Can I create a ʼTaperedʼ extrusion that gets smaller at the top in Rhinoceros 3D?

ByCADbrief Staff

Short Answer

Yes — in Rhino 3D, you can create a tapered extrusion that gets smaller at the top by using ExtrudeCrvTapered, which is the most common professional method for this shape. It extrudes a closed curve while applying a draft angle so the profile narrows as height increases. Limitation: extreme taper angles can cause self-intersecting or invalid geometry.

What You Need to Know Before

Warning: If your base curve is open, non-planar, or self-intersecting, the tapered extrusion may fail or create unexpected surfaces instead of a closed solid. Small profiles with a steep draft angle can also collapse before reaching the target height.

How to Do It

  • Command: ExtrudeCrvTapered

  • Shortcut: No default shortcut; type ExtrudeCrvTapered

  • Quick Steps:

    1. In the command line, run ExtrudeCrvTapered, then select a closed planar curve in the viewport.
    2. Enter the extrusion height, then set the taper angle; use a negative angle if you want the extrusion to get smaller at the top.
    3. Turn Solid=Yes if you want a closed polysurface, then confirm the direction in the viewport.

Variables & Settings

  • Key Setting: Solid=Yes/No

  • Expert Setting: When Solid=Yes is enabled, Rhino caps the extrusion if the input curve is closed and valid, creating a solid instead of open surfaces. This is the preferred setting for manufacturing, 3d printing, and Boolean workflows.

Why it Fails

  • Cause 1 (Geometry): The input curve is open, not planar, or has overlaps, so Rhino cannot generate a proper tapered solid.
  • Cause 2 (layers/Locks): The curve is on a locked layer or is part of a blocked object, preventing direct selection or editing.
  • Cause 3 (Command/Logic): The taper angle is too large for the profile size and height, causing the extrusion to collapse or self-intersect before completion.

Quick Fix & Best Practice

  • Quick Fix: Run SelOpenCrv or Check on the profile, then simplify or close the curve before using ExtrudeCrvTapered with a smaller negative taper angle.
  • Manager’s Verdict: Use ExtrudeCrvTapered for standard drafted forms and production-friendly solids; avoid it for complex variable tapers where Loft, Scale1D, or surface modeling gives better control.

FAQ

Can I taper an extrusion outward instead of inward?

Yes, use a positive taper angle to make the top larger.

Can I taper from a surface instead of a curve?

Not with this command directly; it is primarily for extruding curves.

Can I edit the taper angle later?

Not parametrically in Rhino standard history for every case, so rebuilding is often the fastest method.

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