Dividing E-Book

Alexander du Pre

• Herausgeber: Crowood
• Kategorie: Lebensstil
• Sprache: Englisch

Veröffentlichungsjahr: 2014

Beschreibung

A new practical guide to dividing (indexing) in the workshop. Whether new to the process or looking to enhance your skills, this book will introduce you to a range of dividing methods and explains how to achieve the best results both with and without specialist dividing tools. With step-by-step instructions and photography throughout, this new book explains dividing with the 'coordinate method' and using the lathe; dividing with gears and dividing plates; using the dividing head, the rotary table and the spin indexer; electronic dividing methods and finally a range of case studies to show application of practical techniques. This practical guide to dividing will be of interest to home metalworkers, engineers and model makers. Fully illustrated with 212 colour photographs, 29 diagrams and step-by-step instructions.

Leseprobe

 C R O W O O D   M E T A L W O R K I N G   G U I D E S 

DIVIDING

Tools And Techniques

ALEXANDER DU PRÉ

First published in 2014 by

The Crowood Press Ltd

Ramsbury, Marlborough

Wiltshire SN8 2HR

www.crowood.com

This e-book first published in 2015

© The Crowood Press Ltd 2014

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 839 4

Dedication

To Penny, Daniel and Philip.

Acknowledgements

I would like to offer sincere thanks to the following people who have helped with the preparation of this book. Kirk Burwell of Hemingway Kits (hemingwaykits.com) for dividing head photos; Lester Caine of Model Engineers Digital Workshop (medw.co.uk) for photos of the DivisionMaster; Dr Marcus Bowman and my uncle, Clive Elliott, for invaluable advice; and to my family for their support and understanding.

Disclaimer

Although every effort has been made to describe safe working practice and to supply accurate information in this book, neither the author nor the publisher accept any liability whatsoever for any loss or damage occasioned by the application or misapplication of the advice contained or implied or for any errors included.

Contents

1  Introduction to Dividing

2  Dividing without Special Tools: the Coordinate Method

3  Dividing with Gears

4  Dividing Plates

5  Dividing without Special Tools: Using the Lathe

6  The Dividing Head

7  The Rotary Table

8  The Spin Indexer

9  Workholding

10  Electronic Dividing Methods

Index

1 Introduction to Dividing

SETTING THE SCENE

Imagine you are in your workshop. You have nearly finished machining a large casting involving several hours of careful work. Maybe it is a cylinder for a steam engine. The final job is to drill and tap a circle of bolt holes for the cover and a matching set of holes in the cover itself. You carefully mark out the positions of these holes in both parts before machining the holes. On completion you bring the two parts together only to find that the holes do not quite line up. The only solution is to drill the clearance holes slightly larger until the bolts can pass through and be tightened. At this point, you realize that the circle of holes is not quite centred in the right position. Whilst functional, the work is out of alignment and looks wrong. It ends up in the scrap bin.

This may be a familiar scenario to many inexperienced amateur machinists. The problems just described could have been avoided with the correct use of dividing techniques. The purpose of this book is to explain the theory and practice of dividing, which is perhaps one of the most commonly encountered machining operations after basic turning and milling work.

A typical home workshop garage conversion, equipped with lathes, a milling machine and a range of machine accessories and hand tools.

Since dividing work is so often needed, most metalworkers would consider it highly desirable to gain a good level of competence in dividing techniques and to equip themselves with at least some of the associated accessories.

This book is aimed at the amateur met-alworker keen to expand their repertoire of metalworking techniques and who may be on a limited budget but wanting to make the most out of a small collection of basic workshop machinery. It is envisaged that the reader will have access to a small home workshop, perhaps set up in a shed or garage and will have gained a basic competence in the use of the lathe and milling machine. It is hoped that model makers, model engineers, amateur machinists and anyone with an interest in metalwork will find this book of practical use and that it will help them to improve the quality of their work and the productivity of their time in the workshop.

DEFINITION OF DIVIDING

So, what is dividing and why is it useful? Dividing can be considered to be any operation where the objective is to machine equally spaced features, such as holes or gear teeth, around a circular path. These features are generally, but not necessarily, identical. They may be centred on the axis of a circular workpiece, or on any known point of an irregularly shaped workpiece.

Dividing may be approached in either of two ways, depending on the task in hand:

1.  The workpiece is rotated about a given axis in equal increments whilst the cutting tool is held in the same position and moved across, or into, the workpiece, as in cutting spur gears. This is the technique used by dividing heads and similar devices that provide a means of accurately indexing the work.

