CNC
Trade Secrets
A Guide to CNCMachine Shop Practices
James A. Harvey
INDUSTRIAL PRESS
A full catalog record for this book is available from the Library of Congress.
ISBN 978-0-8311-9301-0
Industrial Press, Inc.
32 Haviland Street
South Norwalk, Connecticut 06854
Sponsoring Editor: John Carleo
Developmental Editor: Robert Weinstein
Interior Text and Cover Design: Janet Romano-Murray
Copyright © 2015 by James A. Harvey
All rights reserved. With the exception of quoting brief passages, no part of this publication may be reproduced or transmitted in any form without written permission from the copyright owner and the publisher.
No warranties are given in connection with the accuracy of the statements made in this publication and no responsibility can be taken for any claims that may arise. Nothing contained in CNC Trade Secrets, shall be construed as a grant of any right of manufacture or sale in connection with any method, process, apparatus, or product and nothing contained in this publication shall be construed as a defense against any alleged infringement of letters patent, copyright or trademark, or as a defense against any liability for such infringement. Comments, criticisms and suggestions are invited, and should be forwarded to:
James A.Harvey
12112 St. Mark St.,
Garden Grove, CA 92845
Manufactured in the U.S.A.
10 9 8 7 6 5 4 3 2 1
TABLE OF CONTENTS
Chapter 4 Chamfering and Edge Dressing
Chapter 5 More Help for Engineers
Chapter 6 Becoming Familiar with CAD
Chapter 7 Becoming Familiar with CAM
Chapter 8 Becoming Familiar with Code
Chapter 9 Fire Up a Machine
Chapter 10 Odds and Ends
Index
I’d like to thank my dad, who blessed me with some of his extraordinary mechanical aptitude, and my mom, who put up with both of us constantly tinkering with some contraption. My daughter Joanna, who at a young age helped me transition into the computer world, and my son Billy, who on the darkest of days, always manages to bring a little sunshine.
I’m thankful for the support of Robert Weinstein, whose tenacity, patience, and forward thinking turned this book into a reality. I’d also like to thank Janet Romano and John Carleo from Industrial Press for their kind support.
And a salute to all the technical people, machine builders, and software developers, who provide the remarkable tools we use in the shop and elsewhere that make our lives easier and more productive.
I’m spoiled. With few exceptions, I now put everything I can now on the CNC machines. In most cases, jobs are less labor intensive, less prone to error, and can be completed sooner than when using conventional machines. With the user-friendly CNC technology available today, even making one or two simple parts is often easier and more efficient than conventional machining.
Does that mean the end of conventional machining is near? I don’t think so. There are certain tasks you can do with conventional machines that CNC machines are just not good at, such as “blending.” CNC machines can’t blend flawed features very well simply because they don’t have eyes. They run on numbers. Many jobs that come through the door don’t have exact numbers to work to or any documentation for that matter.
Often parts that need rework are so beat up, worn out, or outdated that, even if you had a print, there’s a good chance the dimensions on the print won’t match the part. Maintenance machining and mold repair jobs come to mind as jobs that often need rework and manual blending of some sort.
There are craftsmen in our shop who know little about CNC machining and CNC people who are not craftsman. The funny thing is that often these people imagine the other as having some kind of God-like abilities. The fact of the matter — little would get accomplished it weren’t for these two groups working together.
CNC machining involves a combination of three things:
1.Machining knowledge
2.Controller familiarity
3.Programming knowledge
Machining is the art of cutting away material in the proper sequence, selecting and sharpening cutters, setting feeds and speeds, measuring, and determining how you are going to hold the work. The planning and cutting characteristics of conventional and CNC machining are quite similar with the exception that you can machine parts a lot faster using CNC machines because they can read numbers quickly and move accordingly. They also don’t take coffee breaks.
Programming is essentially the art of making the machine move the way you want it to.
CNC programming, at its core, is simply point-to-point programming which in turn obliges the cutter to move from point to point. You don’t have to be especially adept at doing mental gymnastics to program CNC machines because almost all the instructions you give the machine are sequential. CNC programs are a lot like driving instructions: “Go north three miles then turn left.” “Go west ten miles then turn right.” Etc.
My previous book Machine Shop Trade Secrets deals mostly with conventional machining.
The practice of starting out on conventional machines to learn machining may be shifting now as CNC machines become increasingly more popular, less expensive, and easier to use. If you are an experienced conventional machinist, you’ll have the advantage of being able to concentrate your efforts on learning the controller and how to program. I don’t believe it is essential to have experience on conventional machines to learn CNC machining. However, a person with a strong conventional machining background will likely have an easier time getting good parts consistently.
To the untrained eye, CNC machines may look complicated. They did to me at first. I was so