How to draw a smooth

ByCADbrief Staff

Short Answer

To draw a smooth curve in Rhino 3D, the most common professional method is using interpcrv and placing as few control points as possible. This creates a clean, fair curve that passes through your picked points. Limitation: too many points usually make the curve wavy and harder to edit cleanly.

What You Need to Know Before

Warning: In Rhino, a curve can look smooth on screen but still be poorly built if it has too many points or uneven point spacing. This often causes bad offsets, surface failures, or visible bumps later when you use the curve for lofts, sweeps, or cnc prep.

How to Draw a Smooth Curve in Rhino 3D

  • Command: InterpCrv

  • Shortcut: InterpCrv

  • Quick Steps:

    1. Run InterpCrv from the Curve menu or type InterpCrv in the command line.
    2. Click a small number of well-spaced points in the viewport to define the curve shape.
    3. In the command options, set Degree=3 and keep placing points, then press Enter to finish.

Variables & Settings

  • Key Setting: Degree

  • Expert Setting: For most smooth design curves, Degree=3 is the standard choice because it gives a flexible, fair curve without becoming unnecessarily complex. Higher degree settings can make the curve harder to control and may introduce unwanted shape changes.

Why it Fails

  • Cause 1 (Geometry): Too many picked points create oscillations or lumpiness, even if the curve technically remains smooth.

  • Cause 2 (layers/Locks): Snapping to objects on locked or crowded reference layers can place points in the wrong location and distort the curve.

  • Cause 3 (Command/Logic): Using Polyline or an overfit rebuild workflow instead of InterpCrv produces segmented or overly edited geometry rather than a naturally smooth curve.

Quick Fix & Best Practice

  • Quick Fix: If the curve is bumpy, run Rebuild and reduce the point count while keeping Degree=3.

  • Manager’s Verdict: Use InterpCrv for concept and production curves when you need the curve to pass through known points. Avoid adding excessive points early; fewer, cleaner inputs give better downstream surfacing and manufacturing results.

FAQ

What is the best Rhino command for a smooth curve?

InterpCrv is the most common choice when the curve must pass through selected points.

Why does my smooth Rhino curve look wavy?

You likely placed too many points or spaced them unevenly.

Can I fix a rough curve after drawing it?

Yes, use Rebuild to simplify the curve and improve fairness.

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