Sheet Metal Work E-Book

Marcus Bowman

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

Seitenzahl: 312

Veröffentlichungsjahr: 2014

Beschreibung

Sheet metal is a common and widely used material, which can be easily worked using hand tools or simple machinery. There are lots of opportunities for designing, making and using sheet metal parts to produce elegant, effective and low cost solutions for new items, repairs and modifications to existing components. This new guide takes a practical approach to the manufacture of sheet metal parts, and explains how you can make full use of hand tools and machines to produce ambitious work of a high standard. Topics covered include the use of specialist tools such as snips, nibblers, folders, the jenny, the flypress, punches and dies; and techniques for manufacturing a wide range of sheet metal parts, including marking out, cutting, bending, joining and finishing. There are practical projects to illustrate the use of techniques and tools. Fully illustrated with 337 colour illustrations and 109 CAD diagrams.

Leseprobe

First published in 2014 byThe Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

www.crowood.com

This e-book first published in 2014

© 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 DataA catalogue record for this book is available from the British Library.

ISBN 978 1 84797 779 3

DisclaimerSafety is of the utmost importance in every aspect of the workshop. The practical procedures and the tools and equipment used in engineering workshops are potentially dangerous. Tools should be used in strict accordance with the manufacturer’s recommended procedures and current health and safety regulations. The author and publisher cannot accept responsibility for any accident or injury caused by following the advice given in this book.

Contents

Acknowledgements

Safety First

Introduction

  1  Materials

  2  Drawing and Developing Stages

  3  Measuring and Marking Out

  4  Cutting Sheet Metal

  5  Making Holes

  6  Bending Sheet Metal

  7  Rolling, Beading, Flanging and Wiring

  8  Joining

  9  Forming, Pressing and Drawing

10  Surface Finishing

Projects:

  1  Fuel Tank for a Model Aircraft

  2  Motorcycle Ammeter in a Tin Can

  3  Fluidizing Tank

  4  Spigot for a Workshop Dust Extractor

  5  Car Exhaust Expansion Chamber

  6  Panels for a Sack Barrow

  7  Folding Steam Iron Shelf

Further Information

Index

Acknowledgements

The author would like to thank those ­individuals and companies who expended time and effort to contribute photographs, illustrations and information for this book:

Rachael Bowman (photographic assistant)

George Nutt, Dennis Nutt and Chris Visscher at RMS Engineering Ltd

Dennis Nutt (Kilkerran)

Fred Anderson

Dewar Anderson

Sheryn and Steve Clothier at www.corrugatedcreations.co.nz

Tinplate Girl at www.tinplategirl.com

Dave Parker at Buxton Model Works

William Hurt at www.ageofarmour.com

Leslie Chatfield

Brian Walbey

John Saunders at www.NYCCNC.com

Jonas Boni at www.quarz.ch

Gary Tucker

RMT-Gabro and the M J Allen Group of ­Companies

EDMA Outillage

TRUMPF Group

Warren Machine Tools Ltd

RIDGID Tool UK

Irwin Tools

JD Squared Inc.

Jack Sealey Ltd

But most of all, a very special thank you to Hazel and Rachael, my long-suffering personal support team, for making the writing task so much easier.

Safety First

Pause for a moment, before you rush into the workshop to mangle metal for your latest project. The risks in most workshops deserve some careful thought, but the risks attached to working with sheet metal are amongst the greatest posed by any ma­terial. There are two particular risks: one associated with sharp edges, and the other the risk to hearing.

THE RISKS ASSOCIATED WITH SHARP EDGES

During the French Revolution, the guillotine was an effective way of separating head from body, and its effectiveness was largely because sheet metal behaves like a very slightly blunt razor. Because the edge of a sheet is so thin, the pressure it exerts is very high. You might get a nasty bruise or even break a bone if you strike your hand with a hammer or a large flat piece of metal, but strike your hand with the edge of a sheet and the injuries are likely to be much more severe, as the pressure instantly parts flesh, rips tendons, and slices through bone.

The edges left after a cutting operation usually have a fine, almost invisible burr which acts like a sharp razor saw, and the consequences of casually brushing a finger along such an edge are gruesome indeed. Yes: the edges of sheet metal deserve the utmost respect. Whenever possible, avoid handling the edges of sheets, and at the very least, wear good, heavy-duty, protect­ive gloves of leather or Kevlar, and do not allow your hand to slide along an edge.

