Question 1 of 10: Orthographic Projection from an Isometric Pictorial

Question 1: Orthographic Projection from an Isometric Pictorial (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.

Given. The pictorial shows a rotationally-stepped body — three cylindrical bands of decreasing diameter from base to neck — that terminates in an asymmetric wedge/dome-shaped nose. The nose has been notched with a short angled slot on its right flank, and a small round hole passes through the neck section near the top of the largest step. No dimensions are supplied and none are to be added; only view selection, hidden-line/centreline convention, and correctness of projection are graded.

Find. The minimum set of orthographic views (drawn to CSA/ANSI third-angle-equivalent practice — Canadian practice historically also used first-angle on older drawings, but the modern default and the one used here is third-angle, symbol noted in the title block) that fully and unambiguously describes the part, with hidden detail (the through-hole) and centrelines shown correctly.

Approach. Because the part is axisymmetric about its long axis except for the two local features (the notch and the hole), the "minimum necessary views" rule (rubric row 1) is satisfied by exactly two views: a front view lying the part on its side with the axis horizontal, showing the stepped/tapered silhouette and the two local features, and a right-side view looking along the axis, which is the only view that shows the true circular cross-sections and the true angular position of the hole and the notch around the circumference.

1. Orient the part. Standard drafting practice places an axisymmetric part with its axis horizontal and its largest/most stable diameter toward the viewer in the front view — this minimizes hidden lines and matches how the part would sit in a lathe chuck for manufacture.
2. Front view — outline. Project the stepped diameters as horizontal step lines (each change in cylinder diameter is a visible line perpendicular to the axis) and the nose as two converging straight lines to the offset tip seen in the pictorial. The through-hole, since its axis is perpendicular to the page in this view, is not visible from outside the part and is drawn as two parallel hidden (dashed) lines across the neck.
3. Front view — notch. The wedge notch cut into the nose is visible from this orientation (it faces the viewer) and is drawn as a small visible V with solid lines.
4. Centreline. A single long-dash/short-dash centreline is run the full length of the part on the axis of revolution — CSA convention for any feature of revolution, even when no diameter is being dimensioned.
5. Right-side view. Project the largest-diameter circle (true size, since the view looks straight down the axis) and the neck circle. Rotate the notch and hole locations around from the front view by their true angular position (here, the pictorial shows them roughly diametrically opposed) — the hole appears as a small visible circle (it is a through hole seen end-on) and the true wedge shape of the notch appears as a small visible triangular cut, both true-shape only in this view.
6. Check against the rubric. Two views selected (not one, which would lose the circular cross-section information; not three, which would be redundant for an axisymmetric part) — satisfies "Selection of views: minimum necessary." All hole/notch edges not visible in a given view are dashed, never omitted — satisfies "Adherence to conventions." No dimensions were added, per the instruction.