Types of Technical Drawings

Technical drawings are based on the fundamental principles of projection. A projection is a drawing or representation of an entity on an imaginary plane or planes. This projection plane serves the same purpose in technical drawing as is served by the movie screen in a theatre.

A projection involves four components:

  1. The actual object that the drawing or project represents.
  2. The eye of the viewer looking at the object.
  3. The imaginary projection plane (the viewers drawing paper or graphics display in a computer-aided drafting system).
  4. Imaginary lines of sight called projectors

Parallel Projection

Parallel projections is subdivided into the following three categories: orthographic, oblique, and axonometric projections.

Orthographic Projections

Orthographic projections are drawn as multi view drawings which show the flat representations of principle views of the subject.

Oblique Projections

Oblique projections actually show the full size of one view and are of two varieties:

  • cabinet projection (½ scale)
  • cavalier projection (full scale)

Axonometric Projections

Axonometric projections are three-dimensional drawings and are of three different varieties:

  • isometric
  • dimetric
  • trimetric

Perspective Projection

Perspective projections are drawings which attempt to replicate what the human eye actually sees when it views an object. That is why the projectors in a perspective drawing converge. There are three types of perspective projections:

  • one-point
  • two-point
  • three-point