Engineering Drawing from First Principles Using AutoCAD, Revision and Self-Assessment Series 1st Edition by Dennis E. Maguire.
Preface by Dennis E. Maguire:
Thank you for your interest. My first introduction to the subject of technical drawing came at school, when at the age of 11, we started woodwork lessons. At the first meeting of the class Mr Munday, our teacher, told us that we would draw working plans of a simple joint. We were introduced to a drawing board, tee square, set of instruments, one sheet of snowy white paper and two paper clips. We were shown the principles of simple projection and then proceeded to copy views of a Lap Joint from the blackboard. I instantly found this to be a very agreeable relaxing exercise. The controlled use of the pencil, rule, square and compasses also enabled those of us without natural skills in freehand art and painting to be ‘in with a chance’.
At the next lesson we were taught how to prepare the wood, cut and make the two parts and finally check the accuracy of the assembled joint. In addition we could see every edge and corner represented by lines on the drawing.
This particular subject at school was especially popular with the other lads and the general class atmosphere very stimulating and rewarding. When the results compared favourably with the initial drawings I felt that I had really achieved something and soon developed a strong desire to continue studies. We all also took great pride in trying to keep the paper nice and clean and free of pencil smudges. I also always enjoyed the subject of Applied Geometry which is logical and required more constructional work on the drawing board.
When I left home in the mornings for school it was not uncommon to see a new neighbour of ours leaving for work. He was smartly dressed and carried a leather briefcase. Out of curiosity I asked my mother what Mr Oram did for a living and she found out that he was a draughtsman and made ‘plans’. I decided that this was quite a likely career for me and it certainly gave me some sense of purpose at school when I realised that you could actually get paid good money for doing something you really enjoyed. I later bought a small drawing board and tee square for use at home and copied examples from books in our local library and found that regular practice soon improves technique.
Pencil drawings are easily corrected but damage to the paper may arise. More important drawings for manufacturing and publication purposes were required to be produced in ink. This was a skill requiring lots of patience because ink is reasonably permanent and extensive errors on some surfaces needed a redraw. In industry, it was not uncommon for ink tracers to be employed to trace over pencil drawings onto transparent film after original designs had been produced, checked and approved. These days with the aid of a computer it is not necessary to worry about the state of the paper or the need to trace the finished designs to obtain a truly professional result. No need to keep sharpening the pencil to obtain consistent line thicknesses, no need to worry about spelling mistakes after you have inked in notes when you have otherwise nearly finished your work of art.
Variations in the height and slope of letters and numbers during dimensioning always used to separate the beginner from the professional and often spoil an otherwise sound drawing. These days lines and letters are all standardised and a spell checker available at the touch of a button, but it is still necessary for the draughtsman to be completely in charge. We have not reached the stage where the computer can dispense with the draughtsman. This fact needs to be broadcast very widely and regularly. It is definitely not sufficient to only become a proficient keyboard operator. Computers cannot conceive and produce original designs and drawings. With the aid of a computer though you can produce clear unambiguous drawings provided you adhere to the appropriate National and International Standards. This is the area where I hope to assist you and I am convinced that to develop your talents you must keep your hands on the keyboard.
In the following pages are exercises which I am sure will put some basic knowledge and skills into your fingers and also help generate some draughting speed. Do not worry or get disheartened if the results are a little slow in coming – with computing it happens to us all. As the title suggests, this book is about the production of drawings from basics. All of these drawings have been prepared with the aid of the computer but of course there is no reason why you could not redraw them on a drawing board if you so wish, as this would certainly develop manual ability and gain a clear understanding of the principles of Engineering Drawing. Not all drawing offices use CAD.
I started to teach this subject at evening classes in Hayes and the first drawing office I walked into had the following words printed on a strip of paper above the blackboard: ‘Little things make perfection, but perfection is no small thing’. As far as draughtsmanship is concerned there is a lot of truth in this short statement. In themselves, the rules are relatively simple but they need to be employed accurately and consistently, and applied thoroughly. The draughtsman also needs to be a quick and efficient operator and hence the value of practice.
The computer provides a range of facilities which are available for selection by the operator and often allows a job to be done in several different ways. With experience you will make your own pet choice of methods and hopefully achieve the same results. These graded examples start from a completely blank screen. I hope you will soon develop confidence and enjoy draughting with the aid of the computer.
Please note that job vacancies are equally available in drawing offices for both sexes so I wish to apologise for using the widely used collective noun of ‘Draughtsman’ to cover Drawing Office Personnel. It definitely implies equality of status and it is a pleasure to find an increasing number of young ladies enjoying employment in the drawing office. Thank you again for reading this book. I wish you well and every success in your studies and career.
The British Standards Institution was the world’s first national standards body and there are over 80 similar organisations world-wide which belong to the International Organisation for Standardisation (ISO). BSI represents the interests and views of British Industry.
The first edition of BS 308 to cover Engineering Drawing Practice was published in 1927. It is currently published in three separate sections and available in reference libraries throughout the country. The BSI catalogue lists over 10,000 publications and a Yearbook is usually available in reference libraries. Each year new or revised standards are issued to keep the technical contents up-to-date. Revisions encompass new materials, processes and technologies.
I express my thanks to the British Standards Institution, 389 Chiswick High Road, London W4, for kind permission to reprint extracts from their publications. I have enjoyed a long and enjoyable association of over 35 years with The City and Guilds of London Institute, 1 Giltspur Street, London EClA 9DD, and am grateful for their kind permission to include past examination questions in this book. I also thank my friend and colleague Colin Simmons for much helpful information and guidance. The friendly advice and assistance given to me by Dilys Alam, Sian Jones and staff at Arnold is also very much appreciated. My thanks to Ray for much technical help and his invaluable support with my computer equipment, and to Brian for other drawing examples. Finally many thanks to my wife Beryl for her endless patience, encouragement and all her clerical help.
