reading

First published in the United Kingdom by Special Interest Model Books, 2003.

First published in North America in 2012 by Fox Chapel Publishing, 1970 Broad Street,

East Petersburg, PA 17520.

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.

eISBN 978-1-60765-143-7
ISBN 978-1-56523-693-6

Library of Congress Cataloging-in-Publication Data Hall, Harold, 1933-

Metal lathe for home machinists / Harold Hall.

p. cm.

Includes index.

ISBN 978-1-56523-693-6

1. Models and modelmaking–Handbooks, manuals, etc. 2. Turning (Lathe work)–Amateurs’ manuals. 3. Metal-work–Amateurs’ manuals. I. Title.

TT155.H26 2012

684’.083–dc23

2011040393

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eBook Version 1.0

Because working with metal and other materials inherently includes the risk of injury and damage, this book cannot guarantee that following the instructions in this book is safe for everyone. For this reason, this book is sold without warranties or guarantees of any kind,expressed or implied, and the publisher and the authordisclaim any liability for any injuries, losses, or damages caused in any way by the content of this book or the reader’s use of the tools needed to complete the processes presented here. The publisher and the author urge all readers to thoroughly review each process and to understand the use of all tools before beginning any project.

The main aim of this book is to take the newcomer to turning from the novice stage through to an experienced beginner, achieving this by providing a range of projects each one primarily illustrating a particular process. Finally the book concludes with two quite advanced projects that will put to the test the skills learnt in earlier chapters.

Having spent a short while as editor of Model Engineers’ Workshop, I am also aware that many have limited time for workshop activity and these, even if experienced, will find the projects useful as most can be completed in a matter of a few hours. No doubt, some useful tips being gleaned from the book on the way even for the experienced turner.

Whilst just reading the book will provide the beginner with much useful information this will be a poor substitute to actually making the items described. The reader is therefore encouraged to at least make most of the items detailed.

Removing metal using a metal work lathe is a straightforward process with quality work being easily achievable. However, the range of processes possible make the task of coming to terms with operating a lathe quite an extensive course that this book aims to provide.

Using a milling machine is on the other hand quite the reverse with obtaining a presentable finish much more of a problem but with each task being much more like others carried out on the machine. In this case the main requirement is to spend time on the machine to feel at home with its capabilities. A follow-up book to this will address the requirement with a range of projects aimed at giving the necessary time spent using the machine.

Prior to getting to grips with the projects in this book some discussion regarding the lathe and the accessories that go with it is included for the newcomer to turning.

Of course a lathe is a necessity, though for some this may initially be a machine available at the local technical college. If you are purchasing a lathe for the first time it is difficult to advise, as it will depend on the type of work envisaged and what other machines are to be acquired, two points are thought worth emphasising. First, if space and funds are available purchase a lathe of at least 90mm bed to centre height and secondly purchase a lathe with a tee slotted cross slide. The last point is a must if the workshop will not have a milling machine and even if it has many simple milling operations are easier to perform on the lathe as is illustrated in Chapter 13 Photos 14 and 15. However, as the projects are primarily aimed at those with limited experience it is assumed that other activities, typically milling, are even more of an unknown quantity. Their use in the series is therefore limited. A drilling machine will be required, but using the lathe for drilling as an alternative is briefly considered.

Whilst the use of cutting tools with replaceable tips considerably reduces the amount of grinding necessary to produce and sharpen lathe tools, some specials are bound to be required. An off hand grinder is therefore a necessity.

Having dealt with the machines there is a number of accessories that are a must. It is easy to fall into the trap of considering that, due to its ease of use, a 3-jaw chuck is the one to acquire if funds will run to one chuck only, this is not so. Whilst a 3-jaw chuck, even if old and worn, will be accurate enough for most work there will be a significant number of instances where this is not so.

The beginner may not be aware that when material is placed into a 3-jaw chuck the work piece is unlikely to run true, perhaps a total indicator reading (TIR) of up to 0.1mm, more if measured some distance from the jaws. This can cause serious problems with concentricity when an item has to be removed and replaced, say to work from either end.