When moving sheets, avoid the edges and use mechanical aids such as a magnetic clamp or a sling with a metal hook.

Protect your feet from falling sheets by wearing good-quality protective boots, with steel toecaps.

In the UK, the Health and Safety Executive provides good guidance in Engineering Sheet No. 16 in the article ‘Preventing injuries from the manual handling of sharp edges in the engineering industry’. Even if you are not an industrial user, you should avail yourself of this advice.

THE RISKS TO HEARING AND SIGHT

Striking sheet metal produces a distinctive noise that incorporates a great many very high notes and a ringing sound. Repeatedly striking metal, as when shaping a panel for example, produces an astonishingly high level of energy, and endangers hearing. The best protection is found in good-quality ear protectors with at least 30dB attenuation. Invest in the best protection you can, because hearing, once lost, cannot be restored.

Wear good eye protection made to proper industrial standards at all times, even if you wear spectacles. Proper wraparound ski-style industrial goggles with impact-resistant lens material and soft seals around the face allow the comfortable use of spectacles. Eye protection should be able to resist puncture and impact. It should be comfortable to wear, and when it gets scratched, you should replace it. Think of it as a cheap investment in the most sensitive biological devices imaginable. Eyes cannot be replaced, and good protection is cheaper than medical bills.

CREATING A SAFE ENVIRONMENT

Sheet metal tools and machinery deserve your respect and your full attention, as a slip in concentration can easily lead to injury. Folders and press brakes present a temptation to fingers, welders may burn, and plasma cutters simply vaporize their target, so risk assessment and maintaining a keen awareness of potential risks will serve you well.

Read the instructions supplied with machinery and tools, and seek advice where you lack experience. Most skilled workers will be delighted to guide you and make you aware of hazards.

Take particular care when other people are present in the workshop. You have a duty of care to others, especially if they are unfamiliar with the workshop or the equipment. Watch those sharp corners if you are moving sheets when others are present; there is something resembling magnetic attraction between edges and unsuspecting bodies.

Throughout this book there are pictures of cutters and machinery that do not always have guards visible. These pictures are for illustration, to help you to see and understand what is being said or shown. Nothing in this book should be taken as an indication that we suggest, recommend or endorse working practices that are potentially hazardous or unsafe.

The sheet metal workshop is a creative place, and there are few pleasures as great as creating an object that not only serves a useful purpose, but may well be a thing of considerable beauty too. If that can be achieved in a safe environment, so much the better.

Introduction

ABOUT THIS BOOK

The aim of this book is to explain the tools and techniques required to produce sheet metal parts that are fit for purpose, accurately made, and attractively finished. This is a practical book, designed to be enjoyed by those of us who delight in making things, and it includes a set of projects that ­illustrate many of the techniques and tools.

This is a book about accurate methods and predictable, repeatable results. Although sheet metal lends itself to artistry and the kind of free expression that can lead to beautiful one-off objects, that kind of approach is not to be found within these pages. Nor is there any explanation of techniques of car-body manufacture or repair. Instead, the book is about making accurate drawings, then using those drawings to produce accurate components from sheet metal and small-diameter rod. The contents range widely over the materials, machines, tools and techniques which might be found in workshops and small factories. There is much talk of developing accurate shapes and templates, bending allowances, methods of attachment, and attractive finishing techniques.

There is some reference to stretching and shrinking, but this book does not deal with the handwork techniques required for car-body panels or artworks. There are methods and examples of punching, shearing and deep drawing, but little is said about spinning, as the applications of this in the smaller workshop are more restricted.

The approach to technical drawing covers the fundamentals of drawing layout, and looks forwards by explaining the basics of computer-aided design and drawing because that is the modern way. There is no attempt, though, to teach the use of one specific package, as that deserves a book or two on its own. Those readers who wish to develop their abilities in drawing by hand, still a surprisingly useful skill on site, must seek to learn from examples elsewhere in one of the established classics.

