with GOO'in
for CCW direction.
rules, the r/ockwi.\1' clirecfion is
vertical axis towards the horizontal
in any SeH~C(c:O
plane. Counterclockwise direction is always "'P'''''''rI
the horizontal axis towards the
aXIS,
XY plane - 2D
XZ plane - 2D mpid mOlion
l'Zplane-2D
GOO XS.O Y3.0
~
In order to complele a circular
Irol system has 10 receive surficient
parl program. Unli.ke rapid
or linear interpolation with
in
polation requires a programmed
is the command for CW
c
- 2D hileantlO/Jon
7X pla}'!e - 2D IilleDnJlolion
. 2D linear/Jlotioil
G01 X6. 0 Y13. 0 Z -1 24 F12. 0 X1Z - 3D IineannoriOll
10 lool motion along the programmed
not need to be used for
any straight motion
a single axis), unless the cutter
offset or a fixed cycle is in effect. AI! tool mOlions
.... "',..,..,r·Pu·" f"""""~f'III\J by the control. regardless of
any
in
that apply to linear motions
are nol the same ror circular mOlions.
'-----I"'"
X
Z
~03
~
G02'
Figure 31·2
Progressive
with the macnllJp.
X
PLANE ROTATED
AFTER MIRRORING
E 18 PLANE
ON THE MACHINE
272
Cha
arcs does nor change
plane (a), or the malhemali- .
cal plane mirrored (b), or even the milTored plane rotated
by
(c), even if
plane itself is changed.
is not a creallon of any new plane
What
The view still represents a
viewed from a dilfcrenl direcwithin
The
lalion. II is
G 19 plane
cause some problems
is well
the situation is similar.
plane (G 18) match beand the actual axes orienIhal appears to be reversed
Ihe logical structure
of a machinmg plane WIll enable
operations using circular
interpolation, culler radius offset and fixed cymost common applications of Ihis type of ma(blend)
Intersecling radii, circular
counlerbores, cylinders, simple spheres
cones, and other Similar shapes.
(0
undersland the CNC applications of G02 and
in planes,
illustration in Figure 3 J
The following format
grmnming applications for circular
31
pro-
G17 G02 Xl4.4 Y6.8 Rl.4
GIB G03 Xll.S7S Z-1.22 R1.0
G19 G02 Y4.5 ZO RO.85
Some older control systems do not
dius designation specified by the R
vectors 1, J and K must
used.
motion within a selected
must be selected:
G17 G02 (G03) x .. Y.. I .. J ..
Gla G02 (G03) X_. Z
I.
G19 G02 (G03) Y.. Z
J R ..
From the
o XV axes o
o
K..
that:
7
I and J arc center modifiers
XZ axes . G18 plane • I and K arc center modifiers
axes . G19
J
K arc center modifiers
helpful.
•
Absence
in a Block
program example shows a
application in a program where modal axes values
are Hot
in subsequent blocks:
N ..
G20
N40 G17
XY plane selected
X20.0 Y7.5 Z-3.0
N42 GOl X13. 0 FlO. 0
N43 G18 G02 X7.0 R3.0
N44 G17 GOl XO
Sl£ll1po.riJiDHDjli1elool
N41 GOO
31-3
Actual circular rooJ path direction in a/l three machine planes.
Note the
inconsistency fOI the G18 plane
•
611-618-619 as Modal Commands
The preparatory
G 18 and G 19 are all modal
one of them will activate
selection in the program
he in
another plane selection. The
belong to the G codc group
Englishunils
PI[llle selection "..,.pfPIJnnl
Z axis is asswned as absent
PlnJle selection irrelevGlIf
Block N43 represents a contour of a 180" arc in
plane. Because of the G 18 command in N43, (he control
will correclly interpret the 'missing' axis as the Z
its value will be equal to the las! Z axis value
Also examine the G 17 command in
is always a good practice to transfer the control status to
original plane selection as soon as the plane
!hough Ihis is no! absolutely necessary in lhe
PLANE SELECTION
273
Omitting the G 18 command in block N43 wi II cause a serious program error. If G 18 is omitted, the originally selected command G 17 wi II sti II be in effecl and circular interpolation will take place in the XY plane, instead of {he
intended ZX plane.
In [his case, the axis assumed as 'missing' in the G 17
plane will be the Y axis and its programmed value of Y7.5.
The control system will process such a block as if i[ were
specified in a complete block:
N43 G17 G02 X7.0 YI.S R3.0
An interesting situation will develop if the plane selecrion
command G J 8 in block N43 is absent, but [he circular interpolation block contains two axes coordinales ror the end
point of the circular motion:
N43 G02 X7.0 Z-3.0 R3.0
G17 is stilll;1 effect
Although G 17 is still the active plane, [he arc will be machined correctly in the G 18 plane, even if G 18 had not been
programmed. This is because of the special control feature
called complete instruction or complete data priority, provided in block N43 of the last example. The inclusion of
cwo axes for the end point of circular motion has a higher
priority rating than a plane selection command itself. A
complete block is one that includes all necessary addresses
without taking on modal values.
Two axes programmed in a single block
override the active plane selection command.
•
Cutter Radius Offset in Planes
The plane selec\Jon for rapid or Imear motion lS lrrelevant, providing that no cutter radius offset G41 or 042 is in
effect. In theory, it means that regardless of the plane selection, all GOO and GO I motions will be correct That is true,
but seldom practical, since most CNC programs do use a
contour] ng motJOn and they also use the cutler radius offset
feature. As an example, evaluate the following blocks:
N1 G2l
N120 G90 GOO X50.0 YIOO.O Z20.0
Nl21 Gal X90.0 Y140.0 ZO F180.0
When the rapid molion programmed in block N 120 is
completed, the cutter will be positioned at the absolute location of X50.0 Y 100.0 Z20.0. The absolute location of the
cutting motion will be X90.0 Y 140.0 ZO, after the block
N 12l IS completed.
Adding a cutter radius offset command 041 or G42to the
rapid mOlion block, the plane selection will become extremely important. The radius offset will be effective only
for those two axes selected by a plane selection command.
There will no! be a 3-axis cutter radius orfset takIng place!
Tn the next example, compare the absolute tool positions
for each plane when the rapid molion lS complered and the
cutter radius ollset is activated in the program, Tool absoIute position when the culti ng motion is completed depends
on the mOlion following block N 121.
The radius offset val ue of D25= 100.000 mm, stored in
the conlrol offset registry, is used for the next example:
o Example:
Nl20 G90 GOO G41 xso.o YIOO.O Z20.0 D2S
N121 GOl X90.0 Y140.0 ZO F180.0
The compensated tool posit ion when block N 120 is completed, wi I! depend on the plane G l7, 018 or G 19 currently
in effect:
o
If G17 command is programmed with three axes:
G17X .. Y.. Z..
o
If G18 command is programmed with three axes:
G18X .. Y.. Z..
o
XV motion will be compensated
LX motion will be compensated
If G19 command is programmed with three axes:
G19 X.. Y.. Z..
YZ motion will be compensated
The following practical programming example illustrates
both circular interpolation and cutter radius offset as they
are applied in different planes.
PRACTICAL EXAMPLE
The example illustrated in Figure 3 1-4 is a si mple job that
requires cUHing the RO.75 arc in [he XZ plane. Typically, a
ball nose end mill (also known as a spherical end mill) will
be used for a job like this.
In the simplified example, only two main tool passes are
programmed. One pass is the left-to-right motion - across
the left plane, over the cylinder, and over the right plane.
The other pass is from right to left - across the right plane,
over Ihe cylinder. and across the left plane. A slepover for
the tool is also programmed, between the passes. The program of this type for the whole part could be done in the incremental mode and would greatly benefit from fhe use of
subprograms.
Figure 3J-5 demonstrates tool motion for the two passes
Included in the program example. To interpret lhe program
data correctly, note that program zero is at the bOllom left
corner of the part. Both clearances off the part arc .l 00 and
the stepover is .050:
274
Chapter 31
3.5
2.5
-,
Figure 31-5
Too! path fDr programming example 03101
Figure 31-4
Drawing for the programming example 03101
FIXED CYCLES IN PLANES
03101
The last programming item relating to plane selection is
Nl G20
the application of planes in fixed cycles. For cycles in the
N2 Gla
(zx PLANE SELECTED)
N3 G90 GS4 GOO X-D.I YO £600 M03
N4 G43 Z2.0 HOI MOB
N5 GOI G42 ZO.S 001 FB.O
N6 Xl. 0
N7 GO) X2.S 10.75
(= GO) X2.S ZO.S IO.7S
KO)
NB GOl X3.6
N9 G91 G41 YO.OS
NlO G90 X2. 5
Nll G02 Xl.0 1-0.75(: G02 Xl.O ZO.5 1-0.75 KO)
Nl2 GOl X-O.l
N13 091 G42 YO.OS
Nl4 G90 ...
When working with lhis type or CNC program lhe first
lime, it may be a good idea to test the tool path in the air. a
lillIe above the job. Errors can harren quite easily.
Three axes cutting motion is programmed manually only
for parts where ca1culJ.tions are not too lime consuming.
For parts requiring complex motions calculations, a computer programming software is a beuer choice.
G 17 plane (XY hole locations), G 17 is only important if a
switch from one plane to another is contained in the same
program. With special machine attachments, such as righr
an.gle heads, [he drill or other tool is positioned perpendicular to the normal spindle axis, being in G 18 or G 19 plane.
Although the right angle heads are not very common. in
many industries they are gaining in popularity. When programming these allachments. always consider the tool direclion into the work (the depth direction). In the common
applications of fixed cycles, G 17 plane uses XY axes for
the hole center location and the Z axis for the deplh direclion. Iflhe angle head is set to use the Y axis a<; Lhcdepth direction, use G 18 plane and the XZ axes wi II be the hole
cenler positions. If the angle head is sella use the X axis as
the depth direction, use G} 9 plane and the YZ axes will be
the hole center positions. In all cases, the R level always applies 10 the axis that moves along the depth direction.
The difference between the tool tip and tile center line of
spindle is the actual overhang. This extra overhang length
must be known and incorporated into all motions of the
affected axis not only for correct depths, but also for safety.
PERIPHERAL MILLING
Even with the ever increasing use of carbide cutters for
metal removal, [he rraditional HSS (high-speed steel) end
mills still enjoy a great popularity for a variety of milling
operations and even on lalhes. These venerable cutters offer several benefits - they are relatively inexpensive, easy 10
find, and do many jobs quite well. The term high speed
sleel does nOI suggesl much produclivity improvement in
modern machining, particularly when compared \0 carblde
cutters. It was used long time ago to emphasize the benefit
of this tool maLeriallo carbon tool sleel. The new material
of the day was a 1001 steel enhanced wi th tungsten and molybdenum (i.e., hardening elements), and could use spindle
speeds two La three times faster than carbon sleelloois. The
term high-speed-sleel was coined and Ihe HSS abbreviation has become common to this day.
The relalively low cost of high speed steel tools and their
capability to machine a part to very close tolerances make
Lhem a primary dluice for many millillg applications. End
mills arc probably the single most versatile rotary tool used
on a CNC machine.
The solid carbide end mills and end mills wilh replaceable carbide spiral tlutes or inserts are frequently llsed for
many different jobs. Most typical are jobs requiring a high
metal removal rates and when machining hard materials.
The HSS end mill is still a common cutting tool choice for
everyday machining.
Many machining applications call for a harder LOoling
material chan a high speed steel, but not as hard as carbIde.
As the tooling cost becomes an issue, the frequent solution
is to employ an end mill with additional hardeners, for example a cabal I end mill. Such a 1001 ~s a lillie more expensive than a high speed steel tool, but far less expenSlve t~an
a carbide 1001. Cobalt based end mills have longer cullll1g
tool life and can be used the same way as a standard end
mill, wilh a noticeably higher productivity rate.
Solid carbide end mills arc also available in machine
shops and commonly used as regular small to?]s. Larger
lools made of solid carbide would be too expenslve, so special end mi lis with i ndexable j nserts are the lools of choicc.
They can be used for bOlh roughing operations and precision finishing work.
This chapter takes a look at some technological considerations when the CNC program calls for an end mill of any
type or for a similar tool that is used as a profiling tool for
peripheral cutting and cOnlouring. This is an operation
when the side of (he cuttcr does most of work.
END MillS
End mills are the most common tools used for penpheral
milling. TI1ere is a wide selection of end mills available for
just about any conceivable machining application. Traditional end mills come in metric and English sizes, variety of
diameters, styles, number of CUlling flules, numerous flute
designs, special corner designs, shanks, and tool material
compositions.
Here are some of the most common machining operations that can be performed with an end mill - HSS, cobalt,
solid carbide or an indexable insert type:
o
Peripheral end milling and contouring
o
Milling of slots and keyways
[)
Channel groves, face grooves and recesses
o
Open and closed pockets
o
Facing operations for small areas
o
Facing operations for thin walls
o
Counterboring
o
Spotfacing
o
Chamfering
o
Oeburring
End mills can be formed by grinding them into required
shapes. The most common shapes are the flat bottom end
mill (tJ1e most common lype in machine shops), an end mill
with a full radius (often called a spherical or a hall nose end
mill), and an end mill with a corner radius (often called the
bull nose end mill).
Each type of an end mill is used for a specific type of machining. Slandardflat end mill is used for all operations that
require a nat bottom and a sharp corner between the part
wall and bottom. A ball nose el1d mill is used for simultaneous three dimensional (3D) machining on various surfaces.
An end mill similar ro a ball nose type is the hull Hose end
mill used for either some 3D work, or for tlm surraces that
req~ire a corner radius between the part wall and bottom.
Olher shapes are also required for some special machining,
for example, a center CUlling end mill (called a slot drill), or
a taper ball nose end mill.
Figure 32-/ shows the Ihree most common types of end
!llills usecJ ill inuuslry and the relationship of culler radius
10 the culler diameter.
275
276
Chapter 32
NOSE
MILL
•
BULL NOSE
END MILL
informalion
•
D --,
R
0
R
D
R = DJ2
R-···' /
rdating to the size of an end
for CNC machining:
0-o
R < DJ2
o
o
32·1
Basic NlrltmJl""t ..~n of the three most typical end mills
•
High Speed Steel End Mills
high speed sleel end mills are Ihe 'old-limers' in maThey arc manufactured either as a
or a douhle end
.
wilh various
shank configurations. Depending on Ihe cUlling tip
try, they can be used for peripheral motion (XY axes
plunge motion (Z axis only), or all axes
(XYZ axes). Either a single end or a double end can
for CNC machining. When using a double end mill.
sure the unused end is not damaged in the (001
mQunted. On a CNC machine, all end mills are
held in a collet Iype \001 holder, providing the
and concentricity. Chuck lype holders are not recommended for end mills of any kind.
•
End Mill S
Solid Carbide End Mills
End mill
mill length
length
work, the diameter of the end mil I must
nominal diameters are those that are .
various looling companies. Nonstandard
as reground cullers, must be treated differently
work. Even with the benefits of cuUer
offset, it is nm advisable to use reground end mills for
,
. although they may do a good job far emersituations and [or some raughing_ That
nm
mean a reground culler cannol be used for
work
in the shop or for less demanding
length of an end mill projected from the tool holder is
very Important. A long projection
cause
that contributes to the wear of cuLting edges. Another
effect for a long tool is deflection. Deflectjon will
negali~ely influence the size and
quality
the finished parI. nute length is important for 11"""''-'''''''''>lion of the depth of cut.
Regardless of the overall 1001
length from Ihespindle), the
eulting depth. Figure
depth of a rough side cut in
IS a
larly at sharp corners, or
stored. When handled ~~r'~~rt
great efficiency and
•
t
I
1,5D
Indexable Insert End Mills
The indexablc insert
mills
solid carbide end mills, but with the
replaceable carbide insertS. Many
this category as well. The
their internal diameler La the
ground l1al area where the
the 1001 from spinning.
in
match
The tool has a
screw prevents
Figure 32·2
HeJ,atlolnst,~J(J of the end mill diameter to the
for
cuts in
of cut
PERI PH
•
MILLING
7
Number of Flutes
.SPEEDS AND FEEDS
an end mill, particularly
a
hardness, the number of flutes should
mary
For profiling, many programmers se(virtually automatically) a four-flute end mill
tool
than 0.625 or 0.750.
- thai is - it has to cuI into a solid mate- has normally only two flutes,
This 'plunging-lype' of end mill is
a more technical name as a cemer-culling
old-fashioned name, a SIOl drill. The
no relation to the tool called a drill, but La
- just like a drill, a slot drill penelrates
parallel to the Z axis.
II is the area of small
medium end mill diameters thal
the most attention, In this size range, the end mil!s
come in two-,
four-flute configurations. So what
are the benefits of a two-flute versus a three-flute versus a
flute
for example? The type of material is
guiding
In many other sections of Ihe handbook, "'..,"'''''''''''
are mentioned. Tooling catalogues have
charts
recommendations 0/1 speeds and feeds for parlitular
with different materials. However, one
(English version) is used for calculating the
in rlmin (revolutions per minute):
n::ii' where ...
12
ft/min
11:
o
: :;: Spindle speed {revolutions per
Constant to convert feet to inches
Surface speed in feet per minute
Constant for flat to diameter conversion
of
in inches
formula is similar:
compositions. there is (he expected
",,,,u... ,v," or a trade
On a positive side.
mill
better conditions
(0
cuts.
When cutting
as aluminum. magnesium,
a chip buildup is important, so a
practically the only choice, even
somewhat compromised.
A different
for harder materials, behave to considered - LOol chatter
and fool deflection.
is no doubt, that in ferrous materials, the muhi flute end mills will deflect less and chaUer
less than their two-flute
cnd mills? They seem to be compromise between the
two-flute and four-flute
Three-flute end mills have
never become a standard ">J'V''-'-, even if their machining
capabilities are oflen
to excellent. Machinists
have a difficulty to measure
accurately, partools
as a verticularly wHh common
nier or a micrometer.
very well in
most materials.
Ie? where ...
r/min
1000 ==
m/min
1t
o
(revolutions per minute)
to convert mm to meters
speed in meters per minute
Constant for flat to diameter conversion
Ill'!>ln ..f· .. , of the tool in millimeters
a benefit from the reverse
cuning at a certain spindle speed
perfect
for the particular
diameter of (he tool for that
fi nd out the ftlmin rali ng for the
to any cutter size. The next
diameter is in inches):
What about
and in fact they are a
an
mill with a
than a similar end mill with
a small diameter. In addition, the
length of the end
. ,
mill (measured as its overhang
portant. The longer is the lool, the
and thal applies to all tools.
away from its axis (center line).
common physical laws.
ft / min
Metric
IS
meters (mm):
Regardless of (he
laroer
diameter will deflect
o
All entries in the formu
tions and should be
1{
x 0 x r J-min
12
lool diameter is in milli-
278
Chapter 32
To calculate a culling feedrate for any milling operation,
the spindle speed in rlmin must be known first. Also known
has to be the number of Ilutes and the chip load on each
flute (suggested chip load is usually found in tool catalogues). For the English units, the chip load is measured In
inches per IOOTh (3 tooth is Ule same as 3 flute or an insert),
with the abbreviation of in/rooth. The result is the cutting
fcedrate that will be in inches pcr.minute - in/min.
The English units version of the formula is:
in/min
r I min
mm/min
r / min x N
ters per revolution /11m/rev.
~ where ...
in/min
r/min
I,
=
N
=
Feedrate in inches per minute
Spindle speed in revolutions per minute
Chi p load in inches per tooth (per flute)
Number of teeth ~flutes)
=:
=:;
For metric system of measurement, the chipload is measured in millimeTers per looth (per flute), with the abbrevialioll of !'Iull/looth. The meuic formula is similar to lhe one
listed for English units:
N
Metric units formula is very similar, it calculates the feed
per [oolhfi in 111m/tooth:
For a lathe feedralc using standard turning and boring
lOols, the number of {lutes is flut applicable, the result is directly specified in inches per revolution (in/rev) or millime-
in / min ;;: r / min x f t x N
x
When using carbide insert end mills for cUlling steels. the
faster spindle speeds are generally better. At slow speeds,
the carbide culler is in contact with a steel being cold. As
the spi ndJe speed increases, so does the steel temperature at
the tool cuui ng edge, produci ng lower strength of the material. That results in favorable cutting conditions. Carbide
inscrt cutting lools can often be used three limes and up to
five limes faster than standard HSS cutters. The two basic
rules relali ng to the rei ationsh ip of tool material and spindle
speed can be summed up:
High speed steel (HSS) tools will wear out very quickly,
if used at high spindle speeds = high r/min
Carbide insert cutters will chip or even break,
if the spindle speed is too low = low r/min
~ where ...
mm/min
= Feedrate in millimeters per minute
r/min
f,
N
:::
Spindle speed in revolutions per minute
Chip load in millimeters per tooth
Number of teeth (flutes)
As an example of the above formulas, a 0.750 four flute
end mill may require 100 fUmin in cast iron. For the same
cUlling tool and pari material, .004 per flute is (he recommended chip load. Therefore, the two calculations will be:
Spindle speed:
r/min ~ (12 x 100) / (3.14 x .750)
r/min '" 509
CUllingfeedrale:
in/min", 509 x .004 x 4
in/min '" 8. 1
For safety reasons. always consider the part and machine
setup, their rigidity, depth andJor width of cut and other relevant conditions very carefully.
Feed per toothfi (in inches per tooth), can be calculated as
reversed values from the formula listed above.
• Coolants and Lubricants
Using a coolant with a high speed steel (HSS) cutter is almost mandatory for culling all metals. Coolant extends the
tool life and its lubricating attributes contributes to the improved surface finish. On the other hand, for carbide insert
cullers, coolant may not he always necessary, particularly
for roughing steel stock.
Never apply coolant on a cutting edge
that is already engaged in the material!
• Tool Chatter
There are many reasons why a chatter occurs during peripheral milling. Frequent causes are weak tooi setup, excessive LOollength (overhang from tool holder), machining
thin walls of material with laO much depth or lOO heavy
fccdrate, etc. Cutler deflection may also contribute [0 Ihe
chalter. Tooling experts agree that well planned experiments with the combination of spindle speeds and CUlling
feed rates should be the first step. If chatter sti 11 perSists,
look at the machining method used and the setup integrity.
PERIPHERAL MILLING
279
STOCK REMOVAL
o
Although peripheral milling is mainly a semifinishing
and fmishing machining operation, end mills are also successfully used for roughing. TIle flute configuration (flute
geometry) and its cutting edge are different for roughing
and ftnishing. A typical roughing end mill will bave corrugated edges - a typical example is a Sfrasmann end mill.