Even a so-called precision chuck, with a price tag to go with the precision, will be unable to meet the most demanding requirements. A 4-jaw chuck with independent jaws is therefore a necessity as, being able to adjust each jaw individually, precise centring is possible. Of course where a 3-jaw chuck is adequate I will use one and this is evident in the photographs published. Where a reader has only a 4-jaw chuck this will be quite satisfactory. The only result being to slow down the operation a little due to the work necessary to get the part to run sufficiently true for the task in hand.

An essential accessory for the 3-jaw chuck are the reverse jaws that enable larger diameters to be held and are seen on the right of Photo 1. A new chuck will always be supplied with these but if you have obtained a second hand chuck, maybe with a second hand lathe, they may well be missing. Unfortunately, spare jaws are not easily obtained and a replacement chuck may be the only option. One set of jaws will suffice for the 4-jaw chuck as its differing construction permits the single set of jaws to by used either way round.

Changing the jaws on the 3-jaw chuck is straightforward; open the chuck with the normal jaws fitted, and keep turning until the jaws can be removed. Now it will be found that both chuck and jaws are numbered 1, 2 and 3 and must be fitted with the numbers together and in that order. Turn the scroll in the direction to close the chuck, until its leading edge is seen to pass position 1. Next reverse the rotation until the leading edge passes back, fit jaw number 1 pushing it in as far as it will go. Then holding it there, again turn the chuck key as to tighten the chuck. Watch carefully for the scrolls leading edge to pass position 2, repeat the exercise and then also for jaw 3. Now close the chuck until the jaws meet in the middle. If you have made an error it will be large enough to be obvious and it will then be a case of repeat the task until all’s well. Independent jaw 4- jaw chucks also have their jaws numbered and should be assembled with like numbers together, though they can of course be assembled in any order.

Having said that the reverse jaws are for larger diameters it is necessary to know at what diameter the change over must take place. If a new chuck is purchased the data supplied with it should make this clear; my 100mm chuck quotes a maximum of 33mm. Whilst the jaws will open and grip a larger diameter some of the scroll will be disengaging from the teeth on the jaws placing more load on those remaining engaged. Frequently, scrolls will have just two rings, so if a scroll is not engaged only one ring and a single tooth are being used. It is not advisable therefore to go beyond the maker’s recommendations. If these are not available careful observation of the scroll, which becomes visible as the chuck is opened, should make the requirements clear.

At this stage I should add that the book is written assuming a lathe of around 90mm bed to centre height and fitted with at least 100mm diameter chucks. Larger lathes are unlikely to impact on the book’s content in any major way, though smaller lathes will and some comments are added through the series if considered appropriate. If a small lathe is being used then some items may benefit from being made smaller. In this case I would advise taking copies of the drawings and marking them up with the new dimensions in advance of making the item.

Photo 2 shows both fixed (on the left) and travelling steadies. A fixed steady is, I consider, a very underestimated lathe accessory being an essential item, for without it many operations would be totally impossible, or at best very difficult. A fact that is well-illustrated thoughout the book. A travelling steady though is for most lathe users an item that has limited use and can be put on the end of the “items to be acquired list”, though managing without it where a use for it exists can be a problem. Its use is illustrated in chapter 11 Photo 12.

Various cutting tools will be required with the knife tool being that most used, and in both left and right handed versions. Photo 3 shows some variations, I will refer to these throughout the book as, right hand on the right and left hand on the left. Right hand is used for cutting from right too left and Left hand from left to right. I make this precise definition as I find in the wider world there seems to be some variation in the meaning of left and right hand.

Also required are boring tools for a minimum bore of 6mm, say 20mm deep, and larger diameters of 20mm and more with a depth of say 50mm. Whilst knife tools can be ground from high speed steel, ready made brazed tungsten carbide tipped tools or replaceable tip tools are available as seen in the photograph and at a reasonable price. This is certainly not the case for very smaller boring tools which most certainly have to be ground from high speed steel tool bits, as whilst they are available their price probably prohibits their use in most home workshops. Some specialised tools will also be required, thread cutting, etc., and will be discussed at the point in the book where they become necessary.

Parting off is probably the most dreaded of all turning operations for the small lathe user but is a task that must be conquered. Taking the part from the chuck and cutting it off with a hacksaw whilst held in the vice is a possibility and one that we shall adopt initially. Eventually though, parting off must be mastered and hopefully before the end of the book.