Because the book deals with modern methods, laser, water jet and plasma cutting are mentioned as being everyday industrial processes. We are perhaps not quite at the stage where laser cutters for metal are readily available at low prices, but these techniques now have their place in sheet metal work, and being able to order lasercut parts is a natural consequence of understanding computer-aided drawing.

Despite the entrails of Britain’s imperial past, and the rather mixed situation in North America, the units used throughout this book, including sheet metal thicknesses, are metric, as are thread sizes and specifications. That is intended to make the book accessible and usable right around the world.

This is therefore a practical book, to be enjoyed by everyone from the model engin­eer to the light industrial user; to be taken to the workshop and to be used to produce the kind of work that is real, usable, and rather beautiful besides.

SOME HISTORY

It is difficult to imagine modern life without metal objects – in fact, civilization and the history of human progress are inextricably linked with the discovery and use of metals. From the first discovery of gold around 6000BC, and its use in the manufacture of jewellery, to much more modern discoveries such as Lawrencium in 1961, the practical uses of metals have changed the way we live.

The first metals – gold, silver, copper, lead, tin, mercury and iron – brought a range of applications that transformed human cap­abilities. Gold was decorative but soft, and although not strong enough to be used for structural applications (because if the Golden Gate bridge had been made of gold, it would not have been strong enough to support itself), its softness allowed it to be hammered into very thin foil, paving the way, later, for the use of sheet metals.

Although soft by comparison with iron, copper was one of the more useful metals, because it was soft enough to be formed into shape, yet hard enough to be used for tools and weapons. Copper remains an extremely useful metal, in all its forms, and is widely used in sheet, tube and bar form in applications such as sheet roofing, electrical cables and conductors. And where would plumbing have been, without copper tube?

Bronze is an alloy (mixture) of copper and tin, and the discovery of bronze was so significant that it has given its name to a lengthy period in human history and development. In Europe, developments during the period from 3200–600BC were based on the uses of copper and bronze. Bronze is harder than copper, and can be used to make tools and weapons that are more durable (hard-wearing) than similar items made using copper alone. A bronze chisel, for example, holds a sharper edge for longer, and deforms less when struck, than a copper chisel. These characteristics of ­durability and hardness enabled significant progress during the Bronze Age.

But this period also proved the value of creating alloys, which are essentially mixtures of metal elements in various proportions, to make other metals that have different characteristics than the pure metals used in the mix. In more modern times, that same process is used to mix copper with aluminium, both soft metals, to produce an alloy which is much harder and stronger than the original elements, while retaining some of the useful characteristics of both.

Iron is an important element, but the period between the beginning of the Iron Age, and the industrial production of the more important steel (an alloy of iron and carbon with small quantities of other elements) was a long drawn-out process. Although the smelting of iron ore to produce iron was taking place in India by 1800BC, and steel was being produced sometime between AD200 and AD300, the mass production of industrial quantities of steel had to wait until the invention of the Bessemer converter in 1855. Only then could sufficient quantities of steel be produced to power the Industrial Revolution.

From the earliest times, engineers have been concerned with the application of materials, and producing and using a range of materials suited to particular tasks. The efficient use of materials is important because of cost, and good design makes effective use of the properties of particular materials, seeking to produce objects that are effective for their purpose, able to be manufactured efficiently, and at the lowest cost. While some objects might initially have been hewn from lumps of metal by a blacksmith, good engin­eering has seen the production of similar objects that use a fraction of those materials, cleverly arranged to take best advantage of the properties of that material.

For example, in Victorian times a lamppost might have been cast in iron – decorative, but massively constructed, heavy and expensive to produce. Modern lampposts are lighter and may consist of iron, aluminium and/or copper. While the style may be different the cost is lower, yet both old and new perform the same function.

Metal has been available in sheet form since the earliest days of the use of gold, when sheet, foil and rod were used to make jewellery, a practice that continues today. Although the softer metals such as gold, silver and lead could be hammered into sheet and foil, or later, rolled, industrial rolling mills to produce sheet of consistent thickness in quantity were only introduced in Europe and then England in the late sixteenth century.