Strasmann is said to be the original designer and developer
of roughing clItters and the trademarked name is now used
as a generic description of this type of roughing end mill.
Good machining practice for any stock removal is to use
large diameter end mill cutters with a short overhang, ill order to eliminate, or at least minimize, the tool chatter and
tool deflection during heavy cuts.
For deep internal cavities, such as deep pockets, it is a
good practice to pre-drill to the full depth (or at least to the
almost full depth), then use this new hole for an end mill
that is smaller than the drilled hole. Since the end mill
penetrates to the depth in an open space, the succeeding
cuts will be mainly side milling operations, enlarging the
cavity into the required size, shape and depth.
•
Plunge Infeed
Entering an end mill into the part material along the Z
axis alone is called center-cutting, plunging or plunge infeed. It is a typical machining operation and programming
procedure to enter into an otherwise inaccessible area, such
as a deep pocket, a closed slot, or any other solid material
entry. Not every end mill is designed for plunge cutting and
the CNC machine operator should always make sure the
right end mill is always selected (HSS or carbide or indexable insert type of end mill). Programmer can make it
easier by placing appropriate comments in the program.
• In and Out Ramping
A = RAMPING ANGLE
Figure 32-3
Typical entry angle for 8 ramping infeed into a sofid materia!
•
Direction of Cut
The direction of a cut for contouring operations is controlled by the programmer. Cutting direction of the end mill
for peripheral milling will make a difference for most part
materials, mainly in the area of material removal and the
quality of surface fInish. From the basic concepts of machining, the cutting direction can be in two modes:
o
Climb milling - also known as the DOWN milling
o
Conventional milling - also known as the UP milling
Anytime the G41 command is programmed, cutter radius
is offset to the left of part and the tool is climb milling. That
assumes, of course, that the spindle rotation is nonnal, programmed with the M03 function., and the cutting tool is
right hand. The opposite, G42 offset, to the right of the part,
will result in conventional milling. In most cases, climb
milling mode is the preferred mode for peripheral milling,
particularly in fUlishing operations.
Figure 32-4 illustrates the two cutting directions,
Ramping is another process where the Z axis is used for
penetrating (entering) into a solid part materiaL This time,
however, the X axis or the Y axis are progranuned simultaneously with the Z aXIS. Depending on the end mill diameter, the typical ramping angle is about 25° for a 1.000 inch
cutter, 8° for a 2.000 inch cutter, and 3° for a 4.000 inch cutter. Ramping approach toward the part can be used for flat
type, ball nose type, and bl1l1 nose type of end mills.
Smaller end mills will use smaller angles (3°_10°). See Figure 32-3 for an il1ustrotion of a typical ramping motion.
Always be very careful from which XYZ tool position
the cutting tool will start cutting at the top of part. Considering only the start point and the end point may not produce the best results. It is easy to have a good start and good
end tool positions, but somewhere during the cut, an unwanted section of Ole part may be removed accidentally. A
few simple calculations or a CAD system may help here.
."..,.
M03
CLIMB MILUNG
CONVENTIONAL MILLING
G41
G42
Figure 32-4
Direction of the cut relative to material, with M03 in effect
280
Climb Milling
Climb milling - sometimes called the down 111 i II ing - uses
rotation of the cutter in the reeding direction and has the
lendency to push the part against the table (or the fixture).
Maximum (h
of the chip occurs at the heginning of
the cut and upon exit, the chip is very th in. The practical result is that most of the generated heat is absorbed by [he
chip, and hardening of the part is largely prevented.
Do not misunderstand the words climb and down describing
the same machining direction.
Chapter 32
the cut and upon exit, the chip is very thick. The practical
result is possible hardening of the part. rubbi ng the tool into
(he material, and a poor surface finish.
•
Width and Depth of Cut
For good machining, the width and depth of cut should
correspond to the machining conditions, namely the setup,
the type of malerial being machined and the cutting tool
used. Width of cut depends also on the number of flutes of
the cutter that are actually engaged in the cut.
Approximately one third of the diameter for the depth of
Both terms are correct, if taken in the proper context.
Conventional Milling
Conventional milling - sometimes called the up milling uses rotation of the culler againslthc feedi ng direction. and
has the tendency to pull the part from the table (or !he (ixture). Maximum thickness of the chip occurs at the end of
CUl is a good ru Ie of thumb for small end milis, a I iHle more
for larger end mills.
Pcripheralillilllllg requires a solid Illachliling knowledge
and certain amount of common sense. If a successful machining operation in one job is documented, it can be
adapted to another Job with easc.
SLOTS AND POCKETS
for a CNC machining cenler,
to removed from the inside of a
area,
a coni our and a f]at boHom. This
as pocketing. To have a true ,JV'''''-'''.
{he pocket boundary must be
are many orher applicalions, whe((~ Ihe mafrom an open area, with only a parAn open sIal is a good example of this
looks at applicalions of closed pockets,
various programming techniques
for internal material removal.
PROGRAMMING SLOTS
Slots are ofeen considered as special
of
'grooves' usually have one or two radiJI
are [WO ends, they are joined by a straight groove. A
5101 can
either open or l:josed, with the same size
on both ends, twO different radii, or one
A
cal sial that has only one end radius is a keyway.
open Of dosed, straight,
walls or shaped walls
~r'I"\rrt"lm!,Y\
slots with accuracy in
a
the same Lool or wilh two or
on the part material, required disurface finish, and olher condil
OPEN AND CLOSED BOUNDARY
A continuous conlour on which (he slart point and the
point is in a di
localion, is called an open COntOI,It:
Continuous contour defined Ifl the program that starts
ends at (he same ' location, is
a
From the machimng
of view, the major
{ween an
conI our is
the CUlling IDOl
for example keyways, can be done with
called slolli ng cullers, rather than an
a sJolLing cutter is usually a sllnple prow
morc accurate
reaches
in and oul. More complex
are machined with end mills,
walls of lhe slot arc contoured under program control.
•
Open
Figure
An open boundary IS not a true pocket. but belongs !O a
Machini of this kind of a contour is
quite
as the lool can reach the required depth in an
open space. Any
ity end mill in different varieties
can be used Lo
boundary.
•
a drawing of a typical open sial.
10 illustrate Ihe programming tech-
drawing will
niques of an
-
-
0.21
Closed Boundary
The excessive material within a closed boundary can be
removed in two
on the cutling operation.
One way is La use an
move II cowards the
outside of the boundary, another way is to use an internal
1001 and move it towards
of the boundary. In both
cases, the actual
follows,
along the Olllside of a pari is nol
pocketing but peripheral
milling (Chapter
inside
a closed
boundary IS typical
vanous regular and irregular
Some lypical examples of regular
or
shape pockets are
circular
pockets, and !>o on.
can have any
machinable shape, bur they still use the same machining
and programming
pockets.
One of the most commonly machined boundary shapes
in manufacturing IS milling of a
ty, u~ually quitl.!
small, called (J sIaL
1.77
1,8
--
Figure '33 1
A
An open slot programming example 03301
• Open Slot Example
Before programmi
any 1001 mOlion, :'Iudy [hi.: drawing.
That way, the machirll
ilions can be established, a~
well as ~e!up and other
program zero
can be determined quicklyare from the lower
That
left corner (XY) and lOP
will become lhe !"\yr' .....·""' zero.
281
Chapter 33
..........................................
Maximum
will relate to
o
Number of tools
o
Tool size
The
Ihe sial depth as .210.
the depth it may
100
a single CUI,
small cuners or tough
Although a
be used for
full depth. some stock at the
should be left for finishing.
and feeds
o
Depth
Maximum cooing depth
Method of Cutting
of
Number of Tools
If
or two lools can be
siona! lolerances are very critical or
Once alllhe other maChining conditions are
the melhod of CUlling almost presents itself.
be positioned above a clear position and at the
center
line.
1001 will
fed inlo the slot depth,
CUI, use Iwo tools - one 1001 for
bottom, for finishing. ln a
finishing. The tools could have the same
or di fferenl
For [his example, only one (001 wilt be used
for both roughing and finishing.
Tool Size
out the material all
center
Then It will
moved back to the
and al Ihe full depth for conlouring
In
i
of the CUlling 1001 is mainly determined by the
width of (he sial. In Ihe drawing,
.300 radius, so
[he width is .600. l1H~re is no
cutler of 0.600 - but
- even if there were - would it
What about a
inch cutter for .500
slot? 1L is possible, but
the resulting cut would not
IJ")
quality. Toler-
N
1.0
r-....
o:J
IJ")
.,,-
o:J
c0
CI'"i
ances and surFace finish would
10 conrrol. That
means choosing a 1001,
available off-shelf, Ihar
is a litlle smaller then lhe
width.
the slot in the example, a 0.500 inch end
choice. When se-
lecting the 1001 size, always
33-2, the XY 1001
program locations are shown.
.-
1.185
how much stock the
LOol will leave un lilt! slul walls fur lillisllillg. Tau lIIuch
may require some semi
cutler and the slOl width
will be easy [0 calculate:
ing cuts. Wilh the 0.500
the amount of slock left
33-2
Contouring details for the open sial ~xnmn.'F!
create the program is nol difficult at all. The tool is in
the spindle and all typical methods
throughout
are used.
t& where ...
S
W
:=:
o
Stock left on
Width of slot ( slot radius times two)
Cutter diameter
Slock left on the
S ::: (.600 -
111is is a
in the example will be:
I 2 :::: .050
finishing with one CUL
Speeds and FBeds
Spindle speeds
exact situation at
uses a reas.onable
8 in/min.
feed rates will depend on the
machine, so the
01'950 rlmin and culling
03301 (OPEN SLUT)
Nl G20
(INCR MODE)
N2 G17 G40 GSa
UP SETTINGS)
N3 G90 G54 GOO X3.87S YO.SSS 8950 Mal
(START)
N4 G43 ZO.1 HOI MOS
(START POSITION ABOVE)
NS GOI Z-O.2 FSO.O
.01 LEFT ON n~~I'M\
N6 Xl.S F8.0
(CUT TO SLOT RADIUS CNTR)
N7 GOO ZO. 1
(RETRAeI' ABOVE WORK)
N8 X3.875
(RETURN TO START)
N9 GOl Z-O.21 F50.0
TO FULL DEPTH)
NlO G4I Yl.IBS DOl FB. 0
(APPROACR CONTOUR)
Nll Xl.8
(CUT TOP WALL)
NI2 GO) YO.SB5 RO.3
SLOT RADIUS)
Nll GOI X3. 875
BOTTOM WALL)
Nl4 GOO G40 YO.8SS
TO START POINT)
NlS Zl. 0 M09
ABOVE WORK)
N16 G28 X3.87S YO.a8S ZI.O M05
(M/C ZERO)
N17 M30
PROGRAM)
%
AND POCKETS
3
example is quite self evident
included block
comments will offer better
of the programorder and procedure. In this '-"'''"I.'''-, only one tool
used. For high precision
two
will be better, even if it means a
• Closed Slot Example
0.885
an
is in
much.
(001 eotry into the matcnal.
locmion - too! has La
into the
the Z axis, unless there is a
hole.
to use a cel1ter cUlling
mill (known as
If this type of end mill is no!
or maconditions are not suitable, tool will have to ramp
into the material, as a second method.
is a linear
axes.
usually in the XZ, the YZ, or
0.21
Figure 33-4
Roughing operation detail for a closed slot example 03302
Internal Contour Approach
In the
tool is now at the center of the
of slot, ready to start
cut. Climb milling mode
has been selected
(he contour approached In such a
to its left One way is the
way that the tool
current tool location at
make a straight linear cut
the center, LO the 'south'
of the left arc (while applying the cutter radius
This method works, but when approaching an inner conlour it is better to use a tangential approach. An internal
contour approached at a
requires an auxiliary approach arc (so called lead-ill
since the linear approach
1
0.885
A-A
towards the contour is not i.l
Although the tangential
surface finish of
problem.
cutter
interpo/alion
to be added "
Figure 33·3
A closed slot nrfllVlln1mUlr, example 03302
an arc Improves
creates another
cannor be sraned
a non-circular
two motions from the
center to the start
shown in
slot
already established will apA 0.500 inch end mill will be
a center cutting geomClTy thai allows
pom[
the contour:
o First, a linear motion with cutter radius
the tangential approach arc motion
o
technique is illustrated in
Apart from the di
1001 geometry required for Ihe
plunging cut, only the method of cutting will change.
a
closed slot (or a pocket), the tool has to move above work,
to a certain XY starl
In
example, if wJlI be the
cenler of one of the
Portion of sial on the right is
selected arbitrarily.
at a reduced
will be [0 the
.010 on the bOftom)
and, in a linear
be roughed out between the two centers is not nec:ess;arv it can be fed into the
final depth at
same 1001 'v,",,,,,,,'V'
slack is .050 all
around the slot contour.
final depth, and from the
of the sial, Ihe finish contour
center iocalion of the
more complex this lime, bewill start Contouring
cause the tool is in a rather
spot.
1.1
RO.28
33·5
Detail of t",,,,,o"t,,,,1 £lllDrllach towards an inner contDur
2
33
(CUT WALL TOP)
(CUT RADIUS LEFT)
N12 GOl Xl. 5
Nl3 G03 YO.S85 RO.3
N14 Xl.78 YO.86S RO.28
N15 GOl G40 Xl.S YO.aas
(LINEAR DEPARTURE)
N16 GOO Zl.0 M09
Nl7 G2B XI.S YO. BaS 21.0 MOS
Nl8 IDO
AJ30VE WORK}
(M!C
(END OF PR()GRlIM)
%
This program example is also a
10 approach any inside conlour
kinds (angular. circular. eic,), use
(rated in the last two examples.
POCKET MILLING
~ where ...
RI
Radius ofthe
tool
R, ::::
of the approach arc
arc)
Rc
Radius of the contour (slot radius)
Supply some numeric data
be calculatcd.
three radii- The slOI conlOur
dnlwing, Once the cUlling tool
becomes fixed as well CRt).
proach radius (Ru).
lalcd accurately_
From the formula, it is.
radius can
of all
by Ihe
Ihal radius
ap-
thai
must be greater than the culler
must be smaller Ihat the contour
the range (within
only increments of.O I0 are
- .260 or .290? Well, the
rather a larger approach
gential approach takes place at a
a smaller radius. The result is an
For program 03302, .280 is
as
approach radius. This selection meets all the three relationships:
Thai is alilhe information needed beforc wriring the program. Note the programming similarities with the open slot
listed in program 0330 I.
03302 (CLOSED SLOT)
N1 G20
N2 G17 G40 GaO
(INCH MODE)
(STARTUP SETTINGS)
N3 G90 G54 GOO X3.0 YO.SSS 5950 M03
(START)
N4 G43 ZO.l HOl MOS
(START POSITION ABOVE)
N5 GOl z-O.2 F4.0
(0.01 LEFT ON EOTTOM)
N6 Xl.5 F8.0
(CUT TO SLOT RADIUS CENTER)
N7 Z-O.21 F2.0
(FEED TO FULL DEPTH)
NS 041 Xl.22 YO.86S DOL F8.0 (LINEAR APPROACH)
N9 G03 Xl.S YO.585 RO.28
(CIRCULAR
NlO GOI X3. 0
(CUT BOTTOM WALL)
Nll G03 Yl. 185 RO. 3
(CUT RIGHT SLOT RADIUS)
Pocket milling 15 also a Iyplcal and common
on
CNC machining centers, Milling a
means to remove
by
material from an enclosed area,
This bounded area is further
by
tom, although walls and bottom could
tapered, convex,
concave, rounded, and have other shapes. Walls
create the boundary contour. Pockets can have
rectangular, circular or undefined
can be empty
side or they may have islands.
Programming pockets manually is usually
only
for simple pockets, pockets of regular shapes, such as rectangular or circular pockets. For pockets wilh more complex shapes and pockets with islands, the
of a
computer is usually required.
•
General Principles
There are two main considerations when programlTii
a
pockel for milling:
o
Method of cutter entry
o Method of roughing
a
10 slart mllling a pocket (into solid mateculler mollon has to be programmed to enter along
of spindle (2 axis), which means the cutter
center cutting to be able to plunge cut. In cases
cut IS eHher not praetical or not possible,
ramping can be used very successfully.
melhod is oflen used when the center cutting 1001 is
the Z axis to be used toor
This motion will,
or a 3 axis linear motion.
it
V'-,111\.1II
where to
so is the widTh
di
to
in climb
milling mode. It may he difficult 10 I~flve eX:'lctly the same
amount
in the pockeL
AND POCKETS
5
Many cuts will be irregular and s[Ock amount will not
even.
thaI reason, it is quile common 10
nishing cut of the pocket contour, before
cut
place. One or more tools may be
situation, depending on exact requirements.
typical methods for roughing a
are:
o
o
- from the inside of the pocket out
o
One direction - from the outside of the pocket in
other pocketing options are
as a true spiral, morph, one way, and
cases, there is a choice of speci fying Ihe ancut, even a user selected point of entry and ti
overs. Manually, these more complex methods may
as well, but it may be a very tedious work.
•
illustrate the complete
tooling selection is Important. Material is
lant and so are other machining
rectpockets are often drawn with sharp corners, they
always have COrners of the tool
when
The corners in the drawing are
), and
6 center CUlling end mill (0.3125).
may
a good choice, but for finishing, the
a lillie smaller so the tool can actually cur in
comer,
rub there. Selection of a 0.250 end mill is reasonnot
and will be used it in the example.
all the material in lhe enclosed area has to
removed (including the bottom), think about aU
where the cutting tool can enter into the
or ramping. Ramping must always be done in a
area, bUl plunging can be done almost anywhere.
are only two practical locations:
o
Pocket Types
o Pocket corner
The most common
are also the easiest to
gram. They all have a regular shape, without any islands:
o
Square pocket
o
Rectangular
o
Circular
Square
tally the same
there IS no
center
to both selections and the ineviat the pocket center, the tool
path and, after the initial cut,
milling orconventional milling mode.
more math calculations involved in Ibis
method, starling at the pocket corner, is
ar as well, but uses a zigzag motion, so one Cllt
n a climb milling mode, the other cut will be in a
machining. It is a little easier for calIn the eX<.Impk, the corner will be used
are
their
side lengths,
in programming.
RECTANGULAR POCKETS
Any corner
Rectangular and
p<!rticularly jf
an example of a
Figure 33-6 will be
IJV''''''-'''' are quite easy to pro-
are parallel 10 the X or Y axes. As
pocket, the one illustrated in
pocket is equally suitable for the start.
In the
pocket will
03303. the lower lefr corner of
"""""rw,Cl"" factors the programmer has Lo
start location for the CUlling tool in
an
0.15
-a-
---
I
t
...... "J"..,u area:
o
Cutter diameter (or radius)
o
Amount of
o
Amount of stock
left for finishing
for semifinishing
the corner
be known, as well as
to other elements
"._,,-.- - - - - ' - - - - ' \
0.5
dimensions of the pan, as
length, the width, and
pocket - they must always
position and its orientation
are
2,5
I
'"'l 0.5 r-
Figure 33-6
Sample drawing of a rectangular
--
R5/32
program 03303
In the Figure 33-7, the
point is identified as X I
corner (lower left), and all
and Y 1 distance from
additional data are
as well
The letters identify
the programmerl'hrV\-C''''C
L
D
-
-
L
I
s
c
w
w
t
I
Q
I
'-
r
Y1
f
XI
method
.
Figure 33·8
Result of a zigzag pocketing, without a semifinish cut
•
Stepover Amount
X location of tool at start
Vlocation of tool at start
V\
TLR
L::;::
W
Q
•
I
of the description letters is :
I.l$' The
S
C
the comer·
T
t - Xi;--
c
33-7
Pocket roughing start
o
Y1
=
=
Tool radius
diameter / 2)
length as per drawing
Pocket width as per drawing
Calculated stepover between cuts
Calculated length of actual cut
Stock left for finishing
Stock left for semifinishing (clearance)
Stock Amount
are two stock amounts (values) - one relates to (he
finishing operation. usually done with a separate finishing
tool, the other one relates to the semifinishing operation.
usually done with the roughing tool. The cuner moves back
forth in a zigzag direction, leaving behind so
scallops. In 20 work, [he word 'scallops' is
to
uneven wall surface caused by lhe tool shape, and is
in 3D cUlling as well. The result of such a zigzag
is generaHy unacceptable ror the finish machining. JeA ..m,",c
of the difficulty of maintaining tolerances and surface
wh de culting uneven stock.
avoid possible cUHing problems later, a secondary
operation is often necessary. It
is to
elimmate the scallops. Choose semifinishing cut
machining tough materials or when
Semifinishing
allowance.
as the C val ue in the ill ustralion, can
to zero. 1f
thai IS
case, it means no additional
is
Typically
al
11
a small value.
Figure 33-8 illustrates
of a rectangular pockel,
(he uneven stock (scallops)
high spots create the
tool, so semifinishing tool
than
slepover will
cuts (zigzag lype). There is
number of culS is se-
number:
o
number of cuts will terminate the roughing
on the opposite side of the pocket relative
to the start location
o
number of cuts will terminate the roughing
on the same side of the pocket relative
to the start location
Practically, it does not matter which corner is
10
start at or in which direction the rUS( cut begins. What matters is that the stepover is reasonable and, preferably,
for all cuts. There is a simple way of calculating the
over, based on a given number of cuts. [f the
amount is loa small or 100 large, just repeat the calculation
wilh u different number of cuts N.
The calculation can be expressed in a formula:
SLOTS AND POCKETS
In the formula, N is
stepovers and
all other
L
L1
U"'~ULJ'b as before.
END
Q Example:
Il"'n,',,,,..,<.; are
tool
on
START
0.250 (TLR
S as 0.025 and semifrnishing stock
-1-'-"- C
will
Q:
.5 - 2 x 0.125
Q = 0.2360
,
2 x 0.025 - 2 x 0.01) / 5
..
Y1
-....., X11-figure 33·9
to use the pocket
be a better
width. This
is narrower along the X axis, than it is
lJl'-J'LLLLL\.. U
Semifinishing tool path
at the last roughing location,
and leaves equal stock for 11I.....hlf.,., operation
-2x5
• length of Cut
W
il'''LU>.~, the length, the incremental dis-
2x
- 2x 5
to be calculated.
fonnula to calculate the length of
similar to Ole stepover calculation:
In
example, the D value will be:
Q Example:
D
2.0 - 2 x 0.125 - 2 x 0.025 - 2 x 0.01
D
1. 6800
overs
•
is the incremental length of cut between the
cutter radius offset has been used).
