secrets of 5 axis machining pdf

Third-party rotary devices, as shown in Figure 2-3 andelsewhere, can be purchased and mounted on a machine in a variety of ways, Theend result of this flexibility can cause two machines,

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I S B N 9 7 8 - 0 - 8 3 1 1 - 3 3 7 5 7

Library of Congress Cataloging-in-Publication Data

1 l4achine tools Numerical control 2 Machining I Title IL Title:

Secrets of 5-Axis Machining

TJ11B9.A68 20OB

67 1.3'5 dc22

2004027254

Industrial Press, Inc

989 Avenue of the Americas

New York, NY 10018

First Printing, August, 2008

Sponsoring Editor: lohn Carleo

lnterior Text and Cover Design: Paula Apro

Developmental Editor: Robert E Green

Production I\4anagen lanet Romano

Copyright O 2009 by Industrial Press Inc., New York

All rights reserved This book, or any parts thereot may not be reproduced, stored in

a retrieval system, or transmitted in any form without the permission of the publisher.All trademarks and registered trademarks, including Mastercam@ and Vericuto, areproperty of their respective owners All rights reserved

endorsement by the author or publisher of any patent, proprietary right, or product,

1 0 9 B 7 6 s 4 3 2 Printed by Thomson Press India Limited

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Dedication

This book is dedicated, in loving memory/ to my mother Piroska She taught me the meaning of hard work and perseverance Although she passed away before the completion of this book, her spirit continues to live with me.

I would like to thank Yavuz lvlurtezaoglu for giving me the inspiration to write this

D O O K

A special thanks to Laura Norton for her humbling insights

And above all, I would like to thank Paula Apro, my hard-working wife, friend, editotdesigner, and manager For without her this book would never have come to be

All the images in this book, including the virtual machines, were modeled usingf4astercamo (CNC Software, Inc.) The virtual machines were brought to life usingthe machine simulation capabilities of 14achSim (l"loduleworks) and VERICUT6(CGTech)

For more information on these

52072 Aachen, Germany +49.241.4006020 www.moduleworks.com

CGTech/VERICUT

9000 Research DriveIrvine, California 92618949.753.1050

www.cgtech.com

For more information on the author, Dlease visit www.multiaxissolutions.com

H e a d / T a b l e M u l t i a x i s l 4 i l l i n g l v l a c h i n e s 3 1

H e a d / H e a d M u l t i a x i s l v l i l l i n g l 4 a c h i n e s 3 6

F i n d i n g t h e P i v o t D i s t a n c e 3 7

4 - A x i s l \ 4 a c h i n e s 3 SGeneml l4aintenance & Issues for 14ultiaxis lYachines 40I\4illing l4achines With Five- or l.4ore-Axes 43

C h a p t e r 3 : C u t t i n g S t r a t e g i e s 4 5

lulachine Home Position Active Coordinate System ,I\4achine Rotary Center Point , CAD/CAM System Origin Synchronizing lYachine and CAD/CAM coordinate Systems

Behind the Scenes: CAD/CAM Software Development 145

General Guidelines for Researching CAD/CAM Software 146

[4ultiaxis 14achine?

What Tools are Needed to Find MRZP?

Description of Indexing/Rotary Positioning Work .Whal i5 a Post Proccessor?

DefiniLion of an Axis

Defining a Simultaneous 5-axis Toolpath

What are the Three Common Simultaneous lYultiaxis CAMToolpath ConLrols

14ultiaxis Machine Offsels

Finding lYachine Rotary Zero Posilion

Finding the Pivot Distance

1 6 1167

1 6 2164

1 6 6166167767

Are you utilizing 5-axis machining? Could your shop benefit from the efficiencyand power that 5-axis machining offers? The majority of people not embracing thistechnology lack a true understanding of 5-axis practices There are many commonmisconceptions on the subject, and the intent of this book is to demvstifv 5-axismachining and bring it within the reach of anyone interested in using the technology

to its full potential The information presented in this book was gathered during

30 years of hands-on experience in the metal-working manufacturing industry bridging countries, continents, and multiple languages (both human and G-code.)The author worked in Hungart Germany, Canada, and the USA, specializing in

-multiaxis solutions, He spent many years setting up, programming, and reparnngCNC equiprnent, and has used a number of different CAD/CA|Y systems He hasworked as a self-employed multiaxis consultant, as well as djrecuy for CGTech (themakers of VERICUT@) and CNC Software Inc (the makers of ttastercamo.)

