Shell, Draft & Rib
The plastic-part trio — hollow a solid to walls, taper faces for mould release, and add stiffening ribs.
Together these three turn a chunky solid into a mouldable plastic part.
Shell
Hollows the body to a constant wall:
- Start Shell, set the wall thickness.
- Pick the faces to remove (the openings) — none removed = a closed hollow body.
- Need a thicker floor? Per-face multi-thickness overrides let selected walls differ.
Shell late in the tree: features added after it are not hollowed, which is usually what you want for bosses and holes.
Draft
Tapers faces by an angle so the part releases from a mould:
- Pick a neutral plane (stays put) and the faces to draft; set the angle (1–3° typical).
- Applies to existing geometry — an alternative is the draft option built into Extrude while the boss is made.
Rib
A stiffener from a skeleton line:
- Sketch a line (open contour is the point — no closed profile needed) where the rib's spine should run.
- Start Rib: set thickness (spread evenly both sides), the fill direction, and optional draft for moulding.
- The rib grows until it meets the body — walls, floor, curves and all.
When it fails
- Shell fails on tight corners — the wall self-intersects at small radii; thin the wall or enlarge the Fillet & chamfer first.
- Rib "can't find the body" — the fill direction points away from material; flip it.
- Draft conflicts with a fillet — draft first, fillet after, is the reliable order.
Related: Extrude (boss & cut) · Fillet & chamfer · Holes, threads & coils