Semifinishing Motions
purpose of semifmisbing motions is to
nate uneven stock. Since the semifmishing will be nor ..
the same tool as the roughing
to start
cuts is the
roughing sequence. In
case, it was
corner of the pocket. Figure 33-9
the Start to
(of
The length LI and WI are
between the Star! position
value, along both axes.
The fonnula for the
cut, its actual cutting distance, is
Q
Ll ;;;;; 2.0
2 x 0.125
L1 == 1.7000
2 x 0.025
W1 ::::; 1.5 - 2 x 0 125
W1
1 2000
2 x 0.025
• finishing Tool Path
is roughed out and semifirtished, another
tool (or even
same tool in some cases) can be
to
pocket to its fmal size. TIlis programmed tool
will typically provide offsets to maintain maCninl!Jlg
Tolerances and speeds and feeds to maintain required surfinish. Typical staJiing tool position for a small to medium pocket is at its center, for a large pocket the
position should be at the middle of the pocket, away
one of the walls, but not too far.
For the fmish.ing cut, the cutter radius offset should
mainly to gain flexibility in maintaining tolerances
during machining. Since the cutter radius offset cannot
started during an arc or a circular motion, linear
.
lead-out motions have to be added. Tn Figure 33-10 is
illustration of a typical fmishing tool path for a
pocket (with the start at the pocket center).
conditions do apply in these cases. One is that
leading arc radius must be calculated, using
the
same method as for slots:
288
pter 33
03303 (REcrANGUI.J\R POClCET)
Nl G20
N2 G17 G40 G8Q TOl (.250 ROUGHING SLOT DRILL)
N3 M06
N4 G90 G54 GOO XO.66 YO.66 S1250 M03 T02
NS G43 ZO.l HOl MOB
N6 G01 Z-O.15 F7.0
( - - ROUGHING START
------)
N7 G91 X1.68 FlO.D
N8 YO.236
(STEPOVER
N9 X~l. 68 F12 _0
(CUT
NIO YO.236
CJ:'vv""",," 2)
N11 X1.68
3)
N12 YO.236
3)
N13 X-l. 68
4)
N14 YO.236
(STEPOVER 4)
!Iii' where
Ra ;:::: Radius of the approach arc
Rt
Radius of the cutting tool
Rc
Radius of the corner
.------.~
...
~.
- L ................. .......
~
~--
S)
NlS Xl. 68
w
\
Ra
Rc TYP.
33·10
Typical
tool path (or a rectangular pocket
of
Iii CUI is
mode and the radius offset
of the contour.
o Example:
To calculate the approach
drawing, start with the corner
5/32 (.1563) and the lOol
so the condition R, <
the condition R" > Rr.
larger than (he 1001
as
pocket length and width are
possible, choose the approach
pockel widlh W, for a lillie
In (he example,
Ra. = W / 4 .. 1.5 / 4
Ra. c: .375
Condition is satisfied, the
the tool radius, and can be
• Rectangular Pocket Program
Once all selections and decisions have been done,
program can be wrillen for Ihe pockel in
Two lOols will be used, bmh 125.250 end mills,
cuuer must be able or center cUlting.
lower left corner of the parI. All
tlnishlng steps art! documented in the program.
N16 YO.236
5)
N17 X-1. 68
6)
( - - SEMIFINISH START -------)
NIB X-0.01
(SEMIFINISH STARTUP X)
N19 Y-O,OI
(SEMIFINISH STARTUP Y)
N20 Y-1.l9
(LEFr YN2l Xl. 7
(RIGHT X+ MOTION)
(up Y+ MOTION)
N22 Y1.2
N23 X-l. 7
(LEFI' X- MOTION)
N24 G90 GOO ZO.l M09
N25 G28 ZO.l M05
N26 MOL
----------
N27 T02
(.250 FINISHING END MILL)
N28 M06
N29 a90 G54 GOO Xl.S Yl.2S 51500 M03 TOl
N30 G43 ZO.l H02 MOB
N31 GOI Z-0.15 F12.0
(-- FINISHING POCKET ----------------- - ----)
N32 G9l a41 X-0.37S Y-0.37S D02 FlS.O
N33 G03 XO.37S Y-0.37S RO.37S F12.0
N34 GOI XO.8437
N3S G03 XO.1S63 YO.1563 RO.1563
N36 GOl n.1874
N37 G03 X-0.1563 YO.1563 RO.1563
N38 GOl X-l.6874
N39 G03 X-0.l563 Y-O.lS63
N40 GOl Y-l.lB74
N4I GO) xO 1563 Y-O.lS63 RO.1563
N42 XO.8437
N43 a03 XO.375 YO.375 RO.375
N44 GOl G40 X-0.37S YO.37S FlS.O
N45 G90 GOO ZO.l M09
N46 G28 ZO.l MOS
N47 X-2.0 YlO.O
N48 M30
%
the progrrun carefully. It follows all the decisions
and offers many details.
In the program, blocks N 17 and N 18 can be joined tointo a SI
block. The same applies to blocks N 19
N20. They are only separated for the convenience of
Ihe tool mouons to match the llluslrations. There is
In using the incremental mode of programmode would have beenjust as easy.
SLOTS AND POCKETS
289
CIRCULAR POCKETS
'1I
The olher common types of pockets are so called circular
or round pockets. Although the word pDcket somehow implies a closed area with a solid boHom. the programming
method relating to circular pockets can also be used forcircular openings that may have a hole in the middle. for example, some counterboring operations.
o
I
J
To illustrate a practical programming application for a
circular pockel, Figure 33-11 shows the typical dimensions
of such a pocket.
-,
d
-
Condition:
d<O
f--------- 2.0 -.--------,
d
I
>
o
3
Figure 33-12
Relationship of the cutter diameter to the pocket diameter
2.0
01.500
For example, the pockel diameter in the sample drawing
is 1.5 inches. Using lhe formula, select a plunging cutter
(center cutting end mill), that has the diameter larger than
1.5/3, therefore larger than .500. The nearest nominal size
suitable for cutting will be 0.625 (5/8 slol drill).
•
Method of Entry
The next step is to determine the method of the tool entry.
Figure 33·11
Sample drawing of a circular pocket (program examples 03304-06)
In terms of plann ing. the first thing to be done is the selection of the culler diameter. Keep in mind, that in order to
make the pocket bottom clean, without any residual material (uncut portions). it is imporlan[ to keep the stepover
from one cut to another by a limited distance that should be
calculated, For circular pockets, this requirement influences the minimum cutler diameter thal can be used [0 cut
the circular pocket in a single 3600 cut.
•
Minimum Cutter Diameter
In the following illustration - Figure 33-12, the relationship of the cutter diameter to the pocket diameter is shown.
There is also a formula that will determine the minimum
culler diameter as one third of the pocket diameter. The
mi lIing wi 11 start at the circular pockel center, with a si ngle
360" tool motion. In practical terms, selecting a cutter
slightly larger thall the minimum diameter is a much better
choice. The major benefit of this calculation is when the
pocket has to be done with only one tool motion around.
The formula is still valid, even if cutting will be repeated
several times around the pocket, by increasing the diameter
being cut. In that case, the formula determines the maxi
mum width of the cut.
In a circular pocket, the best place to enter along the Z axis,
is al the center of lhe pocket. ff the pocket center is also the
program zero XOYO, and the pocket depeh is .250, the beginning of lhe program may be similar to the following
example (culting tool placed in the spindle is assumed):
03304 (CIRCULAR POCKET - VERSION 1)
N1 G20
N2 Gl7 G40 G80
N3 G90 G54 GOO XO YO S1200 M03
N4 G43 ZO.l HOl MOS
N5 GOl Z-0.25 F8.0
N6
In the next block (N6), the cutting tool will move from
[he pocket center towards the pocket diameter, and apply
culler radius offset "long the way, ThiS motion call be done
in two ways:
o
As a simple straight linear motion
o
As a combined linear motion with a circular approach
•
linear Approach
The linear departure from the pocket center can be direcled inlo any direction, but a direction lowards a quadranl
point is far more practical. In the example. a motion along
the Y positive direction is selected, into the 90° position.
290
Chapter 33
Along the way, cutter radius offset for the climb milling
mode G4! is programmed, followed by the full 3600 arc'
and another straight motion, back towards the center. During this motion, the cuttcr radius offset will be cancelcd.
Figure 33-J3 shows the tool path.
-.
,
N1l M30
%
Another programming technique for a circular pocket is
much morc practical - one Ibal makes better surface finishes and also maintains tight tolerances required by many
drawings. Instead of a single linear approacb directly towards lhe pocket diameter, the CUlling tool can be appJied
in a combi ned Itnear-circular approach.
2.0-
2,0
01.500
i.
N8 GOl G40 YO FlS.0
N9 G28 Z-0.2S M09
mo G91 G28 XO YO MOS
J
Figure 33-13
Linear approach for a circular pocket milling - program 03304
The graphic representation can be followed by a corresponding program segment - approach a quadrant point.
profile the full arc, then return back to the cenler:
N6 G41 YO.7S 001 FlO.O
N7 G03 J-O. 75
N8 GOI G40 YO F1S.0
Now, the tool is back al lhe pocket center and the pocket
is completed. The tool must also retracl first. then move to
machine zero (G28 motion is always in the rapid mode):
N9 G28 Z-0.2S M09
NI0 G91 G28 XO YO M05
N11 M30
%
Tbis method is very simple, but may not always be the
best, particularly for very close tolerances or high surface
finish requirements. Drawing tolerances may be achieved
by roughing operations with one 1001 and finishing operations with one or more addilional tools.
A possible surface (oo! mark, lefl al the contact point with
the pocket diameter, is a distinct possibility in a straight approach to the pocket diameter. The simple linear approach
is quite efficient when the pocket or a counterbore is not too
critical. Here is the complete listing for program 03304:
• linear and Circular Approach
For this method, the cutting motion will be changed.
Ideally, a small one half-arc motion could be made between
the cenler and the pocket start point. That is possible only if
the culler radius offset is /lor used. As a matter of fact, some
controls use a circular pockel milling cycle G 12 or G 13,
doing exactly that (see an example laler in this seclion). If
the,o Fanuc control has the optional User Macros, custom
rnide G 12 or G 13 circular pocket milling cycle can be developed. Otherwise. a step-by-step method is the only way.
one block at a time.
Since the radius offset is needed to maintain tolerances,
and the offset cannot start on an arc, a linear approach will
be programmed first with the culter radius offset applied.
Then, lhe circular lead-in approach is programmed. When
the pocket is completed, the procedure will be reversed and
Ihe rilriillS offset c:mcelerl rluring rI linear motion back to the
pockel center, The approach radius calculation in this application is exactly the same as described earlier in Ihis
chapler, for the slot fLnishing tool path. Figure 33-14 shows
the suggested tool path.
~-
- 2.0
""_m
-~I
RO.625
0.125
L_
A
2.0
01.500
1
Figure 33-14
03304 (CIRCULAR POCKET - VERSION 1)
N1 G20
Combined linear and circular approach for a circular pocket milling·
- program example 03305
N2 G17 G40 G80
N3 G90 G54 GOO XO YO S1200 M03
N4 G43 ZO.l HOI M08
N5 GOl Z-0.2S FS.O
N6 G41 YO.7S DOL FIO.O
N7 G03 J-O. 75
This example uses an approach radius of .625. Any radius
that is greater than the culler radius (.3125) and smaller
thall lite pocket radius (.750) is correct. Tbe final program
O:S305 complements the above illustration in Figure 33 -14
SLOTS AND POCKETS
291
03305 (CIRCULAR POCKET - VERSION 2)
N1 G20
N2 G1. 7 G40 Gao
N3 G90 G54 GOO XO YO S1200 M03
The calculation is logically similar to the one for the rectangular pocket and the desired amount of the stepover can
be achieved by ch.anging the number of steps.
N4 G43 ZO.1 HOI MUS
The example for program 03306 uses three stepovers,
calculated from the following formula:
NS GOl Z-O.25 FB.O
N6 G4l XO.625 YO.125 DOl FlO.D
N7 G03 XO YO.7S RO.625
N8 J-O.75
N9 X-0.625 YO.125 RO.625
NlO GOI G40 XO YO F1.5.0
N11 G28 Z-O.25 M09
Nl2 G91 G28 XO YO MOS
Q ==
l@f
m3 IDO
%
•
TLR -
S
N
where ...
Q
R
This programming technique is by far superior to the
straight linear approach. It does not present any additional
programming difficulty at all, partly because of the symmetry of tool motions. In fact, this method can be - and
should be - used for just about any approach towards an internaJ contour finishing.
R -
TlR
S
=
=
=
N
Calculated stepover between cuts
Pocket radius (pocket diameter 0/2)
Tool radius (cutter diameter /21
Stock left for finishing
Number of cutting steps
In aUf application. {he example values are:
o Example:
Roughing a Circular Pocket
Often a circular pocket is too large for a given tool to
guarantee the bottom cleanup in a single cut around. In this
case, the pocket has to be enlarged by roughtg it first, in
order to remove all excessive material, then the finishing
tool path can be applied. Some controls have special cycles,
for example, a spiral pocketing. On Fanue conlrols, custom
cycles can be created with the User Macros option.
R
S
N
r-
D
TI
--Q
R
I
Diameter D =. 1.5
3
(.75 -
.1875 -
.025)
/
3
Q = .1792
Final roughing program is quite simple and there is no
cutter radius offset programmed or even needed. Note the
benefit of incremental mode G91. It allows the stepover Q
to be easily seen in the program, in the GOl linear mode.
Every following block contains the arc vector J, cutting the
next full circle. Each circle radius (1) is increased by the
amount of stepover Q:
03306 (CIRCULAR POCKET ROUGHING)
L
TLR
=
1.S / 2 = .75
.375 / 2 = .1875
.025
Using Ihe above formula, the stepover amount Q can be
found by calculation:
Q =
As an example, the same pocket drawing will be used as
illustrated earlier in Figure 33-11, but machining will be
done with a 0.375 cutter - Figure 33-15.
=
TLR =
./
-S
Figure 33-15
Roughing our a circular pocket - program 03306
The 0.375 end mill is a small loolthal will not cleanup
the pocket bottom using the earlier method. The method of
roughing is shown in Figure 33-15, and the value ofQ is the
equal stepover amount, calculated from the number of
steps N, the cutter radius TLR and the stock amount S, left
for (he fmishing tool path.
N1 G20
N2 G17 G40 GSO
N3 G90 G54 GOO XO YO 51.500 M03
N4 G43 ZO.l HOI M08
N5 GOI Z-O.2S F7.0
(STEPOVER 1)
N6 G9l YO.1792 F10.O
(ROUGH CIRCLE l)
N7 G03 J-O.1792
(STEPOVER 2)
N8 GOl YO.1792
(ROUGH CIRCLE 2)
N9 GO) J-O.3584
(STEPOVER 3)
mo G01 YO.1792
(ROUGH CIRCLE 3)
Nll G03 J-O.S376
Nl2 G90 G01 XO Fl5.0
Nl3 G28 Z-O.2S M09
Nl4 G9l XO YO MOS
m5 M30
%
292
Chapter 33
----------~--~
.............. .
CIRCULAR POCKET CYCLES
In Chapter 29, circular pocketing cycles were described
briefly. In this chapter, two more examples will provide additional details. Fanuc does not have the useful G 12 and
G13 circular pocketing cycle as a standard feature. ConlIols thaI do have it, for example Yasnac, have a built-in
macro (cycle), ready to be used. Fanuc users can create
their own macro (as a special G code cycle), with the optional User Macro feature, which can be developed to offer
more flexibility than a built-in cycle.
The two G codes are identical in all respects, exceptlhe
cutting direction. The meaning of [he G codes in a circular
pocket cycle is:
Circular pocket cUlling CW
G12
G13
Circular pocket cutling CCW
Either cycle is always programmed with the G40 cutler
radius offset cancel mode in effect, and has the following
formal in the program:
G1/. l.. D.. F..
(CONVENTIONAL MILLING)
or
G12
a,
bl
G13
Figure 33-16
Circular pocket cycles G72 and G13
N2 G17 G40
GBO
N3 G90 GS4 GOO XO YO S1200 M03
N4 G43 ZO.l HOl M08
NS GOl Z-O.25 FB.O
N6 G4l XO.625 YO.125 001 FlO.O
N7 G03 XO YO.7S RO.62S
N8 J-O.75
N9 X-0.625 YO.125 RO.625
NlO GOl G40 XO YO F1S.0
Nl1 G28 Z-0.2S M09
Nl2 G91 G28 XO YO MOS
Nl3 M30
%
G13 1.. D.. F..
(CLIMB MILLING)
!& where ...
I
o ;: ;
F
:::::
Pocket radius
Cutter radius offset number
Cutting feed rate
Typically, the cycle is called at the center and the bottom
of a pocket. All cutting motions arc arc motions, and there
are three of [hem. There are no linear motions. The arbitfary start point (and end point) on the pocket diameter is at
0° (3 o'clock) - Figure 33-16.
Previous example in Figure 33-11 can be used to illustrate the G 12 or G 13 cycle. For comparison, here is (he program 03305, using a 0.625 end mill:
03305 (CIRCULAR POCKET - VERSION 2)
Nl G20
If the G 12 or G 13 cycle or a similar macro is available,
the following program 03306 can be written, using the
same tool and climb milling mode:
03306 (CIRCULAR POCKET - Gl3 EXAMPLE)
N1 G20
N2 G17 G40 G80
N3 G90 G54 GOO XO YO S1200 M03
N4 G43 ZO.l HOI MOB
NS GOI Z-0.25 F8.0
N6 G13 IO.75 D1 FIO.O
(CIRCULAR POCKET)
N7 G28 Z-0.25 M09
Na G91 G2B XO YO MOS
N9 M30
%
Macros are very powerful programming tools, but their
subject is beyond Ihe limits of this handbook.
TURNING AND BORING
There is so much information that can be covered in Ihis
section. that a whole book could be written just on the subject of turning and boring. Selected subjects are presented
in this chapter, others are covered in chapters dealing with
lathe cycles, groovi ng, part-off, single poinllhread ing, etc.
TOOL FUNCTION - TURNING
In terms of distinction, turning are boring are practically
identical operations, except for (he area of metal removal
where the actual machining takes place. Often, terms ex/ernal fUming and internal turning are also used, meaning the
same as turning and boring respectively. From programming perspective, the rules are vinually the same, and any
signi ficant differences wi]] be covered as necessary.
CNC lathes require programming (he selected tool by its
tool number, using the T address. In comparison with a
CNC machining center, the tool function for lathes is more
extensive and calls for additional details. One major difference between milling and turning controls is the facl that
the T address for CNC lathes will make the actuaL tool
change. This is not a case in milling. No M06 function exists on a standard CNC lathe.
• T Address
One difference from machining centers is that a tool defined as TOl in the program must be mounted in the lurret
station # I, tool defined as T 12 must be mounted in turret
station #12, etc. Another difference between milling and
turning tools is in the forma/ of the T address. The format
for turning system is T4, or more accurately, T2+2. The
first two digilS identify the turret station number and geometry offset, the last two digits identify the wear too! offset
number for the selected tool stat ion - Figure 34-1.
Txxyy format represents tool station xx and wear offset
number yy. For example, T0202 will cause the turret to index to the 1001 station #2 (first two digits) which will become the working station (active toot). At the same lime,
{he associated tool wear offset number (the second pair of
digits) will become effective as well.
Selection of the 1001 number (the first pair of digits), also
selects the geometry offset on most modern CNC lathes. In
that case, the second pair of digits will select the tool wear
offsel number. Any tool station selected by the turret station
number identification can be associated with any offset
number within the available offset range. In mosl applications, only one tool offset number is aclive for any selected
1001. In such a case, it is wise to program the offset number
the same as the 1001 number. Such an approach makes the
opera lor's j ob much east er. Consider the f oj low j n g ch oices:
GOO T0214
10
TllOS
GOO T0404.
Tool slation 02, Ivearoff;el 14
Tool slation JI, wear offset 05
Tool SUI/ion 04, wear offset 04
Although all examples are technically correct, only thc
last example format is recommended. When many tools are
used in a program, the offset numbers for individual tools
may be confusing, If they do nOl correspond to the tool Sfation numbers. There is only one ttme when the offset number cannot be the same as the lool station number. That
happens in the cases when /1-tlO or more offsets are assigned
to the same tool, for example T0202 for [he first wear offset, T0222 for the second wear offset.
Leading zeros in the tool function can be omitted for the
tool number selection, but not for selection of the wear offset number. T0202 has the same meaning when written as
T202. Eliminating the leading zero for tool wear offset will
result in an incorrect statement:
n2 means T0022, which is an illegal formal.
TiX,XYIY
...~[ Tool WEAR offset
"T-
..
~ Turret station number
& Tool GEOMETRY offset
Figure 34-1
In summary, the active side of the turret (tool station) is
programmed by the first pai r of dlgtts, the wear offset number is programmed by the last pair of digits in the tool function command:
GOO TQ404
The most useful preference is to disregard the leading
zero suppression and use the tool function in its full formm,
as shown above and in
examples in this handbook.
an
Typical tool function address for eNC lathes
293
294
34
• Offset Entry
lATHE
to some extent covered
the tool function, II is a
"y<;tem<; and <;ome reeach tool as the acpoint 10 ill~ program
value and
The tool offset can be entered into the ....rr\lYr,,",
ferent ways:
o
As a command Independent of the tool
o
As a command applied simultaneously
with a tool motion statement
two
• Independent Tool Offset
For an independent offset entry in the
offset is applied together with the rooiutV,c...<.,"'x
the tool
N34 GOO T0.202
importance of 1001 wear offthat does not use it All proare ideal values, based on the draware not considered, neither is
deviation from programmed dimensions
will produce an incorrect ditool
part is
a very important conwith lighllolerances. The tool wear offset is
tune' the actual machined dimensions against
dimensions.
r"\rr,or":\rTI
of the 1001 wear offset is to adjust the difference
the programmed dImensions and the actual
LOul positioll OI! the pan. If (he wear offset is not available
on the control, (he adjustments are made to the only
- thaI is to the geometry offset.
This command is usually programmed as the
for each tool (in a clearance position). If
position register is used, the offset is
together
coordinate register
with. or immediately following,
block. At this point, the tool is still at indexing position.
When the tool
il will cause a physical
as
in the offset regbefore the tool
command. since it will
to actually take place.
but should be proS,
'
control
control when the power is turned
usually assumes
at the start up, a
it looks rather absurd
it is correct Rapid mothat depending on the
the GOO command
TURRET AT
MACHINE
X GEOMETRY OFFSET
( Diameter is negative]
Figure 34-2
Geometry offset is the distance from tool reference
to program zero, measured along an axis from machine zero
TURNING AND BORING
• Tool Offset with Motion
The second method is to program the wear offset simultaneously with a cuuing tool motion, usually during the tool
approach towards the part. This IS the preferred method.
