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JSS3: BASIC TECHNOLOGY - 1ST TERM

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  1. Materials & Processing - Timber I | Week 1
    5Topics
    |
    1 Quiz
  2. Materials & Processing - Timber II | Week 2
    3Topics
    |
    1 Quiz
  3. Processing of Materials - Metals | Week 3
    5Topics
    |
    1 Quiz
  4. Processing of Clay, Ceramics and Glass | Week 4
    5Topics
    |
    1 Quiz
  5. Methods of Producing Plastics & Rubber | Week 5
    2Topics
    |
    1 Quiz
  6. Drawing Practice - Isometric Drawing | Week 6
    4Topics
    |
    1 Quiz
  7. Oblique Projection | Week 7
    2Topics
    |
    1 Quiz
  8. Orthographic Projection | Week 8
    4Topics
    |
    1 Quiz
  9. Perspective Drawing (One - Point Perspective Drawing) | Week 9
    4Topics
    |
    1 Quiz
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First-Angle-Projection and Third angle projection

There are two main methods or orthographic projection as earlier said, they are:

1. First angle projection

2. Third angle projection

The principal views are the front elevation, side (end) elevation, and the plan.

Principal Views:

orthographic

Front elevation: This is the main view, it is obtained by looking at the given front of the object to be drawn. The front elevation is seen in the vertical plane. The drawing below shows exactly what you would see if you stand directly in front of the L-shape.

Front elevation

End (side) elevation: This is obtained by looking at the given side of the object. The end elevation is also seen in the vertical plane [i.e. auxiliary/side vertical plane (S.V.P)].

ortho6a

Plan: This view is obtained by looking vertically down on the given object from above. The plan is seen on the horizontal plane (H.P).

plan

First Angle Projection:

  • This method was developed in the United Kingdom and it is used in European countries.
  • In first angle projection, the plan is always projected below the front view.
  • It should be noted that the left side elevation is usually placed at the right-hand side and the right-hand side is placed at the left-hand side.
  • Hidden detail is shown by short dashes.

Third Angle Projection:

Third angle projection is used in countries such as the USA and Canada.

  • The front, side, and plan views are in different positions.
  • In this method, the plan is placed above and in line with the front elevation.
  • What is viewed on the left-hand side is drawn on the left-hand side.
  • What is viewed on the right-hand side is drawn on the right-hand side.

Carefully study the symbols shown below. Normally when drawing in first or third angle projection a symbol is drawn underneath which clearly shows which angle of projection has been used.

first angle projection symbol
otho3b

Untitled1

Steps you can use to draw Orthographic Projection:

a) Make a sketch of the required views.

b) Draw both the vertical and the horizontal axis to intersect midway.

c) Determine the placing of the views.

d) Begin drawing with either the plan or front views.

e) From either of the views drawn above, project lines for the other view.

f) Draw the reflector line at 45°

g) Project the horizontal lines from the front elevation.

h) Project the plan to meet the reflector line of the 45°.

i) Take note of hidden details and outline the elevations to complete the job.

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