BASIC TECHNICAL DRAWING Student Textbook Grade 12 Prepared by: Amanuel Berhanu (BSc.) Tolossa Deberie (MSc.) Editor: Tolossa Deberie (MSc.) Reviewed by: Abebe Basazeneu Natenael Abebe Yared Mekuria FEDERAL DEMOCRATIC REPUBLIC OF ETHIO PIA KURAZ INTERNATIONAL MINISTRY OF EDUCATION PUBLISHER Acknowledgements The redesign, printing and distribution of this student textbook has been funded through the  General Education Quality Improvement Project (GEQIP), which aims to improve the quality of  education for Grades 1–12 students in government schools throughout Ethiopia.     The Federal Democratic Republic of Ethiopia received funding for GEQIP through credit/financing  from the International Development Associations (IDA), the Fast Track Initiative Catalytic Fund  (FTI CF) and other development partners – Finland, Italian Development Cooperation, the Neth‐ erlands and UK aid from the Department for International Development (DFID).  The Ministry of Education wishes to thank the many individuals, groups and other bodies in‐ volved – directly and indirectly – in publishing the textbook and accompanying teacher guide.     Every effort has been made to trace the copyright holders of the images and we apologise in ad‐ vance for any unintentional omission. We would be pleased to insert the appropriate acknowled‐ gement in any subsequent edition of this publication.      © Federal Democratic Republic of Ethiopia, Ministry of Education      First edition, 2003(E.C.)    Developed, printed and distributed for the Federal Democratic Republic of Ethiopia, Ministry of  Education by:  Al Ghurair Printing and Publishing House CO. (LLC)  PO Box 5613   Dubai  U.A.E.  Second edition,2007 (E.C.) By Tan Prints India Pvt. Ltd. In collaboration with  Kuraz International Publisher P.L.C  P.O. Box 100767   Addis Ababa  Ethiopia    ISBN: 978‐99944‐2‐096‐4  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 (including electronic, mechanical, photocopying, record‐ ing or otherwise) either prior written permission of the copyright owner or a licence permitting  restricted copying in Ethiopia by the Federal Democratic Republic of Ethiopia, Federal Negarit Ga‐ zeta ,Proclamation No. 410/2004 Copyright and Neighbouring Rights Protection Proclamation,  10th year, No. 55, Addis Ababa, 19 July 2004.  Disclaimer     Every effort has been made to trace the copyright owners of material used in this document. We  apologise in advance for any unintentional omissions. We would be pleased to insert the appro‐ priate acknowledgement in any future edition. Table of Contents Page UNIT 1. FREE HAND SKETCHING .................................................. 1 1.1 Introduction ............................................................................. 2 1.2 Uses of Freehand Sketching ..................................................... 4 1.3 Types of Freehand Sketching .................................................... 4 1.4 Sketching Materials .................................................................. 5 1.5 Fundamentals of Sketching ...................................................... 8 Unit Summary ......................................................................... 29 UNIT 2. AUXILIARY VIEWS ........................................................... 32 2.1 Introduction ............................................................................ 33 2.2 Overview of Orthographic Projection ....................................... 34 2.3 Auxiliary Projection of Objects ................................................ 44 2.4 Types of Auxiliary Views ......................................................... 47 Unit Summary ....................................................................... 53 UNIT 3. SECTIONAL VIEW ........................................................... 56 3.1 Introduction ............................................................................ 57 3.2 Cutting Plane and Section Lining ............................................. 58 3.3 Visualizing a Sectional View .................................................... 60 3.4 Types of Sectional View .......................................................... 61 3.5 Other Sectional View Representation ...................................... 67 3.6 Conventional Representations in sectioning ............................. 69 Unit Summary ....................................................................... 72 UNIT 4. DIMENSIONING ............................................................... 80 4.1 Introduction ............................................................................ 81 4.2 Lines and Symbols .................................................................. 81 4.3 Reading Direction of Figures ................................................... 82 4.4 Theory of Dimensioning .......................................................... 83 4.5 Methods of Dimensioning ........................................................ 85 4.6. Placement of Dimension ......................................................... 89 Unit Summary ....................................................................... 92 UNIT 5. DEVELOPMENT AND INTERSECTION ............................. 95 5.1. Introduction ........................................................................... 96 5.2 Development ........................................................................... 98 5.3 Intersection Between Geometrical Solids ............................... 114 Unit Summary ..................................................................... 122 1 Free hand Sketching UNIT FREEHAND S KETCHING 1 2-D 3-D Learning Competencies: Up on completion of this chapter you should be able to:  Describe the use and application o f freehand sketching;  Identify freehand sketching mater ials;  Use freehand sketching material properly;  P repare a sketch of line in freehand;  Sketch different types of lines, are as, angles, circles, and arcs by applying sketching techniques;  Layout a sketch using proportion;  Sketch multiview drawing of 3D objects;  Prepare a freehand sketch of any 3 D objects in three types of pictorial drawing. 