The author has instructed countless multiaxis training classes over the past decade,These classes covered topics such as operating CNC equipment, programmingCNC equipment, both manually and with CAD/CAM systems, and bujlding virtualmachines with different verification systems Through the years, the author has metmany professionals around the world and has come to a realization that they atlhave the same questions, misconceptions, and concerns, when it comes to 5-axismachining The need for unbiased information on the subject became apparent

Up to this point, the best way to get information on 5-axis machining was to talk

to peers in the industry in the hope that they would share what thev had learned,Visiting industrial trade shows and talking to machine tool and CAD/CAI4 vendorsare other options - except that these people all give their individual points of viewand will promote their own machine or solution Everybodv claims to have the bestmouse-trap, and it is left to the individual to choose the right one

This book is not a training manual for any particular machine or CAD/CAM system.Rather, it is an overview of multiaxis machine tyDes and the common control

methods that CAD/CAM systems use to drive the machines The book will guide youthrough this realm, from basic to complex concepts, and will provide information

to help you choose the right tools, including the machine, work-holding method,CAD/CAM system, and machine simulation package that will best suit your specificapplication The book contains numerous illustrations to help you to precisely

implement these tools

History of S-Axis Machines

Long before CNC controllers appeared,4-5-6-12- and more-axis machines, referred

to as multiaxis machines, were being used Ihe individual axes were controlledmechanically through levers riding on cam plates Some machines had more than 12cam plates, controlling not onJy tool/table and rotary motions, but also clamprng andunclamping of work-holding fixtures These machines were cumbersome ano atmeconsuming to set up, but they were perfecUy suited for mass production

The first NC (numerical control without internal memory) machines were

cumbersome to set up and operate, but they also were great for mass production Atfirst, only the most affluent and established shops could afford them programm,ngwas a lengthy, error-prone process Soon, machine builders added intern;l memory

to their controllers, then they added the ability to execute simple branching loopinglogic, and to calJ subroutines from other subroutines It was possible to us; thesemacro languages directly on the machine and to quickly change set_Lrps, especiallyfor family type parts Different machine builders developed various soluiions, whichcreated a number of CNC (computer numerical control with internal memory)

programmrng tanguages Companies with familiar names like Fanuc, Acramatjc,Heidenhein, Siemens, I\4azatrol, etc., all developed their own languages, but

these quickly became an issue Some shops ran ten machines wiih eigfrt Oifferentlanguages If a repeat job came in, and the originally programmed michine wasbus, a new program would have to be re-writtin from sc-ratch because of the

language differences

N.ext,-the first.rudimentary CAD (Computer Aided Design)/CAM (Computer AidedlYanLrfacturing) systems were devejoped At first, these software soluiions wereintroduced by the same companies that developed the controllers Soon after,

enterprising individLrals wrote their own CAD/CAI4 software This jump in tecnnorogywas huge because it allowed engineers to draw their parts in a CAD program,

generate a toolpath in the CAM systemt generic language, and then translate it intomultiple G-Code languages quickt, using the appropljate post processor

This progress meant that CNC machines were no longer the exception, and tneystarted to become the norm They were no longer used only for mass_production andthey became versatile, accurate, and affordable

