Projection of Solids
Questions here test whether you can project prisms, pyramids, cylinders and cones in simple and tilted positions.
Solids and axis positions
Prisms, pyramids, cylinders and cones are drawn from their base and axis. With the axis perpendicular to HP, the base is parallel to HP and shows its true shape in the top view; the front view shows the height. With the axis perpendicular to VP, the base shows true shape in the front view. When the axis is inclined to HP but parallel to VP, first draw the simple position, then tilt the top view and project the front view. When the axis is inclined to both planes, use an auxiliary plane.
Worked example
A cone has a 40 mm base diameter and 50 mm axis, resting on HP. Top view: circle Ø40 with centre lines. Front view: isosceles triangle, base 40 mm, altitude 50 mm, apex on the axis. Reasoning: the base is parallel to HP, so its true circle appears in plan; the axis is vertical, so the elevation shows true height. Add the base centre line and the apex centre line.
Traps
Drawing the base as an ellipse when it is parallel to HP; using the slant height instead of the axis height; forgetting the hidden part of the base in a tilted view; not drawing centre lines; mixing the order of projection when tilting.