The following two examples illustrate this recommended
programming of the T function for turning systems - the
offset is activated when the second pair of digits in a tool
number call are equal to or larger than 01:
N1 G20 T0100
N2 G96 S300 M03
N3 GOO X .. Z .. T010l MOS
Note the tool change in the first block N 1 - it uses no offsel number - just lhe tool number that is also the geometry
offset number. The offset is applied two blocks later in N3.
In most cases. it makes no difference, whether the offset
is activated with or without a motion command. But some
limitations (Ire possible when programming the 1001 offset
entry without a molion command. For example, If the wear
offset value stored is unusually Jarge and the tool starts
from the machine zero posicion, this type of programming
may cause an overtravel condition.
Even in cases of a small offset value, there wi Il always be
a 'jump' motion of the turret when the offset is activated.
Some programmers do not like this jumpy motion, although it will do no harm to the machine. In these cases, the
besl approach is to activate the tool wear offsct during the
tirst motion, usuaJJy as a rapid approach motion towards
the part. One consideration is very important when the tool
wear offset is activated together with a motion. Earlier In
this chapter was a comment that the lathe 1001 function is
also a function causing the tool indeXing. Without a doubt,
the one situation La avoid IS the Simultaneous toolllldexino
and 1001 motion - it may ~ave dangerous consequences. '"
The best approach is to start each lOa! with the too! indexing only, \vilhoU! any wear offsel:
N34 T0200 M42
The above example will register the coordinate selling for
tool 2, it will also index tool 2 into the working position, but
it will/wI activate any offset (T0200 means index for {ool 2
without tool wear offset). Gear range function may be
added as well, if required, Such a block will normally be
followed by (he selection of spindle speed, and rapid approach to the first position, close to the part. That is the
block where the tool wear offset will be activated - on [he
way towards the first posilion:
295
Also note that no GOO is required for a block containing
tool indexing with zero wear offset entry. The advantage of
programming the tool offset simultaneously with a motion
is the el imination of the jumpy motion; at the same lime, no
overtravel condition will result, even if the wear offset is
unusually large. The wear offset value will only extend or
shorten the progranuned rapid approach, depending on the
actual offset amount stored.
Generally, the tool wear offset register number is entered
before or during the rapid approach motion.
• Offset Change
Most lathe programs require one offset for each tool. In
some cases, however, the program can benefit if two or
even more offsets are assigned to the same tool. Needless [0
say. only one offset can be active at one time. The current
offset can be changed La another offset for the same tool to
achieve the extra fleXibility. This is useful mainly in cases
when individual diameters or shoulder lengths must be machined to ex.act tolerances. Any new offset must be programmed without a cancellation of the previous one. Tn
fact, this is [he preferable method for changing from one
offsel (0 another. The reason is simple - remember that any
offset change serves a purpose only during actual cutting.
Offset cancellation could be unsafe if programmed during
cutting mOlion. This is a very important - and largely unexplored programming technique - that some detailed examples are justified.
MULTIPLE OffSETS
Most jobs machined on CNC lathes require very high
precision. High precision requires tolerance ranges as
specified in the engineering drawing and these ranges may
have quite a variety. Since a single offset per toot is of Len
not enough to maintain these tolerances, two or more wear
offsets are required for one tool.
The follOWing three examples are designed to present a
complete understanding of the advanced subject covering
mulliple offsets. The same basic drawing will be used for
all examples.
The project IS very simple - program and machine three
diamelers as per drawing, and maintain colerances at the
same time. One rule at the beginning - the program will no/
lise the middle tolerance of the X or Z value. This is an unfortunate praclice that makes changes to [he program much
more dirficul[ at a later time, if lhe tolerances are changed
by engineers or designers.
In the drawings, the following tolerances can be found:
N34 T0200 M42
N35 G96 5190 M03
N36 GOO G41 X12.0 ZO T0202 MOB
o
Tolerances only on the diameter
N37 GOI Xl.6 FO.OOa
o
Tolerances only on the shoulders (faces)
o
Tolerances on the diameters and shoulders
2
Chapter 34
•
General
Here is the complete
are
training purin reality. All chamfer
tolerances are
on the project. Matetools are used:
•
TOl
For the face and rough contour
T03
For the
T05
0.125 wide part-off too!
of the contour to size
Diameter Tolerances
o
I"-
ci
03401
(1. S ALUMINUM BAR - EXTEND 1. 5 FROM
(TOl - FACE AND ROUGH TIJRN)
NJ. G20
N2 G50 S3000 TOIOO
N3 G96 5500 M03
N4 GOO G41 Xl.7 ZO TOIOI MOB
N5 G01 X-O.07 FO.OOS
N6 ZO.l
N7 GOO G42 XI.55
N8 G71 P9 Q16 UO.04 WO.004 DIOOO FO.01
N9 GOO XO.365
NlO Gal XO.62S Z-O.03 FO.003
Nll Z-O.4
Nl2 Xl.O C-0.03 (K-O.03)
Nl3 Z-O.75
Nl4 Xl.375 C-O.03 (K-O.03)
Nl5 Z-l. 255
Nl6 UO.2
Nl7 GOO G40 XS.O ZS.O TOIOO
Nl8 MOL
(TOl - FmISH TIJRN)
N19 GSO 53500 T0300
(-- OFFSET 00 AT THE START OF THE TOOL ------)
mo G96 8750 M03
N21 GOO G42 Xl.7 ZO.1 T0313 MOB
(
OFFSET 13 FOR THE 0.625 DIAMETER --------)
N22 XO.365
N23 G01 XO.625 Z-O.03 FO.002
N'24 Z-O.4
N2S Xl.a C-O.03 (K-O.03) T0314
(- OFFSET 14 FOR THE 1.0 DIAMETER ----------)
m6 Z-O.75
N27 Xl.37S C-O.03 (X-O.03) T03l3
(-- OFFSET 13 FOR THE 1.375 DIAMETER -------
The drawing in Figure 34-3
variable tolerances only on the
1.0
- 03401.
o
o
'<:t
c:i
N28 Z-1.255
N29 UO.2
NJO GOO G40 XS.O ZS.Q T0300
(-- OFFSET 00 AT THE END OF TOOL ------------)
NJl MOL
I
L~
__
~~
__-+________________
~
0.03 x 45° (3)
""'
Figure 34-3
Multiple offsets· I::AOIIII)II:: for diBmeters • 03401
programming solution is to include ltvo offsets for
for example, T0313 and T0314. In the I'Ann-t'l\
correct
amounts have to be set before machiningamounts for middle toler.ance are shown:
"""H"UF"
13
14
X-O.003
X+O.003
ZO.OOO
ZO.OOO
shoulders) must be
- 0.125 WIDE
NJ2 TOSOO
NJ3 G97 S2000 MO)
N34 GOO X1.7 Z-1.255 T0505 MOB
N3S Gal Xl.2 FO.002
N36 GOO Xl.4S
lO7 Z-1.1825
lOB GOl Xl.31S Z-1.25 FO.OOI
N39 X-O.02 FO.0015
N40 GOO XS.O
N4l Z5.0 TOSOO M09
N42 MlO
%
TItis is the complete
quired. Since TOI and
not
ing examples, only T03 will be shown
now on.
TURNING AND
7
o
o
o
..IS!
I.l)
N
o
I.l)
1"-
ci
1
,
t
·-,--0.03 X 45" (3)
34~4
34·5
Multiple offsets ~ f!){RfDDIP. for shoulders - 03402
Multiple offsets
• Shoulder Tolerances
•
F!ltJ'J,mnlll
Shoulder Tolerances
shown in Figure 34-5 illustrates
tolerances specified on both
drawing shown in Figure 34-4 illustrates
part with variable tolerances specified only on
shoulders.
is to include four offsets for
13, T0314, T0315 and T0316. In
amounts have to be set before machining amounts
middle tolerance are shown:
programming solution is to include (WO
finishing. for example T0313 and T0314. In the control,
their amounts have to be set before machining - the
amounts for middle tolerance are shown:
13
14
XO.OOOO
XO.OOOO
Z+O.0030
Z-O.0030
Note that in this case, the X offset (which controls
the diameters) mUSl be the same for both offsets.
13
14
15
16
Z+0.0030
Z+O.0030
Z-O.0030
Z-O.0030
but their input amount is also critical.
03402
N3l MOl
X-O.0030
X+O.OO30
X+O.0030
X-O.0030
is the most intensive version. Not only Lt IS eximportant where exactly [he offsets appear in
T03 for progra~03402:
(T03 - FINISH TURN)
N19 GSO S3500 T0300
( - - OFFSET 00 AT THE START OF TOOL
N20 G96 5750 M03
N21 GOO G42 Xl.7 ZO.l TOl13 MOS
( - OFFSET 13 FOR THE O. 4 SHOULDER
N22 XO.365
N23 G01 XO.625 Z-O.03 FO.002
N24 Z-0.4
N25 Xl.0 C-O.03 (K-0.03)
N26 Z-O.7S T0314
{- - OFFSET 14 FOR THE 0.75 SHOULDER
N27 Xl.375 C-O.03 (K-0.03)
N28 Z-l. 255
N29 UO.2
N30 GOO G40 XS.O ZS.O T0300
( - - OFFSET 00 AT THE END OF TOOL
for diameters and shoulders - 03403
Note thalthe four X offsets (which control size
meters) lie up wilh the four Z offsets (which control
icngth of shoulders). Here is the T03 for program
03403
(TO) - FINISH TURN)
NQ9 Gsa S3500 T0300
(-- OFFSET 00 AT THE START OF TOOL ----------)
N20 G96 S750 M03
N21 GOO G42 Xl.7 ZO.l T0313 M08
(- - OFFSET 13 FRCM Z OVER TO Z UNDER ONLY - - -)
N22 XO. 365
N23 Gal XO.62S Z-0.03 FO.002
N24 Z-0.4
N25 X1.0 C-O.03 (K-O.03) T0314
------)
(- - OFFSET 14 FROM X UNDER TO X OVER ONLY - - - )
N26 Z-0.75 TOll5
(-- OFFSET 15 FROM Z UNDER TO Z OVER ONLY
34
N27 Xl.37S C-O.03 (K-O.03) T0316
(- - OFFSET 16 FROM X OVER TO X UNDER ONLY - - -)
.
FUNCTIONS FOR GEAR RAN
N28 Z-l. 255
are designed to work in
feature enables
prorCCluired spindle
with speof the machine. As a
for spindle speed,
raling will be, and vice versa.
and power ralings
by the machine manufacturer,
N29 00.2
N30 GOO G40 XS.O ZS.O T0300
(-- OFFSET 00 AT THE END OF TOOL ------------)
N31 MOl
programnre
cril
can be seen in
J and 03402, one
offsets must always remain
same (X or Z off-
instance, in the program 03401,
03 and
J 3 control diameters. That means the Z
value must be
same always.! Thai also means, if
shift the shoulders .002 to the len, all
by the same amount:
is a need to
must be
X-O.0030
X+O.0030
~3
14
Z-O.0020
Z-O.0020
Depending on
gear ranges may
signed with ultra
grammable
faull gear
is
four gear ranges speed is usually
erage is two
one, two, three, or
Small lathes, or those de-
speeds, may have no
which means only a
delarge lathes may have all
available spindle
The most common av-
Miscellaneous functions
M41. M42. M43 and
live (0 the number of
to do that will result in inaccurate
NG
ranges, are typically
assume the definition relaavailable:
Number of available ranges
Range
screen selected by pressing a
on
will initially display the 1001 geometry and
They are identical. except the tille at
screen. A rypical display will
(no offsets set):
2
low
3
4
M41
Medium low
OFFSET (GEoMETRY)
NO.
ZAXIS
M43
RADIUS
M42
0.0000
0.0000
0.0000
X
0.0000
0
o
Radius
is shown as
either lhe firsl paIr of the T
offset, or the second pair ~
and Z axis are (he columns where
are
for each number, lhe
are only used if a tool nose radius
case, Ihe Radius will be the lool
will
an arbitrary number, as detool tip orientation. This
C'"rlhp·r! in Chapter 30.
M43
a certain gear range is ':>'-'''~'-l~.U
is limited. If the exact
speed
of
porlanl, always make an effort to
IS Im-
alit the available
spindle
in each range. Don't be
that on most CNC machines, one rpm (I
lowest spindle speed may be
don'l be surprised to find that
len quite
for spindle speeds in lWO
if the
J hasarange20to 1400
a range of 750 LO 2500 r/min. When
available in either range, such as 1000
of
is not critical, but low
is an actual, although unrelated,
Low gear range:
High
range:
M44
20 . 1075 r/min (M41)
70 - 3600 r/min (M42)
10 find out
TURNING AND BORING
299
AUTOMATIC CORNER BREAK
03404 (MANUALLY CALCOLATED CORNER BREAK USED)
NSl TOlOO
NS2 G96 5450 M03
turning and boring)
N53 GOO 042 XO.3 ZO.l T010l MOS
cut
a shoulder to a diameter
shoulde;r) requires (\ comer break.
is a cornman practice when
Many
comers are to be
It is up to the .... ,.",,......,.....,,....,
the range of 0.005 to
required corner
angle, or a blend radius
of the comer break is "'1J",,",a,,-,'"
must apply it. Comer
NS4 Gal XO.62S Z-O.0625 FO.OOl
N55 Z-O.4
N56 G02 XO.825 Z-O.5 RO.l
NS7 Gal .:u.125
NS8 Xl.2S Z-O.S62S
NS9 Z-O.9
N60 G02 Xl.45 Z-l.O RO.l
N6l Gal .:u.675
N62 GO) .:u.S7S Z-l.l RO.l
N63 GOl Z-1.437S
N64 X2.C Z-1.S
N65 X2.37S
N65 Xl.55 Z-l.5875
N67 ua.2
N68 GOO G40 XlO.O Z5.0 TOlOO
N69 Mal
o Functionality
... for strength, ease of assembly, and clearances
o
Safety
... sharp corners are dangerous
o
Only the fmished contour is
Appearance
... the finished part looks
In lathe work. many comer
apply to cuts ",pr""" ••"
a shoulder and the
(the cut takes a 90°
tum in one axis at a time).
start and end points calculation is not difficult but can
consuming for some
jobs, such as shaft
with many different diameters.
(no facing cut),
1, with the calculated
at a selected clearance
point has to be
diame:ter at XO.3. Each contour
calculated. At the contour
the last chamfer
been completed at a clearance of 0.025 above the largat X2.55,
Z
at Z-1.5875.
est
in manual work,
For
of programming is
it is easy to forget to
for bOling). The
02.5
of errors can
N56 G02 XO.725 Z~0.5 RO.1
(ERROR Dr X)
of the correct block
NS6 G02 XO.82S Z-O.5 RO.1
(X IS CORRECT)
the program in
corner break?
to
o
N
RO.1
ALLC
Figure 34·6
Example lor an
o
Chamfering method
... for a 45° chamfer
o
Blend radius
... for a 90°
corner break (chamfers and
34-6 shows a simple
comers that will benefit
programming feature
matic comer
the drawing qualify).
Compare
two methods, to better
ferences applied in programming. If the
not use the automatic comer break feature,
change poi.nt must he calculated manually
03404:
will be
in a very similar manner
"''''''0..,'' ..''' in both cases.
•
Chamfering
45 Degrees
Y"'"''''<''''''HV comer chamfering will
two special vectors I
...., ..""",,"" or a C vector on some ,I."""YV.,,,.
For the
specify the
chamfer:
.t",,,,,,,t1t' chamfer generation,
and the amount
300
Chapter 34
The I vector
is used to create a chamfer starting from the X axis,
into the X+Z-, X-Z-. X+Z+, or X-Z+ direction
c+
cC+
C+
The K vector
is used to create a chamfer starting from the Z axis,
...,
into the Z-X +, Z-X-. Z+ X+, or Z+ X- direction
The I and K vector defin ilion is illustrated in Figure 34-7.
c-
c......._ . . L ___ ~ __ ~---I....
K+
K-
i+
c+
c1+
Figure 34·8
X+
Vectors C for automatic corner chamfering
Z+
In either case, the sign of I or K vector defines the direction of the chamfer cUlling within the coordinate system:
X-
o
i-
1&- -
K-
Positive value of I or K vector indicates the
chamfering direction into the plus direction
of the axis not specified in the chamfering block
-
o
K+
Negative value of! or K vector indicates the
chamfering direction into the minus direction
of the axis not specified in the chamfering block
Figure 34-7
The va 1ues of I and K com rna nds are aJ ways sin gle va! ues
(i.e., radius values, not diameter values).
Vectors J and K lor automatic corner chamfering
When the control system encounters a block containing
the chamfering veclor J or K, it will automatically shortell
{he active programmed tool path length by the value of the I
or K vector, as specifIed iryfhe program. If not sure whether
the I or the K veclor shoJld be programmed for aulomatic
chamfering, consult the above illustration, or apply the following rules:
The vector I indicates the chamfering amount alld motion
direction when the 1001 motion is in the order of Diameter-Cham{"er-Shoulder,
which means cUllin!!
'.1'
'-' alonCJ the Z
axis before the chamfer. The chamfer deviation can only be
from lhe Z axis lowards [he X axis, with the I veclor programmed:
Many lalest controls use vectors C+ and C- that replace
[he 1+. 1-, K+ and K- vectors - Figure 34-8. This is a much
simpJer programming method and its applications are the
same as for the blend radius R. described shortly. There is
no distinction bel ween axes vector selection, just the specified direction:
o
The C vector is used
... to create a chamfer starting from the X axis,
into the X+Z-, X-Z-, X+Z+, or X-Z+ direction
(;>
GOI Z-1.7S IO.125
(CUTTING ALONG Z AXIS)
(CONTINUING IN X AXIS AFTER 0iAMFER)
X4.0
- or-
... to create a chamfer starting from the Z axis,
lnto the Z-X +. Z-X-, Z+ X+, or Z+ X- direction
If the unit control allows the C+ or C- veclors, the programming is much easier, as long as the motion direction is
watched. The two previous examples will be:
The vector K indicates the chamfering amounl WId molion direction when the lool molion is in the order of Shoul-
GOI Z-1.7S CO.125
dPr-Clum1jN-f)imnf'It'l; which means cutting along the X
X4.0
axis before the chamfer. The chamfer deviation can only be
from the X axis towards the Z axis, when the K vector is
GOI X2.0 C-O.125
programmed:
GO 1 X2. 0 K- 0 . 125
(CUITING ALONG X AXIS)
Z-3.0
(CON'I'INUING IN Z AXIS AFTER CHAMFER)
Z-3.0
(CUTTING ALONG Z AXIS)
(CONTINUING IN X AXIS AFTER CHAMFER)
(CONTINUING
(CUTTING ALONG X AXIS)
rn z AXIS AFl'ER CHAMFER)
As was the case with the I and K vectors, the C vector is
also spccified as a single value per side, not per diameter.
TURNING AND
•
NG
Blend
301
90 Degrees
A
a shoulder and
(or
10 a similar way as the automalic 45°
exclusively ill the GOl Inode.'
cham
Only one special vector R is used. For automatic blend ra-
dius, the vector
the direction and rhe amount
CUI for the radius:
o
The R vector is used
The radius deviation can also be from the Z axis
the X axis, when the R vector is programmed:
GOl Z-1.75 RO.125
X4.0
(CUTTING ALONG Z AXIS)
(CONTINUING IN X AXIS AFTER RADIUS)
In either ease, the
lion of the radius
R vector defines lhe direethe coordinate
o Positive value of R vector indicates the radius direction
into the plus direction of the axis not specified in the
radius block
starting ffom the X
or X-Z + direction
o
- or... to create a blend radius starting from the Z axis,
into the
,orZ+X-direction
• Programming Conditions
The R vector definition is illustrated in Figure 34-9.
R"
.... .
Negative value of R vector indicates the radius direction
into the minus direction of the axis not specified in the
radius block
corners
modern CNC lathes a
R+
for
contains vectors lor
for blend radius corner.
'"
R+
X+
.
z-
xR-
\
o
Chamfer or radius must be fully contained in
a single quadrant - 90° only
o
Chamfers must have a 45 e
and radii
must have a 90" angle between a shoulder and
a diameter or a diameter and a
o
The values of chamfering vectors I and K or e,
as well as the radius vector R, are
single values ",",,::onlrll'lper side values, not
values
R-
R-
o Direction of cut before the corner rounding must be
to the direction of the cut after rounding.
one axis only
34-9
Vector R lor automatic comer rounding
control system encounters
o
The direction of the cut following the chamfer or radius
must
along a single axis only, and must have
the
equivalent to at least the chamfer length or the
radius amount the cutting direction cannot reverse
o
Both
takes
o
eNe program, only the known
the drawing . the sharp point - is
That is the point between the shoulder and the
without the
or radius being considered
block containing
a blend radius vector R, it will automatically shorten the actool path length by
value of the R vector, as speci tied in Ihe program. If noc sure whether the R
vector should be programmed for
blend radius,
consult the above illustration or apply the following rule:
The vector R indicates the radius amount
when the CUlling is in
which means
X axis
same vector is
when the /'Qmotion direction is in the opposite order
which means cutting along
These rules appJy equally \0 turning and
lathe
Study them carefully Lo avoid
•
deviation can be from the X
The
axis, when the R vector is programmed:
lheZ
GOI X2.0 R-O.12S
Z-3.0
(CONTINUING IN Z AXIS AFTER """'''''''',);;>J
Programming Example
The
03405 combines the use
radius vector, mio a complete p.xampIe. The same
is used for this version, as
traditional method, illustrated earlier in Figure 34-6.
302
Chapter 34
In order to fully appreciate the differences between (he
two programming melhods (both are technically correct),
compare Ihe followIng program O}405 wiUl the earlier
program 03404. The I and K vecrors are used for chamfering, as they are more dinicu!lthen the C vectors:
03405 (AUTOMATIC CORNER BREAKS USED)
NSI TOIOO
N52 G96 5450 M03
N53 GOO G42 XO.3 ZO.l TOlOl MaS
NS4 Gal XO.625 Z-0.0625 FO.OO3
N55 Z-O.5 RO.l
NS6 X1.25 K-O.062S
N57 Z-l.O RO.l
N58 X1.875 R-O.l
N59 Z-1.5 IO.0625
N6D X2.375
N6l X2.55 Z-l.5875
N62 UO.2
N63 GOO G40 XIO.O Z5.0 TOlOO
N64 MOl
Although the program is a little shorter, the five blocks
saved in Ihe program offer the least benefit. Where are the
G02s and Gms. where are the calculations of each contour
change point? Where arc the center point calculations?
