Solids, polysurfaces and Booleans
A closed polysurface is a solid — needed for volumes, Booleans, 3D printing and clean exports. Learn to build, combine and repair solids.
In this lesson you will
- Create solids from primitives and surfaces
- Join and cap polysurfaces
- Use Boolean operations
- Fillet edges and repair open solids
Solids in Rhino
A polysurface is joined surfaces. When it encloses a volume with no naked edges, it's a closed polysurface — a solid. Primitives like Box, Cylinder and Sphere are solids from the start; ExtrudeCrv with Solid=Yes makes solids from closed curves.
Join and cap
Join surfaces along matching edges. Cap fills planar openings to close a polysurface. Check Properties (or What) — it says closed or open. ShowEdges shows naked edges to fix.
Booleans
BooleanUnion combines solids; BooleanDifference subtracts (cut openings, voids); BooleanIntersection keeps the overlap; BooleanSplit splits into parts. Booleans work best on clean closed solids; failures usually mean an open or bad object, or coincident faces — nudge one object slightly.
Edges and repair
FilletEdge and ChamferEdge round or bevel solid edges. For stubborn open objects: ShowEdges, JoinEdge for small gaps (within tolerance), rebuild the problem surface, or check model tolerance (Document Properties › Units) — a very loose or very tight tolerance causes many issues.
Quick reference
| Command / tool | How to start it | What it does |
|---|---|---|
| Join / Cap | Command line | Build closed polysurfaces |
| BooleanUnion / Difference / Intersection | Command line | Combine solids |
| FilletEdge | Command line | Rounds solid edges |
| ShowEdges | Command line | Finds naked edges |
Common mistakes
Boolean fails.
Check both objects are closed; avoid exactly coincident faces.
Solid won't close after Join.
Find naked edges with ShowEdges and fix the gap or tolerance.
Booleans on objects with coincident faces.
Offset one object slightly so faces overlap instead of coinciding exactly.
Exercise
A building block with openings
- Extrude a closed floor outline as a solid 3 m tall.
- Subtract window boxes with BooleanDifference.
- Union a roof extrusion to it.
- Fillet a few edges and confirm the result is closed.
You should end up with: A clean closed solid with openings.
Checklist
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Lesson quiz
A closed polysurface is treated as a solid.
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