Ivlultiaxis machines went through a similar process, but because thev were morecomplicaled, this process look longer First, Ihe machines were expensive to

purchase and maintain, and harder to program, Only large aerospace companieshad the need, the money, and the personnel to handle multiaxis applications Somecompanies kept their own processes closely guarded in order to gain an advantage,Many software packages were born out of necessity - in order to solve specificapplication challenges Software, in general, is always on the very leading edge oftechnology - pushing the limits of software possibilities and hardware restrictions.Today, there are many machine builders offering a variety of multiaxis equipment

in a wide range of configurations, quality, and price Computers have become veryaffordable, and CAD/CAM systems now offer excellent multiaxis cutting strategieswith great tool control and large post-processor libraries As a result, even smaller

s h o p s c a n , a n d d o , i m p l e m e n t m u l t i a x i s m a c h i n i n g

M o s t m a c h i n e b u i l d e r s a r e e x p a n d i n g p r o d u c t i o n a n d e m b r a c i n g n e w t e c h n o l o g y ,Many believe that it is imperative to compete in the global market, especiallyagainst countries with abundant cheap labor This attitude has resulted in increased

to see both machine builders and CAD/CAM vendors showino off their most

complicated creations

Figures 7-7 Example of induction pump set-up

Secrets of s-Axis Machining

Figure I-2 Example of induction pump design.

In reality, the majority of s-axis users don,t ever make an impeller, or finish

ports for a.racing-engine cyrinder head Most of them machine paris using simpre 3-axis drilling, contouring, and pocket milling routines, while roiating the-part' occasionally in a rotary indexing mechanism, as illustrated in Figurei 1-3 and 1-4 very elaborate parts can arso be machined by apprying 3D surfa-cing toorpaths and engaging the part from different angles by indexing a rotary table -

Figures t-g and l-4 Examptes of positioning work

Using a multiaxis machine will greatly simplify the motions required, the

programming effort, and the amount of fixturing needed for machining complexworkpieces other benefits include the eliminati-on of multiple set-upsf increasedaccuracy, and better surface finish

History of s-Axis Machines

common Misconceptionr I don't ilo enough S-axis work to warrant

a S - a x i s m a c h i n e

M a n y s h o p s a r e c u r r e n t l y m a k i n g p a r t s b y m o v i n g th e m m a n u a l l y t o d i f f e r e n tfixtures on 3-axis machines Compared with this procedure, production can be

Figure 7-7 Example of tombstone fixture

Secrets of s-Axis Machinino

Figure 7-8 Example of 4-axis positioning.

O n c e y o u enter the multiaxis r e a l m , n e w doors will be opened f o r y o u r s h o p y o u r

c o m p a n y w i l l q u i c k l y b e c o m e m o r e a d e p t and able to tackle more comDlex w o r k

B e f o r e t o o l o n g , y o u r shop will start taking on more and more jobs, and will need

t o o l

Historv of s-Axis Machines

If you do a lot of simultaneous multiaxis work, the price of the CAD/CAM will be

o n l y a s m a l l fa c t o r M o r e tr a i n i n g w i l l b e n e e d e d , b u t y o u w i l l b e a b l e to c h a r g e

a l m o s t d o u b l e f o r y o u r h o u r l y m a c h i n e t i m e T h e ' h a r d to u s e ' p a f t a l w a y s c o m e sdown to training - was it easy to learn how to operate your first CNC machine?

D o n ' t e n t e r th e m u l t i a x i s w o r l d b y s t a r t i n g w i t h a c o m p l e x , s i m u l t a n e o u s j o b If

y o u already o w n a 3 - a x i s m a c h i n e , s t a r t w i t h a s i n g l e - o r d u a l - r o t a r y t a b l e a n dapply indexing techniques You will make parts faster and more accurately, and you

w i l l b e a b l e to i n v e s t i n m o r e e q u i p m e n t W h e n y o u d e c i d e t o b u y n e w e q u i p m e n t ,see if you can bundle a CAD/CAM purchase with the machine's purchase order.This is also a good time to make sure your CAD/CAM system speaks your specificmachine's language - in other words, that it has the correct post processor

