Graphical Communication
Graphical Communication in the MATSEC Advanced Matriculation exam tests how accurately you produce and read technical drawings: first-angle orthographic projection, sectional and auxiliary views, intersections and developments, isometric and perspective work, and dimensioning. Marks reward construction and linework as much as the final outline.
Core rules and conventions
- Projection: use first-angle projection. The plan sits below the front elevation, and a view from the left is placed on the right.
- Line hierarchy: continuous thick lines (about 0.7 mm) for visible outlines; continuous thin lines (about 0.3 mm) for dimension, extension and projection lines; dashed thin lines for hidden detail; chain thin lines for centre lines, extending 2–3 mm past the outline.
- Dimensioning: place dimension lines parallel to the measured feature, with a small gap between object and extension lines; arrowheads touch the extension lines; figures sit above the dimension line; never dimension to hidden lines or repeat a dimension.
- Keep construction arcs, centre marks and projection lines visible so the examiner can follow your method.
Worked example
A wedge has a 60 mm × 40 mm base and a top face sloping from 0 mm at the front edge to 25 mm at the back edge. Draw the front elevation and plan, then find the true shape of the sloping face. The front elevation appears as a 60 mm wide shape with a sloping top; the plan is a 60 mm × 40 mm rectangle. To find the true shape, draw projectors perpendicular to the sloping edge in the elevation, set an auxiliary plane parallel to that edge, and transfer the 40 mm depth from the plan. The true slope length is √(60² + 25²) = 65 mm, so the true shape is a 65 mm × 40 mm rectangle. The reasoning: an auxiliary view perpendicular to a sloping face removes its foreshortening.
Marks-losing traps
- Placing the plan above the elevation, a third-angle habit, in a first-angle paper.
- Dimensioning a hidden edge, or giving the same dimension twice.
- Drawing non-isometric lines at true length instead of plotting endpoints.
- Omitting centre lines on circles, or letting chain lines stop at the outline.
- Forgetting to name views and complete the title block.