In the early twentieth century, the adoption of sheet metal bodies for mass-­produced cars brought about developments in the engineering design and shaping of sheet metal not only for the bodywork but for ancillary items such as the chassis, brackets, radiators and trim. Making the car as light as possible reduced the cost while increasing the performance, and a major contribution to low weight was the clever use of thin sheet metal. Latterly, the body itself was designed to act as the chassis, by using monocoque construction made possible entirely because of sheet metal design techniques. The development of alloys designed to allow deep pressing without excessive stress enabled the production of body parts featuring complex curves and folds.

The mass production of aircraft brought similar developments, mainly in aluminium and its alloys, and together with the automobile industry, became a great driving force behind developments in the design and use of sheet metal in manufacture. The heating and ventilation industry adopted sheet metal for ducting, and became a major user of this form of metal, which could be made sufficiently rigid yet allowed the use of techniques for forming complex bends, transformations from square to round, and ease of assembly and on-site fixing.

Together, the automobile, aircraft and heating and ventilation industries became, and remain, major employers, contributing in a very significant way to the economies of the major industrial areas of the world.

Sheet metal roofing, in use worldwide but perhaps more popular in the USA than elsewhere, makes use of the simple characteristic whereby changing the shape of a sheet, in this case by adding corrugations or repetitive folds, adds to its strength, allowing it to span a considerable distance without appreciable deflection. The use of zinc coating to protect steel made sheets sufficiently durable to be able to resist corrosion outdoors, adding to the capability of roofing materials made from sheet. Currently, steel and aluminium roofing and guttering is available in convenient, large, lightweight panels with protective coatings and factory-injected insulation, making the assembly of large roofs a relatively straightforward job.

Laser cutting and CNC forming of components from sheets has brought an increase in the complexity of design but ease of assembly with lower cost. These new techniques sit alongside the traditional techniques and machines that our forebears would recognize, and together they allow the design and fabrication of sheet metal parts for a large range of jobs, whether for mass production in a factory, small batch production in a smaller industrial unit, or on a one-off basis in a garage or home workshop. A collection of hand tools and some small machines will allow sheet metal to be cut, folded, rolled and joined, making the production of specific parts quite straightforward. Finishing those parts using some of the basic processes of filing, grinding and polishing will result in completed work-pieces of which both the light industrial factory and the home workshop user can be proud.

A replacement hub cap for a 1924 Bullnose Morris Oxford, made from stainless steel tube and sheet, embellished with a brass ring, and topped by an aluminium hemisphere.

1 Materials

This book deals with sheet, tube and rod in a range of metals, and all manner of items made from those basic forms.

CATEGORIES OF SHEET METAL

Sheets of metal are available in various sizes and thicknesses, varying from extremely thin 0.025mm (0.001in) to 150mm (6in) thick, or more. Working methods at the extremes of the range are quite different, so sheets are grouped in the following ­categories:

Leaf: A thin sheet, often of precious metal, varying in thickness from a few atoms thick to 0.025mm (0.001in). The most common example might be gold leaf.

Foil: A thin sheet, thicker than leaf and thinner than sheet. Foil varies in thickness from 0.025mm (about 0.001in) to 0.15mm (0.060in). Foil is typically available in the precious metals – gold, silver, platinum and palladium – as well as other semi-precious metals such as copper and brass. Other, more commonly available metals such as aluminium are often used as foils, for example baking foil.

Sheet: A flat sheet, thicker than foil, and thinner than plate. Sheet varies in thickness from 0.15mm (0.06in) to 6mm (0.24in). In this book, most sheet will fall between 0.15mm and 3mm (0.125in) simply because anything over 3mm thick becomes difficult to shape, and usually needs heavier machinery and a different set of techniques. The ease with which a sheet can be shaped varies with the properties of the material, with steel being more difficult to work than copper, for example, so the material determines how feasible it is to work with sheet in the range 3–6mm (0.125–0.25in).

Plate: Anything thicker than sheet (over 6mm) is termed plate.

SHEET THICKNESS

Sheet thickness can be expressed in millimetres or inches, but it is often easier to use standard reference numbers from the standard wire gauge (SWG), Brown & Sharp (B&S), which is sometimes called American wire gauge (AWG), manufacturer’s standard gauge (USA), Birmingham gauge (UK). The number of different ‘standards’ is confusing, and the gauges used for ferrous (steel) and non-ferrous (aluminium, brass, copper) sheets are different, so this book will use metric thicknesses and the sheet metal gauges and imperial (inch) equivalents as shown in Table 1.

