Engineering Drawings, Symbols and Welding Terminology
This domain checks whether you can read an engineering drawing and extract dimensions, views, tolerances and welding information without guessing. The exam favours interpretation of line types, projection method and limits.
Core rules
- Orthographic views show an object from front, top and side. In first-angle projection, the top view is placed below the front view and the left view is placed on the right. In third-angle projection, the top view is above the front view and the right view is on the right. Check the projection symbol in the title block.
- Line types: continuous thick lines are visible edges, dashed lines are hidden edges, chain lines mark centre lines, and thin lines carry dimensions and extension lines.
- Dimensions are normally in millimetres. A nominal size with tolerances gives upper and lower limits. A datum is a reference from which dimensions are measured.
- Read notes, material specification, weld symbols and surface finish notes before planning the job.
Worked example
A plate dimension is 50 ±0.5 mm. The upper limit is 50.5 mm and the lower limit is 49.5 mm. A measured 50.6 mm is outside the upper limit and must be rejected or referred for engineering decision. A measured 49.5 mm is at the lower limit and is acceptable if the tolerance is inclusive.
Traps that cost marks
- Scaling a dimension from the drawing instead of reading the stated value.
- Mixing first-angle and third-angle view positions.
- Ignoring hidden lines that show a hole or pocket.
- Treating a general tolerance note as applying to a dimension that has its own tolerance.