Projection of Solids and Sections of Solids
This domain tests the projection of prisms, pyramids, cylinders and cones in simple and inclined positions, and the true shape of sections cut by planes. You must be able to choose the correct starting position and find the section points accurately.
Solids
Start with the axis perpendicular to HP and the base on HP. Draw the top view first: a true-shape polygon or circle. Project up for the front view. For an inclined axis, first draw the solid with the axis parallel to VP and inclined to HP, then rotate the top view to the required position and reproject.
Section planes
A section plane is shown as a line in the view perpendicular to it. If the plane is perpendicular to VP and inclined to HP, its true shape appears in an auxiliary view taken perpendicular to the section plane. Hatch the cut surface with thin, equally spaced 45° lines; do not hatch the background.
Example: square pyramid
A square pyramid, base 40 mm side and axis 60 mm, rests on HP. A section plane perpendicular to VP and inclined 45° to HP cuts the axis at mid-height. Draw the front view with the axis vertical; draw the section line at 45° through the axis midpoint. Where the line cuts the edges, project down to the top view to get the section points. For true shape, draw an auxiliary line parallel to the section line and project perpendicular to it; transfer distances from the section line. The true shape is a trapezium, not the square base.
Traps
Students often hatch the whole solid instead of only the cut face. The top view must be drawn before tilting the solid. Do not assume the section line's angle is the true shape; always use an auxiliary view. Hidden edges behind the cut must be removed or shown correctly.