Projection of simple solids and sectional views
Projection of simple solids and sectional views
This domain tests the front view, top view and side view of prisms, pyramids, cylinders and cones, and the correct representation of a cut surface after a section plane is applied.
Core rules
- Start with centre lines and the axis. For a solid resting on HP, draw the top view first when the base shape is known, then project upward for the front view. Keep the height constant across the views.
- A section plane is usually perpendicular to VP or HP and is shown by a chain line with arrows. The cut surface is hatched with thin continuous lines at 45° and 2–3 mm spacing; hatch only the cut surface, not the whole view.
- The true shape of a section appears when the section plane is parallel to the plane on which it is projected. Project every cut point to the other view before joining the section outline.
- Draw visible cut edges with thick lines and retain hidden lines behind the cut where they are needed. Label the section plane and the cut points consistently.
Worked example
A triangular prism stands on HP. A horizontal section plane cuts it 20 mm above the base. In the front view, draw the section line 20 mm above the base and mark where it crosses the two visible edges. Project these points down to the top view; because the plane is parallel to the base, the cut surface is the true triangle. Hatch the triangle in the top view. Reason: a plane parallel to HP shows its true shape in the top view.
Traps
Hatching the entire front view, omitting the cut points on hidden edges, and using the wrong line type for the section plane are common. Also check that the section plane arrows point in the viewing direction, and do not forget the centre line on a cylinder or cone.