# Lesson Notes By Weeks and Term - Junior Secondary 3

Orthographic projection

TERM – 3RD TERM

WEEK TEN

Class: Junior Secondary School 3

Age: 14 years

Duration: 40 minutes of 5 periods each

Date:

Subject: BASIC TECHNOLOGY

Topic: ORTHOGRAPHIC PROJECTION

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Define orthographic projection
2. Identify the types of orthographic projection
3. Draw Orthographic Views of Simple Objects
4. Explain dimension Techniques for orthographic projection.

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers,

demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures, mathematical sets, drawing instruments

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

 PRESENTATION TEACHER’S ACTIVITY STUDENT’S ACTIVITY STEP 1 INTRODUCTION The teacher explains the meaning of orthographic projection to the students Students pay attention STEP 2 EXPLANATION Teacher discuss the types of orthographic projection Students pay attention and participate STEP 3 DEMONSTRATION Teacher explains dimensions techniques and guide students to construct simple objects Students pay attention and participate STEP 4 NOTE TAKING The teacher writes a summarized note on the board The students copy the note in their books

NOTE

ORTHOGRAPHIC PROJECTION

An orthographic drawing, also known as an orthographic projection, is a drawing in which a three-dimensional object is represented in two dimensions. This is is done making multiple two-dimensional drawings of the object, viewed from different angles.

Types of orthographic Projection

The methods used in orthographic projection, a technique for representing a three-dimensional object in two dimensions are:

1. First Angle Projection: In this method, the object is imagined to be located in the first quadrant (positive quadrant) of the imaginary coordinate system. The object is positioned between the observer and the plane of projection, with the principal planes (front, top, and side views) arranged accordingly.

2. Third Angle Projection: In contrast, third angle projection assumes the object is in the third quadrant (negative quadrant) of the imaginary coordinate system. The object is placed behind the plane of projection, and its views are projected onto the planes with the principal views arranged similarly to how they would be seen by the observer.

Drawing of Orthographic Views of Simple Objects

Procedure

The following steps take you through the creation of an orthographic projection.

1. Choose a front view. This is the view that shows the most about the object.
2. Decide how many views are needed to completely describe the object. If you are unable to determine which views will be needed, draw the standard views (front, top and right side).
3. Draw the visible features of the front view.
4. Draw projectors off of the front view horizontally and vertically in order to create the boundaries for the top and right side views.
5. Draw the top view. Use the vertical projectors to fill in the visible and hidden features.
6. Project from the top view back to the front view. Use the vertical projectors to fill in any missing visible or hidden features in the front view.
7. Draw a 45° projector off of the upper right corner of the box that encloses the front view.
8. From the top view, draw projectors over to the 45° line and down in order to create the boundaries of the right-side view.
9. Draw the right-side view.
10. Project back to the top and front view from the right-side view as needed.
11. Draw center lines where necessary.

Dimension Techniques

The three principal dimensions of an object are width, height, and depth. The front view shows only the height and width of the object and not the depth. In fact, any principal view of a 3D object shows only two of the three principal dimensions; the third is found in an adjacent view.

EVALUATION: 1. What is orthographic projection

1. Identify and describe the types of orthographic projection
2. Using third angle projection, represent the object below.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively