Book Title Student’s Book FET FIRST
Level 3
NATED Series Author
Engineering drawing N1
Student's Book
M. Cameron
FET FIRST Engineering Drawing N1 Student’s Book © M. Cameron, 2013
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, photocopying, recording, or otherwise, without the prior written permission of the copyright holder or in accordance with the provisions of the Copyright Act, 1978 [as amended]. Any person who does any unauthorised act in relation to this publication may be liable for criminal prosecution and civil claims for damages.
First published 2013 by Troupant Publishers [Pty] Ltd Suite 10, Private Bag X12 Cresta 2118
Author: M. Cameron Copy editing by D. Hawkins Proofreading by B.M. Davies Cover design by R. de Wet Typesetting by The Purple Turtle Publishing Distributed by Macmillan South Africa [Pty] Ltd
ISBN: 978 1 430800 45 3 It is illegal to photocopy any page of this book without written permission from the publishers.
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Contents Module 1: General engineering terms...........................................................1 Introduction ............................................................................................................ 1 Unit 1: Terms used in Engineering Drawing................................................................... 2 Unit 2: Basic computers, storage devises and terms associated with computer aided design (CAD)........................................................................................................... 5
Module 2: Drawing instruments and drawing technique...............................12 Introduction to technical drawing.................................................................................12 Unit 1: Instruments, equipment and their uses..............................................................12 Unit 2: Line types.................................................................................................... 22 Unit 3: Freehand lettering and dimensioning................................................................ 23
Module 3: Freehand drawing....................................................................28 Introduction to freehand............................................................................................ 28 Unit 1: Draw freehand.............................................................................................. 29
Module 4: Geometrical construction..........................................................35 Introduction .......................................................................................................... 35 Unit 1: Use geometrical constructions involving lines and circles..................................... 35
Module 5: Reproduction drawing..............................................................49 Introduction to reproduction drawing............................................................................49 Unit 1: Geometrical plane figures................................................................................49 Unit 2: Single objects or castings drawn to scale.......................................................... 52
Module 6: First-angle orthographic projection.............................................57 Introduction to first-angle orthographic projection...........................................................57 Unit 1: First-angle orthographic projection....................................................................57
Module 7: Axonometrical drawing............................................................. 81 Unit 1: Oblique drawings............................................................................................81 Unit 2: Isometric drawings........................................................................................ 85
Module 8: Orthographic projection of prisms and pyramids..........................99 Introduction .......................................................................................................... 99 Unit 1: Creating an orthographic projection of prisms and pyramids................................101
Module 9: Sectional drawing of single items............................................. 106 Introduction .........................................................................................................106 Unit 1: Basics of sectioning......................................................................................106
Module 10: Examination hints................................................................ 114 Syllabus Grid........................................................................................ 116
Module 1: General engineering terms Learning outcomes On completion of this module you should be able to: Unit 1: Identify and correctly use the abbreviations for the following terms used in Engineering Drawing: • • • • • • •
Centres Cylinder and cylindrical Diameter Outside diameter Hexagon Maximum Millimetre
• • • • • • •
Centre line Degree (of angle) Internal diameter Drawing Material Metre Radius
Unit 2: Give the basic function of the following hardware and software as used in Computer Aided Design (CAD): • • • • • • • • •
DOS (Disk operating system) Keyboard Tablet CPU (central processing unit) ROM (read only memory) Hard drive/fixed disk Floppy disk Stiffy disk Directory
• • • • • • • • •
Sub-directory Files CAD (computer aided draughting) Mouse Scanner RAM (random access memory) Monitor CD ROM (compact disk, read only memory) Plotter/printer
The weight value for this module should be allocated as 5% and the approximate time allocated during the course is 3 hours 45 minutes.
