First-Angle vs. Third-Angle Projection: 04-BS-15, December 2014, Q7

Question 7: First-Angle vs. Third-Angle Projection (10 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

[Figure not reproduced: Given isometric pictorial: L-shaped stepped block with a hole. See the official exam paper or the cited reference text.]

Given isometric pictorial: L-shaped stepped block with a hole

Both systems use the same six principal views, but they place the object differently relative to the projection planes: third-angle (Canadian/US standard) puts the object BEHIND the plane of projection, so each view is placed on the side it was seen from (top view above the front view). First-angle (common in Europe/much of the rest of the world) puts the object IN FRONT of the plane, so each view is placed on the opposite side from where it was seen (top view goes BELOW the front view).

Approach. Sketch the same front and top views of the L-block for both systems, but swap the top view from above the front view (third-angle) to below it (first-angle); label each sketch with its own projection symbol (the truncated-cone/circle symbol) so the two are unambiguous.

Answer — third-angle (top view above front) vs. first-angle (top view below front); same object, different view placement.

System	Object position	Top-view placement
Third angle	behind the picture plane	above the front view
First angle	in front of the picture plane	below the front view

Check: the L-block's exact proportions are read qualitatively from the given isometric; the graded content is the correct relative PLACEMENT and LABELLING of the two systems, per the rubric.

Question 7 of 10: First-Angle vs. Third-Angle Projection

Question 7: First-Angle vs. Third-Angle Projection (10 marks)