Except for the contour beginning and end, this type of
programming greally enhances program development and
allows ror very fast and easy changes during machining. if
necessary. If a chamrer or u blend radius is changed in the
draWing, only a single value has 10 be changed in the program. withoul any rcci.llculations. Of course, the rules and
condilions mentioned earlier must be always observed. The
main benefit of the auromalic contouring are the ease of
changes and the absence of manual calculations.
ROUGH AND FINISHED SHAPE
The vast miljorily of material removal on CNC lathe is
done by using various cycles, described in detail in the next
chapler. These cycles require inpul of data that is based on
machining knowledge, such as a depth of cuI. stock allowance, speeds and feeds. etc.
Rough and finished shapes often require manual calculatiOllS, using algebra and trigunuHlelry. Tllese calculalions
should be done on separale sheels of paper, rather than in
lhe drawing iLSd!'. ThaI wuy, the work is better organized.
Also, if there is a change later, for example, an engineering
design change, it is easier to keep lrack of what is where.
•
Rough Operations
A great part of Imlle machining amounts LO removal of
excessive slock \0 create a part, almost completed. This
kind of machining is generally known as roughing, rough
turning, or rough boring. As a machining operation, rough-
ing does nol produce a high precision parl, that is not the
purpose or roughing. Its main purpose is to remove unwanted slOck efficiently, which means fast and wilh maximum tool life, and leave suitable all-around stock for finishing. CUlling tools used for roughing are strong, usually
with a relatively large nose radius. 'I'hese tools have to be
able to sustain heavy depths of cut and high cutting feeds.
Common diamond shaped tools suitable for roughing are
80° inserts (up \0 2+2 CUlling corners), and trigon inserts
(up 10 3+3 cutting corners). 2+2 or 3+3 means on 2 or 3
CUtllllg edges 011 each Side of the Insert. Not all inserts can
be used from both sides. Figure 34-10 shows some typical
lools and orientation for rough turning and boring.
Light cut only I
•
.Li9ht cut only I
,
0
•+
• U---.U----
•
•
I
n·h
'-
+
•0-·-· •v··----· ··8 r-
',/
,
n
'---/
.
+light cut only +light cut only
~
I
l)
I
i
I
Figure 34-10
Tool orientalion and cutting direction for roughing.
Upper row shows external tools, lower row shows internal tools.
Allhough a number of tools can be programmed in several directions, some directions are not recommended at
al!, or only for light or medium light cuts.
In practice, always follow one basic rule of machining this rule IS valid for all types of machines:
Always do heavy operations before light operations
This basic rule means that all roughing should be done
before the first finishing CUt is programmed. The reason
here is to prevent a possible shift of the material during
roughing, after some finishing had already been done,
For example, the requirement is to rough and finish both
external and internal diameters. If the above rule is applied
to these operalions, the roughing out the outside of the part
will be first, {hen roughing out the inside of the parl, and
only then applying the finishing cuts. It really does nOI malter whelher the roughing is done first externally or internally. as long flS il gets done b~fore any finish cuts, which
also cLln be in either order.
TURNING AND
303
of cut IS suftlskin' of the mR- .
is usually a must
before
tool ac-
•
Operations
Finish operations take
cutting mOlions,
removed (roughed OUL).
after mosl of the stock
stock for finishing.
leaving only a small amount of
nose radius and. for even
The cutting 1001 can
spindle
and lower cuta better surface finish,
ling feeds are lypical.
I
IIlg shoulders at 90°) IS much more cnhea!. If
the positive X axis only
turning}, or the
(for boring), with a lool that has a lead angle of
to
not
more (han .003 (0.006 inch (0.080 to 0.150
mm) on any straight shoulder. Figure 34-/2 shows the
of too much stock allowance for certain cutting direcand a method to eliminale it
. . Light cut only
.~
•
•
/ Medium cut
•
Light I Medium cut
. •
.~~
.'
Light cut only
•
As before, there is a general rule of
axis, thai is forculting
to or slightly larger than
radius of the
jog 1001. For example. if a .O~ I inch (001 nose
mm) is used for finishing, leave
to
(about I mm). That is the physical
amount assigned per side, not on diameter!
The amount of stock left on the Z axis (typically
Many different tools can be
as well, bUI the most tYPIcal
mond shaped inserts, wilh a
Their shape, common orientation and
shown in Figure
JJ.
. , Light cut only
specifics the amount of material left for these
operalions. If 100 much material or too I ittle
is len to be
cut during finishing, the part
finish
quality will suffer. Also, carefully
allowance overall on the part. but individual
ances for (he X and Z axes.
-- W
l+- = Direction of cut.
-_.,
a
R
\
f - - - Z POS
x POS
Light cui only
Figure 34-11
34·12
Effect of stock allowance Won depth of cut D
Tool orientation and cutting direction for finishing with
common lathe tools. Upper row shows external tools,
lower row shows internal tools.
Z
In
calculate
Note that some cutting directions are only recommended
for light or medium cuts. Why? TIle answer has a lot to do
with (he amount of material (stock) the tool removes in the
direction .
• Stock and Stock Allowance
material machined is often called stock. When
tool removes the stock to cut a desired shape, it can
a certain amount of it at a time. The insert
Inthe
and
In
on the alimportant
allowance
~ where
D
A
R
W
X POS
ZPOS
::::; Actual depth of cut at
== lead angle of the insert
Radius of the insert
== Stock left on
for finishing
TBrget position for the X axis
Target position for the Z
304
Chapter 34
The illustration applies equally Lo (he boring, when the X
axis direclion is opposite the one shown. To understand
better the consequences of a heavy sLock left on the face,
evaluate ibis example:
o Example:
The amount of slack left on face is .030, the too! radius is
.03 t and the tool lead angle is 3°:
W = .030,
R = .031,
A = 3
In CNC lathe programming, a recess can be machined
very successfully wilh any 1001 (hal is used wilh Ihe proper
depth of cut, and a suitable back angle clearance. It is lhe
second requirement [hat will be looked at next.
Figure 34-13 shows a simple drawi ng of a roller 1n the
middle of the obiect, there is an undercut (recess) between
the 01.029 and the 0.939. The objective is to calculate, not
to guess, what is the maximum back angle tool that can be
used for CUlling the recess in a single operation.
.,
There is enough data available Lo calculate the unknown
depth D, using llle above formula:
R9/16 (2)
'j
-
D = tan3/2 x .031 + .030 / tan3 + .031
D = .60425
For an insert wilh a 0.500 inch inscribed circle (such as
DNMG-432, for example), the actual depth of CUI at the
face will be .60425 - more rhan any reasonable amounti
ThaL is a more reasonable depth of cut at the face, so the Z
axis slock allowance of .006 can be used. For facing in Ihe
opposite X direction or for not unidirectional faces, leave
stock much bigger, usually close to the tool radius.
PROGRAMMING A RECESS
Another very important aspect of programming for CNC
lathes is tnc change of cult i ng di rection. Normally, program
a tool motion in such a way Ihal Ihe mOlion direction from
the starling point will be:
o Positive X direction for external machining
... and / or ...
Negative Z direction for external machining
o
A recess is commonly designed by the engineers to relieve . or undercut - a certain portion of the part, for example, to allow a matching parlto tit against a shoulder, face,
or surface of the machined part.
00.939
___--i---=.<~!«<
-
-.1_
1.25 ROLLER
Figure 34·13
Back angle clearance calculation example
TIle first step is to consider the drawing - that is always
the given and unchangeable source of data. The difference
between the diamelers and the recess radius will be required. Figure 34-14 illustrates the generic details of the
provided data (except the angle b) from the drawing.
Drawing detail
<
~
\
R
\
a = Tool back angle
R = Spedified radius
b = Clearance angle req'd
D Depth of recess
=
\
\
Negative X direction for internal machining
... and / or ...
Negative Z direction for internal machining
There arc also back ruming or hack boring operations
used in CNC programming, but these are just related and
Jess common variations of the common machining. In the
most common machining on CNC lathes, any change of direction in a single axis imo the material constitutes an undercut, a cavity. or more commonly known - a recess.
--r
I
I
tan3/2 x .031 + .006/tanJ + .031
.14630
D
------:---=-- -
01.029
Since the earlier suggestion was no more (han .006, recalculate lhe example for the largest depth, if the W=.006:
D
-./
r
I
D-'
Tool detail
Figure 34-14
Data required to calculate angle 'b'
The formula required to calculate the angle b uses simple
lrigonomclric formula. First, calculate the depth of thc recess D, which is nothing more that one half of the difference between the two given diameters:
D =
LARGE DIA - SMALL DIA
2
TURNING AND BORING
Once the recess depth D is known, the formula to calculate the angle b is:
For the example, the calculation will be:
b == cos -I ( .5625 - .045 ) =: 23.07392
.5625
For actual machining, select a tool with the back angle a
greater than the calculated angle b. For the illustrated drawing (23.07° required c!carance), the selected tool could be
either a 55° diamond shape (back angle clearance Q is 30°
to 32"), or a 35" diamond shape (back angle clearance a IS
50" (0 52") - both are greater than the calculated minimum
clearance. The actual angles depend on the Lool manufacturer, so a tooling catalogue is a good source of data.
This type of calculation is important for any recesses, undercuts and special clearances, whether programmed with
the aid of cycles or developed block by block. The example
only illustrates one possibility, but can be used for any calculations where the back angle clearance is required.
SPINDLE SPEED IN CSS MODE
From several earlier topics, remember thatlhe abbreviation CSS stands for Constanl SllIjace Speed. This CNC
lathe feature will constantly keep recalculating the actual
spindle speed in revolutions per minute (r/min), based on
the programmed input of surface speed: The su:face speed
is programmed infeer per minute - ftiman (English system)
or in meters per minute - mfmin (metric system).
In the program, the 'per minure' input uses Ihe preparatory command G96, as opposed [0 the direct rlmin input
using tlie cOlllrnand G97.
The Constant Surface Speed is a powerful feature of the
conlrol system and without it, we would lo?k back many
years. There is a rather small problem assocIated wlth tJus
feature, orten neglected altogether, or at least not considered important enough. This rather 'small problem' wIll be
illustrated in a simple program example.
The program example covers only a few blocks at (he b~­
ginning. when the cutting tool approaches the part. 1l1at 15
cnough data to consider the question that follows.
03406
N1 G20 T0100
N2 G96 8450 M03
N3 GOO G41 XO.7 ZO T0101 MOB
N4 ...
305
The queslion is this: What is the actual spindle speed (In
r/min), when the block N2 is executed? Of course, (he spindle speed is unknown at the moment. It cannot be known,
unless the current diameter, the diameter where the tool IS
located at thai moment, is also known. The control system
keeps track of the current tool position al all limes. So,
when block N2 is executed. the actual r/min of the spindle
will be calculated for the current diameter, as stored in the
control, specified in the geometry offset enlry. For the example, consider (hat the current diameter is 23.5 or X23.5.
From the standard r/min formula, the spindle speed calculated for 450 fUmm and 023.5 as 73 rIm in is rather slow,
but correc\. At the nex.t block, block N3. the tool position is
rather close La the part, at diameter of .700 (XO.7). From the
same stand<lrd formula, the spindle speed can be calculated
for that diameter as 2455 r/lnin - considerably fast but also
correct. The problem? There may not be one for every
machine, but if ever there is a problem, the following solution will eliminate it
The possible problem will be linked to the rapid motion
from the 023.5 to the 0.700. The actual travel distance
(per side of part) is (23.5-.700)/2, which is 11.400. During
the rapid {ravel rate, the CUlling tool has [0 move I J .400
inches and - at [he same time - change the spindle speed
from a slow 73 r/min, to a fast 2455 rlmin. Depending on
the control system and its handling of such a situation, the
tool may actually start cutting at a slower spindle speed
thall was originally intended.
If such a situation docs happcn and presents a problem,
Ihe only step that can be done is to preprogram the expected
spindle speed in r/min, before the cutting tool approach
motion, then switch to the constant surface speed (CSS)
mode and continue.
03407
Nl G20 TOlOO
N2 G97 52455 M03
N3 GOO G41 XO.7 ZO TOlD1 MOS
N4 G96 5450 M03
N5
(R/MIN PRESET)
What had been done requires more evaluation. What had
been done is thai the spindle was started at the final expected r/mil1, before the tool reaches [he part, in blo~k N2.
In block NJ, the tool moves to the start of CUl, while the
spindle is already at the peak of Ihe ~rogrammed speed.
Once the target position along the X aXIs has been reached
(block N3), the corresponding CSS mode can be In effect
for all subsequent cuts.
This is an example that does not necessarily reflect everyday programming of CNC lathes. In this situation, some
additional calculations have LO be done, but if they solve the
problem - they are worth the extra effort! Some CADICAM
system can be set to do exactly that automatically. If [he
current X position of the tool is unknown, estimate it.
306
Chapter 34
• Approach to the Part
LATHE PROGRAM FORMAT
In a review of the already presented examples, a certain
consistency can be seen in the program output. This may be
called a style, a format, a form, a template, as well as several other terms. Each programmer develops his or her own
style over a period of timc. A consistent style is important
for efficient program development, program changes and
program interpretation.
• Program format - Templates
Most examples have followed a cenain program formal.
Note that each CNC lathe program begins with the 020 or
G21 command and perhaps some cancellation codes. The
block that follows IS a lool selection, next is spindle speed
data, etc. This format will not basicaJly change from one
job to another - il follows a certain consistent pattern which
forms the basic femplate for writing the program.
An important part of any lathe program structure is the
method of approaching a revolving part. If the part is concenlric, the approach can be similar lo the A option in Figure 34-15. Although a facing cut is illustrated, the approach
would be logically the same for a turning or a boring cuL
Keep the slarting point SP well above the diameter, at least
.100 per side and more, if the actual diameter is not known
exactly. The B option of the tool approach is two single axis
at a lime. It is a variation of the first example, and the X axis
motion can be further split into a rapid and cutting motion,
if required. Finally, the C option uses the clearance in the Z
axis, far from the front face. Again, the tinal motion toward
the face can be split into a rapid and linear motion.
~-
SP - - - - -
• General Program format
To view the format often enough will forge a mental im-
A
age in the programmer's mind. The detajls thaI are not understood yet will become much clearer after acquiring the
general underst.anding of Ihe relationships and details used
in various programming methods. Here is a suggested template for a CNC lathe program.
0..
ill
(PROGRAM NAME)
G20 G40 G99
(PROGRAM START up)
(TOOL AND GEAR RANGE)
(STABILIZE R/MIN)
N2 T .. 00 M4 ..
N3 G97 S .. M03
N4 GOO [G41/G42)
NS G96 S ..
x .. Z .. T.. M08
(APPROACH)
(ClJ'I'"£ING SPEED)
N6 GOl [X .. /Z .. ] F ..
(FIRST CUTTING MOTION)
c
N7
(MACHINING)
N.. GOO (G40] X ..
z .. T .. OO(TOOL CHG POSITION)
Q
r.~ ~-__________w
lJt;-]
_------w
QEd--I
B
Q General Program Pattern - Lathe:
--
~­
SP :: Start point
for cutting
Figure 34-15
Safe approach to a parr - example for a facing cut shown
%
There are many variations on these methods, lOO numerous to list. The main objective of considering the approach
to the part in the first place is safety. A collision of a tool
with a revolving part can have serious consequences.
This generic structure is good for most lathe programs.
Feel free to adjust it as necessary. For example, not every
job requires spindle speed stabilization, so block N3 will
not be necessary. It also means that M03 rotation has to be
moved to block N5. Take the general program pattern as an
example only, not as a fixed forma\.
Turning and boring is a large subject. Many other examples could have been included in this chapter. Other chapters in this book also cover turning and boring, but in a
marc specialized way, for example, turning and boring cycles. The examples that were presented in this chapter
should be useful (0 any CNC lathe programming.
N .• MOL
(OPTIONAL STOP)
N .. M30
(PROGRAM END)
LATHE CYCLES
•
Complex Cycles
STOCK REMOVAL ON LATHES
One of tbe most time
gramming for a CNC lathe is
siock, lypicaJJy from a
rough turning or rough
as
1b manually program a
ries of coordinated rough u""",~"'''.
gram for each tool motion.
tour, such a method is
inefficient, as well as prone to errors.
try Lo sacrifice programming
an uneven sLock for finishing,
wear out prematurely.
ished profile often suffers as
It is in the area of rough
lathe controls are very useful
CNC lathe systems have a
lhar
tool path to be processed automatically,
des. Roughing is not the
application for
there are also special cycles available
simple grooving. The grooving and
outside of this chapter, but will be covered in
next three chapters.
•
Simple Cycles
Fanuc and similar controls suppOrt a number of special
lathe cycles. There are three rather simple cycles that have
been part of Fanuc controls for quite a while. They first appeared with the early CNC units and were limited by the
technological progress of the time. Various manuals and
lextbooks refe!: to them as the Fixed Cycles or Simple
or even Canned Cycles, similar in nature to cheir
cousins for drilling operations on CNC mills and machining centers. Two of these early cycles are used for turni
and boring, the third cycle is a very simple threading cycle,
This ch'lpter covers the fi~t two cycles.
Don'l gel misled by the
cles are only complex in the
then, only internally. TIley are
system only. In fact, these very
are much easier to program than
In addition, they can also be
control, to optimize them
on the job.
PRINCIPLES OF LATHE CYCLES
Similar to drilling operations for CNC machining cenall cycles for lathes are based on the same technologIcal principles. The programmer only enters the
data
(typically variable CUlling parameters), and the CNC system will calculate the details of individual cuts. These
are based on the combinalion of the fixed and
variable data. Return LOol motions in aillhese cycles are automatic, and only (he values to be changed are specified
within
call
are designed exclusively to cui a straight
tapers or radii and also wlth no unsimple cycles can only be used to cut verlihorizontally, or at an angle, for taper cutting, These
original
cannot do the same cutting operations as the
and
multiple repetitive cycles - for
they cannot
out a radius or change directhey cannot contour,
307
308
Chapter 35
G90 - STRAIGHT CUTTING CYCLE
Before going further. a reminder. Do not confuse G90 for
lathes with G90 for machining centers. In turning, G90 is a
lathe cycle, G90 is the absolute mode in milling;
The second format adds the parameter I or R to the block
and is designed for taper cutting motions, with the dominance of the Z axis - Figure 35-2.
G90 is absolute mode for milling,
X and Z axes are absolute mode for turning
:-
-w
,. . ,
--z-
'I-
G91 is incremental mode fOT milling,
U and Waxes are incremental mode for turning
I
A cycle identified by G90 preparatory command (Type A
group of G codes) is called the Straight CUlling Cycle (Box
cycle). Its purpose is to remove excessive stock between the
start position of the culling Lool and (he coordinates specified by the X and the Z axes. The resulting cut is a straight
turning or boring cut. nornUllly parallel to the spindle centerline and the Z axis is the main cUlling axis. As the name
of the cycle suggests, the G90 cycle is used primarily for removing a stock in a rectangular fashion (box shape). The
G90 cycle can also be used for a taper cutting. In Figure
35-1, the cycle structure and motions are illustrated.
I
Figure 35-2
G90 cvcle structure -taper cutring application
o
Format 2 (two versions):
G90 X(U) .. Z(W) .. 1.. F..
G90 X(U) .. Z(W) .. R.. F..
,.. ------w --------..-;
(4)
~ where ...
L
x
UJ2
- -v
r
I (R)
""
X
F
::::
I
Figure 35-1
690 simple cycle structure - straight cutting application
• Cycle format
The G90 cutting cycle has two predetermined programming formats. The ~irst one is for straight cUlling only,
along the Z axis, as ill ustrated in Figure 35- J.
o
Format 1 :
~ where ...
F
=::
End of cut in Z position
Distance and the direction oftaper
(1=0 or R=O for straight cutting}
Cutting feed rate (usually in/rev or mmJrev)
In both examples, the designation of axes as X and Z is
used for the absolute. programming, indicating the tool posicion from program zero. The designation of axes as U and
W is used for the incremental programming. indicating actual travel distance of the tool from the current position.
The F address is (he cutting feedrate, normally in incites per
revolution or millimeters per revolution. The I address is
llsed for taper cutting along the horiwmal direction. It has
an amount equivalent to one half of the distance from the
diameter at the taper end, to the diameter at the taper beginning. The R address replaces the I address, and is available
on newer comrols only.
To cancel the G90 cycle, all that is necessary to do is to
usc any motion command - GOO, GO l. G02 or G03. Commonly, it will be the GOO rapid motion command:
G90 X(U) .• Z(W) .. I .. F ..
x = Diameter to be cut
Z
== Diameterto be cut
Z
End of cut in Z position
Cutting feed rate (usually inJrev or mm/rev)
GOO
LATHE CYCLES
309
• Straight Turning Example
To
a
35-3. It
from a 04. J
the length of
i
and no radii. This
the G90 cycle 10 a
the manual al[ernalive.
application of G90
rather a simple diameter
down to a 'final 02.22 inch, over
There arc no chamfers, no
the practical
simple roughing only, but still
-1
r
04.125
rXrl'III1JIt'
• programs 03501 &03502
of G90 cVcle in
the depth of each cui has
Since G90 is a roughing
amount left for finishing,
first, then the
find out how much
decide on the depth of
,'p'nnr".!pn from the diameter.
slock is aclua[ly there to
amount of Siock is "' .... ,..." ........ per side, as a ravalue, along the X
NlO X2. 28
(PASS 6)
Nll GOO X10.O Z2.0 T0100 M09
Nl2 MOl
(END OF ROUGHING)
If prefen'ed, use
incremental programming rnp,nr,n
However, it is
Lo trace the program progress with the
absolute coordinates
ever, here is the
03502
(G90 STRAIGHT TtJRNING CYCLE - INCREMENTAL)
Nl G20
N2 T0100 M41
N3 G96 S450 M03
(START POINT)
N4 GOO X4.32S ZO.l T010l MaS
N5 G90 U-0.507S W-2.655 FO.Ol
(PASS 2)
N6 U-0.307S
(PASS 3)
N'7 U-0.3075
NB U-O.307S
(PASS
N9 U-0.3075
(PASS 5)
(pASS 6)
NlO U-0.3075
Nll GOO XlO.O Z2,Q T0100 M09
Nl.2 MOl
(END OF ROUGHING)
cycle is quite simple in both versions - all that is
is La calculate the new
for each roughing
cut. If the same roughing tool path had been programmed
the block-by-block method (withollt G90), the finaJ
would be more than
longer.
