Question 6 of 9: First-angle vs. third-angle projection

Question 6: First-angle vs. third-angle projection

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.

The given L-shaped block (with a rear notch and a through-hole) is sketched twice: once in third-angle projection (Canadian/US standard, object "inside the glass box," each view unfolded onto the plane BEHIND it) and once in first-angle projection (used in much of Europe/Asia, each view unfolded onto the plane IN FRONT of, i.e. beyond, the object). The two conventions place the top and side views on OPPOSITE sides of the front view.

Approach. Keep the front view identical in both layouts (it is not affected by which angle convention is used), then place the top view above the front view for third-angle and below it for first-angle; place the side view to the right of the front view for third-angle and to the left for first-angle.

1. Third-angle: top view directly above the front view, right-side view directly to the right — each view shows what you would see LOOKING TOWARD that plane from outside the box.
2. First-angle: top view directly below the front view, side view directly to the left — each view shows the projection THROUGH the object onto the far plane.
3. Label each set "THIRD ANGLE PROJECTION" / "FIRST ANGLE PROJECTION" and note the standard projection symbol (the truncated-cone symbol) alongside, per CSA/ANSI practice.