Basic Benchwork for Home Machinists

Les Oldridge

• Publisher: Fox Chapel Publishing
• Year: 2020
• ISBN:
  9781607657279
• Topic: Technology & Engineering
• Subtopic: Technical & Manufacturing Trades
• Index: Technology & Engineering

For apprentices and amateur metalworkers, this book is a practical, hands-on guide to engineering benchwork that teaches all the valuable hand tool skills and procedures for files, punches, hand filers, and more. Well-illustrated with concise technical diagrams, tables, and black and white photos, you'll learn all the tricks and gain a solid foundation in the basics of engineering benchwork that will become second nature over the course of your career as a metalworker. Not only are these proper practices essential knowledge to get started in the industry, but they will also save you spoiled work and tools.

Chapter 1

Introduction

Modern engineering workshops are equipped with machine tools capable of producing components to such accurate limits that hand fitting at the bench is no longer necessary. Mass production methods render the skills possessed by old-time fitters in danger of being forgotten forever. This is a pity, as in many situations, the ability to complete a job using only hand tools is a great asset. In any case, it is often quicker to bring a component to the correct dimensions using a hand method than it is to spend time setting up the job in a milling machine or shaper, even if one is available.

Machine tools owned by the model engineer are often limited to a lathe and, perhaps, a bench drilling machine, so he has to become skilled in the use of hand tools. The purpose of this book is to describe the basic skills he must acquire. It takes a great deal of practice to reach the standard required, and although disappointment may be experienced at first, with the slow progress made, the satisfaction when the job is concluded is well worth the work involved.

It must be emphasized that no textbook, however comprehensive, can take the place of actual experience at the bench. The best advice is to “have a go,” perhaps on a bit of scrap material, to gain the necessary skill and confidence before working on a valuable casting.

Throughout this book, special emphasis will be made on safe working. In industry, this is looked after by the Health and Safety at Work Executive, but in the amateur’s workshop, there is no legislation to ensure the worker has a safe working environment. It is up to the individual to look after himself and to help to this end the various hazards likely to be encountered will be outlined from time to time.

A simple first aid kit, and the knowledge of how to use it, is desirable. A fire extinguisher is also a good investment and the Fire Prevention Officer from the local fire department will be pleased to give free advice as to the best type to purchase to suit your particular needs.

If good work is to be produced, a sturdy, rigid bench, fitted with a good quality vise, is essential. Most model engineers are not wealthy and setting up a workshop is a costly business. I hope to suggest, where possible, ways of cutting costs without sacrificing quality. For example, good secondhand timber is often available at low prices; when buildings are being demolished, a tactful word with the site foreman may provide just what is needed to build a bench at low cost.

Fig. 1.1 Vise clamps bent up in aluminum, copper, or lead, dimensions to suit vise.

Legs made from at least 3 in. square timber and the top from 2 in. planks should be aimed at. The space between the legs can be used to house a useful cupboard.

The size of the vise will depend on the type of work to be undertaken, but it is better to have one a little larger than is thought to be necessary, to allow for “future expansion,” that is, for the bigger jobs which may come along later.

The height of the bench should be such that the top of the vise jaws are in line with the point of the user’s elbow. This makes filing accurately much easier, but more about that later.

The vise jaws are serrated to prevent the work slipping when roughing down. Clamps, sometimes called clams, to fit over the jaws are needed to prevent these serrations from damaging finished surfaces. They may be made of lead, copper, aluminum, or fiber or any other soft material (see Fig. 1.1).

Various special clamps can be made to hold round, or odd, shaped work securely in the vise. Fig. 1.2. shows an easily made and useful device for holding round bar or pipe. Holes of a size to suit the bars in common use are drilled, as shown, in a piece of mild steel 25mm × 12mm (½ in. × 1 in.) and of a length to accommodate the number of holes required. A saw cut is made through the center of all the holes, except the end one. A similar gadget for holding threaded material can be made in a like fashion, except that the holes are threaded before the gadget is split with the type of thread generally used. These two projects form a useful exercise after reading the chapters on hacksawing, drilling, and cutting screw threads!

Fig. 1.2 Vise clamp for holding round bars.

Chapter 2

Materials

Before looking at the various tasks which are performed at the bench, the materials on which we shall be working and their properties must be discussed. It is important that the most suitable material for the job in hand is chosen. Often this will be specified in the drawing from which we are working, but sometimes we have to decide what to use.

The following properties then have to be considered:

STRENGTH. The strength of a material is its ability to withstand stress without breaking. The load, or stress, may tend to stretch, compress, twist, or cut the material. These are termed tensile, compressive, torsional, or shear forces. See Fig. 2.1. The strength of a material varies with the type of stress to which it is subject. For example, cast iron has good compressive strength but relatively poor tensile strength; it is about four times stronger when it is squeezed than when it is stretched.

ELASTICITY is the ability of a stressed material to return to its original shape when the load is removed. Spring steel has a high elasticity factor. Plasticine has practically no elasticity. Most materials are elastic below a certain limit, known as their elastic limit. If the stress applied exceeds this limit, the material is permanently deformed.

