Can I extract the edge of a 3D surface as a new wire in Rhinoceros 3D?

Short Answer

Yes — in Rhino 3D, you can extract the edge of a 3D surface as a new wire using DupEdge, which is the most common professional method for creating edge curves from surfaces or polysurfaces. It generates real curve geometry from selected edges. Limitation: trimmed or messy geometry can produce segmented or unexpected curves.

What You Need to Know Before

Warning: If the surface edge is part of a trimmed face, the extracted wire may follow the trimmed boundary rather than the underlying untrimmed surface edge. On imported STEP/IGES models, bad joins or tiny edge gaps can also create multiple small curves instead of one clean wire.

How to Extract a 3D Surface Edge as a New Wire

• Command: DupEdge

• Shortcut: DupEdge

• Quick Steps:

  1. Run DupEdge from the command line, or use Surface menu tools if available in your workspace.
  2. Click the surface or polysurface edge you want to extract.
  3. Press Enter to create the new curve, then check the ChainEdges option if you want connected edges selected as one continuous result.

Variables & Settings

• Key Setting: ChainEdges
• Expert Setting: Turn ChainEdges=Yes when you need a continuous wire from connected surface edges. Leave it off when you need only one specific edge for downstream trimming, detailing, or CNC reference work.

Why it Fails

• Cause 1 (Geometry): The object has trimmed, split, or poorly joined edges, so Rhino duplicates several edge segments instead of one continuous wire.
• Cause 2 (layers/Locks): The source object or target layer is locked, preventing selection or making the extracted curve seem missing.
• Cause 3 (Command/Logic): DupEdge only works on actual surface or polysurface edges, not arbitrary isocurves or visual display edges.

Quick Fix & Best Practice

• Quick Fix: Run ShowEdges first to find naked or bad edges, then Join or repair the surface before using DupEdge again.
• Manager’s Verdict: Use DupEdge when you need exact manufacturing or reference curves from real model boundaries; avoid it when the model is dirty or when you actually need interior surface curves, where other curve tools are more suitable.

FAQ

Can I extract all edges of a surface at once?
Yes, use DupBorder for full outer boundaries in suitable cases.

Will the extracted edge stay linked to the surface?
No, the new wire is independent curve geometry.

Can I extract edges from a polysurface or solid?
Yes, DupEdge works on polysurface and solid edges too.

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