Third Angle Projection

So far we have only covered one method of Orthographic Projection, this is known as First Angle Projection. First Angle Projection is used in Europe and most of the world. However America and Australia use a method known as Third Angle Projection.

In First Angle Projection we place our object in the First Quadrant (see above figure). This means that the Vertical Plane is behind the object and the Horizontal Plane is underneath the object.

In Third Angle Projection the Object is placed in the Third Quadrant. This means that the Vertical Plane is in front of the object and the Horizontal Plane is above the object. To see the effects of this watch the animation below.

You may have noticed that the Plan is above the Elevation and the End Elevation of the right hand side is on the right of the Elevation. These changes in the position of the views are the only difference between projection methods.

Because the difference between projection methods is so small this presents little or no difficulty for engineers to interpret drawings, provided we indicate on the drawing which system we are using. The symbols for First Angle and Third Angle projection are shown below. The symbols are derived from a cut cone which has been projected in First or Third Angle respectively

The recommended proportions for the projection symbols are shown below

With a little bit of practice you can become fluent in both First and Third Angle projection.