PLASTICITY is the reverse of elasticity and is the property of a material to retain any deformation produced by loads after the load has been removed. Steel is plastic at red heat and can be forged to shape.

DUCTILITY is the ability in a material to be drawn out by tensile forces beyond its elastic limit without breaking. This property is important in the production of wire, the wire being produced by drawing metal through dies that get progressively smaller.

MALLEABILITY is a similar property to ductility, except that the material is deformed beyond the elastic limit by compressive forces, such as rolling or hammering, instead of by a tensile force. Lead is a malleable material but lacks ductility because of low tensile strength.

BRITTLENESS. A material is brittle where fractures occur with little or no deformation. Glass is a classic example of a material with this property.

TOUGHNESS is the ability to withstand shock loads.

HARDNESS is the ability of a material to resist penetration, scratching, abrasion, indentation, and wear. In the laboratory, it is measured by applying a load to a small area of material by a hard steel ball or pointed diamond, and measuring the depression made into the material under a given load. Chisels, lathe tools, and center punches, for example, must have this quality to do the job for which they are intended. Unfortunately, the harder carbon steel tools are made the more brittle they become, so some hardness must be sacrificed for toughness in the tempering process. This will be discussed more fully in the chapter on hardening and tempering.

Fig. 2.1 Compressive, tensile, shear, and torsional stresses.

SOFTNESS, obviously, is the opposite property to hardness. Soft materials may be easily shaped by filing, drilling, or machining in a lathe, milling machine, or shaper. In many cases the component is hardened by one means or another, to be discussed later, after the shaping process is completed.

MATERIALS

Materials can be divided into a number of groups, such as:

1. Metals, which can be subdivided into ferrous and non-ferrous metals. This is the group with which we are most concerned but the others will be met from time to time.

2. Plastics, are now widely used in industry and which the model engineer will occasionally use them.

3. Timber.

4. Ceramics—the name originally given to materials made from clay but now used to cover a wide range of materials.

FERROUS METALS

These are the metals containing iron. Metals are rarely used in their pure state but are combined with other metals to form an ALLOY. In the case of iron, carbon is the most important addition. Although it is only present in small amounts, it causes big changes in the property of the metal.

CAST IRON this form the iron has been melted and poured into a mold, usually made of sand, in which it is allowed to solidify. This is a simple, convenient, and relatively cheap process to manufacture components of a complicated shape. Cast iron is an alloy of iron and carbon with small amounts of manganese, silicon, sulfur, and phosphorus. It contains about 3% of carbon.

There are two types, gray and white. Both get their names from the appearance of the metal when fractured. In white cast iron, all the carbon present is cementite; in gray cast iron, most of the carbon is present as flakes of graphite, and there is usually a remainder which is in the form of pearlite. Because cementite is intensely hard, white cast iron is hard and durable, though very brittle. Graphite is soft and is a good lubricant, so gray cast iron is readily machinable, less brittle, and suitable for sliding surfaces. Being hard and brittle white cast iron is rarely used alone but it is the material used for the production of malleable iron.

GRAY CAST IRON, then, is the type in common use; it is cheap and easy to cast and machine. As a typical example, a motor car cylinder block contains 93.32% iron, 3.3% carbon, 1.9% silicon, 0.8% manganese, 0.14% sulfur, and 0.18% each of phosphorus, molybdenum, and chromium. The carbon content of approximately 3.3% consists of about 0.7% of combined carbon and about 2.6% of free carbon.

Because of the free carbon content, cast iron is easy to machine and file; the carbon flakes act as a lubricant, enabling the cast iron to be machined dry. Drilling or tapping of cast iron components is fairly easy, no lubricant being required. There is, however, a hard skin in which some of the molding sand may still be present. This is particularly hard on lathe tools, and when it has to be filed, an old file should be used; a new one would probably be ruined.

Cast iron is used for model engine flywheels, internal combustion engine cylinders...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Chapter 1 Introduction
• Chapter 2 Materials
• Chapter 3 Reading Engineering Drawings
• Chapter 4 Hacksaws
• Chapter 5 Files and Filing
• Chapter 6 Hammers, Chisels, and Punches
• Chapter 7 Scrapers and Scraping
• Chapter 8 Measuring
• Chapter 9 Marking Out
• Chapter 10 Drills and Reamers
• Chapter 11 Screwed Fastenings, Spanners, Screwdrivers, and Pliers
• Chapter 12 Taps and Dies
• Chapter 13 Riveting
• Chapter 14 Soft Soldering
• Chapter 15 Silver Soldering, Brazing, Bronze Welding, and Engineering Adhesives
• Chapter 16 Welding
• Chapter 17 Hardening and Tempering Tools
• Chapter 18 Keys, Keyways, Splines, Collars, and Shafts
• Chapter 19 Sheet Metalwork
• Appendix
• Acknowledgments