Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 2nd Term
Week: 3
Age: 15 years
Duration: 45 minutes
Subject: Technical Drawing
Curriculum Theme: Technical Drawing
Previous Lesson: Polygons Construction: Square, Circle and Diagonal Methods.
Topic: SCALES AND ITS USES
Subject Matter: meaning and use of scales, types of scales, construction of plain scale, construction of diagonal scale, reading values on plain and diagonal scales

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define ‘scale’ in technical drawing.
State the uses of scales in technical drawing.
Identify different types of scales.
Explain the principles of constructing plain and diagonal scales.

Affective Domain:

Appreciate the importance of accuracy in using and constructing scales.
Show interest in learning technical drawing concepts.

Psychomotor Domain:

Construct plain scales for given representative fractions.
Construct diagonal scales for given representative fractions.
Accurately read values from constructed plain and diagonal scales.

Collaborate with peers during practical construction exercises.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Technical Drawing.
State Unified Scheme of Work for Senior Secondary Technical Drawing.
Technical Drawing for Senior Secondary Schools by A.B. Oladapo.
https://www.education.gov.ng/
https://www.waecnigeria.org/

Instructional Materials

The teacher will teach this lesson with the aid of:

Scale ruler
Drawing board
Tee square
Drawing paper
Pencils
Eraser
Set squares
White board/Chalkboard and markers/chalk

Rationale for the Lesson

Understanding scales helps pupils represent real-world objects accurately on paper, whether the objects are very large or very small. This knowledge is fundamental for all technical drawings and various engineering fields, ensuring designs are proportional and understandable.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of drawing instruments like rulers, pencils, and an understanding of basic measurements and ratios.

Lesson Content/Board Summary

SCALES AND ITS USES

Meaning and Use of Scales

A scale in technical drawing is the ratio of the linear dimension of an element of a model or drawing to the same dimension of the actual object. It allows large objects to be drawn on small paper and small objects to be drawn larger for clarity.

The following are the uses of scales:

To represent large objects (e.g., buildings, roads) on a smaller sheet of paper.
To represent very small objects (e.g., watch parts, micro-components) larger for detailed drawing.
To ensure all features of a drawing are in correct proportion to the actual object.

Types of Scales

There are different types of scales used in technical drawing.

The following are common types of scales:

Plain Scale
Diagonal Scale
Vernier Scale

Construction of Plain Scale

A plain scale is used to read measurements in two units or a unit and its sub-divisions (e.g., metres and decimetres).

The following are the general steps for constructing a plain scale:

Determine the Representative Fraction (RF) and the maximum length to be measured.
Calculate the total length of the scale (RF x maximum length).
Draw a line equal to the calculated total length.
Divide the line into major divisions representing the main unit.
Divide the first major division into smaller sub-divisions representing the sub-units.
Number the divisions correctly, starting from zero after the first sub-divided section.
Draw a double line to make the scale visible.

Construction of Diagonal Scale

A diagonal scale is used to read measurements in three units or a unit and its two sub-divisions (e.g., metres, decimetres, and centimetres). It provides more precision than a plain scale.

The following are the general steps for constructing a diagonal scale:

Determine the Representative Fraction (RF) and the maximum length to be measured.
Calculate the total length of the scale (RF x maximum length).
Draw a line equal to the total length and divide it into major divisions.
Divide the first major division into smaller sub-divisions horizontally.
Draw a vertical line at the start of the first major division and divide it into the desired number of sub-divisions (e.g., 10 for centi-units).
Draw diagonal lines from the points on the horizontal sub-divisions to the points on the vertical sub-divisions.
Number the divisions correctly to allow reading of three units.

Reading Values on Plain and Diagonal Scales

To read a value on a plain scale, locate the main unit on the main divisions and then count the sub-units from the zero mark.

To read a value on a diagonal scale, locate the main unit, then the sub-unit along the horizontal division, and finally move vertically up or down to the required diagonal line to find the third unit.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and reviews the previous lesson briefly. The teacher then asks pupils how they would draw a very large object like a building on a small sheet of paper or a very small object like a microchip to show details. This leads to the topic of scales.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils are introduced to the concept of scales and its relevance.

Step 2: Meaning and Use of Scales

Time: 8 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains the meaning of ‘scale’ in technical drawing, emphasizing it as a ratio. The teacher then discusses the various uses of scales, providing practical examples.
Pupils’ Activity: Pupils listen, ask questions, and take notes.
Learning Point: Pupils understand what a scale is and why it is important.

Step 3: Types of Scales

Time: 5 minutes
Teaching Skill: Listing/Classification
Teacher’s Activity: The teacher introduces the different types of scales used in technical drawing, specifically mentioning plain, diagonal, and vernier scales, and states that the lesson will focus on plain and diagonal scales.
Pupils’ Activity: Pupils listen and note the different types of scales.
Learning Point: Pupils can identify various types of scales.

Step 4: Construction of Plain Scale

Time: 10 minutes
Teaching Skill: Demonstration/Practical
Teacher’s Activity: The teacher demonstrates the step-by-step construction of a plain scale on the drawing board, explaining each step clearly and using a relevant example (e.g., 1:100 to show metres and decimetres).
Pupils’ Activity: Pupils observe the demonstration carefully and ask questions for clarification. Some may attempt to follow along if resources permit.
Learning Point: Pupils learn the procedure for constructing a plain scale.

Step 5: Construction of Diagonal Scale

Time: 10 minutes
Teaching Skill: Demonstration/Practical
Teacher’s Activity: The teacher demonstrates the step-by-step construction of a diagonal scale, highlighting the differences from a plain scale and showing how it offers greater precision (e.g., 1:100 to show metres, decimetres, and centimetres).
Pupils’ Activity: Pupils observe the demonstration and compare it with the plain scale construction. They note key differences.
Learning Point: Pupils learn the procedure for constructing a diagonal scale.

Step 6: Reading Values on Plain and Diagonal Scales

Time: 5 minutes
Teaching Skill: Demonstration/Application
Teacher’s Activity: The teacher demonstrates how to read specific values from the constructed plain and diagonal scales, providing clear examples and guiding pupils through the process.
Pupils’ Activity: Pupils practice reading values from the demonstrated scales.
Learning Point: Pupils can accurately read values from plain and diagonal scales.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

What is a scale in technical drawing?
Mention two uses of scales.
List two types of scales.
Briefly explain the main difference between a plain scale and a diagonal scale.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization/Consolidation
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the importance of scales in technical drawing. The teacher assigns homework for pupils to practice constructing and reading plain and diagonal scales with different representative fractions.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils review the lesson and receive further practice.

Lesson Keywords

Scale – The ratio of the linear dimension of a drawing to the actual object.
Representative Fraction (RF) – The ratio between the length of the drawing and the actual length of the object, expressed as a fraction.
Plain Scale – A scale used to read measurements in two units or a unit and its sub-divisions.
Diagonal Scale – A scale used to read measurements in three units or a unit and its two sub-divisions, offering greater precision.
Construction – The process of drawing a scale accurately according to specific rules.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex scale construction problems or introduce the concept of vernier scales. For pupils needing more support, the teacher can provide simplified examples, offer one-on-one guidance during practical sessions, and use visual aids more extensively.

Note for teachers using this lesson plan

Ensure all drawing instruments are available and in good condition for practical demonstrations and pupil activities. Encourage pupils to maintain neatness and accuracy in their constructions. Emphasize the real-world applications of scales to enhance understanding and engagement.