FIRST TERM e – LEARNING NOTES
Subject :Technical Drawing
Topic : Freehand Drawing and Sketching (Woodwork and Metalwork)
Class :SSS 3 (BASIC 12)
Term : FIRST TERM e – LEARNING NOTES
Week :WEEK 3
Instructional Materials :
- Measuring tools
- Drawing tools
- Scheme of Work
- Online Information
- 9 Year Basic Education Curriculum
Previous Knowledge :
The pupils have previous knowledge of
Freehand Drawing and Sketching:
(a) Principles of freehand sketching.
(b) Freehand sketching of hand tools used by builders and engineers e.g. hammers, pliers, saws, trowels, calipers, etc.
Behavioural Objectives : At the end of the lesson, the pupils should be able to
- mention at least four
- enumerate the
- list drawing
- differentiate the difference
TOPIC:Engineering Designs and Working Drawings
CONTENT: (a) Engineering design process.
(b) Preparation of working drawings.
Sub-topic 1: Engineering design process.
The first step a manufacturer must take when he wishes to make an article is to produce a drawing. First a designer will make a preliminary sketch and then a draughtsman will make a detailed drawing of the design. Since neither the designer nor the draughtsman will make the article, the drawing must be capable of being interpreted by the men in their workshops. This workshops may be sited a long way from the drawing office, even overseas and so the drawings produced must be standardized so that everyone familiar with these standards could make the article required.
Engineering drawing is therefore, a language: in this modern age of rapid communication and international buying, from pins to complete atomic power sections, it is essential for the language to be international. This is why you will often see symbols used on a drawing instead of words or abbreviations.
Types of Projection
The first rule of engineering drawing is to standardize the projection that is used. There are many to choose from, they are: Isometric, Oblique and Orthographic. These three are probably the best known. Both isometric and oblique have two big disadvantages. First, it is possible to see only two sides and either the top or bottom in any view. It is of course, possible to draw more than one view, but this brings us to the second disadvantage. On any object except the simplest, there are curves or arcs or circles. It takes considerable amount of time, and in industry time costs money. For this reasons, isometric, oblique and like projections are most used as the standard projection.
The standard projection used is orthographic. This is the obvious projection to use because of its many advantages. It presents a true picture of each face: circles remain as circles, eclipse remains as eclipse, horizontal lines remain horizontal; and vertical lines remain vertical. There is no limit to the number of views that you can draw.
We still need to decide whether to draw in first or third angle orthographic projection, but unfortunately it is impossible to give a definite ruling on this. It is traditional for the British Isles and the commonwealth to draw in first angle projection, but the United State of America or more recently, continental countries have adopted third angle projection. There is no doubt that eventually third angle will become the international standard, but it will take a considerable time. First angle projection is still widely taught in this country.
1. Why is engineering design necessary and standardized?
2. Why is orthographic projection preferred to isometric and oblique projection in engineering design?
3. With free hand sketches, show the arrangement of first and third angle projection.
Sub-topic 2:SKETCHING OF FIRST AND THIRD ANGLE PROJECTION
The topic is presented step by step
The class teacher revises the previous topics
He introduces the new topic
The class teacher allows the pupils to give their own examples and he corrects them when the needs arise
- compare sketching tools and drawing tools
- explain the uses of two drawing tools
- write out four drawing tools
- discuss the use of two sketching tools
- itemize and write out five sketching tools
The class teacher wraps up or conclude the lesson by giving out short note to summarize the topic that he or she has just taught.
The class teacher also goes round to make sure that the notes are well copied or well written by the pupils.
He or she does the necessary corrections when and where the needs arise.
Prepare for the next lesson by reading about