The following should also be noted:

◆  Metric sheet is now available in standardized thicknesses, so the full range of possible SWG thicknesses cannot be obtained in metric sheet

◆  Not all thicknesses are available in all sizes of sheet, nor are all thicknesses available from all suppliers

◆  SWG differs from AWG

◆  Sheet thicknesses are nominal, and exact thicknesses depend on ­manufacturing processes and ­tolerances, and may vary from one supplier to another, or one batch to another

◆  Some thicknesses are only available in particular finishes: 0.7mm steel sheet, for example, is often only available as Zintec galvanized sheet

SHEET STEEL

Sheet steel is available in a wide range of thicknesses, and is produced by rolling thicker material to a final size by reducing its thickness. The rolling process may be carried out when the steel is hot (above the recrystallization temperature of steel), or cold (below the recrystallization temperature). Recrystallization affects the strength of the finished sheet, and cold reduced (CR) sheet is stronger than hot rolled (HR) sheet, as well as having a better surface finish. It requires less pressure and less power to hot reduce a sheet, however, and recrystallization produces a more uniform internal structure as well as making the metal more ductile.

Sheet steel is commonly available in cold reduced form (sometimes referred to as ‘cold rolled’) to specification EN 10130:1991 (formerly BS1449-1:1983/CR4), European steel specification DC01:1.0330: this steel is commonly referred to as DC01 or CR4. The characteristics of grades D01 to D06 are listed in Table 2.

Table 1: Sheet steel (ferrous) thicknesses

Hot rolled sheet is available to specification EN 10051:1991 +A1:1997 (formerly BS1449 –S1.2 (1991) HR4-Dry/P&O) ­European steel specification.

Fig. 1-1 shows a modern replica of a ­traditional suit of armour which demonstrates creative use of mild steel sheet and wire, as well as brass detailing. Fig. 1-2 shows an unusual use for a very ­traditional sheet material: corrugated iron, which is still widely used as a roofing and cladding ­material in many parts of the world.

Table 2: Sheet-steel grades D01 to D06

Grade

Properties

Applications

DC01

Drawing quality

Stretching, bending, roll forming

DC03

Deep drawing quality

Deep drawing, demanding stretch forming

DC04

Non-ageing deep drawing

Demanding deep drawing and stretch forming

DC05

Non-ageing deep drawing

Demanding deep drawing and stretch forming

DC06

Low-carbon non-ageing special deep drawing grade

The most demanding deep drawing and stretch forming

Fig. 1-1: Mild steel sheet, wire chainmail and brass detailing on a replica suit of armour. William Hurt is the maker. WILLIAM HURT.

Fig. 1-2: Nikau detail: a tree made from corrugated iron. The makers are Sheryn and Steve Clothier at Corrugated Creations. SHERYN AND STEVE CLOTHIER .

ALUMINIUM

Available in its soft form, aluminium sheet is also commonly available in harder grades, with properties as shown in Table 3.

Aluminium is readily available in sheets with the following specifications (seeTable 4).

Table 3: Hardness of aluminium

Strength code

Properties

F

As manufactured; no heat treatment

O

Annealed, soft

T4

Heat-treated; naturally aged; stable

T5

Artificially aged

H12

Hardened: quarter hard

H14

Hardened: half hard

H16

Hardened: three-quarters hard

H18

Hard

Table 4: Aluminium grades

Grade

Characteristics

Properties

1050–‘0’

Temper: ‘O’ softSurface finish: good (can be highly reflective)Anodizing: goodCorrosion resistance: very goodCan be more easily cold formed but has less strength than 1050AWelding qualities: excel-lentMachinability: poor

Tensile strength 80N/mm

2

Yield strength 35N/mm

2

(approx.)Shear strength 50N/mm

2

Elongation 42%Vickers hardness 20

1050A–H14 Formerly S1B H4

Temper: H14 ½ hardSurface finish: very goodAnodising: goodCorrosion resistance: very goodCan be cold formed. Ideal for bending or spinningWelding qualities: goodMachinability: poor

Tensile strength 100-135N/mm

2

Yield strength 75N/mm

2

(approx.)Shear strength 70N/mm

2

Elongation % (A50) 4-8Brinell hardness 35

3003–‘0’

