Communication and graphic techniques
What the domain tests
Communication and graphic techniques checks whether you can record and communicate design information accurately. Questions may cover freehand sketching, isometric and orthographic views, dimensioning, scale, line conventions, sectioning, and simple CAD conventions. The exam rewards clarity and correct convention, not artistic shading.
Core rules and concepts
- Use continuous thin lines for dimensions and projection lines, continuous thick for visible outlines, dashed for hidden edges, and chain lines for centrelines.
- In isometric drawing, vertical edges remain vertical and the two receding axes are usually drawn at 30° to the horizontal; do not foreshorten along the axes unless instructed.
- Dimension from a clear datum, give each dimension once, and place dimensions outside the outline where possible. Do not dimension hidden features on the hidden view.
- State the scale and units. At 1:2, every drawn length is half the real length; at 2:1 it is double.
- Use the projection convention named in the question. First-angle and third-angle place the views differently; the symbol identifies the convention.
Worked example
A rectangular plate is 80 mm long, 50 mm wide and 10 mm thick, with a Ø12 mm hole centred 20 mm from the left short edge and 25 mm from the front long edge. Draw at 1:2. The front view is drawn 40 mm × 5 mm; the plan is 40 mm × 25 mm. The hole appears as a Ø6 mm circle in the plan and as hidden dashed lines in the front view. Dimensions are written at full size-80, 50, 10, Ø12, 20 and 25-because scale changes the drawing, not the dimension values. The hole is located with two datum dimensions, not by a diagonal.
Traps that cost marks
Mixing hidden and visible lines, omitting units or the diameter symbol, repeating dimensions, drawing isometric axes at 45°, and scaling the dimension numbers as well as the drawing all lose marks.