Stages of the design process (hinge assembly): 04-BS-15, May 2015, Q9

Question 9: Stages of the design process (hinge assembly)

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 hinge assembly (bottom latch, top latch, and latch pin, item numbers 1–3) is used below to walk through the standard engineering design process, from problem statement to final production drawings.

Fig. Q9 — hinge assembly items (bottom latch, top latch, latch pin) referenced through each design stage.

Problem statement / identification of need. A requirement exists for a simple, low-cost pivoting latch that lets two panels rotate relative to one another about a common axis while resisting side-load separation — e.g. a gate or access-panel hinge.
Preliminary ideas / concept generation. Alternative concepts are sketched (a piano hinge, a butt hinge, this two-leaf pin hinge) and compared for cost, part count, and ease of manufacture; the two-leaf-plus-pin concept (as shown) is selected for its low part count.
Refinement / preliminary design. Rough proportions are set for the bottom latch (with its two knuckles), the top latch (single knuckle, offset to interleave), and the pin diameter; a rough sketch or 3-D pictorial (as in the exploded view) is produced to check that the knuckles interleave and the pin fits with running clearance, not a press fit.
Analysis. The pin is checked for shear/bending under the expected side load, and the knuckle wall thickness is checked so the latch does not crack under repeated pivoting; the mounting-hole pattern (Face 1/Face 8) is sized for the fasteners that will attach each latch leaf to its panel.
Decision. Final material (e.g. mild steel or brass for corrosion resistance), pin fit class, and finish (plating/painting) are chosen and locked in.
Implementation / detail drawings. Individual part drawings are produced for the bottom latch, top latch, and pin (each fully dimensioned and toleranced per CSA/ANSI convention), plus an assembly drawing with a parts list (matching the given item-number table) showing how Face 3/Face 5 of the bottom latch interleave with the top latch and how the pin passes through both, referencing Faces 7–9 for the fastener locations.

Stage	Reference to the hinge
1. Problem statement	Need for a low-cost pivoting panel connection
2. Concept generation	Two-leaf pin-hinge concept selected over piano/butt hinge
3. Preliminary design	Knuckle interleave and pin clearance sketched (exploded view)
4. Analysis	Pin shear/bending, knuckle wall strength, fastener sizing
5. Decision	Material, fit class, and finish locked in
6. Implementation	Detail drawings (items 1–3) + assembly drawing with parts list

Topic: The engineering design process

Key relations: Problem statement → concept generation → preliminary design → analysis → decision → implementation (detail + assembly drawings); iteration can loop back from any later stage to an earlier one.

Why this works: Each stage narrows the solution space using progressively more detailed information (a rough concept sketch is cheap to change; a toleranced detail drawing is not), so moving through the stages in order minimizes wasted design effort.

Common pitfall: Treating "drawing the part" as the first step (skipping problem definition and concept comparison) is the classic novice mistake — the hinge’s two-leaf-and-pin concept was only one of several considered before detailing began.

Source: Giesecke et al., Technical Drawing / Engineering Graphics, ch. on the topic below.

Question 9 of 9: Stages of the design process (hinge assembly)

Question 9: Stages of the design process (hinge assembly)