Combinations of Right Regular Solids
≈ 40 minCombinations of Right Regular Solids
Grade 10 sectioned single solids. Grade 11 combines them — a cylinder standing on a prism, a cone on a cylinder — and then sections the combination.
The method does not change; the bookkeeping does. Draw the plan of the combination first, since a solid standing on the HP shows its true base there. Project the elevation from it. Where the two solids meet, decide carefully which edges are visible and which are hidden — that decision is where most marks are lost.
Visibility rules. In the elevation, an edge is visible if nothing lies between it and the viewer. Where a smaller solid sits on a larger one, the smaller solid's base is hidden inside the larger only if the larger surrounds it; otherwise part of that base edge shows.
Worked example. A 40 mm cylinder standing centrally on a 70 mm square prism: in the elevation the cylinder's outline is visible, and the top face of the prism is visible on both sides of it. The cylinder's circular base is not drawn as a full ellipse in the elevation — it appears as a straight line, because the elevation sees that circle edge-on.
Core checkpoint: Draw the plan first, project up, then resolve visibility edge by edge.
How does a horizontal circle appear in the elevation?
Which view should be drawn first for a combination of solids standing on the HP, and why?
In the elevation of a combination, how do you decide whether an edge is drawn visible or hidden?
A learner draws the join between a cylinder and the prism it stands on as an ellipse in the elevation. What has gone wrong?