S o m e c o m p a n i e s b u y e q u i p m e n t w i t h a t u r n - k e y s o l u t i o n , w h i c h e n s u r e s t h a t t h e i rspecific job will run on the machine upon delivery from the manufacturer Many

m a c h i n e t o o l b u i l d e r s e m p l o y c a p a b l e t e a m s o f a p p l i c a t i o n s e n g i n e e r s , w h o i nturn, work closely with CAD/CAM developers, Together, the teams determine themost efficient way to machine any specific part, based on many factors such as;

m a t e r i a l , q u a n t i t y , t o l e r a n c e r e q u i r e m e n t s , a n d t o o l i n g a v a i l a b i l i t y

Reasons to Use Multiaxis Machines

Reduced Set Up work

One important reason to use multiaxis machines is to reduce set-up time for partssuch as those shown in Figures 1-9 and 1-10 Extra custom fixturing for secondaryoperations is very costly and time-consuming Most parts can be manufactured inone or two set-ups, eliminating the need for extra fixturing and time

Figure 7-9 Example part requiring positioning multiaxis machining

Secrets of s-Axis Machining

Figure 7-7O Part requires two separate set-ups for machining.

Accuracy

Every time you move a workpiece from one fixture to another, there is a risk

of misalignment - either during the set-up itself or during operation It is easy

to build up (stacked) errors between machined surfaces when they are milled

in multiple set-ups The use of indexing rotary tables, or dedicated multiaxis

m a c h i n e s , a s s h o w n in F i g u r e s 1 - 1 1 a n d 1 - 1 2 , allows p r e c i s e m o v e m e n t o f s h o r t ,rigid, high speed cutters for the best cutting engagement More aggressive cuts canthen be taken, with higher RPM and feed rates, while the highest levels of accuracy

a r e m a i n t a i n e d

Figurc 7-17 Dedicated dual-rotary machine set-up

History of s-Axis Machines

Figure 7-72 Dedicated dual-rotary machine set-up.

Better Surface Finishes

U s i n g s h o r t e r t o o l s w i l l c a u s e l e s s to o l d e f l e c t i o n , w h i c h w i l l m i n i m i z e v i b r a t i o n a n dproduce smooth, precise, cuts When using ball-nose cutters it ls recommendedthat the contact point be moved away from the tip of the cutter that isn't spinning

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s o m e p a r t s are impossibre t o c u t on a 3-axis machine o t h e r p a r t s wourd t a k e

t o o m a n y set-ups o n a 3 - a x i s machine t o b e p r o f i t a b l e O n c e y o u r shop gets

c o m f o r t a b l e w i t h i n d e x i n g w o r k , y o u will be able to start machining p a r t ; such as

t h o s e in F i g u r e s 1 - 1 5 , 1-16, and 1-17, using simurtaneous m u r t i a x i s m o t i o n s , a n d

o p e n y o u r buslness t o m a n y n e w p o s s i b i l i t i e s

Figures 7-75, 7-76, and l-t7 More examples of parts that require simultaneous

cutting motions

A word of caution: Simultaneous multiaxis work is inevitably Jess

accurate than indexing work because the machine must be run in

a loose mode with the rotary drives unlocked It is recommended

that all possible roughing operations be done by indexinq the

rotaries to optimum angles, because the machine in lockld

mode is much more rigid This type of work is also called 2+3

machining The two rotary axes are first positioned and locked into

the optimum attack position, then a standard 3-axis program is

executed.

11

History of s-Axis l\ilachines

The physical properties of the machine

The physical properties of the machine describe the wav tne axes are

s t a c k e d , t h e r i g i d i t y a n d f l e x i b i l i t y o f t h e i r o n , th e h o r s e p o w e r , t o r q u e ,

a n d m a x i m u m R P M o f t h e s p i n d l e m o t o r , t h e q u a l i t y a n d w o r k m a n s h i p o f

t h e g u i d e s / s l i d e s , a n d t h e r o t a r y b e a r i n g s

The CNC drive system

T h e d r i v e system is the muscles o r t h e c o m p o n e n t s t h a t m a k e th e

Figure 2-7 Typical arrangements of multiaxis CNC machines.