⏩Chapter 1: First steps
By the end of this chapter, you will be able to understand the following commands and perform these activities:
• Open the drawing software program. Click and browse through each of the options on the menu bar in turn and note that many sophisticated and advanced features are available.
• Reposition the movable toolbox.
• Note standard drawing sizes.
• Appreciate Portrait and Landscape orientation of the drawing.
• Select and position an A4 size drawing sheet.
• Set Snap and Grid values.
• Draw lines between given coordinates.
• Operate the ZOOM command.
• Become familiar with the ORTHO button facility.
• Experiment with ERASE and BREAI( commands.
• Use the REDRAWcommand to clean up the screen.
• Draw circles and arcs.
• Use the RUNNING OBJECT SNAP OPTION to draw tangents and position tangency points.
• Gain experience with the FILLET feature.
• Convert lines and arcs to polylines for finished outlines.
• Experiment with the TEXT command. Set text types and sizes.
• Note the minimum height of drawing characters and text abbreviations.
• Experiment with the MOVE, COpy and ROTATE commands and learn how to reposition detail.
• Experiment with the ARRAY command.
• Choose screen preferences.
• Select coloured layers for different parts of a drawing.
• Note recommended thicknesses for various types of linework.
• Check available printers. Save your drawings with suitable file names and add drawing numbers.
You will find that information retrieval is an important part of CAD work. Set up the printer and follow the PRINT/PLOT procedure to make an A4 copy
⏩Chapter 2: Geometrical applications
This chapter introduces you to:
• Dimensioned tangency examples.
• Tangency points and intersecting arcs.
• Polar and Rectangular arrays.
• Ellipse construction and properties.
• Scale factors.
• Wire parts.
• Symmetrical layouts.
• Double lines and arcs.
• Wire springs.
• Setting out exact rotation angles using the Gear Wheel example.
• Gear Wheel terminology.
• UNDO, REDO, BREAI(, EXTEND and TRIM features.
• Archimedian Spiral.
• Cylindrical and conical helix.
⏩Chapter 3: Pictorial projections
This chapter introduces the following topics:
• Isometric principles and planes.
• Oblique, Cavalier and Cabinet projections.
• Planometric projections.
• COpy and ROTATE features applied to animation.
⏩Chapter 4: Orthographic projection
This chapter introduces:
• First angle or European projection.
• Third angle or American projection.
• Projection examples and the selection of views.
• Standard projection symbols.
⏩Chapter 5: Text and dimensions
This chapter introduces you to:
• Text types and editing options.
• Special characters.
• Overscoring and underscoring.
• Dimensioning principles.
• Functional and Auxiliary dimensions.
• Toleranced dimensions.
• The selection of limits and fits from ISO tables with shaft and hole combinations.
• Combining characters to produce limits and fits for use on drawings.
⏩Chapter 6: Three-dimensional projection exercises
This chapter introduces examples where three-dimensional components need to be presented on the screen with sufficient views to define their shape accurately. At the end of the chapter you will be able to project relevant linework between views in order to complete them. Examples show component views in line vertically and horizontally and introduce the projection of curves, tapers and angular surfaces. Conic sections are given to demonstrate constructions for the hyperbola, parabola and ellipse. Intersections are shown between parts of solids joined to each other with examples of pyramids, prisms,cones and sphere.
⏩Chapter 7: Pattern development
By the end of this chapter you will be able to draw patterns for various hollow objects and make useful models to check dimensions, shape, appearance and the position of joins. These practical exercises assist in the overall comprehension of three-dimensional forms. Applications of this type of work are found in thin sheet metal and plastics fabrications. Development exercises include:
• Parts of rectangular and triangular prisms.
• Cylinders with branches.
• Cones and intersections.
• Hexagonal pyramid developments.
• True length applications.
⏩Chapter 8: Fastenings
This chapter introduces commonly used fastenings which are necessary for assembly drawings. It is possible with CAD to store frequently used details in your own data bank, then recall and reposition items, as required. At the end of the chapter you will be able to draw accurately:
• Nuts, bolts, studs and washers from standard dimensions.
• Understand the terminology and conventions relating to nuts and bolts.
• Draw fastenings on sectional views and assemblies.
• Draw isometric views of nuts and bolts.
⏩Chapter 9: Blocks and technical diagrams
At the end of this chapter you will be able to make a block containing information which can be used in your current drawing or stored for later use elsewhere. Examples of typical diagrams are given for:
• Pipework and heating layouts.
• Electrical schematic line diagrams.
• Electrical wiring diagram for construction purposes.
• Floor layout diagram for a social event.
• Model Hi-Fi Midi sequencer connections.
⏩Chapter 10: Technical drawings for industry
Examples are given here of typical technical drawings and may be copied to demonstrate competence as a CAD draughtsman. The drawings are chosen to provide experience of applications of engineering standards, conventions, principles and practice and include:
• Drawing sheet layouts with title blocks, parts lists and borders.
• Webs and fillets applied to castings.
• First and third angle alternative solutions.
• Assembly drawing from given details.
• Transferring information from one drawing to another.
• Sectional views
This chapter deals with complete component and assembly drawings to current industrial standards. The examples are graded to provide the CAD draughtsman with useful experience and skill in manipulating the main features of AutoCAD 2-D software which must be learned in order to pursue a career in a typical industrial drawing office.
⏩Size: 14.5 MB
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