Temper: H14 ¼ hardSurface finish: goodAnodizing: goodCorrosion resistance: very goodCan be cold formed and has more strength than 1050AWelding qualities: very good

Tensile strength 200–240N/mm

2

Yield strength 130N/mm

2

(approx.)Shear strength 125N/mm

2

Elongation % (A50) 4-8Brinell hardness 60

3103–H14

Temper: H14 ½ hardSurface finish: goodAnodizing: goodCorrosion resistance: very goodCan be cold formed and has more strength than 1050AWelding qualities: very good

Tensile strength 140N/mm

2

(minimum)Yield strength 110N/mm

2

(approx)Shear strength 90N/mm

2

Elongation 8% (minimum)Vickers hardness 46

5251–H14 Formerly NS4 H3

Temper: H14 ½ hardSurface finish: goodAnodizing: goodCorrosion resistance: very goodCan be cold formed and has more strength than 1050AWelding qualities: very good

Tensile strength 200–240N/mm

2

Yield strength 130N/mm

2

(approx)Shear strength 125N/mm

2

Elongation % (A50) 4-8Brinell hardness 60

Fig. 1-3: Bracket made from aluminium angle.

Fig. 1-3 shows a simple bracket made from commonly available aluminium angle.

BRASS

Brass sheet is available in different grades (seeTable 5), and the colour is slightly different depending on the exact composition of each grade, varying from a yellow to a deeper gold colour. Not all thicknesses and sizes of sheet are available in all grades.

Brass is often plated with other materials, to protect its surface, or for decorative effect (seeFig. 1-4).

Table 5: Brass grades

Grade

Characteristics

Properties

CW505Formerly CZ106

Machinability: goodFormability: poor

70/30 ‘cartridge’ brass with a high copper content

CW508Formerly CZ108

Strength: excellentHardness: excellent

High purity brass alloy

CW612Formerly CZ120

Cold working: goodMachinability: good

Leaded brass alloySuitable for engraving

CW712Formerly CZ112

Corrosion resistance: suitable for marine environmentsStrength: higher than normalMachinability: not as good as CW612

‘Naval’ brass, containing tin

Fig. 1-4: Brass plates used as instrument housings; these items would originally have been plated with nickel or chrome. The vehicle in this photograph is owned by Dennis Nutt.

STAINLESS STEEL

The addition of at least 10.5 per cent chromium gives stainless steels improved corrosion resistance as compared to ‘ordinary’ steel. There are three commonly used grades of sheet: 304, 316 and 410, as listed in Table 6.

Stainless steel can be given an attractive polished finish, and is widely used in structural and decorative applications, despite carrying a higher price than mild steel. Fig. 1-5 demonstrates the difference between polished and unpolished finishes on ­stainless steel items.

COPPER

Most commonly available to specification ASTM B370, copper sheet is available in six tempers: 060 (soft), H00 (cold rolled), H01 (cold rolled, high yield), H02 (1⁄2 hard), H03 (3⁄4 hard), and H04 (hard). Copper sheet is normally 99.9 per cent pure, but lead-coated copper is also available.

Copper is a soft metal and is very malleable, so it is easily beaten, pressed or rolled into shape. Cold-rolled copper is less malleable but stronger than soft copper, so that H00 1⁄8 hard is less malleable but stronger than 060 (soft). Grades up to H04 (hard) are increasingly strong but have decreasing malleability.

Copper has excellent electrical conductivity, and good resistance to corrosion.

It can be easily welded, brazed or soldered. Fig. 1-6 shows a piece of copper sheet, as well as copper used as a hammer head, a task for which it is well suited despite its initial softness, as it work hardens with repeated impact.

Fig. 1-7 demonstrates the change in colour as copper cladding on a roof is exposed to the weather.

Table 6: Common grades of stainless steel

Grade

Characteristics

Properties

304

Corrosion resistance: goodFormability: excellentWeldability: excellentGrade 304L recommended for welding

18% chrome, 8% nickel

316

Corrosion resistance: better than grade 304Formability: excellentWeldability: excellentGrade 306L recommended for welding

Has added molybdenum.Better characteristics at high temperatures than grade 304

410

Corrosion resistance: moderateFormability: reasonableWeldability: poorGrade 306L recommended for welding

Can be heat-treated to produce excellent hardness properties

Fig. 1-5: Stainless steel discs, before and after polishing.