Multiaxis Machine Configurations

The arrangements shown in Figure 2-1 are all very popular configurations, butnone of them is "standard." There is no such thing as a standard S-axis machine.First, let's establish the definition of an axis Any motion controlled by the NCcontroller, either linear or rotational is considered an axis For instance, in the

i f l u s t r a t i o n i n F i g u r e 2 - 2 , b o t h th e s p i n d l e h e a d a n d t h e q u i l l a r e c a p a b l e o f m o v i n g

in the same direction, but are controlled by two separate commands, Movements ofthe head are controlled by Z and those of the quill by W

Figure 2-2 Thespindle head and the spindle quill move along parallel axes.TU

1 4 Secrets of s-Axis Machinino

T h e te r m s m u l t i a x i s a n d s - a x i s are often used interchangeably a n d t h e s e terms

ABC are rotary axes rotating around XyZ respectively

UVW are parallel linear axes along XyZ respectively

Know Your Machine 1 5

Unfortunately, different machine builders abide by this standard in different ways.Some builders allow the end user to change the machine's rotational directions

or behavior on the fly Third-party rotary devices, as shown in Figure 2-3 andelsewhere, can be purchased and mounted on a machine in a variety of ways, Theend result of this flexibility can cause two machines, of the same make and model,

to have completely different S-axis behavior

Every machine is a compromise of some sort Rotational directions, sta rt positions,and limits, will be different from one machine to another The effective work

envelope is greatly modified by changing those variables, Some rotary axes canrotate in both directions Some axes will choose the rotary direction based on theexisting position - shortest distance versus clockwise (CW) or counter-clockwise(CCW) Some machines that are equipped with dynamic rotary fixture offsetmode will move the linear axis while rotating the rotary one based on a rotary

c o m m a n d

To understand these machines completely, it is necessary to look at every machine

as a unique entity, to look under the skin and understand how the skeleton isconstructed, You need to know where all the joints are, where the rotary axes are,where the rotary zero positions are, what makes them move, and how the whole

u n i t fu n c t i o n s i n u n i s o n

Different manufacturers and CAD/CAM systems have many different names for thesame things Let's establish some common terms that will be used in this book inorder to avoid assumptions and confusion

Machine Home Position (MHP) - Most machinists recognize the home position

a s t h e p l a c e t o w h i c h a l l t h e a x e s m o v e w h e n y o u i n i t i a l l y t u r n t h e m a c h i n e o n a n dselect Zero return

Figure 2-3 Machine at Home Position X0 Y0 20 A0 80

1 6 Secrets of s-Axis Machining

Machine Rotary Zero Position (MRZP) - On multiaxis machines, machine rotary zero shown in Figure 2-4, is at the intersection of the rotary/pivoting axes This

point may be unreachable by the machine.

Figure 2-4 Close-up showing Machine Rotary Zero position.

lrogram Zero Position (PZP) - program Zero position is the part datum in the

CAM system.

Figure 2-5 Another view showing the relationship between Machine

Rotary Zero Position and program Zero position

Know Your Machine 1 7

Head/Table multiaxis machines execute the rotary motions by thetable, which carries the work piece, The spindle head articulatesthe tool with tilting motions.

Head/Head multiaxis machines execute all rotary/pivotang motions

by articulating the spindle head of the machine, The work piece isstationary

K e e p i n m i n d th a t t h e f o c u s of this book is milling, a l t h o u g h t h e l i n e b e t w e e n t h e

one of the rotary axes some will have unlimited rota ry motion on the other axis.

Some even have the capability to spin the work, as a lithe woutd.