• Taper Cutting Example
to
(4.125 - 2.22) / 2
to that used for the
Will be cui, also
35-4 is a
example. In this
the G90 simple
= .9525
r
a
Slack per side
finishing cuI, the .030
will subtracted from the total X
so the total depth
amount to remove will be .9225.
is the selection of cut
for the toral depth.
five even cuts, each
cut will be .1845, for six cuts, .1538. Six cms will
;'''''l\,A.\~,U and .030 left per
or
on the diilmeter
the first diameter will be X3.8175.
.005 stock allowance will
left on the face, so the Z
end cut will be
actual
and in
part will be the
03501
(G90 STRAIGHT TUlmDJ'G CYCLE - ABSOLUTE)
Nl G20
N2 T0100 M4l
N3 G96 S450 M03
(START POINT)
N4 GOO X4.32S ZO.l T010l MOB
(PASS 1)
N5 G90 X3 B175 Z-2.555 FO.Ol
(PASS 2)
N6 X3.51
(PASS 3)
N'7 X3. 2025
(PASS 4)
N8 X2.895
(PASS 5)
N9 X2.5875
02.25
I
t
Figure 35-4
l::xa·mO,le of
In
the
musl
to
cycle in taper cutting - program 03503
between the
cUlting methods, using the same
a
to distinguish these two
there is one
cuning and
cycle, there
of CUL, and
310
Chapter 35
The difference is the addition of an I parameter to the cycle
calL indicating the taper amount and its direction per side.
This value is called a signed radius value. It is an I value because of its association with the X axis. For straight cutting,
the I value will always be zero and does not have to be written in the program Irs only significance is for raper cutting,
in which case it has a non-zero value - Figure 35-5.
FIRST
TAPER LENGTH
. MOTION
rmAL TOOL TRA\.7Eli DIRECTION
Figure 35-6
Known and unknown values for taper culling -program 03503
Amount 'i' is known, amount 'J' has to be calculated
I
. ····-2.5
'I
~ 1
aoRK£t\jAL
+
-~-·····~··r
0.875
RST
MOTION
DIRECTION
I
Figure 35-5
The I amount used for G90 turning cycle - extemal and internat
o
a
If the direction of the first tool motion in X is negative,
the I value is negative
If the direction of the first tool motion in X is positive,
the I value is positive
On a CNC lathe with the X axis positive direction abpve
the spindle center line, the typical I value win be negative
for external taper cutting (turning) and positive for internal
taper cutting (boring).
To program the part in Figure 35-4. keep in mind that the
illustration represents the fmished item and does not contain any clearances. Always add all necessary clearances
flIst, then calculate the I amOlillt.
In the example, a clearance of 0.100 will be added at each
end of the taper, increasing its length along the axis from
2.5 to 2.7. The I amount calculation requires the actual
length of tool travel, while maintaining the taper angle at
the same time. Either the method of similar triangles or the
trigonometric method can be used for such calculation (see
Chapter 52 for details on shop mathematics). Figure 35-6
and Figure 35-7 illustrate the details of the known and unknown values for the I amount calculation.
-I
~l
The illustration shows that the r amount is calculated as a
single distance, i. e., as per single side (a radius value), with
specified directiol'1; based on the total traveled distance and
the direction of the first motion from the start position.
There are two simple rules for G90 taper cutting:
2.7-
T
i
0.875
I
1 . . . . . . . . . .;. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .:~
Figure 35-7
The I distance calculation using the similar triangles method
The example shown above almost suggests the simplest
method of calculation, a method that is known in mathematics as the law ofsimilar triangles. This law has several
possible deflnitions, and the one that applies here is that ...
Two triangles are similar, if the corresponding sides
of the two triangles are proportional.
In programming, quite often there is a situation that can
be solved by more than one method. Choose the one that
suits better a certain programming styJe, then try the other
method, expecting the same result. Both methods will be
used here, to conflrm the accuracy of the calculation.
311
LATHE CYCLES
=
Method
Using Similar
I,
First, calculate
<1ltlcerence i between the two known
diameters, as per drawing:
i
= (4 - 2.25) I 2
0.875
therefore, the ratio of v~, ... , ..,
I
I 2.7 = i
will be
101.75
/ 2.5
We know i to be 0.875, so the relations can
by filling in the known ammmt:
I / 2.7 = 0.875 / 2.5
""m~~_
I :::: (0.875 x 2.7) / 2.5
I :::: 0.945
... is Jhe required alYlQunl!or programming
=
Figure 35-8
Example of G90 cycle used on 8 taper to a shoufder - 03504
Using Trigonometric Method
The second method of
I amount requires
trigonometry. At this point, it is known
I
::::
Using the
pered cut
a
can be used in this case as
a tathe machining
shoulder. A single G90
but could result in some ex(too much or too little stock).
aOltlroach is to use two modes of the cycle - one
","",,,IT'''''
tapered roughing.
2.7 x tan a
and the tangent value has to
amount of I can be calculated
Similar to the "'''''''''''' ~n'.... u."x"'. the I taper amount has to
be calculated,
of similar triangles as
fore. TIle height i
triangle over the length of
2.5 is calculated as one
difference between the
02.750 and the 01
2.7 x 0.35
0 . 945
... is the required amowllfor programming
i
tan a ::::: i / 2.5
tan a :::: 0.875 / 2.5
tan a ::::: 0.350
I
I
3.50 ------.-;
both cases) the calculations have the same
.LlllJ.Jll"'E accw:acy ofthe process.
I amount \"'d.LI~Ul<:IUUI
Figure 35-6 and detailed in Figure
is the fmal result - five cuts with 0.03 ",-:"l'{."
03503
TAPER 'I't.JRNrnG EXAMPLE 1 -
w/0. 03 X-STOCK)
Nl G20
N2 T0100 M41
N3 G96 S450 M03
N4 GOO X4.2 ZO.l T010l M08
N5 G90 X3 752 Z-2.6 I-0.945 FO.Ol
N6 X3.374
(1)
(4)
(5)
(CLEAR PeS )
NlO GOO XlO.0 Z2.0 T0100 MD9
(END
OF ROUGHING)
Nll MOl
• Straight and Taper Cutting Example
v",,'''~t'''\M of a taper is also common in
35-8 shows another
and a shoulder.
= 2.75 - 1.75 / 2
= 0.500
For the extended
0.005 stock amount is
at the shoulder for DnlS.O:lDg and
is extended by
0.100 at the front
of 2.595:
2.5 - 0.005 + 0.100 = 2.595
nal
I amount can now be calculated, based on the origithe extended values:
I / 2.595 = 0.500 / 2.5
(3)
N"J X2 996
N8 X2.618
N9 X2.24
i
I
I
:=
:=
(0.500 x 2.595) / 2.5
0.519
... negaiive direclion
For roughing, a 0.030
X
which is 0.060 on dlalIDt:~ter
side along the
to select a
In roughing operations, it is
as the cutsuitable depth of cut, with safety
selection
conditions. In this example,
will benefit from one simple ·ogJ:amm.ulg teclmique. If
of cut is selected
last depth will be
"'''''A''''V is left to cut. A
a calculated
n1.lI'!lnl~r of equal cuts - Figure
312
Chapter 35
----
0
I.()
0')
("")
(!)
~
..-,
N
N
N
G94 - FACE CUTTING CYCLE
I.()
(!)
i'-
0,
N
--~--~---------------~
..00
NN
0.865---- 0.865 --!-0.865
,
/START
.•I ~ X4 . 100
. ; -X3.778
X3.456
X3.134
.- X2.812
X2.466
X2.120
X1.774
I
L.
0.173
0.1-73
0.173
C-
Figure 35-9
A cycle that is very similar to 090 is another simple turning cycle, programmed with the G94 command, This cycle
is called the face cutting cycle. The purpose of C,g4 cycle is
[0 remove excessive stock between the start position of the
cutting tool and the coordinates specified by the X and Z
axes. The resulting cut is a slTaight turning cut, normally
pelpendicular to the spindle center line. In this cycle, it is
the X axis that is the main CUlling direction. The 094 cycle
is used primarily for facing cuts and can be used for simple
vertical taper cutting as well. similar to the 090 cycle.
The G94 cycle is logically identical to the G9a cycle,
except the emphasis is on the X axis cutting,
rather than the Z axis cutting.
Depth of cut calculation for program example 03504
For the ca1cul ation, aillha! is required is to divide the dislance per each side by the number of required cuts. The result wlll be an equal depth of cut for the whole roughing operation. If Ihe cutting depth is LOa smal! or too large, JUSl
recalculate it wilh a different number of CUIS. Knowing
what is a suitable depth of cut is a machining knowledge,
expected from CNC programmers.
As the cycle description suggests, the 094 is normally
used to perform a rough face-off of the part, towards the
spindle center line or to face-off a shoulder.
• Cycle Format
Similar to all cycle, lhe face culting cycle 094 also has a
predetermined programming format. For straight facing.
the cycle fonnat is:
In Figure 35·9, there are four cuts of .161 for the slraight
roughing and three cuts of .173 for Lhe tapered cutting. All
slack allowances are in effect.
G94 X(U) .. Z(W) .. F..
For tapered turning, the cycle format is:
The program 03504 will usc the calculations:
G94 X(U)" Z(W) .. K.. F..
03504
(G90 TAPER TURNING EXAMPLE - 2)
N1 G20
N2 TOlOO M41
N3 G96 S450 M03
N4 GOO X4.1 ZO.l TOI01 MOS
N5 G90 X).778 Z-2.495 FO.Ol
(START)
(STRAIGHT 1)
N6 X3.456
(STRAIGHT 2)
N7 X3.134
(STRAIGHT 3)
N8 X2. 812
(STRAIGHT 4)
N9 GOO X3. 0
(CHANGE STRAIGHT TO TAPERED)
mo G90 X2.B12 Z-O.765 I-O.173
(TAPERED 1)
The axes X and Z are used for absolute programming, the
axes U and Ware used for incremental programming, and
lhe F address is the cutting feed rate. The K parameter. if
greater than zero, is used for taper culling along the vertical
direction. Figure 35-10 shows all programming parameters
and cutting steps, Apply lhe same process as for 090 cycle.
Nll Z-1.63 I-0.346
(TAPERED 2)
Nl2 Z-2.495 1-0.519
(TAPERED 3 - FINAL)
N13 GOO XIO.O Z2.0 TOIOO M09
(CLEAR PeS.)
Nl4 MOL
(END OF ROUGlITNG)
In a review, to calculate the amount of I or R parameter
used in 090 for the taper cUlling - ex/ernal or intemal. use
[he following formula:
[
........................
_ ............
I (R) =
SMALLER DIA - LARGER DIA
2
G94 - STRAIGHT
G94 - TAPERED
Figure 35·10
The rcsult will also include thc sign of fhe J amount.
G94 turning cycle structure· straight and tapered application
LATHE
313
MULTIPLE REPETITIVE CYCLES
• Cycle format Types
Each cycle is governed by very
do's and don'rs. The f ollowi
them In detail, except the
be covered separately in Chapter
etc, sj
are used for contouring. Tool nose
applied, if applicable to
Mulliple
as
quire a computer memory in order to
NC machines controlled by a punched
from them. Tn tape operation,
codes sequentially, in a forward
control. on the other hand, is
more
evaluate and process information
both directions, forwards
can process mathematical
of a second, simplifying the
of
which will
An important fael (0 Lake a n01e of, is Ihal
programming for these cycles,
method
different for the lower level
very popular OT or {he 16/18120/21T
higher level, such as the 1011 IT Or the I
cycles. if they are available for the
require their programming formal in twO blocks. not the normalone block. Check the parameter
conlrol, (0 find about compatibility
both
formals is also Included in this chapler.
•
Cutting Cycles and Part Contour
Probably the mOSI common multiple
in
turning and bor~ng are those thai are used for profile cutting
or coJJtou/, cultmg. There are three
available within
the roughing category:
o
G71,
and G73
• General Description
and olle cycle is available for rllli~liing:
In total. there are seven multiple r"r",l>nih,,'"
o
able, identified by a nY-F'n",'"''
G70
finishing cycle is designed to finish profile
by allY one of the three roughing cycles.
Profile cutting cycles - Roughing:
In some respects, Ihere is an interesting situation in promultiple repetitive cycles. So far, the emphasis
,vas 10 program roughing cuts before finishing cuts. 111is
approach
perfect sense - it is also the only logical
from the lechnological point of view. Don't be surprised if Ihis 'rule' is suddenly broken when com pUler
G71
G72
G73
rules and has its
Pauern repealing
lake over.
implication here is (hal when
the
multiple repetilive roughing cycles,
contOllr musl always be defil1edfirst, then its
elm appllcd to the roughingcyperhaps, Wh~n working with
easy to see that it is actually
although hardly a re-
Profile cutting cycles· Finishing:
Finishing cycle for 071. 072 nnd 07J
Chipbreaking cycles:
G74
Peck drilling cycle
in Z axis - horizontal
G75
Peck grooving cycle
in X axis - verticill
Threading cycle:
The G76 threading cycle is described separately and In
sufficient detail in Chapter 38.
•
Chipbreaking Cycles
314
Chapter 35
CYCLES
CONTOUR
(contouring cycles), are
lalhe programming. They
anrl internal (horing) maleany machinable contour.
•
Boundary Definition
The roughing cycles are
boundaries, typically
is (he outline of
blank,
on the detinition of two
material boundary, which
the
boundary, which is
(he outline of the pan conlour,
is not a new concepl at
all, several
programming
were using this
method, such as the Compact JI, a
based
system of the I
• Start Point and the Points P and 0.
The poinL A in the illustration is
fi Ie cuui ng cycle. It can be
Typically,
SlarL point will
where the rough cuuing begins. It is
start point very carefully.
it is more
point', In fact. this special
ances and the actual depth of
The generic points Band C in the last
come points P and Q in the
Point P represents the block number of
the first Xl coordinate of the finished contour.
The two defined boundaries create a
!h,:\l defines the
the material is removed in an
tied machining paramcters in thc
Mathematically, the minimum
define an area is Lhree. These lhree
(meaning not on the same line),
pie boundary wiLh only
Point Q represents the block number of
last Xl coordinate of the finished contour.
Olher in-depth considerations relating to (he P and Q
boundary poinrs are equally important, and there are quite a
few of (hem:
sisLing or many points,
D
- -
c
~----------
>~!
Part bou~dary
~
Roughing area
by
three points only
1/
f
I
,
I
B
material removal defined by the starting point and
D
nose radius offset should not be included between
the P and a points, but programmed before the cycle is
called, usually during the motion to the start point.
D
For roughing, the material to be machined will be divided
into a
of
cuts. Each roughing cycle
""'I"'nte a number of user ""r'I-'"<''''
o
The tool motion 1)!'![Wflfm
Roughing area
defined by more
than three points
Figure 35-1 7
Material and part boundaries as applied to turning
A number of points may be defined between the P and a
representing the XZ coordinates of the f.n,e,h<:>1i
contour. The contour is programmed using GOL G02,
and G03 tool motions, including teed rates.
the p.Q contour must include all necessary clearances.
_ .- Material
--------:..--.,A/'
Part boundary
[J
rlQ4tu'I':'1"I
B
c
will
must be
steadily ",.,""., ....."""
In the profile cutting cycles. each poinl represents a
position and the POllltS A, B, and C represent the extreme
corners of the selected (defined) machining area,
material boundal), is nOt actually defined, it is only
impl
It is between points A and S, and point~ A and C.
Material boundary can not contaill any other points; it must
a straight line, but not always a line parallel [Q an
is defined between
B
C,
between. For CNC
used rather
"''''.\A, ....." P and Q points is allowed
is available and programmed, and then
. see the next section for
nlr.orT,,'m
Inane
D
Blocks
coordinate of the
contour and the
of the contour a,
must have a sequence number N, not duplicated
:>n\,f\hln,<>r<> else in the program.
<
•
I AND TYPE II CYCLES
In the initial versions of the contour cutting cycles, a
of the contouring direclion into the Opposile direction
one axis was not allowed. That limited these cyto some extent, because common undercuts or recesses
were nol possible [0 use in the
yellhey were common m
shops.
Presently, {his older
is
modern controls use
ware features and the
lowed. This newer method
more programming flexibi
cavities (undercuts). Figure
and shows a disallowed contour
to
I external cutting
a cycle. The example
cycle, but can be modified for any internal cutting.
TYPE I CYCLE
... is roughed out
in a single depth
315
«---_._-Programming Type I and Type If
system supports
boring cycles, it also
II
for some special
not replaced one type
JI. Of course. the question is
the two lypes in the
is in the contents
follows the cycle call:
o
o
.,. only one axis is
II
'" two axes are
I:
a7l U .. R ..
P10 Q •. U •. W•. F •. S ••
mo GOO X..
(ONE AXIS FOR TYPE I)
an
Q Example· Type II :
G71 U •. R •.
Gn P10 Q •• U .• W•• F •• S ••
NlO GOO X.. Z..
('!WO AXES FOR TYPE II)
TYPE II CYC
... is roughed out
in several depths
BI-DIRECTIONAL
... contour
is not allowed
Figure 35·12
Comparison of Type land
. bi·directional change
Type 1 allows a
increasing profile (for
cutting) or steadily decreasing profile (for'
from U1e point P to
point Q (typical cutting directions).
On older conlrcls,
X or Z direction is not allowed.
an undercut to be machi
with
Modern controls
Type I, but the
will be done with a single
That
metal removal in
which lype Ihe
supports.
may be
'O..i";';:"U
Type l! allows a continually increasing profile or
ally decreasing
from the point P to
change into the
direction is allowed
axis only,
on
active cycle.
of an undercut will a multiple 1001 path.
Type lor Type 11 is applicable to the cycle, by
both axes in the block represented by Ihe P
This
lypically
block immediately following. the cycle call in
the
I, G72, elc.).
Iflhere is no motion
Z axis in the first
11
is still required.
fer the cycle call and
program WO as the "",""'11
• Cycle Formatting
On the next few
is a description of the six
It is important to understand
cycles. covered in
format of each cycle as it applies 10 a particular
Several Fanuc conlrol
are available and for
of programming
multiple repelitive
can be
into two groups:
o
Fanuc
o
Fanuc system
21T
1ST
". tower/eve!
level
Practically, il only means a change in the
programmed, but the
is also important
some incompatibility
Note that the tool function
oflhe examples, although it IS also
T is not specified in
allowed as a
in all multiple repetitive
Its
only need maybe
a tool offset change.
G71 - STOCK REMOVAL IN TURNING
The most common roughing cycle is 071. Its
to remove
horizontal cutting, primarily
Z axis,
the right to the left. It is
roughing oUi
OUl of a solid cylinder.
cles, it romes in two formats - {\ one-block
block formal.
on the conlrol
all cy-
316
Chapter 35
• G71 Cycle Format - 10T/11 T/15T
RO.125
The one-block format for the G7 J cycle is:
03.0
G71 P.. Q.. 1.. K.. U.. W.. D.. F.. 5 ..
02.500
-02.250
..".....".....,....-.. ,--.. . . . . . 02.000
~ where ...
<
p
0
= The first block nu mber of the fin ishi ng profile
I
=:
K
=
U
W
0
F
=::
=
=
S
The last block number ofthe finishing profile
Distance and direction of rough
semifinishing in the X axis - per side
Distance and direction of Tough
semifinishing in the Z axis
Stock amount for finishing on the Xaxis diameter
Stock left for finishing on the Z axis
The depth of roughing cut
Cutting feed rate (in/rev or mm/rev) overrides
feed rates between the P block and the Q block
Spindle speed ~ft!min or m/min) overrides spindle
speeds between the P block and the Q block
................
o
o
1.0
0
1.0
N
~.....
0
1.0
,.......
0
01.250
i-- 00.625
00.875
"c········
RO.
0
I.()
1.0
0
CHAMFERS 0.05 x 45° - CORE 09/16
Figure 35-13
The I and K parameters. are not available on alJ machines.
They conlrol lhe amount of cuI for semifinishing, the last
continuous cut before final roughing motions.
• G71 Cycle format - OT/16T/18T/20T/21 T
If thc control requires a double block entry for the G71
cycle, the programming format is:
G71 U.. R..
G71 P.. Q.. U.. W.. F.. 5 ..
IB.T' where ...
First block:
U
R
= The depth of roughing cut
=
Amount of retract from each cut
Second block:
P
The first block number of the finishing profile
The last block number of the finishing profile
Stock amount for finishing on the X axis diameter
W = Stock leftforfinishing on the Z axis
f ::: Cutting feedrate (in/rev or mm/rev) overrides
feedrates between the P block and the Q block
S == Spindle speed (ftJmin or m/min) overrides spindle
speeds between the P block and the Q block
Q
U
:;;;;;
Do not confuse the U in the iirst block, depth of cut per
side, and the U in the second block, stock lefl on diameter.
The rand K parameters may be used only on some controls
and the retract amount R is sel by a system parameter.
The external and inlernal usc of the G71 cycle will use the
drawing data in Figure 35-/3.
Drawing example to illustrate G7l rQughing cycle - program 03505
•
G71 for External Roughing
The slack material in the example has an existing hole of
09/16 (.5625). For external CUlling of this part, a standard
80 0 tool will be used for a single cut on the face, as well as
for roughing the ouler shape.
Program 03505 covers these operations.
03505
(G71 ROUGHING CYCLE - ROUGHING ONLY)
Nl G20
N2 TOIOO M41
(OD ROUGHING TOOL + GEAR)
N3 G96 S450 Me3
(SPEED FOR ROUGH TURNING)
N4 GOO G4l X3.2 ZO TOlOl MOe (START FOR FACE)
N5 GOI XO.36
(END OF FACE DIA)
N6 GO 0 ZO. 1
(CLEAR OFF FACE)
N7 G42 X3.l
(START POSITION FOR CYCLE)
NS G7l P9 017 UO.06 WO.004 D1250 FO.Ol4
N9 GOO Xl.7
(P POINT = START OF CONTOUR)
mo GOI X2.0 Z-O.OS FO.OOS
Nll Z-O. 4 FO. 01
Nl2 X2.25
N13 X2.5 Z-O.6
Nl4 Z-O.87S RO.12S
NJ.S X2. 9
NJ.6 GOI X3.05 Z-O.95
Nl7 UO.2 FO.02
(0 POINT = END OF mN'TOUR)
Nl8 GOO G40 XS.O Z6.0 TOlOO
Nl9 MOl
The external roughing bas been completed at thiS point in
the program and the internal roughing can be programmed
for the next tool. In all examples that include a 1001 change
between a short tool (such as a turning tool) and a long tool
(such as a boring bar), it is important to move the short tool
Curther from the front face. The motion should be far
enough to accommodate the incoming long tool. The clearance is 6.0 in the above example (block N18 with Z6.0).
