Precision Dividing for Small Shop Metalworkers E-Book

Harold Hall

• Herausgeber: Fox Chapel Publishing
• Kategorie: Lebensstil
• Sprache: Englisch
• Veröffentlichungsjahr: 2022

Seitenzahl: 113

Beschreibung

A skill that consists of precisely spacing cuts, dividing is a crucial technique for gear cutting and radial work on a metalworking lathe. This complete guide to dividing clearly explains its principles  and covers everything a model engineer needs to know about dividing and several methods that can be achieved – from simple applications without specialized equipment to the use of a semi-universal dividing head and a rotary table. The mathematics of dividing are also included and written in an easy-to-understand format that won't intimidate. Author Harold Hall was the editor of Model Engineers' Workshop magazine and established himself as a mentor to Tyro model engineers worldwide. He is also the author of seven books in the indispensable Home Machinists Series.

Leseprobe

PRECISION DIVIDING

FOR SMALL SHOP METALWORKERS

PRECISION DIVIDING

FOR SMALL SHOP METALWORKERS

HAROLD HALL

Copyright © 2022 by Harold Hall and Fox Chapel Publishing Company, Inc., Mount Joy, PA.

Copyright © Special Interest Model Books Ltd 2005

First published by Special Interest Model Books Ltd. 2005

First published in North America in 2022 by Fox Chapel Publishing, 903 Square Street, Mount Joy, PA 17552.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior permission of the copyright holder.

Print ISBN: 9781497101968eISBN: 9781637411322

Library of Congress Catalog Number: 2021945099

To learn more about the other great books from Fox Chapel Publishing, or to find a retailer near you, call toll-free 800-457-9112 or visit us at www.FoxChapelPublishing.com.

We are always looking for talented authors. To submit an idea, please send a brief inquiry to [email protected].

For a printable PDF of the patterns used in this book, please contact Fox Chapel Publishing at [email protected], with 9781497101968 Precision Dividing for Small Shop Metalworkers in the subject line.

CONTENTS

Chapter 1

An introduction to Dividing

Chapter 2

The Machinery. Discusses the major items of equipment, Dividing heads, Rotary tables, Indexers, etc.

Chapter 3

The Methods. Explains how to use the equipment in Chapter Two to achieve the required result. Also explains though how even complex dividing can be achieved using no other equipment than that normally found in the workshop, typically the lathe and milling machine.

Chapter 4

The Mathematics. While the tables provided with a dividing head, or those published in this book, will provide the information for most applications, occasionally recourse to calculation may be necessary. This chapter explains the process, fortunately, the mathematics is not complex.

Chapter 5

Holes on a Pitch Circle Diameter (PCD) Explains the mathematics for placing holes on a PCD using a milling machine’s X and Y table movements and their calibrated leadscrew dials. Also shows how using a computer spread sheet program can be used to limit considerably the work involved.

Chapter 6

Shop Made Simple Dividing Devices. Some simple devices that will enable dividing activities without the need for a dividing head.

Chapter 7

Shop Made Basic Dividing Head. A simple dividing head that is easy to construct, and for most, will be adequate for all the dividing tasks required in the workshop.

Chapter 8

Shop Made Full Function Dividing Head. A dividing head that is more adaptable than a commercially available semi-universal head and providing a wider range of divisions. It is not over complex to make and would be a very satisfying project to complete.

Chapter 9

Shop Made Lining Tool. Engraving a dial with its different length lines is made easy with this lining tool. It is also an interesting project to construct.

Chapter 10

Prime Numbers. Prime numbers and their uses explained and listed.

Chapter 11

Tables. Tables for a wide range of dividing head ratios and division plate hole numbers are included. These should make the need for calculation a rare occurrence.

Preface

While in the home workshop, dividing is not a frequent operation, there are though many ways of carrying out the task. This is quite different to the major workshop activities where round items will invariably be the domain of the lathe and rectangular items, that of the milling machine, with the shaper chipping in in a few cases.

Dividing, however, can be carried out on the lathe, milling machine and even the drilling machine. It is though, the wide range of accessories and methods that make the task a daunting one for many workshop owners.

In addition to choice of method, setting it up correctly will often require recourse to some mathematics. These, mathematically, are fortunately quite simple, but some understanding of their purpose is essential.

The book can therefore be loosely divided into three sections.

1. The machinery

2. The methods

3. The mathematics

In addition to the explanations of the equipment and how it is used, the book also includes some designs for items that can be made in the workshop itself. In the main these just give the necessary drawings but with some manufacturing tips where considered desirable.

Dividing will almost certainly be a small proportion of workshop activity, but without the required provisions, and understanding, some projects will either be impossible, very difficult or of a very inferior quality.

Harold Hall January 2005

1. Cutting a gear using a shop made dividing head.

Chapter 1

An Introduction to Dividing

While the term dividing can be applied to a range of values, typically length, weight, angle, even voltage, in the metal working workshop, home or commercial, it is used almost entirely for angular division. The range of uses will be varied but with a high proportion of the activity limited to a small range of tasks, making gears Photo 1, dials, placing holes on a PCD (pitch circle diameter) and producing squares and hexagons, typically for application of a wrench to a turned component.

The methods of achieving the division will though be large and varied and range from the simple to the complex, each finding a use in at least some workshops. Perhaps not fully appreciated is the fact that simple methods are not just limited to lower numbers, in some applications, dials typically, even higher numbers can be achieved without any expense being incurred.

For many years the predominant method in the home workshop, at least for the simple task, was to make attachments for the lathe spindle to control angle of rotation. Today, greater availability and reduced price of modern accessories have made this less necessary. There are still instances where it is worth considering. Carrying out some work on a component in the lathe mounted chuck having just been machined there, may be quicker than setting up the dividing head on the milling machine and transferring the component to this.