Introduction What is engineering drawing? For one thing, it is an effective means of communicating technical ideas and problem solutions. Look at what happens in engineering design. The process starts with the ability to visualize, seeing the problem and the possible solutions. Then, sketches are made to record initial ideas. Next, geometrical models are created from those sketches and are used for analysis. Finally, detail drawings or three-dimensional models are made to record the precise data needed for the production process. Visualizing, sketching, modelling, and detailing are how engineers and technologists communicate as they design new products and structures for our technological world. Actually, communication using engineering drawings and models is a language, a clear, precise language with definite rules that must be mastered if you are to be successful in engineering design. Once you know the language, it will influence the way you think, the way you approach problems. Universally accepted, conventional and standardized methods of communication through engineering drawings are used. This is so that any designers here, and in other countries, will be able to ‘read’ and interpret each other’s drawings in exactly the same way. Components (machine parts) shown in a drawing can therefore be made by suitably skilled craftsmen of any nationality, provided they can ‘read’ an engineering drawing. If the drawings are correctly drawn and annotated (described) by means of notes, dimensions, etc., the finished product will be exactly as visualized by the designer. Any misunderstandings when describing shapes and size by using only words and no drawings are thus avoided. 1
Unit 1: Terms used in engineering drawing Centres Abbreviation: CRS
Centre line Abbreviation: CL
Cylinder and cylindrical Abbreviation: CYL
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Degree (of an angle) Abbreviation: DEG
Diameter Abbreviation: DIA (Ø)
Radius Abbreviation: R
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Internal diameter Abbreviation: ID
Outside diameter Abbreviation: OD
Material Abbreviation: MATL Maximum Abbreviation: MAX Metre Abbreviation: m Millimetre Abbreviation: mm Drawing Abbreviation: DRG
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Hexagon Abbreviation: HEX A hexagon is a polygon of six sides of the same length and six internal angles all of 120 DRG (120°).
Activity Give the abbreviations for the following: centre line, internal diameter, centres, material, drawing and radius.
Unit 2: Basic computers, storage devices and terms associated with computer aided draughting (cad)
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Central processing unit (CPU) The central processing unit (CPU) is the portion of a computer system that carries out the instructions of a computer program to perform the basic arithmetical, logical and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in use in the computer industry at least since the early 1960s. The form, design and implementation of CPUs have changed dramatically since the earliest examples, but their fundamental operation remains much the same. On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single silicon chip called a microprocessor. Since the 1970s the microprocessor class of CPUs has almost completely overtaken all other CPU implementations. Modern CPUs are large-scale integrated circuits in packages typically less than four centimetres square, with hundreds of connecting pins. Memory In order for the CPU to do anything, it must have data to process. The CPU gets data to process from memory. Memory must be able to accept data from external sources, retain it for a length of time, route it to and from the CPU, and finally route the results back to the user. There are two types of memory in a microcomputer. Random access memory (RAM) Random access memory (RAM) is a form of computer data storage. RAM is a series of chips that can accept, retain, and have data erased when no longer needed by the user. It is important to note that any data stored in RAM will be erased when the computer is turned off, which means that work done on the computer should be stored and backed up on a regular basis. Read-only memory (ROM) Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to need frequent updates). In its strictest sense, ROM refers only to mask ROM (the oldest type of solid state ROM), which is fabricated with the desired data permanently stored in it, and thus can never be modified. Despite the simplicity, speed and economies of scale of mask ROM, field-programmability often makes reprogrammable memories more flexible and inexpensive. Input devices In order for the CPU to do anything, it must have data to process; this data has to be fed into the computer by using various input devices. The most widely used input device is called a keyboard. Various other devices are also used. 6
Keyboard In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches. Following the decline of punch cards and paper tape, interaction via teleprinter-style keyboards became the main input device for computers. Despite the development of alternative input devices, such as the mouse, touchscreen, pen devices, character recognition and voice recognition, the keyboard remains the most commonly used and most versatile device used for direct (human) input into computers. A keyboard typically has characters engraved or printed on the keys and each press of a key typically corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence. While most keyboard keys produce letters, numbers or signs (characters), other keys or simultaneous key presses can produce actions or computer commands. In normal usage, the keyboard is used to type text and numbers into a word processor, text editor or other program. In a modern computer, the interpretation of key presses is generally left to the software. A computer keyboard distinguishes each physical key from all others, and reports all key presses to the controlling software. Keyboards are also used for computer gaming, either with regular keyboards or by using keyboards with special gaming features, which can expedite frequently used keystroke combinations. A keyboard is also used to give commands to the operating system of a computer, such as Windows’ ControlAlt-Delete combination, which brings up a task window or shuts down the machine. Keyboards are the only way to enter commands on a command-line interface. Mouse A mouse is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held under one of the user’s hands, with one or more buttons. It sometimes features other elements, such as ‘wheels’, which allow the user to perform various system-dependent operations, or extra buttons or features that can add more control or dimensional input. The mouse’s motion typically translates into the motion of a pointer on a display, which allows for fine control of a graphical user interface. Tablet A graphics tablet (also digitizer, digitizing tablet, graphics pad, drawing tablet or pen tablet) is a computer input device that enables a user to hand-draw images and graphics, similar to the way a person draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures. It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the surface. Capturing data in this way, either by tracing or entering the corners of linear polylines or shapes, is called digitizing. A graphics tablet (also called pen pad or digitizer) consists of a flat surface upon which the user may ‘draw’ or trace an image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear on the tablet itself but instead is displayed on the computer monitor. Some tablets are intended as a general replacement for a mouse as the primary pointing and navigation device for desktop computers.