LATHE CYCLES
•
317
G71 for Internal Roughing
Cutting direction
The face has been done with the previous 1001 and the
roughing horing bar can conlinue the machining:
I
1
1
mo T0300
(In ROUGHING TOOL)
N21 G96 8400 M03
(SPEED FOR ROUGH BORING)
N22 GOO G41 XO.S ZO.1 T0303 MOS
(START pas.)
N23 G71 P24 Q31 U-O.06 WO.004 01000 FO.012
N24 GOO Xl.5S
(p POINT '" START OF CONTOUR)
N25 GOl Xl.2S Z-O.05 FO.004
N26 Z-O.55 R-O.l FO.OOB
N27 XO.875 K-O.OS
N2B Z-O.75
N29 XO.625 Z-1.2S
N30 Z-l. 55
N31 U-O. 2 FO. 02
(Q POINT
END OF CONTOUR)
N32 GOO 040 X5.0 Z2.0 T0300
N33 MOl
The part has been completely roughed out. leaving only
the req uired stock on diameters and faces or shoulders. Fi 11ishing with the G70 cycle, described laler, is possible wilh
(he same 1001, if lolerances and/or surface finlsh arc nOlloo
crilicaL Otherwise, another 1001 or 1001s will be required in
the same program, after a Lool change.
At 11m stage, evaluate what has been done and why.
Many principles Ihat applied to the example are very common 10 other operalions that also use the mUltiple repetitive
cycles. It is important 10 learn them weI! allhis point.
•
Direction of Cutti ng in G71
The last programming example 03505, shows Ihal G71
can be used for roughing externally or infernally. There are
two important differences:
o
Start point relative to the P point (SP to P versus P to SP)
o
Sign oi the U address for stock allowance on diameter
The control system will process the cycle for external
cUlling, if the X direclion from Ihe starl pain! SP 10 lhe
point P is !legal il'e. In the example, the X slart poi nt is X3. I,
the P point is X 1.7. The X direction is negalive or decreasing and an eXlernal cUlling will take place.
The control syslem wi II process the cycle for internal cutling, if (he X direction from stan point SP to Ihe point Pis
posiTive. In the example, the X start puinl is XO.5, the P
point is XJ.55. The X direction is positive or increasing,
and an internal culling will take place.
Figure 35-14 illustrates the concept of G71 cycle, as applied to both,
::Inc! intern::!l cU!ling
By (he way, although the sign of the stock U value is very
important ror the final size of the part, it does lIot determine
the mode of cUlling. This concludes the section relating to
the G71 multiple repetitive cycle. The face roughing cycle
Gn is similar, and is described next.
J
----, :::i"P
I
SP to P direction
is negative for
external cutting
t
P
p
/
'" _...
-----------~.§E
SP to P direction
is positive for
external cutting
- Cutting direction
Q ,
Figure 35-14
External and internal CUl1ing in G71 cycle
G12 - STOCK REMOVAL IN fACING
111C Gn cycle is identical in every respect to the G71 cycle, excep[ the stock is removed mainly by vertical culting
(facing), lypically from (he large diameter towards the
spindle center line XO. II is used for roughing of a solid cylinder, using a series of vertical cuts (face culS). Like all
olher cycles In Ihis group. It COllies in two formats - a one
block and a double block formal, depending on Ihe control
system. Compare G72 with the G71 structure on examples
in this chapter.
• G72 Cycle Format ~ 101/111/151
The one-block programming formal for the G72 cycle is:
G72 P.. Q.. I.. K.. U.. W.. D.. F.. S..
~ where ...
P
= The first block number of the finishing profile
Q
The last block number of the finishing profile
I
Distance and direction of rough semifinishing
in the X axis - per side
Distance and direction of rough
semifinishing in the Z axis
Stock amount for finishing on the X axis diameter
Stock left for finishing on the Z axis
The depth of roughing cllt
Cutting ieedrate (in/rev or mm/rev) overrides
feedrates between the P block and the Q block
Spindle speed ~ft/min or m/min) overrides spindle
speeds between the P block and the Q block
K
U
W
o
F
S
The meaning of each address is (he same as rar the G71
cycle. The I and K parameters are nOI available on ail
machines. These parameters conlrol (he amount of cut for
semifinishing, which is the last continuous cut before final
roughing motions are completed.
318
Chapter 35
+ G72 Cycle Format - OTj16T/1 BT/20T/21T
If the control system requires a double block enlry for lbe
G72 cycle, the programming formal is:
G72 W.. R..
G72 P.. Q .. U.. W.. F.. 5 ..
03506 (G72 ROUGHING CYCLE - ROUGHING ONLY)
m G20
N2 T0100 M41
(OD FACING TOOL + GEAR)
NO G96 8450 M03
(SPEED FOR ROUGH FACING)
N4 GOO G4l X6.2S ZO.3 T010l MOB
(START POS.)
N5 G72 P6 Q12 UO.06 WO.03 D1250 FO.014
N6 GOO z-O.87S
(p-POINT :::: START OF CONTOUR)
N7 GOl X6.05 FO.02
N8 XS.9 z-o.a FO.ooa
Ia" where ...
N9 X2. 5
mo n.s ZO
First block:
W
R
= The depth of roughing cut
= Amount of retract from each cut
Second block:
p
= The first block number of the finishing profile
== The last block number of the finishing profile
Stock amount for finishing on the X axis diameter
W = Stock left for finishing on the Z axis
Cutting feedrate (in/rev or mm/rev) overrides
F
feedrates between the P block and the Q block
Spindle speed (ftlmin or m/min) overrides spindle
S
speeds between the P block and the Q block
Q
Nll XO.55
Nl2 WO.1 FO. 02
(Q-POINT :::: END OF aJNTOUR)
Nl3 GOO G40 XS.O Z3.0 TOlOO
Nl4 MOl
The concept of G72 cycle is illustrated in Figure 35-16.
Note the posicion or (he poinl P as it relales lo Ihe start puinc
SP and compare it with Ihe G7) cycle.
U
,
,
I
I
I . Cutting direction
I
1n the G7 J cycle for the doubJe block definition, rhere
were two addresses U. In the 072 double block definition
cycle, !.here are two addresses W. Make sure you do not
confuse the W in the first block - depth of cut (actually il is
a 'width of cut), and the W in the second block - stock left on
faces. The I and K paramelers may be available, depending
on the control.
f
I
I
l
I
I
I
Q
An example program 0350() for the G72 cycle uses the
drawi ng data in Figure 35- J5.
a
a
co
a
CHAMFER 0.05 x 45°
-06.0
- - 0.25 FACE STOCK
- 02.500
·01500
03/4 CORE
,~.Q.i
Figure 35-15
Drawing example to illustrate G72 roughing cycfe - program 03506
10 lhis facing application, all the main data will be reversed by 90". because the cut will be segmented along the
X axis. Roughing program using the Gn cycle is logically
similar to the G71 cycle:
Figure 35-16
Basic concept of G72 mUltiple repetitive cycle
G13 - PATTERN REPEATING CYCLE
The pattern repeating cycle is also called the Closed Loop
or a Profile Copying cycle. lIS purpose is to minimize the
CUlling lime for roughing material of irregular shapes and
forms, for example, forgings and ca..c;tings.
+ 673 Cycle Format -10Tj11Tj15T
The one-block programming format for Gn cycle IS
similar to (he G71 and G72 cycles:
G73 P.. Q.. 1.. K.. U.. W.. D.. F.. S..
IQj" where ...
P
=:::
Q
1
K
U
=:
=:
The first block number of the finishing profile
The last block number of the finishing profile
Xaxis distance and direction of relief - per side
Z axis distance and direction of relief
Stock amount tor finishing on the X axis diameter
319
w
o
left for
on the Z axis
The number of
divisions
Cutting feedrate !in/rev or mm/rev) overrides
feed rates between the P block and the Q block
F
s
important input parameters in the G73
One pClJameter seems to be missing - there
cut specification.! Tn the G73 cycle, it is not
actual depth of cut is calculated au[omatically,
Spindle speed (ft/min or m/minl overrides spindle
between the P block and the Q block
•
Cycle Format OT/16T/18T/20Tj21T
w
control
requires a double block entry
cycle, the programming format is:
parameters:
o I ... amount of
material to remove in the X
oK ... amount of
material to remove in the Z axis
o D ...
this
u =
X axis distance and direction of relief· per
W
Z axis distance and direction of relief
The number of cutting divisions
In the example, the largest expected material amount per
will be chosen as .200 (10.2) and the
Second block:
The first block number of the finishing
The last block number of the finishing profile
Stock amount for finishing on the X axis
Stock left for finishing on the Z
Cutting feedrate (in/rev or mm/rev) CHI<>"""'"
feed rates between the P block and the Q
Spindle speed {ftlmin or m/min} overrides spindle
speeds between the P block and the Q block
S
In the two-block cycle entries, do nOI
up
the firs! block thal repeat in the second block (U
the
example). They have a different
•
repeating cycle G73
35-17.
material amount on the face as .300 (KO.3).
divisions could be either two or three, so the r-\rr,,,r·,\rn
use D3. Some modification on the control
during actual setup or machining, .... ~I"/v".~,
exact condition and sizes of the
or
This cycle IS suitable for roughing contours where the
finish contour closely matches the contour
the
forging. Even if there is some
this
be more efficient than the selection of
J or
cyThe program 03507
and finishing
with Ihe same tool (as an example):
03507 (G73 PATTERN REPEATING CYCLE)
Nl G20 M42
G7J Example of Pattern Repeating
uses the
In
N2 T0100
N3 G96 S350 M03
N4 GOO G42 X3.0 ZO.l TOlOl MUS
NS G73 P6 Q13 IO.2 KO.3 UO.06 WO.004 D3 FO.Ol
N6 GOO XO.35
N7 GOl Xl.OS Z-O.25
N8 Z-O.62S
N9 Xl. 55 Z-l. 0
N10 Z-1.625 RQ.2S
Nll X2.4S
N12 X2.75 Z-1.95
N13 UO.2 FO.02
Nl4 G70 P6 Q13 FO.006
N15 GOO G40 XS.O Z2.0 T0100
Nl6 MJO
%
01.050
00.550
Figure 35-17
Pattern repeating cycle 673 program
can
with a reasonable efficiency, but some 'air'
an unwanted side effect for odd shaped
First block:
P
Q =
U -=W
F
with care - its
amount rough stock to be rprnr\'''IU!
Z axes. That is not the typical
castings, where the stock varies all over
the illustration in Figure 37·17.
~ where ...
R
of cutting 111\11<:1(\1'" or number of
03507
320
- - - -. --------
A
. . . . . . .,
,
B'--
,
Chapter 35
For safety, use the same start point for G70
as for the roughing cycles.
A
'1
The earlier roughing progTam 03505, using the G71 repetitive cycle for rough turning and rough boring, can be
compleled by using another IWO tools, one for external. one
for internal finishing lool path:
(03505 CONTINUED ... )
A
N34 TOSOO M42
(00 FINISHING TOOL + GEAR)
N35 G96 5530 M03
(SPEED FOR FINISH TURNING)
N36 G42 X3.1 ZO.l TOSOS MOS
(START POS.)
N37 G70 P9 Q17
(FINISHING CYCLE - OD)
N18 GOO G40 XS.O Z6.0 TOSOO
N39 MOl
=1+ U/2
B= K+W
Figure 35·18
Schematic representation of 673 cvcle
Note that (he pallern repealing cycle does exactly thaI - it
repeals (he machining contour (pattern) specified between
the P and Q points. Each Indlvidual 1001 path IS offset by a
calculated amount along the X and Z axes. On the machine.
watch the progress with care - particularly for the firsllool
path. Feedrate override may come useful here.
G10 - CONTO
ING CYCLE
The last of the contouring cycles is G70. Although il has a
smaller G number than any of the three roughing cydes
G71, G72 and Gn, the !imshing cycle G70 is normally
used after anyone of these three rough ing cycles. As ils description suggesls, it is siriclly usedJor the finishing CUf oja
previously defined conrow:
•
G70 Cycle Format· All Controls
For this cycle, there is no difference in the programming
rormal for various controls - il is all the same, and the cycle
call is a one-block command.
The programming format for G70 cycle is:
trIir where .. "
P
Q
F
S
;;=
The first block number of the finishing profile
The last block number of the finishing profile
Cutting feedrate (in/rev or mm/rev)
Spindle speed (ft/min or m/min)
The cycle G70 acceplS a previously defined finishing
contour from either or the three roughing cycles. already
described. This finishing contour is defined by the P and
Ihe Q points of Ihe respective cycles. and is normally repealed in the G70 cycle. allhough It can change.
N40 T0700
(In FINISHING TOOL)
N41 G96 S47S M03
(SPEED FOR ROUGH BORING)
N42 GOO G41 XO.S ZO.l T0707 MOS
(START POS.)
N43 G70 P24 Q31
(FINISHING CYCLE - ID)
N44 GOO G40 XS.O Z2.0 T0700
(END OF PROGRAM)
N45 M30
%
Even for the ex ternal Ii nishing. the cutting tool is still programmed 10 start above the original stock diameter and off
the from face, although all roughing morions have already
been completed. A similar approach applies to the internal
cut. For safely reasons, this is a recommend praclice.
There are no feed rates program med for the G70 cycle, although the cycle formal accepts a feedratc. The defined
block segments Pta Q for Ihe roughing 1001 already include
feedratcs. These progmmmed feedrates will be ignored in
the roughing mode and will become aClive only for the G70
cycle, duri ng fi nishi ng. If Ihe fi n ish conlour did not include
;:lny feerir:1tes, lhr:n progrllm rI comm(!fljeedmle for l~nish­
ing all contours during the G70 cycle processing. For example, program block
N17 G70 P9 Q17 FO.007
will be a waste of time, since the .007 in/rev feedra\e will
never be used. It will be overridden by the feedrate defined
between blocks N9 and N 17 of program 03505). On the
Olher hand. if [here is no feedratc programmed for the finishing contour al all, then
N ..
G70 P .. Q .. FO.007
will use .007 in/rev exclusively for the finishing tool path.
The same logic described ror G7 t cycle, appl ies eq ually
La Ihe G72 cycle. The roughing program 03506, using the
G72 cycle for rough turning of Ihe pan face, can be completed by using another external lool for finishing euls
uSing Ihe G70 cycle:
LATHE CYCLES
321
G14 - PECK DRILLING CYCLE
(03506 CONTINUED ... )
N15 TOSOO M42
N16 G96 5500 M03
(00 FACING TOOL + GEAR)
(SPEED FOR FINISH FACING)
Nl7 GOO G41 X6.2S ZO.3 TOSOS M08
N1e G70 P6 Q12
(START POS.)
(FINISHING CYCLE)
Nl9 GOO G40 X8.0 Z3.0 TOSOO
mo M30
%
The rules mentioned earlier also apply for the contour
finishing defined by the G72 cycle. Program 03507, using
the G73 cycle, can be aJso be programmed by using another
external Lool for finishing, applying the same rules.
BASIC RULES FOR G10-G13 CYCLES
In order 10 make the multiple repetitive stock removal cycles (contouring cycles) work properly and efficiently, observing the rules of their use is very important. Often a
small oversight may cause a lengthy delay.
The G74 cycle is one of two cycles usually used for non
finishing work. Along with G75 cycle. it is used for machining an interrupted cm, such as chips breaking during a
long CUlling moLion. C74 cycle is used along rhe Z axis.
This is [he cycle commonly used for an interrupted CUl
along the Zaxis. The name of the cycle is Peck Drilling Cycle, similar 10 the G73 peck drilling cycle, used for machining centers. FOr Ihe lathe work, G74 cycle application is a
lillie more versatile than for its G73 equivalent on machining centers. Although its main purpose may be applied towards peck drilling, Ihe cycle can be used with equal
eftlciency for interrupted eUls in turning and boring (for example, in some very hard materials), deep face grooving,
difficull part-off machining. and many other applications.
• G74 Cycle Format - 10Tj11Tj15T
The one-block programming format for G74 cycle is:
Here are Ihe most important rules and observations:
o
Always apply tool nose radius oHset
before the stock removal cycle is called
o Always cancel tool nose radius offset
after the stock removal cycle is completed
o
Return motion to the start point is automatic,
and must not be programmed
o
Th e P bloc k in G71 should not include
the Z axis value (Z or W) for cycle Type I
o
Change of direction is allowed only for Type II
G71 cycle, and along one axis only (WO)
o
Stock allowance U is programmed on a diameter,
and its sign shows to which side of the stock it is to
be applied (sign is the direction in X, to or from the
spindle centerline)
G74 X.. (U .. ) Z.. (W .. ) 1.. K.. D.. F.. S..
!Gf where ...
X(U)
=
Z(W)
I
=
K
D
F
S
o
D address does not use decimal point, and must be
programmed for leading zero suppression format:
The two-block programming format for G74 cycle is:
G74 R..
G74 X.. (U .. } Z.. (W .. ) P.. Q .. R.. F.. S..
Il..-:W where .,.
First block:
R
D0750 or D750 is equivalent to .0750 depth
Only some control systems do allow a decimal point
to be used for the D address (depth of cut)
in G71 and G72 cycles.
=:
• G74 Cycle Format - OTj16Tj18Tj20Tj21T
o Feedrate programmed for the finishing contour
(specified between the P and Q points) will be
ignored during roughing
;:::
Final groove diameter to be cut
Z position of the last peck - depth of hole
Depth of each cut (no sign)
Distance of each peck (no sign)
Relief amount at the end of cut
(must be zero for face grooving)
Groove cutting feedrate (in/rev or mm/rev)
Spindle speed (ft/min or m/min)
=:
Return amount (clearance for each cut)
Second block:
X(U)
=:::
Z(W)
p
Q
==
R
=
F
S
=
Final groove diameter to be cut
Z position of the last peck (depth of hole)
Depth of each cut (no sign)
Distance of each peck (no sign)
Relief amount at the end of cut
(must be zero for face grooving)
Groove cutting feed rate (in/rev or mm/rev)
Spindle speed (ft/min or m/min)
322
Chapter
If both the X(U) and I (or P) are omitted in
machining is along the Z axis only (peck
cal
drilling operation, only the Z, K
programmed - see Figure 35·19.
= Depth of each cut (no sign)
I
the
K
arc
II"T~,n ..... oerwelm grooves (no sign)
(for multiple
only)
Relief amount at the end of cut
zero or not used forface groove)
Groove cutting feedrate lin/rev or mm/rev)
Spindle
1ft/min or m/minl
D
F
S
K - - K --,
• G75 Cycle format - OTj16Tj18Tj20Tj21T
ng fomlal for G75
The two-block
z
35-19
Schematic format for 674 cvcle example
~ where ...
First block:
The followmg program example il
cycle:
R
03507 (G74 PECK DRILLING)
N1 G20
N2 T0200
N3 G91 51200 MO)
N4 GOO XO ZO.2 T0202 MOB
NS G74 Z-3.0 KO.S FO.012
N6 GOO X6.0 Z2.0 T0200
N1 M30
block:
IN RPM)
POSITION)
(PECK DRILLING)
POSITION)
X{U)
(END OF PROGRAM)
R
Z(WJ
P
S
A
075
simple, non
cle, il is used for
of two lathe cycles available
''''''rr\J.'r with the G74 cy-
example for break
or
an inten'upted cuI, for
designed 10 break
axis - used mainly
Il? where ...
Z(W) =
diameter to be cut
of the last groove
(for multiple grooves only)
Z
will
in {he
nOles are common to both
o
a
grooving operation. The
cycle is identical to G74, except the X axis is replaced with the Z axis.
G75 Cycle format - 10Tj11TjlST
example of G75
the
BASIC RULES fOR G14 AND G75 CYCLES
motion. C75 cycle is
XIU)
=::
Depth of each cut (no sign)
Distance between grooves (no sign)
Relief amount at the end of cut
(must be zero for face grooving)
Groove cutting feedrate
(usually In/rev or mm/rev)
Spindle speed (usually ftlmin or m/minJ
the Z(W) and K (or Q) are
is along the X axis only
G15 * GROOVE CUTTING CYCLE
•
Zposition of the last groove
F
Drilling willtuke place to a
cremenls of one half of an
peck is calculated from
an interrupted groove is
the
= Final groove diameter to be cut
Q
%
This is also a very 5i
during a rough cut
Return amount (clearance for each
In both
the X and Z values can be programmed
absolute or
mode.
o Both cycles allow an
o The relief amount at the end of cut can be
in that case It will be assumed as zero.
D
Return amount (clearance for
is only
programmable for the two-block method. Otherwise.
it is set by an internal parameter of the control system.
o
If the return amount is programmed (tINo-block method),
and the relief amount is also programmed, the
presence of X determines the
If the X value
is programmed, the Rvalue means
relief amount.
II
GROOVING ON LATHES
Groove cutting on CNC lalhes is a multi step machining
operation. The term grooving usually applies to a process
of forming a narrow cavity of a certain depth. on a cy]i nder,
cone, or a face of the part. 1l1e groove shape. or at least a
significant part of it, will be in the shape of the cUlling tool.
Grooving tools are also used for a variety of special machining operations.
The grooving tool is usually a carbide insert mounted in a
special tool holder, similar to any other tool. Designs of
grooving inserts vary, 1T0m a single tip, 10 an lnsert with
multiple lips. Inserts are manufactured !O nominal sizes.
Multi tip insert grooving tools are used (0 decrease costs
and increase prmJuclivity.
GROOVING OPERATIONS
The cutting tools for grooving are either external or internal and use a variety of inserls in different configuraeions.
The most important difference between grooving and turning is the direClion of cut. Turnmg lool can be applied for
culs in multiple directions, grooving tool is normally used
to cut in a single direction only. A notable exception is (1n
operation known as necking (relief grooving), which lakes
place at 45", where the angle of the cUlling insert and the
angJe of infeed must be identical (usually aI45°). There is
another applicalion of a two axis simultaneous motion in
grooving, a corner hreaking on the groove. Strictly speaking. this is a turmng operation. Ahhough a grooving tool is
not designed for turning, it can be used for some light machining, like cutting a small chamfer. During the corner
breaking cut 011 a groove, the amount of material removal is
always very small and the applied feed rate is normally low.
•
Main GroDving Applications
Groove is an essential pan of components machined on
CNC lathes. There are many kinds of grooves used in
industry. Most likeJy, programming will include many undercuts, clearance and recess grooves, oil grooves. etc.