Fig. 1-6: Copper-headed hammer on a copper sheet.

Fig. 1-7: Copper changes colour dramatically when exposed to the weather.

Tinplate

Tinplate is thin steel sheet which has been coated with tin. Plating was formerly applied by dipping the steel sheet in a bath of molten tin. Current practice is to electroplate the sheet to apply a very thin coating of tin, typically 800 millionths of a millimetre (30 millionths of an inch) thick.

Tinplate has the mechanical properties of steel, but the non-toxic properties of tin, and is easily soldered. It is often used to make tins and similar containers (seeFig. 1-8), and is also used for manufacturing household items, and some electrical components such as shielding for electronic equipment.

Fig 1-8: Still commonly used for everyday items, tinplate is also available in sheet form.

NICKEL SILVER

Nickel silver contains no silver! It is an alloy of copper, nickel and zinc, often in the following proportions: copper 60 per cent, nickel 20 per cent, zinc 20 per cent. It is available in several forms, including sheet, and it has good electrical conductivity, good machinability, and its corrosion resistance is good, although it is not suitable for applications involving prolonged contact with acidic foods or drinks. It also solders easily. And it looks a lot like silver. . .

WIRE

Wire is available in a range of materials: steel, stainless steel, copper, silver, gold, aluminium and many others. In the same way that sheet is thinner than plate, wire is considered to be thinner than rod, and is usually specified by diameter, with the SWG numbers being widely used.

The term ‘wire’ refers to a single strand, although the term has come to be used loosely, with multi-stranded electrical conductors being called ‘wire’, for example. Several strands of wire, intertwined, is properly termed a ‘rope’, no matter how small its diameter.

Fig. 1-9: At the rear, from the left: steel, brass, stainless steel and phosphor-bronze wire. At the front: nichrome wire. .

Piano wire is made from spring steel which is hardened and tempered high-­carbon steel. Its original use is for piano strings, but it is in common use for many other tasks that require the characteristics of a spring. Heating piano wire alters the temper and removes much of the spring, which distinguishes it from steel wire.

Nichrome wire is an alloy of nickel and chromium which may also contain iron. It has a high electrical resistance and is often used as a heating element in electric fires, electronic cigarettes, hair dryers and many other domestic products. It is also used in foam cutters.

Fig. 1-9 shows a small range of wire made from different materials.

Vent stacks: stainless steel sheet and mesh.

2 Drawing and Developing Shapes

An artist might use a drawing to represent an object, and the style of the drawing might evoke a mood or highlight some aspect of the object to draw attention to its shape, its colour or its surroundings – but the way the drawing is interpreted by different viewers will depend partly on the viewer and their emotional connection with the subject of the drawing.

An engineer, on the other hand, uses a precise system of drawing which has strict rules for the use of lines and points so that everyone viewing the drawing will interpret it in the same way. An engineering drawing will provide all the information needed for an engineer to be able to make a particular object, and all the objects produced by following the drawing will be identical. Aside from any notes written in a specific language, engineers of any nationality should be able to interpret the drawing because it is based on a tightly specified set of visual rules.

In the UK, the rules governing engineering drawing are contained within the British standard ‘Technical product documentation and specification’ BS 8888:2011 (published in December 2011). BS 8888:2011 incorporates the International Standards Organisation standard ISO/TC 213 (GPS – Geometrical Product Specification) which applies across Europe and much of the rest of the world.

In the USA, the most widely accepted standards are based on the American Society of Mechanical Engineers standard Y14.5M (revised in 2009) and the American National Standards Institute standard Y14, both of which also recognize ISO/TC 123.

In this book, drawings are shown using third angle projection, where convenient, so that they are compatible with most systems and conventions. Furthermore all dimensions (‘sizes’) are shown in milli­metres, because that is the preferred unit of measurement in the BS and ISO standards, and may also be used under ASME Y14.5M.