I know you will be tempted to cut off a part using the hacksaw whilst the part is still held in the lathe, we all are. I would not recommend this but if you do succumb to the temptation, do protect the lathe bed with a block of wood and move the saddle well down the lathe to avoid catching ones knuckles on the cutting tools. Even with this done, cover the tools with a few layers of substantial cloth and DO NOT UNDER ANY CIRCUMSTANCES carry out the operation with the lathe running.

We therefor need parting off tools of varying widths to use with differing diameters. It should be obvious that you would not use a 3mm wide tool to part off a part from a 4mm diameter bar and that a 0.5mm wide tool would be more appropriate. On the other hand a 0.5mm tool would not be at all appropriate at 50mm diameter and a wider tool would be required.

Whilst parting off tools can be used mounted on the top slide the use of a rear tool post will significantly ease the task. Having one available cannot be too strongly advised particularly for larger diameters, Photo 4 shows a typical example.

A dial test indicator is required, as some projects will need precisely centring in the 4-jaw chuck to a level of accuracy that is difficult without one.

Hard (dead) and Soft (live) centres will be necessary for turning between centres and driving dogs for these operations. When facing the end of a part supported by the tailstock centre, machining the end fully is impossible no matter what tool is used. This problem is overcome by the use of what is called a “half centre”, in fact it is more a case of a five eight’s centre as it is not cut away totally to the centre. The cut away permits the cutting tool to access the face right up to the drilled impression, (see SK 1 Chapter 2). A small half centre made from silver steel and held in the drill chuck avoids the expense of an additional centre and is perfectly adequate for finishing the end of a part otherwise turned between conventional centres. Why not make this a mini project before turning starts in earnest in the next chapter.

A drill chuck and a 25mm outside micrometer also fall into the essential category with a 25 to 50mm micrometer and a 150mm vernier being highly desirable. Other simple items will be required and we will attempt to make some of these as the work progresses. This is in some cases essential as they are not available commercially. An important lesson to learn here is that even if a task can be undertaken with the equipment to hand, it can often be carried out, more simply, more quickly, or more accurately, by the addition of some simple home made accessory. Examples of this certainly surface throughout the book, typically the collet holding fixture in Photos 12 to 15, Chapter 13.

This is detailed with each individual project and in the case of mild steel will probably be sizes that are already available in the workshop, though some larger sizes will no doubt have to be purchased. I would strongly recommend that all mild steel should be a genuine, free cutting grade purchased to specification rather than relying on unknown materials that are to hand.

If as a beginner you have yet to build up a stock of materials, do ensure that materials you purchase are of a known grade, as one supplier’s so called “free cutting mild steel” may be quite different from that from another. I would suggest steel to BS970 1983 ref. 230M07 is obtained, (very similar to the older specification BS970 1955 ref. EN1A that is still frequently referred to) and the ends marked, perhaps stamped FC, so that its grade is known when used in the future. For non-UK readers 230M07 is an international standard and is likely to be understood by your local supplier. Even more easily machined is a similar grade but with lead added this has the reference of 230M07Pb (ENIAPb). The lead content makes it very much easier to machine but also unsuitable for welding; it is of course a little more expensive and not available in so many shapes and sizes.

I cannot stress to strongly the benefit of taking such an approach; advice that I give gained from bitter experience. Recently, I made a gear hobbing machine that had two very similar spindles but one having a slightly larger diameter. Having completed the one satisfactorily I found the finish being obtained with the second was very inferior. Using the same tools, but re-sharpened in view of the problem, trying differing tools, speeds and feeds was all to no avail. The only answer was that the material, being a different diameter, was of a different and inferior grade.

With the book being especially, though not entirely, aimed at the beginner, descriptions and photographic evidence of methods used is more extensive than is the norm. Operations will in some cases prompt for greater precision than perhaps is necessary, purely to acquire the experience. Similarly, set-ups will err on the side of caution, both for safety and experience. A typical case being the use of a fixed steady where perhaps with greater, first hand experience this could be avoided. I would therefore say, please do work to the methods proposed. You can take your own approach in the future as knowledge of the operations and the ability of the machines you are using is gained over years of use.

