Question 8 of 10: Size, Location, and Coordinate Dimensioning

Question 8: Size, Location, and Coordinate Dimensioning (9 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. No part is supplied. A simple rectangular plate with a round hole and a small square boss is used here, since it cleanly carries one example of every dimension type the question requires.

Find. A two-view sketch (front + a suitable second view) with one clearly-labelled example each of a size dimension, a location dimension, and a coordinate dimension.

Approach. The three dimension types answer three different questions about a feature: size answers "how big is it," location answers "where is it, measured from a nearby reference feature," and coordinate answers "where is it, measured from one common, fixed datum (0,0) shared by every feature on the part" — the last is preferred on parts with many features because errors do not accumulate feature-to-feature the way they can with a chain of successive location dimensions.

1. Sketch the plate outline in the front view (a rectangle) with a second view (a thin profile) showing its thickness.
2. Add a SIZE dimension. The hole's diameter, ⌀32, is a size dimension: it describes only how big that one feature is, independent of where it sits on the plate.
3. Add a LOCATION dimension. The distance from the plate's left edge to the hole's centre, 60, is a location dimension: it fixes the hole relative to one adjacent reference edge.
4. Add COORDINATE dimensions. A second feature (the small square boss) is dimensioned as an (X, Y) pair — 170 and 110 — both measured from a single common datum point (here, the plate's bottom-left corner, marked 0,0) rather than from the nearest edge; every other feature on a coordinate-dimensioned drawing would likewise reference that same one datum.
5. Label all three directly on the sketch ("SIZE dim.", "LOCATION dim.", "COORDINATE dims.") as the question explicitly requires labelling, not just correct drafting.