Engineering Drawing and Graphics
This section covers Engineering Drawing and Graphics: projection methods, line conventions, dimensioning, sections, scales and freehand sketching. The exam tests whether you can read a drawing and apply standard conventions rather than produce artistic sketches.
Core rules
- First-angle projection places the object between observer and plane; the view from the front appears above the top view. Third-angle places the plane between observer and object; the top view appears above the front view. Check the projection symbol.
- Use continuous thick lines for visible outlines, dashed lines for hidden edges, chain thin lines for centre lines, and continuous thin lines for dimension and extension lines.
- Dimension to visible outlines, not hidden lines. Give each dimension once, avoid closing a chain, and use leaders for circles and radii.
- A scale is drawing length : actual length. A 1:20 drawing is smaller than life; a 5:1 drawing is enlarged.
- Sections show internal detail; hatch adjacent parts in opposite directions and do not dimension hidden features that a section already shows.
Worked example
A drawing at 1:20 shows a dimension of 35 mm. Actual length = drawing length × scale denominator = 35 × 20 = 700 mm. Do not multiply by 20 again or convert to 0.035 m unless asked.
Traps
Do not confuse extension lines with dimension lines. Do not place the first-angle top view below the front view. Do not dimension to centre lines when an outline is available. Hidden lines should not cross dimension text.