Solid Geometry: Orthographic Projection — CSEC Technical Drawing

Orthographic projection represents a three-dimensional object using two or more flat two-dimensional views.

The principal views

Front elevation — the main view, looking horizontally at the front.
End (side) elevation — looking horizontally at the side.
Plan — looking vertically down on top of the object.

Each view shows the true shape of the face that is parallel to the projection plane. The planes of projection are mutually perpendicular (at right angles).

First-angle and third-angle projection

There are two systems:

First-angle: the plan is placed below the front elevation, and the end elevation is on the opposite side to the direction of viewing.
Third-angle: the plan is placed above the front elevation, and views are arranged on the same side as viewed.

The system used is shown by the truncated-cone symbol in the title block.

Line types in orthographic views

Visible edges — continuous thick lines.
Hidden edges — short dashed lines.
Centre lines — thin chain lines.

Method

Choose the projection system and a suitable scale.
Draw light construction lines and project related views from each other.
Line in the visible edges and add hidden detail and centre lines.

Views are aligned so that heights, widths and depths can be projected between them.

Exam tips

Name the three views: front elevation, end elevation, plan.
The plan is the view looking down.
Each view shows the true shape of the face viewed.
Remember the first-angle vs third-angle arrangement and the projection symbol.