Table/Table machines are the most common types of murtiaxis machines Most

people will enter the s-axis world by purchasing-a single- or dual-rotary device and bolt it to their 3-axis milling machine

Figure 2-6 Simulation of a dual rotary mechanism fastened to the tabte of a

standard 3-axis CNC milting machine

Figure 2-7 A third-party rotary mechanism fastened to the tabte of a standard

3-axis CNC milling machine

Know Your Machine 1 9

Figure 2-8 Third-pafty single rotary mechanism and tailstock, fastened to the

table of a standard 3-axis CNC milling machine

After machining one side of the work piece it is possible to index the rotary unit

to machine the second side, and so on This type of work is called indexing orpositioning work Some manufacturers use specialized dual rotary mechanisms.such as the one shown in Figure 2-9, which is designed for machining internal

c o m b u s t i o n e n g i n e c o m p o n e n t s

Figure 2-9 Specialized dual rotary mechanism used in engine manufacture.

20 Secrets of s-Axis Machining

D e d i c a t e d T a b l e / T a b l e machines a r e v e r y capable o f d o i n g in d e x i n g / p o s i t i o n i n g

w o r k a n d are equarry c a p a b r e o f s i m u r t a n e o u s w o r k T h e inherent d i f l e r e n c e s

b e t w e e n t h e t w o are worth mentioning

T h e r n d e x i n g method hords t h e w o r k p i e c e m u c h m o r e rigidry t h a n i t i s h e r d for

s i m u l t a n e o u s m a c h i n i n g w o r k because t h e r o t a r y axes are-rocked w h e n m a c h i n i n g

w h e n r o t a t i n g a n a x i s , the rotary axis must firsl be unrocked w i t h a d e s i g n a t e J

-M - c o d e T h e a x i s is then rotated, a n d i t i s r o c k e d w i t h a n o t h e r M - C o d e b - e f o r e

m a c h i n i n g i s r e s u m e d T h i s s e q u e n c e a l l o w s m a c h i n i n g t o b e d o n e in the machine,s

m o s t r i g i d state

w h e n u s i n g simurtaneous mi||ing t e c h n i q u e s , a I t h e b r a k e s m u s t be disengaged,

w h i c h w i l l p u t the machine i n i t s r o o s e m o d e For this reason i t i s a r w a y s u g - o o i

i d e a to use (when possible) i n d e x i n g / p o s i t i o n i n g m i l l i n g t e c h n i q u e s f o i r o u j h i n g

c u t s

Machine Rotary Zero position (MRZp)

Commonly, MRZP represents the intersection point of the rwo rorary axes,

although sometimes the two rotaries may be offset by a specific disfance This

d i s t a n c e m u s t c o i n c i d e o r b e r e l a t i v e t o t h e p a r t datum pZp (program Zero

P o i n t ) of the CAM system

T o a c c u r a t e l y s e t u p , operate, a n d p r o g r a m t h e s e m a c h i n e s , i t i s n e c e s s a r y t o

f i n d the intersection o f t h e r o t a r y centers o f t h e m a c h i n e a x e s s o m e but not ali,

manufacturers have the varues stamped on their rotary devices However, those

n u m b e r s a r e n o t to be trusted, and must be recalibrated r e g u l a r l y

F i n d i n g the precise center of rotation is the foundation of

Here are the steps to be taken:

1 Level the table by "zeroing" the indicator on either side of the table, as

s h o w n i n F i g u r e s 2 - 1 O a n d 2 - 1 1

Figures 2-7O and 2-77 Method of checking the level by dial-indicating both sides

of the workholding table

Figure 2-72 Setting the dial indicator to zero before checking the level of the

table

Secrets of s-Axis Machining

2 Find the XY zero, using the dial indicator, Zero xy and A at this point, asshown in Figure 2-13,

Figure 2-73 Zeroing XY and A positions on the work-holding table.

3 Rotate A+9O degrees and touch the OD of the table as shown in Flgure 2-t4,

Figure 2-74 After rotating the A axis through 90 degrees, touch the outside

diameter of the table with the dial indicator.