Some of the main purposes of grooving are to allow two
components to fit face-Io-face (or shoulder-la-shoulder)
and. in case of lubrication grooves, to let oil or some other
lubricant to flow smoothly between two or more connecting parts. There arc also pulley or V-belt grooves thai are
used for belts to drive a motor. O-ring grooves are specially
designed for insertion of melt,1 or rubber rings, that serve as
stoppers or sealers. There are many other kinds of grooves.
Many industnes use grooves unique [0 [heir needs, mOst
others use the more general groove lypes.
•
Grooving Criteria
For a CNC programmer, grooving usually presents no
special difficulties. Some grooves may be easier to program than others, yet there could be several fairly complex
grooves found in various industries thaI may present a programming or machining challenge. In any case, before a
groove can be programmed, have a good look at lhe drawing specifications and do some overall evaluations. Many
grooves may appear on the same parI at different locations
and could benefit from a subprogram development. When
planning a program for grooving, evaluate the groove
carefully. In good planning, evaluate the selected groove by
al leasl lhree criteria:
o
Groove shape
o
Groove location on a part
o Groove dimensions and tolerances
Unfortunately, many grooves are not of the highest qualilY. Perhaps it is because many grooves do no! require high
precision and when a high precision groove has to be done,
the programmer does not know how to handle it properly.
Watch particularly for surface finish and tolerances.
GROOVE SHAPE
The first evalulltion before programming grooves is the
groove shape. The shape is determined by the part drawing
and corresponds to (he purpose of the groove. The groove
shape is the single most important factor when selecting the
grooving insert. A groove with sharp corners parallel to the
machine axes requires a square insert, a groove with radius
requires an insert having the same or smaller radius. Special purpose grooves, for example an angular groove shape,
will need an insert with the angles corresponding to the
groove angJes as given in the drawing. Formed grooves require inserlS shaped into the same form, etc. Some typical
shapes of grooving inserts are illustrated in Figure 36- J.
UUV~U[)u
Figure 36-1
Typical shapes of common grooving tools
323
324
Chapter 36
• Nominal Insert Size
In many groove ctllting operations, the groove width wIll
be greater than the largest available grooving insert of a
nominal size (i.e., off the shelf size). Nominal sizes are normally found in various tooling catalogues and typically
have widths 1ike I mm,2 mm, 3 mm or 1/32,3/64, 1/16, 1/8
in inches, and so on, depending on the units selected.
For example, a groove width of .276 inches can be cuI
with a nearest lower nominal insert width of .250 inch. In
such cases, the groove program has to include at least two
eulS - one or more roughing cUls, in addition to alleast one
finishing CUL Another grooving 1001 may be used for finishing, if the tolerances or excessive 100] wear make it more
practical - Figure 36-2.
Allhough some variations are possible, for practical purposes, only these three categories are considered. Each of
the three locations may be either e:rtemal or internal.
The two most common groove locations are on a cylinder, i,e.. on a straight outside - or exlemal- diameter, or on a
straight inside - or internal- diameter. Many other grooves
may be located on a face, on a taper (cone), even in a corner. The illustration in Figure 36-3 shows some lypical locations of various grooves.
....'
2
1
. LJ
,'
3
- --
Figure 36-3
Typical groove locations on a parr
Figure 36-2
CUI distribution for grooves wider than the insert
•
Insert Modification
Once in a while, programmers encounter a groove that requires a special insert in terms of its size or shape. There are
two options to consider. One js \0 have a custom made insert, if il is possible and practical. For a large number of
grooves, it may be a justi tied solution. The other alternative
is 10 modify an existing insert in-house.
Generally, in CNC programming, off-the-shelf tools and
inserts should be used as much as possible. In special cases.
however, a standard rool or insert can be modified 10 suil a
particular job. For grooving, it may be a small extension of
the insert cUlling deplh, or a radius modification. Try 10
modify lhe groove shape itself only as the last resort. Modification of srandard tools slows down the production and
can be quite costly.
GROOVE LOCATION
Groove location on a part is determined by the part drawing. The locations can be one of three groups:
o
Groove cut on a cylinder
o
Groove cut on a cone
o
Groove cut on a face
... diameter cutting
.«
taper cutting
... shoulder cutting
GROOVE DIMENSIONS
The dimensions of a groove are always important when
selecting the proper grooving insert. Grooving dimensions
include the width and the depth of a groove, as well as the
corners specifications. It is not possible to cut a groove with
an insert thut is larger than the groove width, Also, it is not
possible to feed into a groove depth that is greater than the
depth clearance of the insert or tool holder. However, there
is usually no problem in using a narrow grooving insert to
make a wide groove with multiple ClltS. The same appbes
for a deep culling insert used 10 make a shallow groove. The
dimensions of a groove determine the method of machining. A groove whose widlh equals the insert width selected
for the groove shape, requires only one cut. Simplefeed-in
and rapid-out tool motion is all that is required. To program
;j groove correctly, Ihe width and depth of the groove must
be known as well as its position relative to a known reference position on the parI. ThiS position is the distance to
one side - or one wall - of the groove.
Some extra large grooves require a special approach. For
example, a groove thai is 10m m wide and 8 mm deep cannO[ be Cul in a single pass. In this case, the rough cuts for
lhe groove will control not only its widlh, but also ils depth .
It is not unusual to even use more than one tool for such an
operation. Program may also need to be designed in seclions. In case of an insert breakage, only (he affected program section has to be repeated.
ON
325
• Groove Position
are shown two most common methods of
a
The groove width is aiven
in both cases as dimension W, bUl tile distance L fro;;; lhe
front
is d
in the example a and the example D.
and boltom diameter of the
I::; method has a major benefit that
of the groove will actually appear as
A disadvam3e:c
is that the
'-'
and a proper grooving
36-5b docs show !he
bottom diameter WIll
have to
dlmensionin <='o examfire about equally common in CNC
are usually grooves that have a
have a much deeper
top diameter and its bartom
but
SIMPLE GROOVE PROGRAMMING
L
L
,b
l
simplest of aU grooves is the One that
and shape as the tool cutting edge -
dimensioning two common methods
the dimension L is
the groove. For programming purposes,
is more convenient', because it will
as specified in the drawing.
1001 reference poim of a grooving 1001 is sellO
of the grooving insert.
The example in Figure 36-4b, [he
right side of the £roove. The left side
found easily, by adding the groove width
ming considerations will be slightly different,
if the dimensionallolerances are specified.
that the specified dimension
imporrant dimension. If a tokrance
any dimension, the tolerance must always
finished groove. and it will affect the
1 programmethod. A groove may also
dimensioned from anolher
localion, depending on
•
Figure 36-6
Simple groove example· program 03601
Insert width is equa/l0 the groove width
The program
a
is
rapid mode, move the gTooving lool to
Depth
Tn Figure 36-5, there are two
dimen-
siomng the groove depth.
~I
r
bl
Figure 36-5
Groove depth dimens.ioning . two common methods
d
Jn
position
~eed-in ,to the groove depth, then rapid out back to the start~
mg posltlOn, and - the groove is finished.
arc no corner breaks, no surface tinish conlrol, and no special techniques used. Some will say, and no quality
A dwell
at the bottom of the
the only improvement.
TalC, the quality of such 11
will not be the ""'oreatesl ,
a
it will
is slrictly a utility Iype
,'W'V"'" and is
111
.
manufacturing. At the same
such grooves is a good
stal1 to learn more
The following
square
The groove
diameters
(2.952 - 2.63'7)
12
.15'75
326
Chapter 36
uses the 1001
The
as Ihe
03601 (SIMPLE GROOVE)
(G20)
N33 TOSOO M42
(TOOL 8
N34 G97 5650 M03
(650 RPM SPEED)
N3S GOO Xl.1 Z 0.625 Toaos MaS
(START POINT)
N3S GOl X2.637 FO.003
(FEED-IN TO
N37 G04 XO. 4
(DWELL AT THE BOTTOM)
IDB X3.1. FO. 05
(RErRAC"r FROM
N39 GOO X6.0 Z3.0 TOSOO M09
(CLEAR POSITION)
(END OF PROGRJl,M)
N40 IDO
%
the following. First, the
from the beginning of
N34 are startup
selected. Constant Swface
Speed (eSS) in
can be selected instead. N35 is a
block where the 1001 moves [0 the position from which the
groove will be
poi nt). Clearance at this
10calion is the clearance
the part diameter, which is
.074 inches in the
(3.1 - 2.952)
PRECISION GROOVING TECHNIQUES
A simple in-ouf
will nOl be good. I[s
have a rough surface,
comers will be sharp
its width is dependent on
insert width and its wear.
most of maChining
a groove is not
To p:-ogram and
precision groove
eXira effort, but
be a high quality
This effort is nol
justified, as high quality comes
with a price. The next two illustrations show the groove di
mensions and program
details. Drawing in Figure
36-7 shows a high
groove, although its width is
Intentionally
impact of the example.
0.1584
I 2 = .074
same block, during the tool
cut, at a
of 0.4 seconds,
diameter and complellon
actual groove plunging
Block N37 is a dwell
the tool return to the slanthe rrogram.
Although Ihis parlicular
pie, tel's evaluate the program a
importanl principles thal can
of programming any
face finish are very critical.
,
.......
BREAK CORNERS 0.012 X
example was very slm-
more. Il contains sevapplied to rhe method
its precision and sur-
the clearance before the
cutting begins. The
the pari diameter. at
100. Always keep this ',,"'ll"',- to a
safe minimum. Grooves are usually cut at a
and it may
lOO much rime just (Q cut in the
note Ihe actual
has increased
.003 in/rev in block
to a rather high feed rate of
in/rev in block N38.
motion command GOO could
used instead.
OUI al a heavier feedrate
than using a rapid
motion). may improve [he groove
tinish by elimithe lool drag on the
1001 is positioned .074 inches
in the
diThe tool width of .125 never
width of the
or indirectly. That means
groove. It
will
means a di
groove width, if
the program structure
structure will remain unaffected even if
grooving
[001 shape is changed. Combination of the shape and the
size
will offer endless opponunilies,
of them be
mg
without a single change to
for a precision groove eX<3lm/Jle
What is
best cutting
plunge rough cut
two finish cuts, one for each
are reasonable; so is
.006
added to the
Also, sharp
corners will
broken with a .012 chamfer at the 04.0.
shows the distribution of the cuts.
Figure 36-8
Precision groove· distribution of cuts for the example 03802
GROOVING ON LATHES
Before the first block can be programmed, se!eclion of
the cutting tool and machining method is a sign of a good
planning. These are important decisions because they directly influence the final groove size and its condition.
+ Groove Width Selection
The grooving Lool selected for the example in program
03602 will be an exlernaltool, assigned to the tool station
number Ihree - T03. Tool reference point is selected at {he
left edge of the insert. wh icll is a standard selection. The insert width has to be selected as well. Grooving inserts are
available in a variety of standard widths, usually with an increment of I mm for metric tools, and 1132 or 1116 inch for
(ools in the English system. In (his case, [he non-standard
groove width is .! 584 inch. The nearest standard insert
width is 5/32 inch (0.15625 inch). The question is - should
we select the 5/32 inch insert width? rn a short answer, no.
In theory, this insert could cut the groove, but because the
actual difference between the Insert width and the groove
width is so small (.00215 inch over two walls), there is very
little material to cut.
The dimensional difference would allow only slightly
more than .00 I per each side of (he groove. which may
cause the insert to rub on the wall rather than cut It. A better
choice is to step down LO Ihe next lower standard insert
width, !.hat is 1/8th of an inch (.1250). There is much more
flexibility with 1/8 width than with 5/32 width. Once the
grooving tool is selected, the initial values can be assignedthe offset number (03), the spindle speed (400 rUmin), the
gear range (M42) - and a note ror the selup sheet:
o
T0303 = .1250 SQUARE GROOVING TOOL
327
chined with a, 1250 wide grooving insert, will need oJ least
two grooving cuts. But what about a groove that is much
wider than the groove in the example?
There is an easy way to calcu late the minimum nWl1her of
grooving ClllS (or plunges), using the following formula:
Cmln =
rrw where ...
em,"
Gw
Tw
=
Minimum number of cuts
Groove width for machining
Grooving insert width
Applying the formula to the example, the starting data are
the groove width of .1584 of an inch and tbe groovi ng insert
width of .1250 of an inch. That translates into the minimum
of fWO grooving cuts. Always round upwards, to the nearest
integer: . J584/1250= /.2672=2 cuts.
A possible decision could be to plunge once to finish the
left side of Ihe groove and, with one more plunge, to finish
the groove right side. The necessary overlap between the
two cuts is guaranteed and the only remaining operation is
the chamfering. A groove programmed Ihis way may be acceptable, but will not be of a very good quality.
Even if only an acceptable quality groove is produced
during machining, such a result does nOL give the programmer much credit. What can be actually done lo assure the
highest groove quality possible?
The first few program blocks can now be written:
In order to write first class programs, make the best efforts
to deliver an exceptional quality at the programming level,
in order to prevent problems at the machining level.
03602 (PRECISION GROOVE)
(G20)
N41 T0300 M42
N42 G96 8400 M03
+ Machining Method
Once the grooving tool has been selected and assigned a
(001 station number (toollurrel rosition), the actual method
of machining the groove has to be decided. Earlier, the machining method has been descrlbed generally, now a more
detailed description is necessary.
One simple programming method is not an option - the
basic in-ollt lcchmque used earlier. llUll means Q better
method must be selected, a method that will guarantee a
high quality groove. The first step towards that goal is the
realization of the faclthat a grooving insert with the width
narrower than the groove width, will have to be plunged
into the groove more than once. How many times? It is not
difficult to calculate that a groove .1584 wide and ma-
How call this suggestion be applied to the example? The
key is the knowledge of machining processes. Machining
experience confirms that removing an equal stock from
each wall (side) of the groove will result in better CUlling
conditions, better surface fi nish control and better toollifc.
If this observation is used in the current example, an important conclusion can be made, If two plunge euls of uneven width will yield at least acceptable results, three cuts
Ihat are equally distributed should yield even better results.
If at least Ihree grooving cuts are used to form the groove
rather (han the minimum two cuts, the CNC programmer
will gain control of two always Important factors:
o
Control of the groove POSITION
o
Control of the groove WIDTH
Tn precision grooving, these two factors are equally important and should be considered logether.
328
Chapter 36
Look carefully at how these factors are implemented in
the example, The first factor applied under (he program
control is the groove position, The groove position is given
in the drawing as .625 inches from the front face of the pan,
to the left side of the groove. There is no plus or minus dimensionaltolerance specified, so the drawing dimension is
used as arbilJary and is programmed directly. The second
factor under the program control is the groove width, That
is .1584 of an inch on the drawi ng and the selected !ool insel1 width is .1250. The goal is to program the culting mo[ions in three steps, using the technique already selected:
Q STEP 1
Rough plunge in the middle of the groove, leaving an
equal material stock on both groove faces for finishing
. also leave small stock on the bottom of the groove
Q STEP 2
Program the grooving tool operation on the left side
of the groove, including the chamfer (corner break)
Q STEP 3
Program the grooving tool operation on the right side
of the groove, including the chamfer (corner break) and
sweep the groove bottom towards the left wall.
The last two steps require chamfer cutting or a comer
break. The width of [he chamfer plus the width of the subsequent cut should never be larger than about one half to
three quarters of the insert width. In the third step, sweeping of the bottom is dcsircd.ll11ll suggests the need to consider stock allowances for fmishing.
•
Nex[ look is at the X axis positions. The first position is
where the plunge will start from. the second position is the
end diameter for the plunging cuL A good position for the
start is about .050 per side above the finished diameter,
which in Ih is case would be a clearance diameter calculated
from the 04.0;
4.0 + .05 x 2 = 4.1
(X4.1)
Do nol start the cuI with a clearance of more than .050
inch (),27 mm) - with slow feed rates that are typical to
grooves, there will be too much air to cut, which is not very
efficient. The end diameter is the groove bottom, given on
the drawing as 3.82. Dimension of X3.82 could be programmed as the targel diameter, but it does help to leave a
very small Slack, such as .003 per side (.006 on diameter),
to make a sweep finish of the groove bottom, That wi II add
two times .003 to the 3.82 groove diameter, for the programmed X target as X3.826. Once the plunge is done, the
(001 reI urns 10 the start diameter:
N43 GOO X4.1 Z-O.6083 T0303 MOB
N44 GOI X3.826 FO.004
N45 GOO X4.1
The rapid motion back above the groove (N4S) is a good
choice in this case, because the sides will be machined later
with the finishing culS, so the surface finish of Ihe walls is
not critical at this moment. After roughing the groove, it is
lime to Slarllhe finishing operations.
All the calculated amounts can be added to the previous
Figure 36-8, and creale dala for a new Figure 36-9:
finishing Allowances
During the first step, the first plunge has [0 take pJace at
the exact center of the groove. To calculate the Z axis position for the starl, fi nd fi rsl the amou nt of slack on each waJ I
that is left for finishing. The slock amount will be one half
of (he groove width minllS the insert width - see details in
the previous Figure 36-8:
(.1584 - .1250) I 2
;0.0167'
/
04.1
04.0
- 03.976
= .0167
The tool Z position wi II be .0167 on the positive side of
the len wall. If this wall is at Z-0.625, the grooving tool
Slm1 position will be at Z-O.60{l3. When the tool completes
the nrsl plunge, there will be an equal amount of materia!
left for finiShing on bOlh walls of Ihe groove.
Do your best to avoid rounding off the figure .0167, for
example, 10 .0170 inch. It would make no difference for the
machining, but it is a sound programming practice to usc
only the calculated values. The benefit of such approach is
in eventual program checking, and also with general consistency in programming. Equal stock amounts offer this
consistency; .0167 ond "0167 is a better choice than .0170
and .0164, although the practical results will be the same,
03"826
03.82
0.1250
·0.1584·
Z-0.6083
Z-0.6250
. Z-0.6870
Figure 36-9
Precision groove - groove data used in program 03602
GROOVING ON LATHES
•
Groove Tolerances
As in any machining, program for grooves must be structured in such a way, that maintaining tolerances at the machine will be possible. There is no specified tolerance in the
example, but it is implied as very close by the four-decimal
place dimension. A tolerance range, such as 0.0 Lo +.00 I \ is
probably a more common way of specifying a tolerance.
Only' the dimensional value thai falls within the specified
range can be used in a program. In Ihis example, the aim is
the drawing dimension of .1584 (selected intentionally).
A possible problem often encountered during machining
and a problem that influences the groove width'the most, is
a tool weQJ: As the insert works harder and harder, it wears
off at ils edges and actually becomes narrower. Its cutting
capabilities are not necessarily impaired, but the resulting
groove width may not fall within close tolerances. Another
cause for an unacceptable groove width is {he insert wid!h.
Inserts are manufactured within high level of accuracy, bUI
also within certain tolerances. If an insert is changed, the
groove width may change slightly, because the new illseli
may not have exactly [hc same width as the previous onc.
To eliminate, or al least minimize, the possible our oftolerance problem, use quite a simple technique - program an
additional offset for finishing operations only.
Earlier, when the precision groove was pJanned, offset 03
had been assigned to the grooving tool. Why would an ad·
dilional offscr he needed at all? Assume for a moment, that
all machine settings usc just a single offset in the program.
Suddenly, during machining, the groove gets narrower due
to 1001 wear. What can be done? Change the insert? Modify
the program? Change (he offset? If the Z ax is offset set! ing
is adjusted, either to the negative or positive direction, that
will change Ihe groove position relative [0 the program zero
but it will nor change Ihe groove widthi What is needed is a
second offset, an offscr (hal cont[ols the groove wiJth only.
In the program 03602, the left chamfer and side wlll be
finished with one offset (03), the right chamfer and side
will use a second offset. To make Ihe second offset easier 10
remember. number 13 wi II be used.
329
the grooving (001 will nOI contact the right side wall stock.
That means do not retract [he tool further then the position
of Z-0.6083. It also means do nol rapid OuL because of a
possi ble contact during the 'dogleg' or 'hockey Sl ick' motion, described in Chapter 20 - Rapid Posiliolling. The best
approach is (0 return 10 the initial stan position at a relatively high bur l1on-cuuing feedratc:
N49 X4.1 Z-O.6083 FO.04
At this point. the left side wall is finished. To program the
motions for the right side wall, the tool has to cut with the
righl side (right edge) of the grooving insert. Onc method is
to chnnge the GSO coordinates in the program, if this older
setting is still used, or use a different work coordinale offsel. The method used here is probably the simplest and also
the safest. All molions relating to the right chamfer and the
right side groove wall will be programmed in the incrementa/ mode. applied 10 Ihe Z axis only, using the W address:
NSO WO.0787 T0313
N51 X3.976 W-O.062 FO.002
In block N50, the tool tTavels the total distance equivalent
to the sum of the right wall stock of .0167, the chamfer of
.012 and the clearance of .050. In (he same block, the second offset is programmed. This is the only block where offset 13 should be applied - one block before, it's too early,
and one block, afler it's too lale.
Block N51 contains the target chamfer position and Ihe
absolutc mode for Ihe X axis and is combined with {he incremenlal mode for the Z axis.
To complete the groove righl side wall, finish the cur at
the full bottom diameter, block N52, then continue (0 remove the stock of .003 from the bollom diameter (block
N53) - this is called sweeping the groove bottom:
NS2 X3.82 FO.003
N53 Z-O.6247 T0303
One other step has to be Ilnished firSI - calculalion of [he
left chamfer start position. Currently, the tool is at Z-0.6083
but has to move by the wall stock oLO 167 and the chamfer
as clearance of .050 - for a total travel of
width .012 as
.0787,10 Z-0.6S7 position. AI a slow feedrale, the chamfer
is done first and [he cut continues to finish the left side, 10
Ihe same diameter as for roughing, which is X3.826:
Also look at the Z axis end amount - It IS a small value
that is .0003 short of the .625 drawing dimension! The purpose here is to compensate for a possible 1001 pressure.
There \(Jill nor be a srep ill the groove comeri Because the
sweep will end at the left side of the groove, the original
o('[<;ct (03) must be reinstated. Again, lhe block N53 is the
only block where the offset change is correct. Make sure
not to change the tool numbers - {he {urrer ,vill index .'
N46 Z-O.687
N47 GOl XJ.976 Z-O.62S FO.002
N48 X3.826 FO.003
The intcnded program 03602 can now be completed. All
thal remains to be done is lhe return to the groove starting
position, followed by the program termination blocks:
The next slep is [0 return the tool above parl diameler.
This mOlion is more important than it seems. In the program, make sure Ihe finished lefl side is not damaged when
the tool rctracts from the groove bottom. Al~o make sure
N54 X4.1 Z-O.6083 FO.04
N55 GOO X10.O Z2.0 T0300 M09
NS6 IDO
%
330
--_.
Al (his point, (he complete program 03602