Dividing

Tools and Techniques

Alexander du Pre

• Publisher: Crowood
• Year: 2014
• ISBN:
  9781847978394
• Topic: Technology & Engineering
• Subtopic: Technical & Manufacturing Trades
• Index: Technology & Engineering

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.

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 enabl...