Know Your Machine

4 Rotate A-axis through 18O degrees from the previous position and make sure the indicator reads zero on the other side.

Figure 2-75 After rotating the A axis through -90 degrees, touch the outside

diameter of the table with the dial indicator'

5 Move the Z-axis in minus direction the radius of the rotary table and set

up a gage tower The gage tower is used to set all the tool length offsets

This location is the machine's rotary zero position (MRzp), as illustrated inFigure 2-17,

outlined procedure

Note that the intersection of the dual rotary center lines is above the table in

the example given This location will be different for every machine, even fromthe same manufacturer It is imperative that this position be checked regularry,

e s p e c i a l l y a f t e r a h e a v y workload o r a c r a s h , S m a l l m i s a l i g n m e n t s c a n c a u s e ia r q eerrors because the tool position is measured from this intersection point

All the Active coordinate systems also referred to as Nesting positions orLocaf Coordinate Systems, for example G54 - Sg, are relative to the MachineRotary zero Point (MRZP) position It is good practice to set one of the nestingpositions here, so that it will be captured in the Registry allowing it to be recalle-d

q u i c k l y , u s i n g M D I ( M a n u a l Data Input)

F o r e x a m p l e : c 9 0 c 5 4 x 0 y 0 A 0 c 0

Figure 2-77 The rotary zero position of the machine, as established by the

The PZP (Program Zero point) of the CAM systems must be set exac v

to the Machine Rotary Zero point, as seen in Fiqure 2-19.

Know Your Machine

Figure 2-78 Relationship between the MRZP and the PZP.

Some CAM systems call this position the World Zero, Master Zero, or the Origin.The main thing to remember is to draw the part in the same specific positionrelative to this World Zero as it sits on the machine, relative to Machine RotaryZero Point

Nesting Positions

Nesting positions are widely used for positioning work These positions, shown inFigure 2-19, are temporary Active Coordinate Systems and are typically set inrelation to different faces of the part or fixture face, tooling ball, or dowel pin

Figure 2-19 Sketch showing some ofthe many local coordinate systems used in

CNC programming.

Secrets of s-Axis Machining

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The advantage of using these Locar.coordinate systems is that you can easiry

f o l l o w th e p r o g r a m o n t h e c o n t r o l l e r , s d i s p l a y s c e e n b e c a u s e t h e a b s o j u t e

values shown there will reflect the values relative to each locally-nested position

Z + 1 0 0 0 , fo r example w i l l b e 1 0 0 0 (i n c h ) above the part face

Despite the fact that cAM systems a use different naming conventions for their

c o o r d i n a t e s y s t e m s / t h e y a l r handre t h e r o c a r c o o r d i n a t e s y s t e m in a simirar w a y Some.of the names used by_ CAD/CAM systems include: p'art Datum, Active

Coordinate System, Local Coordinate System, System View, and Tool plane

w i t h a n Origin

The disadvantage of using a number of different rocar coordinate systems is the

p o t e n t i a r f o r m i s a r i g n m e n t w h e n p i c k i n g u p t h e s e p o s i t i o n s m a n u a i r y w i t h a d i a lindicator Many programmers us_e only _one coordinate system for S_axis wort< itreyusethe Machane Rotary zero point (MRzp) as the pirt datum and ret either thecAN4 system or the machine's controler carcurate the speciar rou"r"nt nui"iruiy.

