Geometrical Construction
FIRST TERM
SCHEME OF WORK WITH LESSON NOTES
Subject :
BASIC TECHNOLOGY
Term :
FIRST TERMTERM
Week:
WEEK 7
Class :
JSS 2 (BASIC 8)
Previous lesson:
The pupils have previous knowledge of
Material and Their Common Uses
Topic:
Geometrical Construction
.
Behavioural objectives:
By the end of the lesson, the pupils should be able to
1. Definition of lines
2. Mention types and uses of line
3. Construction of lines and angles
4. Bisections of lines
5. Mention various types of division of lines
Instructional Materials:
 Wall charts
 Pictures
 Related Online Video
 Flash Cards
Methods of Teaching:
 Class Discussion
 Group Discussion
 Asking Questions
 Explanation
 Role Modelling
 Role Delegation
Reference Materials:
 Scheme of Work
 Online Information
 Textbooks
 Workbooks
 9 Year Basic Education Curriculum
 Workbooks
Content:
 Definition of lines
 Types and uses of line
 Construction of lines and angles
 Bisections of lines
 Division of lines
Lines
It is important to understand the following terms before proceeding to the construction of lines and angles.
A point is defined as something which has a position and an extremely small magnitude so that it is barely visible. A point can be made on paper by a well sharpened pencil or a needle. A point is used to indicate position only, and in technical drawing it is usually represented by a cross or a dot.
A line has position and length, but has virtually no thickness. A line may either be straight or curve. A straight is defined as the shortest distance between two points. Two lines are said to be parallel if they are always the same distance apart and cannot meet, however far they may be produced (extended) in either direction.
——————————–
Types and Uses of Lines
Lines are represented in drawings in various ways;
Thick continuous lines are used for visible outlines and edges. The thickness of this kind of line is about 0.7mm. However, you do not have to measure the thickness of lines each time you draw. If you draw with a wellsharpened HB or 2Hpencil and apply a moderate pressure, you will produce a thick line.
Thin continuous lines are used as dimension lines, projection lines, construction lines, and outlines of adjacent parts and resolved sections. They are also used as hatching lines. Thin lines are usually drawn with wellsharpened 3H, 4H or harder pencils with moderate pressure and resolved sections. They are also used as hatching lines.
Thick long chain lines are used for cutting planes and viewing planes. They are also used ac centre lines, path lines and indicating movement, or extreme positions of movable parts, and for pitch circles. Like thick longchain lines, thin longchain lines, with thick ends may be used to indicate cutting planes.
Thick continuous wavy or irregular lines are used for short break lines and boundary lines.
Thin ruled lines with short zigzags are used for long break lines.
Thin continuous wavy lines are used for limits or partial views or for sections when the line is not an axis.
Arrowheads are used at the ends of dimension lines. They are also used to indicate viewing planes and to indicate labeled parts. Arrowheads should be sharp, filledin, and should be about 3mm long.
TYPES OF LINES  THEIR USES 
Thin continuous lines 
For dimension lines, projection lines and construction lines. 
Thick continuous wavy line 
For limits of partial waves. 
Thin ruled line with short zigzags 
For long break lines.

Thick continuous line 
For short break lines and boundary 
Thin long chain line 
For short break lines and boundary 
Thick long chain line 
For cutting and viewing planes as centre lines and path line for indicating movement. 
…………………………………..
Thin short 
For hidden outlines and edges 
Construction of Lines and Angles
Important guides to good construction;
 In technical drawing, all horizontal lines are drawn with the Tsquare and all vertical lines are drawn with a triangle (or a setsquare) placed on the Tsquare.
 When drawing a line with the triangle, ensure that its edge rests firmly on the edge of the Tsquare.
iii. Always ensure that the edge of the stock or head of the Tsquare slides firmly on the left hand side edge (the square of the drawing board. The Tsquare should never be used to draw a line in any other position.
 Use well pointed pencils and take utmost care to draw lines through the required points, otherwise the result will not be satisfactory.
 In using dividers and compasses, avoid pressing the points deeply into the drawing paper, as this will cause in accuracy. Remember that a point has position only and should have no magnitude.
 In joining two points, adopt the following procedure: with the pencil point firmly placed on one point, slide the triangle up to meet it. Then swing the lower portion of the triangles until the lines up the other point on a straightline with the first point. Check the second point for alignment by putting the pencil on point. Then draw the line joining the two points.
vii. There is no alternative to constant practice if you intend to draw accurately, neatly and fast.
Bisection of Lines
To bisect a given line;
 Draw the given line AB
 With centre A and any radius greater than half AB, draw the arcs above and below the line.
iii. With centre B, draw arcs of the same radius to cut the previous ones.
 The line is drawn through the intersections of the arcs.
Division of Lines
(A) To divide a straightline into a number of equal parts;
Suppose it is required to divide a straightline 70mm long into 5 equal parts –
 Draw AB 70mm long.
 Draw AC at any convenient acute angle and set off from A, five equal divisions on this line using either a pair of dividers or a scale and pencil.
iii. Join point 5 to B using at 60^{0 }triangle. Through the other points draw lines parallel to 5B by sliding the triangle on any straight edge, such as a Tsquare. The line AB is divided into five equal parts by the line 1 – 1, 2 – 2, 3 – 3, and 4.
Division of Lines in a Given Line Proportion
Suppose it is required to divide a straightline 9cm into four parts in the proportion of 2:3:7:4:
 Draw AB9cm long
 Draw line AC at a convenient angle and set off on it from A 2 + 3 + 7 + 4 = 16.
iii. Join point 16 to B. Through the point 12 = 2 + 3 + 7, 5 = 2 + 3, and 2 = 0 + 2 draw lines parallel to 16B. The parallel lines divide AB in the required proportion.
ASSESSMENT
 What is the definition of a point?
 What are the steps in bisecting a line?
 Mention 5 guides in making good construction.
 List 5 types of lines.
Presentation: The topic is presented step by step
Step 1:
The class teacher revises the previous topics
Step 2.
He introduces the new topic
Step 3:
The class teacher allows the pupils to give their own examples and he corrects them when the needs arise.
Evaluation
 Give two examples of softwood and their uses.
 Give two examples of hardwood and their uses.
 List 5 uses of bronze
 List 4 types of brass
 What is the definition of a point?
 What are the steps in bisecting a line?
 Mention 5 guides in making good construction.
 List 5 types of lines.
 List 5 uses of brass
 List 5 uses of wood
 List 5 uses of metals
Conclusion:
The class teacher wraps up or concludes the lesson by giving out a 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 makes the necessary corrections when and where the needs arise.