Class: Senior Secondary School 2 (SS2 / SSS 2)
Term: 3rd Term
Week: 2
Age: 16 years
Duration: 45 minutes
Subject: Technical Drawing
Curriculum Theme: Geometric Construction
Previous Lesson: Planes and Views in Space: Inclined Lines and Angles.
Topic: ORTHOGRAPHIC PROJECTION
Subject Matter: Meaning of orthographic projection, principles of orthographic projection, types of orthographic projection

Specific Objectives

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

Cognitive Domain:

Define orthographic projection.
State the principles of orthographic projection.
Identify the two main types of orthographic projection.
Explain the differences between first angle and third angle projection.

Affective Domain:

Appreciate the importance of orthographic projection in technical drawing.
Show interest in accurately representing objects using orthographic views.

Psychomotor Domain:

Sketch simple orthographic views of basic objects.
Draw the standard symbols for first angle and third angle projection.

Collaborate with peers in discussing concepts related to orthographic projection.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
Technical Drawing for Senior Secondary Schools by A.B. Oluyemi
https://www.waeconline.org.ng/
https://www.nerdc.gov.ng/
https://www.educ.gov.ng/

Instructional Materials

The teacher will teach this lesson with the aid of:

Models of simple objects (e.g., blocks, prisms)
Charts showing orthographic projections (first and third angle)
Drawing instruments (set squares, rulers, pencils, protractor)
Whiteboard/Blackboard

Rationale for the Lesson

This lesson helps pupils understand how to represent three-dimensional objects in two dimensions, which is fundamental for communicating design ideas in engineering and manufacturing. It enables pupils to interpret and create technical drawings accurately.

Prerequisite/Previous Knowledge

Pupils have prior knowledge of basic geometric shapes, types of lines, and the concept of viewing objects from different directions.

Lesson Content/Board Summary

ORTHOGRAPHIC PROJECTION

Meaning of Orthographic Projection

Orthographic projection is a way of representing a three-dimensional object in two dimensions by projecting a series of two-dimensional views onto mutually perpendicular planes. Each view shows the object as seen from a specific direction (e.g., front, top, side) with all lines of sight parallel to each other and perpendicular to the projection plane.

Principles of Orthographic Projection

The principles of orthographic projection are based on projecting views of an object onto three mutually perpendicular planes: the Horizontal Plane (HP), the Vertical Plane (VP), and the Auxiliary Vertical Plane (AVP) or Profile Plane (PP).

Projection Planes: Imaginary planes onto which the views of the object are projected.
Lines of Sight: Parallel to each other and perpendicular to the projection plane.
True Shape and Size: Each view shows the true shape and size of the object’s features as seen from that specific direction, without perspective distortion.
Alignment of Views: Views are arranged in a specific relationship to each other, maintaining alignment to represent the object’s dimensions consistently. For example, the front view and top view must align vertically, and the front view and side view must align horizontally.

Types of Orthographic Projection

There are two main types of orthographic projection, distinguished by the relative position of the object, the observer, and the projection planes:

1. First Angle Projection

In first angle projection, the object is assumed to be in the first quadrant. This means the object is placed between the observer and the projection planes.

Position of Object: Between the observer and the projection plane.
Arrangement of Views: The view seen from the front is placed at the top. The view seen from the top is placed at the bottom. The view seen from the left side is placed on the right, and the view seen from the right side is placed on the left.
Symbol: The symbol for first angle projection is a truncated cone viewed from the side, with the smaller end on the left.

2. Third Angle Projection

In third angle projection, the object is assumed to be in the third quadrant. This means the projection planes are placed between the observer and the object.

Position of Object: The projection plane is between the observer and the object.
Arrangement of Views: The view seen from the front is placed at the front (usually center). The view seen from the top is placed at the top. The view seen from the left side is placed on the left, and the view seen from the right side is placed on the right. The views are arranged as if unfolding the faces of a box around the object.
Symbol: The symbol for third angle projection is a truncated cone viewed from the side, with the smaller end on the right.