The beginner to using a metal working lathe can be forgiven for considering that coming to terms with the turning process is as follows. Chose the correct cutting tool for the job, the correct speed and the correct rate of feed and with this done the skill has been conquered. As important as these are, they do have considerable tolerance as to their choice. In most cases the critical decisions are the methods to use, typically, whether to use the 3 jaw, 4 jaw, faceplate or turn between centres. Of even greater importance in many cases is the machining sequence. It can be very frustrating to have machined a part to a stage where it is found difficult to progress further, say due to difficulty in holding it for the remaining operations. An example of this would be the need to support a part with a fixed steady but not having left a suitable portion of the component where the steady can be applied.

Frequently the difficulty in machining a part will be due to the design and if this is someone else’s there is less scope to overcome the problem, though some minor changes may be possible. If you are producing your own design, then manufacturing the item on the machines available should be an essential early consideration of the design process.

Much has been written regarding the use of metric dimensions and this is not the place to expand still further on the subject. The book is though dimensioned almost exclusively in metric dimensions, only where a part is to marry with a genuine imperial dimension will the imperial value be given. Realising though that many readers will have imperially calibrated machines some guidance is necessary, especially as the articles are aimed at the novice.

The complications in working to metric dimensions on an imperial machine are very overstated; in fact it is quite easy. Replacing your machinery for metric calibrated ones is quite unnecessary, the answer being in HAVING metric measuring equipment, NOT converting the metric dimensions given to their imperial equivalents. As some items are dual calibrated such as rules, verniers, height gauges, we are left only with micrometers. Purchasing a 0-25mm micrometer and if possible a 25-50mm version also, is a very cheap way out of the problem if the following approach is taken.

When carrying out machining operations, few if any will attempt to arrive at the final size taking just one sizeable cut. The work will be carried out on the basis of, measure, large cut to get closer to size, measure, small cut to get very close, measure, final very small cut to arrive at size. With that approach the following will make working to metric dimensions on an imperial machine a very easy operation. Measure the part and determine how many millimetres have to be removed then set the depth of cut on the basis that 1mm equals 0.040 in. (40 thou.). This will of course introduce a small error but as the part is to be measured again and a further cut taken the error will be of no importance. When getting closer to the size required, work on the basis that 0.1 mm equals 0.004 in. (4 thou.). Again this will introduce an error but now very small, but will also be eliminated by further measurement if greater precision is required. If the part requires greater precision then work on the basis that 0.01mm equals 0.0004 in. (0.4 thou.) As 0.01 mm equals 0.0003937 in, this is an error of 0.0000063 in., which is quite insignificant even if you are taking a cut of many times this amount.

The point to realise is that the errors introduced by using these conversion factors get eliminated at each stage by the part being measured again in metric dimensions.

Having first decided that an item is a project worth undertaking there are a number of preliminary actions that should be considered a must. First, and vitally important, is to study the drawings so that you fully understand what has to be made and in particular how the parts interrelate. In industry, part drawings would include tolerances so that parts made at separate times, and maybe in different locations, can be guaranteed to fit together when coming together for assembly. In the home workshop this is rarely necessary as the second part can be made to fit the first. If tolerances were quoted and a small error was made in the first part, few would be prepared to scrap this if a small adjustment to the size of the second would permit the first still to be used. Understanding the drawings is therefore an essential part of this approach. Next, as far as is practicable, determine the manufacturing methods. However, through this book I will be detailing these and would advise staying with them to gain the experience intended. For any projects undertaken beyond those in the book you will of course be “on you own”.

TIR. Total indicator reading. When a part is running out of true an indicator applied to it will deflect positively on one side by the amount of the error. At 180 degrees from this position however the deflection will be negative, again by the error. The movement of the indicator is therefore called the ‘Total indicator reading” being twice the error present.

DTI. Dial test indicator. Strictly speaking this is a measuring instrument for measuring small differences in position. This usually has a small swinging arm for applying to the workpiece and its measuring range is in the order of +/- 1mm only. This compares with a “Dial Indicator” that normally has a plunger to apply to the workpiece and has a range of 10mm plus. Of course a Dial Indicator can be used in place of a Dial test indicator, and in home workshop terminology the two terms are often confused.