I f a p a r t is p l a c e d i n t h e same position i n t h e cAM and in the machine, t h e c i M i ; 'very capable of generating the correct code

The advantage of using a singre coordinate system is that the part needs to be

i n d i c a t e d o n l y o n c e The disadvantage i s t h a t i t i s harder to visuallv f o l l o w the

program on the controller's display screen The system will have to be switchedover to Distance to Go for safer operation

using a real s-axis machine as a verification system is inefficient, cumbersome,

a n d v e r y dangerous T h e r e are many machine s i m u l a t i o n s o f t w a i e t ; k ; & ; - '

a v a i l a b l e t h a t c a n save a rot of time and money, and these are covered in another

ch a Dte r

Rotary Table Dynamic Fixture Offset

The Problem

cAM generates,code for a given position of the program zero point (pzp) rerative

to the center of rotation machine zero point, (MRZF) The machine operito, maylun th: c.ogg later, on the night shift, at a different tocation ApZp (Actual part

Zero Point) He or she may not be able to place the part exacfly where the CAD/cAM programmer intended it to be If the operator does not have the access or tireability to make the change, then the job wiri have to wait for a reposted code to be

s u p p l i e d

Modern CAD/CAM systems can easily calculate new code if the part is moved

But as previously mentioned, the part will have to be moved to exacfly the sameposition in the cAM system and then the code wil have to be recarcurited

Rotary Table Dynamic Fixture Offset (RTDFO).

When the Rotary Table Dynamic Fixture Offset function is activated on thecontroller, the Program Zero Point (CAM datum) is offset to correspondwith the set fixture offset amount, as shown in Figure 2-20 This offset is thedistance between the center of rotation (MRZP) and the Part Zero Point (PZP)and it must also take into account the angle of the rotary table This function isconvenient because multiple-face machining can be executed by setting one point

as the reference when machining a complex workpiece

Figure 2-2O Potential problems in establishing the rotary table dynamic fixture

offset (RTDFO).

There are 2 wavs to use RTDFO:

1 Set the fixture offset amount manually on the Fixture Offset screen of the machine, illustrated in Figure 2-21,

28 Secrets of s-Axis Machining

E-1grylo1selection + rey E (oFFSET)

IFIXTURE OFFSETI

Figure 2-21 A Fixture Offset Screen on a CNC machine

2 S p e c i f y the values in the machining program (G-Code)

The fixture offset amount is the distance between the rotationai center (MRZp)

and the workpiece zero point, used by the CAM program as the program Zero

( P z P )

GlO L21 Pn X_Y_Z_B_C_

n Fixture offset number (1_g)

X_Y_Z_B_C_ Fixture offset amount for each axis

W h e n u s i n g the c90

W h e n u s i n g the G91

s e t

m o d e / the specified v a l u e s a r e s e t

m o d e , the sums of the specified a n d t h e p r e v i o u s v a l u e s a r e

Know Your lvlachine 29

A c t i v a t i n o R T D F O :

G54,2 Pn; RTDFO - ONG54,2 PO, RTDFO - OFF

n Fixture offset number (1-8)

G 0 c 1 7 G 4 0 G 8 0 G 9 0 c 9 4 G 9 8

c 2 8 X O Y O , B O , ( l a o L 3 1 D r a a ! F 3 : L L E N - 3 1 ( c 4 3 1 G 5 P 1 A 0 O 0 )

T 3 t M6

H e a d / T a b l e M u l t i a x i s M i l l i n g M a c h i n e s

A s t h e i r n a m e s u g g e s t s , t h e s e m a c h i n e s h a v e a r o t a r y ta b l e a n d a t i l t i n g h e a d

Figures 2-23, 2-24, and 2-25 Example of Head/Table multiaxis milling machines,

which have rotary tables and tilting spindle heads

Know Your l\y'achine

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H e a d / T a b l e m a c h i n e s a r e a r g u a b l y t h e m o s t c a p a b l e o f t h e t h r e e g r o u p s

i l l u s t r a t e d a n d c a n m a c h i n e l a r g e , h e a v y p a r t s On some machines, t h e r o t a r v ta b l ecan be supported by a steady rest and it rotates the paft only around its own axis

How does axis substitution work?

Axis substitution is shown in Figure 2-26, and is effected by the following

Figure 2-26 A part produced by means of axis substitution

After these blocks are read, all Y-axis moves will be replaced by instructions for