Lesson Notes By Weeks and Term - Senior Secondary 2

TERM – 2^ND TERM

WEEK TWO - THREE

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Technical Drawing

Topic: ORTHOGRAPHIC PROJECTION

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

I.) Describe orthographic projection

II.) Identify the types of orthographic projection

III.) Construct objects in orthographic projection.

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures,

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

NOTE

ORTHOGRAPHIC PROJECTION

Orthographic drawing is a technique used in technical and engineering fields to represent a three-dimensional object in two dimensions. It uses multiple views, such as front, top, and side views, to accurately depict the object's shape, size, and details. Orthographic drawing is the only drawing type used in technical drawing that allows a technician to see all the drawing details in an object. It does this by placing three faces of the object on a drawing sheet. These faces are gotten by looking at the object from three positions or locations namely:

1. Front of the object called Front View (FV)also known as Front Elevation (FE).
2. Sides (right side or left side) of the object is called End View (EV)or Side View (SV).
3. Plan View (PV) which is the most commonly used. It is call the Plan Top (PT).

Basically, there are two ways of drawing in orthographic - First Angle and Third Angle. They differ only in the position of the plan, front and side views.

First Angle elevation: The object is placed at the top of the horizontal plane and the front of the vertical plane. The first angle projection is widely used in our country and most of the European countries. The object is always put between the observer and projection planes.

Rules for First Angle Projection

1. The main face of the object that the eye looks atfirst is normally called the Front Viewor Front Elevation. The shape or nature of the Front View that eye sees is placed on the First Quadrant or Second Quadrant to produce the same type of drawing placement.
2. The Side Views are placed either to the left or to the right sides of the Front Elevation. How this is done is that, you look at, for instance, the leftside of the object. Whatever shape or form you see, you draw it on the right side of the object. And the main object here is represented by the Front View, which you had drawn.
3. In the same way, if you look at the object from the leftside, you draw what you see on the right side of the FrontView.
4. The same method is applied when presenting the Plan Top on the paper. What the eye sees after looking at the object from the top is placed below the Front View.
5. Hence, the idea here is that in First Angle projection, what the eye sees once it had looked at an object is placed on the other side of the object, and not on the same side the looking is positioned to look at the object. This means that the Front View stands between the End View and the looking eye.

Third angle projection

Third angle projection is commonly used in engineering drawing because it is the standard method in many countries, including the United States and Canada. 3rd Angle project is where the 3D object is seen to be in the 3rd quadrant. It is positioned below and behind the viewing planes, the planes are transparent, and each view is pulled onto the plane closest to it. The front plane of projection is seen to be between the observer and the object.

Rules for Third Angle Projection

The rules stated above are the same and applicable to Third Angle projection. The only difference is that the Front View or Elevationin Third Angle is placed on the Third or Fourth Quadrant. But the nature or shape of the object remains the same. In this case, the End View is placed between the looking eye and the Front View. This is because the rule stipulates that whatever the eye sees should be placed in front of

the eye, somehow between the eye and the Front View and the looking eye.

Projecting Simple Objects in First Angle

Projecting Simple Objects in Third Angle

EVALUATION: 1.   The figure below shows two views of a block drawn in first angle orthographic projection. Make a free hand pictorial sketch of the block making X, the lowest point. (WASSCE)

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively