Design communication and graphical presentation
Design communication and graphical presentation is examined through sketching, orthographic and isometric drawing, dimensioning, sections and assembly views.
Core rules
- Isometric uses three axes at 30 degrees to the horizontal; lengths along axes are true, circles become ellipses.
- Orthographic shows separate views at 90 degrees. In third-angle projection the plan is above the front view and the right side view is to the right; first-angle places them differently, and the symbol identifies which.
- Line types: continuous thick for visible edges, dashed for hidden, chain for centre lines, thin for dimensions and hatching.
- Dimensioning uses extension lines, arrowheads and a value; do not duplicate a dimension, and dimension to visible features, not hidden ones.
- Sections use a cutting-plane line and hatching to show internal detail; exploded views show assembly order.
Worked example
A bracket is drawn in third-angle orthographic: front view 60 mm x 40 mm, plan above showing 60 mm x 25 mm depth, side view to the right showing 25 mm x 40 mm. To sketch it isometrically, draw verticals and two 30-degree axes, mark 60 mm along one axis, 25 mm along the other and 40 mm vertically, then add the 10 mm hole as an ellipse. Check that the three overall dimensions agree with the orthographic views.
Traps
Mixing first- and third-angle layouts; drawing isometric circles as true circles; dimensioning hidden edges; forgetting hidden lines; leaving out the projection symbol.