2.  The workpiece is fixed and the tool is moved around a circular path, as might be required when drilling a circular array of holes in a large casting, where it is not practicable to rotate the casting. This is the basis of the coordinate method, which can be used in circumstances where it is possible to control the position of the cutting tool accurately relative to the work.

Dividing is an essential technique for producing gears, ratchets, splines, dial graduations and similar items, or where equally spaced holes are required such as on pipe flanges, wheel hubs, brake discs, steam engine cylinders and any number of other applications. Whilst accurate dividing is generally made easier by using specialist accessories, there are often several ways of achieving the same results. This book will give you a range of options that will enable you to choose one that is most suitable for the job in hand and the equipment available, and hopefullyenable you to achieve the necessary results with minimum investment.

Dividing techniques were used to mill the spokes and drill the bolt holes on this model wheel.

Spur gears machined using a dividing head.

THE MATHS

This book aims to empower the reader by explaining the calculations supporting the various methods. Maths has only been included where essential, but some calculations are needed for the coordinate method and when calculating gear trains or working out dividing plate set-ups. Look-up tables have generally been avoided since they take up considerable space and do not make very interesting reading. Furthermore, it is difficult to make them relevant to your specific equipment due to the wide range of tooling available.

The maths involved is not particularly challenging but it can be rather repetitive. A calculator is essential, but a computer is even better if time is to be saved. The book is supported by the author’s personal website, www.amdengineer.com, which provides some of the free electronic resources referred to in the text.

The operation of pitching out equally spaced, and indeed irregularly spaced features, in non-circular arrangements is sufficiently closely related to dividing to merit inclusion in this book. For this reason, the coordinate method is described in application to both dividing work and to machining more generally.

Whilst this book is specifically about dividing techniques, some of the information included is of more general use. So whilst, for example, methods for setting up work have been explained in the context of dividing operations, the same methods can be used for other machining operations. The same applies to some of the work- and toolholding methods, which have broader applicability. One of the challenges faced by the amateur is to achieve maximum versatility from a limited range of tooling, and this has been in the author’s mind throughout the writing of this book.

EQUIPMENT REQUIRED

As well as a lathe or milling machine, or ideally both, with their standard toolholding and workholding accessories, a range of cutting tools will be needed, including milling cutters and drills and their associated collets or chucks. For setting-up purposes an accurate engineer’s square will be required as a minimum and preferably a dial test indicator.

As some dividing work can be achieved with a bare minimum, or indeed no accessories, the above equipment will be sufficient to get you started. A collection of more dedicated accessories can be gathered as the work requires and the pocket allows. A rotary table would be high on the list of priorities, followed perhaps by a dividing head.

In a small workshop, it is always desirable to extract the maximum value from the tools available by using or adapting them to perform a wide range of operations. Both the lathe and milling machine can be used for certain dividing operations without further tooling. The lathe in particular can readily be modified with some very simple accessories that can make it function well as a capable dividing head.

SCOPE AND LAYOUT OF THE BOOK

The book is intended to explain all commonly used dividing tools and techniques to the extent necessary to enable you to understand and use them competently. Whilst hopefully giving you a mastery of the basic mechanical equipment, the book introduces some more advanced electronic tools that can help you to complete the same operations more quickly and with less scope for error.

The book is laid out in a logical order with later chapters building on the principles covered earlier. It starts by explaining the coordinate method, which at its most basic can be achieved with just hand tools, but is more accurately applied using the graduated dials on the machine tool handwheels. The technique is attractive as it requires no specialist tools.

The coordinate method being used to position a circle of holes accurately without marking out.

Positioning a non-circular arrangement of holes using the coordinate method.

A dividing tool fitted with a gear train.

A dividing tool fitted with a dividing plate mechanism.

THE DIVIDING HEAD

The dividing head is a tool designed specifically for dividing work. It achieves this using a spindle that can be rotated in precise increments generally using either a gear train or dividing plates. Although you may assume that a dividing head is an essential tool for dividing work, this is far from being the case. Whilst its utility in this regard is undeniable, the function of the dividing head can generally be achieved by other means.

A simple home-made dividing head.

The dividing head in use on the milling machine.

