Is an ʼOpen Curveʼ able to be turned into a solid block in Rhino?

Short Answer

Yes — in Rhino 3D, an open curve can sometimes be turned into a solid block, but not directly as-is. The most common professional method is to first make it a closed profile, then use ExtrudeCrv with Solid=Yes. If the curve is not planar or cannot be closed cleanly, it will fail.

What You Need to Know Before

Warning: An open curve does not define a closed boundary, so Rhino cannot create a valid closed solid from it until the gap is fixed. A very common failure is tiny endpoint gaps that look closed visually but still prevent a watertight solid.

How to Turn an Open Curve into a Solid in Rhino

• Command: ExtrudeCrv

• Shortcut: _ExtrudeCrv

• Quick Steps:

  1. Select the open curve, then use CloseCrv if possible, or edit the endpoints from the standard curve editing tools to create a closed shape.
  2. Run ExtrudeCrv from the command line or modeling tools, then select the corrected closed curve.
  3. Set Solid=Yes and enter the extrusion distance to create a closed solid.

Variables & Settings

• Key Setting: Solid=Yes

• Expert Setting: This option adds caps to the extrusion so the result becomes a closed polysurface instead of an open surface. If the curve is still open or non-planar in a way Rhino cannot cap, Solid=Yes will not produce a valid solid.

Why it Fails

• Cause 1 (Geometry): The curve has open ends, overlaps, or is not truly planar, so Rhino cannot generate a closed capped extrusion.
• Cause 2 (layers/Locks): The curve or related construction geometry is on a locked layer, preventing editing or closing before extrusion.
• Cause 3 (Command/Logic): ExtrudeCrv can extrude an open curve, but that creates an open surface, not a solid, unless the profile is closed and cap-able.

Quick Fix & Best Practice

• Quick Fix: Run SelOpenCrv to find open curves, then use CloseCrv or rebuild the missing segment before running ExtrudeCrv with Solid=Yes.
• Manager’s Verdict: In professional Rhino workflows, always verify the profile is closed and planar before extrusion. If the source is an open curve, fix the geometry first rather than trying to force a solid from invalid input.

FAQ

Can Rhino extrude an open curve?
Yes, but it will normally create an open surface, not a solid.

What command checks for open curves in Rhino?
Use SelOpenCrv.

Can I cap every extruded curve into a solid?
No, only closed and properly planar profiles can reliably cap into solids.

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