Marcus Bowman - CNC Milling in the Workshop

First published in 2013 by

The Crowood Press Ltd

Ramsbury, Marlborough

Wiltshire SN8 2HR

www.crowood.com

This e-book first published in 2013

Dr Marcus Bowman 2013

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 978 1 84797 630 7

Frontispiece: machined aluminium face by Tommi Salminen

The aim of this book is to introduce a range of concepts and techniques for producing parts using a computer-controlled milling machine. This is a practical book containing techniques to put your own CNC machine tool to work.

The book explains the machines, the software and the methods for producing a range of parts varying from the simple to the complex and the functional to the artistic, and includes guidance on tooling, speeds, feeds and fixtures. Throughout the book there are a number of projects that you can use to try out the various techniques.

SOME ASSUMPTIONS

This is a practical book about using a computer-controlled machine tool to do useful work, and assumes you have a CNC milling machine set up to move under software control.

The book makes reference to Mach3, LinuxCNC, software from the Vectric range (including Cut2D and VCarve Pro) and software packages from other companies, but the techniques are applicable to most similar software.

A Word about the Hardware

This book assumes that you will be using a benchtop CNC mill designed for metalworking, or a larger knee mill such as a Bridgeport. A range of materials is used throughout the book, so it is not restricted to metalworking. The workpieces in the projects are relatively small and will fit on most benchtop CNC mills. This means that they will fit on most gantry mills, of course. However, when it comes to chewing substantial lumps out of steel, most gantry mills are just not designed for that. If you use a softer material, they will work just fine.

A Word about the Software

This book does not provide detailed stepby-step instructions for any software package. There are detailed instructions for two of the most popular packages in the section on basic movement, just to make sure you can get your machine moving, but the rest of the book assumes you can read the software manuals for the packages you are using.

The book deals both with programming and with the use of software that will generate a program for you from a drawing. The program generators are easy to use and are essential for many jobs, but they can be used for very simple tasks too.

Programming by hand is another kettle of fish entirely, and simple jobs can often be programmed directly, instead of always having to use a program generator. Sometimes, too, the program generators cannot cope with the way a workpiece has been set up on the mill, so the technique there is to use the program generator to create the main parts of the program and to add a few lines of your own program instructions to link those elements.

So you, as the user, will need a knowledge of both programming and program generators. In the real world, one cannot wholly exist without the other. Besides, some knowledge of what is going on under the hood is useful.

Skip lightly across the deeper waters at any point; move on and continue reading. You may wish to come back later to any of the sections of the book as you gain experience and feel the need.

The machine control software packages Mach3 and LinuxCNC are used for the examples throughout the book. Both packages do the same job, but while Mach3 is a more graphically oriented system, with many accessible menus for setting up the links between software and the machine tool, LinuxCNC provides a much more elegant programming environment.

Most CNC packages share a common core, and that includes many of the other CNC control programs that are available. By using examples from both Mach3 and LinuxCNC, this book should be applicable to most CNC control software currently available from commercial vendors as well as the packages being used by hobbyists who have built or assembled their own CNC systems.

It is quite possible to use both software packages with the same machine at different times, and reading about both software approaches might help you decide what is most appropriate for you.

Vectric software has been used in many examples in the book. Vectric has a range of software applicable to a lot of the techniques illustrated in this book. The Vectric packages are essentially program generators that can convert drawings or photographs into programs that can be used by a CNC control program to machine the end product.

A Word about the Approach

The approach throughout is focused on practical aspects of CNC machining. The book explains a range of techniques, from the simple to the ambitious, which can be used to machine various features on a workpiece. The simple techniques can be put to use straight away, while the more ambitious are there to encourage you to use your machine to the full. A manual mill can carry out a good range of machining tasks, and the point of owning a CNC mill is to push the boundaries of what can be machined on a workpiece. You might, for example, mill a simple rectangular lid for a box; but with a CNC mill, it is a very small step to engrave the top, give the edge a complex smooth and flowing curve, or texture one of the faces. These are all things that would be very difficult to do with a manual mill, but they really bring a piece of work to life.

There are suggested projects throughout the book that are designed to allow you to practise what you have read. Later projects deliberately provoke thought. They are all there for you to enjoy.

A BIT OF HISTORY TO SET THE CONTEXT

The modern machine tool has its origins in the fifteenth century, but computer control of machine tools is a much more modern phenomenon, dating from the 1950s.

Hand tools have a longer history, and since early times, skilled artisans have used tools like files, chisels, hammers and scrapers to produce work that has sometimes been of astonishing accuracy and beauty. Accurate clocks and scientific instruments, for example, were initially produced using hand tools. Skill is an important factor, though, and two craftsmen working from the same set of drawings or instructions will inevitably produce work that differs in accuracy and finish, according to their individual levels of skill.

The rise of mass production in the early 1900s demanded that components produced by individual workers be sufficiently similar to allow interchangeability of parts so that a complete assembly, like a car or a firearm, could be made from parts produced by any worker.

This also meant that repairs could be made by replacing individual parts from a stock of standard parts. The demands of mass production led to the development of standards for drawings, systems of measurement and tolerances on components, and repeatable accuracy in manufacture . All of those are important for CNC machines.