Although it is useful to have an understanding of both manual ‘paper and pencil’ methods and computer-based drawing techniques, this chapter provides only an overview of computer-based methods, and no practical details of paper and pencil methods. There are several classic manuals available for paper and pencil methods (see Further Resources), with many practical examples, and each of the major software packages has its own manuals and training materials. Both approaches are valuable, but deserve a much more complete explanation in greater depth than can be given here.

The rest of this chapter discusses drawing views, then illustrates the basic methods used to draw sheet metal parts using a computer-aided design package.

BASIC DRAWING VIEWS

Although sheets of metal begin life as flat surfaces in two dimensions with a uniform thickness, most assembled real-life objects are three-dimensional, so it is natural to begin with the completed object, and then work out the shapes and sizes of the ­component parts.

Fig. 2-1: Sketch of a sheet metal bracket.

Fig. 2-1 shows a sketch of a bracket. To show the full details of the bracket we need to be able to see it from different angles. Convention and the rules of engineering drawing suggest we should show the front, the side, and the view from the top. Here’s how it is done:

◆  Imagine standing directly in front of the object, looking directly at it. Draw what you see, and put the drawing on the centreline of the page, a little less than halfway up the page (see Fig. 2-2). This is the front elevation (elevation meaning simply ‘view’).

◆  Imagine standing to the right of the object, looking directly at the right side, then draw what you see. Put the drawing on the right of the page, on the same level as the front elevation (so the bottom of the bracket will be at the same level in both views): this is the right side elevation (seeFig. 2-3).

◆  Repeat for the left side of the object, putting the drawing on the left (Fig. 2-4). That is the left side elevation.

◆  Then imagine looking directly down from above; draw what you see, then put the drawing directly above the front elevation. That is the plan view.

Fig. 2-2: Drawing of the bracket, showing the front elevation.

Fig. 2-3: Drawing showing the front and right side elevations.

The terms ‘front’ and ‘side’ are relative, as is the term ‘plan’, but they are useful in referring to views on the drawing because these are all accurately related to one another.

Those views are usually enough for an engineer to be able to see all the details on the object. In fact, one elevation is usually enough, in which case it is just called the side elevation. If the other side elevation shows hidden detail, include that view. There are occasions where additional views will be needed to see some details, but this basic set of three views is the best place to start, and is well understood by all ­engineers.

There are different ways of placing the views of the faces of an object in a drawing, and in order that an engineer should know which layout is being used, the symbol shown in Fig. 2-6 is used to denote third angle projection, which is a particular arrangement of views. If the symbol is as shown in Fig. 2-7 it denotes a different layout system, termed first angle projection, once common in some parts of the world but now superseded.

Fig. 2-4: Drawing showing the front, right and left side elevations.

Fig. 2-5: Drawing showing the front, right and left side elevations and plan.

Fig. 2-6: Symbol denoting Third Angle projection layout.

To allow accurate manufacture, dimensions can be added to a drawing, and lines used to connect the dimensions with particular features of the drawing. Place the dimension values above, on or below the dimension lines, oriented so that they are the right way up when the drawing is read from the bottom, or from the right-hand side.

Fig. 2-7: Symbol denoting First Angle projection layout.

COMPUTER-BASED DRAWING

In the beginning, some forty years ago, the approach to producing technical drawings using a computer was based firmly on a simulation of manual methods. In more recent times, drawing has become a subset of design, and computer-aided design (CAD) software now allows the user to draw in three dimensions, then produce the classic two-dimensional flat drawings often used for manufacture.

Drawing in three dimensions (3D) has many advantages, although the approach differs considerably from that of classic manual drawing. Packages such as Autodesk Inventor, Solidworks, RhinoCAD and Turbo-CAD 3D create 3D objects by using a set of tools to manipulate a basic 2D sketch to produce the 3D shape. This means that the kind of inner mental conceptualization required for manually drawing a 2D representation of the object – which very often does not exist at that stage – is, to a large extent, bypassed, and the user is very quickly working with a 3D object which can be rotated, scaled and altered on screen using the tools provided by the software.

Thus a physical drawing board with parallel motion mechanism and precision drafting head is replaced by screen, cursor, mouse and software tools, and once an object exists within the computer, the production of standard 2D drawings is a trivial exercise taking a few clicks of the mouse. Production of the developed shapes of component parts is a similarly simple procedure, taking little mental effort on the part of the operator.