2. A commercial semi universal dividing head with tailstock

3. A rotary table, useful for dividing in some applications.

If dividing is to become an important activity then acquiring a semi-universal dividing head, commercially made Photo 2 or made in the workshop, should be considered. As a dividing head will likely get only limited use and the expense as a result difficult to justify, the latter may well be the way to proceed. Because of this, designs for two shop made items are included in Chapters 7 and 8.

Using a rotary table Photo 3 is also a possibility and while this item of equipment is primarily intended for the machining of curved surfaces and slots and the like, its use for dividing is also possible.

When placing holes on a PCD, working out the X and Y co-ordinates of each hole and using these to place the holes using the milling machine table dials as shown in Photo 4 can give a very accurate result. This can be particularly useful if requiring a dividing plate for use on the dividing head especially if for a one off application.

4. Making a dividing plate on a milling machine table using calculated X and Y coordinates.

Chapter 2

The Machinery

The equipment available for dividing applications, even for the home workshop, is very varied, though in general terms, the methods can be reduced to just five.

Using the lathe spindle.

Using a dividing head.

Using a rotary table.

Using an indexer.

Dividing with no special equipment. The latter will be dealt with when discussing the actual processes. As will be seen however the demarcation between these is not always that clear, especially methods 2, 3 and 4.

1. Using the lathe spindle

This primarily consists of indexing the spindle using a detent locating into the teeth of a gear or holes in a disk that is mounted on the lathe spindle. The latter may even be in the chuck’s backplate. The most common is to use the gear in the back gear assembly that is rigidly fitted to the spindle, frequently referred to as the bull wheel. One well-known lathe manufacture does provide this facility and others may do also, it is though more common for the lathe owner to adapt the lathe to provide this function. Photo 1 shows a typical shop made item.

1. Indexing using the lathes Bull wheel

2. Indexing using a gear on the rear end a lathe’s headstock.

One aspect of the lathe that may make the method a non starter is the number of teeth on the gear, if say this was 49 there would be no useful divisions, only 7 being available. The gear in the above example has 60 teeth and will provide 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 and 60 divisions. If a forked detent is used this could be increased to include 8, 24, 40 and 120 also. More about forked detents later.

If your lathe does not have a suitable bull wheel then mounting a gear on the rear of the lathe spindle, as illustrated in Photo 2, and erecting a detent from some convenient point, probably the changewheels quadrant, will overcome the limitation. Even where the lathe has a suitable bull wheel this arrangement will increase the number of possible divisions. Mounting the gear, or even a dividing plate, is not difficult and a simple method for achieving this is illustrated in the section on shop made items in Chapter 6. A similar method for simpler numbers is to drill the chuck back plate with a series of holes around its periphery using a detent mounted off the lathe bed to locate in these.

A limitation of all of the above methods is that there is no facility to lock the spindle in the set position, relying solely on the detent to hold it in place. Backlash in the detent assembly will permit some variation in the position set, and more important, movement during the machining operation. It is though quite adequate for many tasks as will be seen through the book.

3. A semi universal head.

2. Using a dividing head

This is the most complex and costly of the dividing techniques covered in this book but as would be expected the most versatile; Photo 3 shows a typical example. As well as being used horizontally it can be set up vertically, Photo 4, or any angle in between. The first point to note is that the rotating spindle, which carries the workpiece, can be firmly locked in any position. This helps to minimize errors of position but more importantly permits quite heavy machining operations to take place.

4. A semi universal head can also be used vertically

Rotation of the spindle is achieved using a worm and worm wheel such that many turns are required at the manual input, for one turn at the dividing head output. A ratio of 40:1 appears most common but others may be available.

A dividing plate is fitted to the body of the device and the input spindle fitted with an arm and detent for locating in the dividing plate holes so that repetitive input can be achieved precisely. Dividing plates are available with a wide range of hole numbers. By choosing the correct one and with the 40:1 ratio the required division can be obtained by bypassing the appropriate number of holes for each division. However, even with a wide range of dividing plates there will be many divisions that cannot be achieved, particularly at the higher numbers. At one time dividing plates were very expensive but modern computer controlled production methods enable the punched sheet steel variety to be produced very cheaply.

Mounting the workpiece onto the dividing head follows very closely that of the lathe having the facility for fitting a faceplate or chuck, Also a center can be fitted and with a tailstock, either supplied or available as an accessory, between centers work can be carried out.

5. Two shop made rotary tables.

2a. Universal dividing head

Universal dividing heads, (the above being known as semi-universal) are capable of a much wider range of divisions, typically all values between 2 and 380 and many higher values. This being achieved by the addition of a gear chain between the dividing head spindle and the dividing plate itself, but while still using the limited number of dividing plate values normally supplied.

The drive from the manual crank handle to the dividing head spindle is still via the worm and worm wheel. However, a gear chain from the rear end of the head spindle is then arranged to rotate the dividing plate itself by a small amount. This has the effect of marginally altering the rotation of the crank handle for a given number of holes. The outcome of this is that divisions not obtainable with the semi-universal head can be set up. The gear chain is set up for differing ratios, rather like the changewheels used on a lathe for screw cutting.

The gear chain also has another purpose and while too complex to be discussed in detail it is worth noting for completeness. Rather than being between spindle and dividing plate, the gears are set up between spindle and one end of the milling machine leadscrew resulting in the output from the dividing head rotating as the machine table is traversed. By this method helical flutes can be cut. Should this be of interest, search out other reading on the subject.

3. Using a Rotary table