Sectioning a Combination of Solids

Sectioning a Combination of Solids

Cutting a single solid gives one section outline. Cutting a combination gives a section made of several parts, and the skill is keeping track of which solid each part of the outline belongs to.

The procedure. Draw the plan and elevation of the combination. Mark the cutting plane. Then work solid by solid: find where the plane crosses the first solid and plot those points, then do the same for the second. Number the points within each solid separately, then join each solid's points in its own order.

Hatching. If the two solids are one component the whole section is hatched the same way. If they are separate components, hatch them at different angles — the rule from assemblies applies here too.

Worked example. A vertical cutting plane through a cylinder standing on a prism gives a rectangle from the prism and a rectangle from the cylinder, joined into one outline. An inclined plane through the same combination gives a trapezium from the prism and part of an ellipse from the cylinder — two quite different curves in one section.

Core checkpoint: Work solid by solid and keep each one's points in its own numbered sequence. Mixing the sequences is what produces a crossed outline.