04-BS-15 · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Reference texts: Bertoline & Wiebe, Technical Graphics Communication; Giesecke, Mitchell, Spencer et al., Technical Drawing / Engineering Graphics (ASME Y14.5 dimensioning practice, CSA B78.1 Canadian drafting conventions).
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 with labelled vertices A-G. See the official exam paper or the cited reference text.]
An edge on an isometric pictorial is scalable (its true length can be read off directly with a scale) only if it is parallel to one of the three isometric axes — i.e. it is an edge of the block's own principal directions. An edge that lies in an inclined (non-isometric) cutting plane is foreshortened by the projection and is not scalable: its endpoints must instead be located by coordinates measured along the three scalable axes, then joined.
Approach. Vertices C, D, G, B bound the slanted cut face that bevels the block's top corner — that face is not parallel to any principal plane, so every edge of its boundary (CD, DG, GB, BC) is a non-isometric line. Vertices E, F, A lie on the block's original base/side faces, which ARE parallel to the isometric axes, so EF, FA and AB are scalable.
| Edge | Scalable? | Reason |
|---|---|---|
| C–D, D–G, G–B, B–C | No | bound the inclined cut face; not parallel to any isometric axis, so foreshortened — locate endpoints by coordinates, not direct measurement |
| E–F, F–A, A–B | Yes | lie along the block's original principal edges, parallel to an isometric axis — true length is preserved |
| D–E, G–F, C–A | No | connect a cut-face vertex to a base vertex across the bevel — also non-isometric |