The G. H. Thomas Versatile Dividing Head is a popular design suitable for home construction from available castings. The device uses either a sprung detent for simple dividing or dividing plates. Work can be supported either with the integral overarm or the separate tailstock. PHOTO: HEMINGWAY KITS

The E. Westbury Dividing Head is another design suitable for the small workshop. It is available as a kit and can be used on the lathe or milling machine. It can also be fitted to the lathe spindle to index work held in the lathe.PHOTO: HEMINGWAY KITS

The next two chapters explain how to use single or multiple gears and dividing plates to increment the spindle of a dividing device. As these methods are to some extent independent of the dividing accessory itself, they are explained in isolation.

Chapter 5 returns to the theme of dividing without specialist tools. Whilst Chapter 2 focuses on the milling machine, Chapter 5 is concerned with using the lathe as the basis for dividing. This can be achieved with the aid of some simple, easily made accessories.

The next three chapters focus on explaining the use of the more specialist dividing equipment, addressing in turn the dividing head, the rotary table and the spin indexer. These accessories can be used to rotate a workpiece in accurately controlled increments.

THE ROTARY TABLE

A rotary table equipped with a set of dividing plates can do more or less everything that a basic dividing head can, plus a wide range of other machining operations. That said, its design is not optimized for dividing work, with its main limitation being the lack of a spindle nose to fit workholding accessories. But this can be overcome with a little ingenuity, possibly making the rotary table a higher priority purchase than the dividing head.

A rotary table. Either a dividing plate or a graduated handwheel can be fitted, to suit the work in hand.

THE SPIN INDEXER

The spin indexer is like a simpler version of the dividing head and it is similar in design and use. It can achieve a more limited range of divisions but is slightly quicker to set up since the dividing mechanism is built in and does not require the fitting of interchangeable parts such as gear trains or dividing plates.

A spin indexer adapted to hold ER32 collets.

A digital read-out display system fitted to a milling machine. This system makes the coordinate method quick and easy.

A spin indexer fitted with a stepper motor controlled by a computer or microcontroller. This arrangement allows any number of divisions to be achieved quickly and easily.PHOTO: L.S. CAINE OF MODEL ENGINEERS DIGITAL WORKSHOP

Workholding is a vital part of any machining operation including dividing, where the workpiece must be held securely and rotated concentrically with the axis of the dividing device’s spindle. A chapter on workholding is therefore included.

The final chapter is an introduction to electronic dividing methods, focusing firstly on using digital read-outs in conjunction with the coordinate method and then on dividing devices driven by a stepper motor controlled by a microcontroller.

The approach used throughout the book is to explain the design and functionality of the equipment together with the theory of its use. These are then brought together in worked examples that demonstrate the equipment in a practical, real-world context. Later examples build on the preceding examples, minimizing repetition of the same instructions.

CONCLUSION

The examples in this book use basic equipment typical of a modest home workshop, with the intention of showing that most dividing work can be achieved without a great range of specialist tooling. However, a mastery of the techniques described will enable you to use more advanced equipment with confidence.

WORKSHOP SAFETY

No book on workshop practice would be complete without a brief reminder of safety. Whilst metalwork and machining could not be considered dangerous activities, there are many hazards that can catch the unwary and steps should be taken to reduce or eliminate these. Machine tools have powerful motors and sharp cutters which can do serious damage if things go wrong. Always keep body parts and loose hair and clothing away from moving machinery. Jewellery, including rings, can get caught on rotating parts so should be removed. Machine tools should be wired correctly by a qualified electrician. Machine accessories and workpieces should be securely clamped in place. Safety glasses should always be worn, as should protective clothing commensurate with the work in hand. Work methodically and safely at all times, avoiding short cuts and always consider any hazards involved and how they can be avoided before operating tools and machinery.

Safety precautions are not specifically detailed in the practical examples that appear throughout this book, but it is to be understood that safe working practice is intended at all times and that all safety precautions such as machine guards and protective equipment are to be used as a matter of routine. Although every effort has been made to describe and illustrate safe working practice in this book, you are ultimately responsible for your own safety, so please make this a priority to ensure continued enjoyment of your time in the workshop.

2 Dividing without Special Tools: the Coordinate Method

Special tools and accessories such as the dividing head and rotary table are naturally extremely useful for dividing operations. Making such accessories is well within the scope of the home workshop but can be time-consuming and requires special tools, including, annoyingly, dividing equipment. So dedicated dividing equipment may not be available in the newly established workshop, although it should certainly be near the top of the shopping list.