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 on types of lines and basic drawing instruments. The teacher then introduces the topic of orthographic projection by asking pupils how a 3D object can be represented on a 2D paper.
Pupils’ Activity: Pupils respond to the teacher’s questions and share their ideas on representing 3D objects.
Learning Point: Pupils recall prior knowledge and are introduced to the concept of representing 3D objects.

Step 2: Meaning of Orthographic Projection

Time: 8 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines orthographic projection, explaining it as a method of representing a 3D object using multiple 2D views projected onto perpendicular planes. The teacher uses a model to demonstrate how different views are obtained.
Pupils’ Activity: Pupils listen attentively, observe the model, and ask questions for clarification.
Learning Point: Pupils understand the definition and basic concept of orthographic projection.

Step 3: Principles of Orthographic Projection

Time: 8 minutes
Teaching Skill: Elucidation/Demonstration
Teacher’s Activity: The teacher explains the underlying principles, focusing on projection planes (HP, VP), lines of sight, and the concept of true shape and size in each view. The teacher uses diagrams on the board or charts to illustrate these principles.
Pupils’ Activity: Pupils observe the diagrams and listen to the explanation, making notes.
Learning Point: Pupils grasp the fundamental principles guiding orthographic projection.

Step 4: Types of Orthographic Projection (First Angle)

Time: 8 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains first angle projection, detailing the object’s position relative to the observer and projection planes. The teacher demonstrates the arrangement of views and draws the standard symbol for first angle projection on the board.
Pupils’ Activity: Pupils listen, observe the demonstration, and copy the symbol and key characteristics into their notebooks.
Learning Point: Pupils understand first angle projection, its view arrangement, and symbol.

Step 5: Types of Orthographic Projection (Third Angle)

Time: 8 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains third angle projection, contrasting it with first angle projection regarding object position and view arrangement. The teacher draws the standard symbol for third angle projection on the board.
Pupils’ Activity: Pupils compare the two types, copy the symbol, and note the characteristics of third angle projection.
Learning Point: Pupils understand third angle projection, its view arrangement, and symbol, and can differentiate it from first angle.

Step 6: Comparison and Application

Time: 5 minutes
Teaching Skill: Comparison/Discussion
Teacher’s Activity: The teacher uses charts showing both first and third angle projections of the same simple object. The teacher highlights the differences in view placement and discusses the common usage of each type (e.g., First Angle in Europe, Third Angle in North America).
Pupils’ Activity: Pupils observe the charts, participate in the discussion, and clarify any lingering confusion.
Learning Point: Pupils reinforce their understanding of the differences and applications of both projection types.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

Define orthographic projection.
State any two principles of orthographic projection.
Name the two main types of orthographic projection.
Draw the standard symbol for first angle projection and explain its meaning.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 3 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the definition, principles, and types of orthographic projection. The teacher assigns homework: “Sketch a simple rectangular block and show how its front, top, and end views would be arranged in both first and third angle projection.”
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils consolidate their learning and prepare for further practice.

Lesson Keywords

Orthographic Projection – A method of representing a 3D object in 2D using multiple views.
First Angle Projection – A projection method where the object is between the observer and the projection plane.
Third Angle Projection – A projection method where the projection plane is between the observer and the object.
Projection Plane – An imaginary flat surface onto which views of an object are projected.
View – A 2D representation of an object as seen from a specific direction.

Differentiation

For struggling learners, the teacher will provide simpler models and more direct guidance during sketching activities, focusing on identifying views before arranging them. Advanced learners will be challenged to project more complex objects or to sketch a simple assembly of two objects using orthographic principles.

Note for teachers using this lesson plan

Ensure models are clearly visible to all pupils. Encourage active participation and provide individual feedback during practical sketching. Emphasize the standard symbols and their importance in technical communication.