04-BS-15 · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
04-BS-15 Engineering Graphics & Design Process — May 2013, 3 hours, closed book (candidates may use a Casio or Sharp approved calculator). Ten questions of equal value; all sketches must be freehand and neat; each question carries a printed grading rubric (criterion / grade) reproduced beside its solution below. Canadian (CSA/ANSI, now CSA B78.1 harmonized with ASME Y14.5) drafting conventions are used throughout.
Reference texts: Bertoline & Wiebe, Technical Graphics Communication; Giesecke et al., Technical Drawing / Engineering Graphics (ASME Y14.5 dimensioning, CSA B78.1 drafting practice).
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.
Two of the three terms are addressed below (revision block and tolerance specification), each with a definition, its purpose in the design/manufacturing process, and a worked example.
(a) Revision block. A revision block is a small table, usually in the upper-right corner of the drawing near the title block, that records every change made to a released drawing after its first issue: a revision letter or number (A, B, C… or 1, 2, 3…), a brief description of what changed, the date of the change, and the initials or name of the person who approved it. Its purpose is traceability — anyone building, inspecting, or purchasing against the part needs to know they are working from the current revision, and needs a documented history if a part built to an old revision turns up defective. Example: a bracket's mounting-hole diameter is enlarged from ⌀10 mm to ⌀12 mm after a fastener change; the drawing's revision block gains a new row: "Rev B — Hole ⌀ changed 10→12 mm to suit new fastener — 2013-06-02 — J.K." — every earlier printed copy of "Rev A" is now obsolete and should be pulled from the shop floor.
(b) Tolerance specification. A tolerance specification states the permissible variation on a dimension — the range within which the manufactured size may fall and still be considered acceptable — because no manufacturing process can hit an exact nominal size every time. It may be given as a bilateral tolerance (e.g., 50 ± 0.1 mm, meaning anywhere from 49.9 to 50.1 mm is acceptable), a unilateral tolerance (e.g., 50 +0.2/−0.0), or a limit dimension (49.9–50.1 directly), and a drawing's title block usually also carries a general/default tolerance ("unless otherwise specified, ± 0.5 mm") that applies to every dimension not individually toleranced. Its purpose is to balance function against cost: a tighter tolerance guarantees better fit/interchangeability but is more expensive and slower to manufacture, so the designer specifies only as tight a tolerance as the function actually requires. Example: a shaft that must slide freely inside a bushing might be specified ⌀25.0 −0.05/−0.10 mm (always slightly under nominal, guaranteeing clearance), while the bushing bore is specified ⌀25.0 +0.10/+0.05 mm (always slightly over), so the two toleranced ranges never overlap and a running clearance fit is guaranteed on every assembled pair.