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Optical scanners In computing, an image scanner – often abbreviated to just scanner – is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop (or flatbed) scanner where the document is placed on a glass window for scanning. Hand-held scanners, where the device is moved by hand, have evolved from text scanning ‘wands’ to 3-D scanners used for industrial design, reverse engineering, test and measurement, orthotics, gaming and other applications. Mechanically driven scanners that move the document are typically used for large-format documents, where a flatbed design would be impractical. Output devices Once the computer has performed its tasks, the results of the processing phase must be conveyed back to the user in understandable form via the output devices. Primary output devices used today are monitors and printers. Monitors A monitor or display (also called screen or visual display unit) is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) thin panel, while older monitors use a cathode ray tube about as deep as the screen size. Originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality. Printers Printers produce paper output. Printers differ from one another in print method, speed, range of capabilities, print quality and interface method. Types of printers available are: dot matrix, ink-jet and laser. Technology regarding printers is so advanced that it is now possible to get photo-quality images printed.
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Plotters The plotter is a computer printer for printing vector graphics. In the past, plotters were used in applications such as computer-aided design, although they have generally been replaced with wide-format conventional printers. It is now commonplace to refer to such wideformat printers as ‘plotters’, even though technically they are not. Secondary storage devices Secondary storage devices are always accessible to the CPU. Data can be sent from the system to the device and stored. Stored data can be recalled and sent from the device to the CPU. In this way, these devices serve both input and output functions. Hard disk drives A hard disk drive (HDD; also hard drive, hard disk, or disk drive) is a device for storing and retrieving digital information, primarily computer data. It consists of one or more rigid (hence ‘hard’) rapidly rotating discs (platters) coated with magnetic material, and with magnetic heads arranged to write data to the surfaces and read it from them. Hard drives are classified as non-volatile, random access, digital, magnetic data storage devices. Introduced by IBM in 1956, hard disk drives have decreased in cost and physical size over the years while dramatically increasing in capacity and speed. Hard disk drives have been the dominant device for secondary storage of data in general-purpose computers since the early 1960s. They have maintained this position because advances in their recording capacity, cost, reliability, and speed have kept pace with the requirements for secondary storage. Floppy disk drives A floppy disk is a disk storage medium comprising a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles. They are read and written by a floppy disk drive (FDD). Floppy disks, initially as 8-inch (200 mm) media and later in 5,25-inch (133 mm) and 3,5-inch (89 mm) sizes, were a ubiquitous form of data storage and exchange from the mid-1970s well into the first decade of the 21st century. By 2010, computer motherboards were rarely manufactured with floppy drive support; 31⁄2 inch floppies could be used as an external USB drive, but 51⁄4 inch, 8 inch, and non-standard drives could only be handled by old equipment. While floppy disk drives still have some limited uses, especially with legacy industrial computer equipment, they have been superseded by data storage methods with much greater capacity, such as USB flash drives, portable external hard disk drives, optical disks, memory cards, and computer networks. 9
Laser disks (CD ROM) Laser disks provide an extremely high volume of storage, but are used mostly in the form of read-only memory. Disks are removable. Storage capacity of 650 MB is possible on one disk. A vast amount of software is currently available on CDs. Operating systems Before a computer can perform the tasks we want it to perform, it must be prepared to accept and execute instructions. The initial preparation is performed by a program called the operating system. Examples of operating systems available on the market today are Microsoft’s Windows and DOS. The operating system controls the basic functions of the computer, namely: • screen control • keyboard input • memory allocation • interfacing between the different components of the computer system. DOS (disk operating system) is fast becoming obsolete. CAD CAD is the term used for Computer Aided Design. The term refers to the practice where computers are used to create engineering drawings which include the following disciplines: electrical, mechanical, architectural and civil engineering. Typical software packages available at the moment include AutoCAD and Caddie. Directory The hard drive or fixed disk is divided up into directories containing sub-directories and files. A directory can be equated to a filing cabinet. Sub-directory The sub-directory is contained within the directory and can be equated to the drawers of the filing cabinet.
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Files The contents of the sub-directory are called files and contain different types of information. Information is also stored in these files.
Activity Describe and give the functions of the different hardware and software components found in a computer.
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