1 Freehand sketching not upon the technique of sketching the idea. 1.1. Introduction Sketching, similar to writing, is a skill that • Have you ever sketched? If you do what is the can be developed through practice. Some thing you sketched and why did you sketched it? examples of analytical sketches are illustrated. These represent the type of Consider an Architect who wants to design a sketches you might be asked to produce in building, a Mechanical Engineer who wants industry or on the job site. In this unit the to design a machine or a machine part; an basic techniques of both two-dimensional Industrial Engineer who wants to design a sketching and pictorial sketching are plant layout; how would he/she start the discussed. design? Practically all starts and put their idea with freehand sketch. Freehand Comparison between freehand sketching and sketching is one of the most effective ways to instrumental drawing communicate a pictorial or verbal idea to a Freehand sketching Instrumental drawing workman. Sketching may be schematic, • The process of • The process of producing a producing a final expressing new ideas, or instructional to rough preliminary drawing. convey ideas to draftsmen. After these ideas, drawing • It’s a final stage of concepts, and details for a project have been representation. a design process. • A first stage of • Done with finalized, precise technical drawings are the design instruments. produced using instruments so that parts process. • Used to clarify the may be manufactured or constructed. • Done in freehand. design to technical • A stepping tone personnel. Freehand sketches are also used by engineers to the next • Takes relatively to clarify, evaluate and record preliminary sketch or longer time to ideas and concepts. Sketches can be used by drawing; where draw. ideas are refined, all persons irrespective of their specialization detailed is added to support their ideas with figures. and new ideas are formed. The fundamental concepts in technical • Used to clarify drawing are the same weather instrumental the design idea to non technical or freehand drawing is used in representing individuals. or transferring ideas. But freehand sketching • Takes less time is preferable to draw easily and freely as hand writing, and the mind of the sketcher would be free to concentrate upon an idea, 2 1 Free hand Sketching Application of sketching Sketch of typical mechanical technology application Typical sketch for 2-D statics problem Aeronautical engineers typically sketch effects of forces acting on aircraft Mechanical, chemical or civil engineers might use this type of sketch Metallurgical engineers sketch microstructures of materials Sketch of a cellular phone Architects often sketch buildings Electrical engineers often sketch circuits Fig.1.1 Typical applications of freehand sketching 3 Freehand sketching 1.2. Uses of Freehand Sketching • What do you think is the use of sketching for engineers and designers? Sketching is as much a thinking process as it is a communication technique and it is a rapid method of drawing. In addition to gaining speed freehand sketches have the following uses; • Transferring information, obtained in the field or shop, to the engineering office. • Conveying the ideas of the designer to the draftsman. • Making studies of the layout of the views required in an instrumental drawing. • A means of making preliminary studies of a design to show how it functions. • Furnishing a three-dimensional pict- ure of an object; this will help to interpret the orthographic views. 1.3. Types of Freehand Sketching Fig. 1.2 Communication of information using Freehand sketches can be categorized into charts and graphs three: 1. Sketches which communicate techn- 2. Sketches which illustrate two dimen- sions of an object such as a multi- ical data such as charts, graphs, view representation of an object as maps, and diagrams as shown in shown in Fig. 1.3. Fig.1.2. 4 1 Free hand Sketching 1.4. Sketching Materials • What kind of sketching materials do you suggest from the drawing materials you know? One of the advantages of freehand sketching is that it requires only pencil, paper and eraser, items that anyone has for ready use. Pencil: there are different types of pencil used in technical drawing. Technical Fig. 1.3 Multi-view representation of an object sketching is usually made by the pencils in 3. Sketches which are two dimensional the medium group, F, H, and 2H. The H representations of three dimensional pencil is more recommended for sketching objects such as pictorial sketches of purpose. an object. See Fig. 1.4. • Sharpening the sketching pencil: A sketching pencil should be sharpened on a file or piece of sandpaper to conical point. The point then should be rounded slightly on the back of the sketch pad or another sheet of paper to the correct degree of dullness. The alphabets of lines that are sketched Fig. 1.4 Pictorial representation of an object freehand are all made with the same pencil grade. The variation in the Checkpoint 1.1 lines is achieved by varying the Practice sketching multi-view and sharpness of the pencil point as pictorial represent ation of any object, shown below in Fig. 1.5. which is familiar to you. 5 Freehand sketching Papers: When sketches are made in the field, where an accurate record is required, a small note book or sketching pad is frequently used. Often clip boards are employed to hold the paper. Sketching paper might be blank, rectangular grid, isometric grid or perspective grid paper. Blank paper: Blank paper of durable and high quality can be used as a sketching paper for all types of sketches. In this course we shall be using the blank paper to learn the different techniques of sketching. Rectangular grid paper: This type of paper helps in estimating distances easily. It is used in sketching two-dimensional figures such as multi-view drawings. It is also used for making oblique sketches. (a) Rectangular grid Fig. 1.5 Pencil points and sketch lines Eraser: A good eraser that will not cause dirty mark should be used. A soft eraser should be used to remove construction lines and incorrect markings. (b) Freehand sketching in rectangular grid paper Fig. 1.6 Using rectangular paper grids 6