Decide the cutting plane first

Before drawing a single part, choose where the blade goes. Most teaching cutaways use a vertical plane through the middle of the object, or a quarter-cut that removes one corner. The plane decides what the reader sees, so pick the one that exposes the most interesting internals while leaving enough of the object to recognise it.

Keep the direction consistent across the whole figure. If the left half is a true section, the right half should not be a perspective view of the outside — mixing the two is the fastest way to make a drawing confusing.

Hatched cut faces tell the reader what was sliced internal chamber valve body cut plane Same material, same hatch direction, everywhere it is cut.
Figure 1 — The sliced walls are hatched; the parts you look at face-on are smooth. The dashed line records where the cut was made.

Hatching means "this is solid material"

The diagonal hatch is a borrowed convention from technical drawing, and it still works because nobody has to be taught it twice. Any surface that the cutting plane passed through gets the hatch; any surface you are looking at directly does not. That single rule separates "wall sliced open" from "wall seen flat", which is exactly the confusion a beginner cutaway usually suffers from.

Use one hatch angle for metal, another for rubber or gasket material, and leave fluid areas unhatched so flow stays visually distinct. Keep the hatch light — thin, evenly spaced lines — so it reads as texture rather than a competing pattern.

A small, fixed set of line weights section outline ¡ heavy internal edges ¡ medium fine detail ¡ light Heavy lines say "important outline"; light lines stay quiet.
Figure 2 — Three weights do all the work. More than three and the drawing starts to look accidental.

Build an outline hierarchy

A clean cutaway has a clear ranking of edges. The heaviest line is the outline of the section itself — the thing the reader should see first. Medium lines mark the edges of internal parts. Light lines carry minor detail, holes and surface clues. When every line is the same weight, nothing leads the eye and the drawing reads as a texture instead of a structure.

Let the shell reveal, never cover

If you keep an outer shell in the drawing, it must be far more transparent than the internals. The shell is context — it shows the reader the shape of the whole object — but it is never the subject. Draw it after the internals, set it to a low opacity, and disable pointer events on it so it cannot swallow the clicks meant for the parts underneath.

Bottom line: choose one cutting plane, hatch every sliced face, rank your line weights into three levels, and let the shell fade back. The internals become the story.