Rhino 3D Tip: Weld and UnifyMeshNormals for Clean Meshes

Clean meshes render better, export reliably, and play nicely with downstream tools. Two fast, high-impact commands in Rhino are Weld and UnifyMeshNormals—use them to eliminate shading seams, black faces, and faceting without remodeling.

When to reach for Weld and UnifyMeshNormals

• Viewport shows sharp seams or faceted bands on otherwise smooth forms.
• Dark/inside-out patches appear due to flipped mesh face normals.
• Renders look segmented despite adequate polygon density.
• External apps (OBJ/FBX) import your mesh with broken shading.

Quick cleanup workflow

1. Diagnose normals
   • In Shaded (or Rendered) mode, enable Backface color: Display Modes > Shaded > Backface settings > Single color. Opposite-colored faces indicate inverted normals.
2. Unify directions
   • Run UnifyMeshNormals to make all mesh face normals consistent.
   • If the whole mesh flips inward, run Flip to invert it once.
3. Soften shading across intended smooth edges
   • Run Weld and set an angle:
     • 180° for organic surfaces and scans.
     • 30°–60° for most product and automotive exteriors.
     • 10°–30° for hard-surface details where slight breaks are acceptable.
4. Protect crisp creases
   • If an edge should stay hard, use Unweld (or UnweldEdge) on that edge after a general weld.
5. Recompute normals for final shading
   • Run RebuildMeshNormals to ensure clean, consistent vertex normals.

Export tips

• OBJ/FBX/glTF: enable welding on export to preserve smooth shading across edges in other apps.
• If a target app ignores OBJ “smoothing groups,” pre-weld in Rhino and verify with UnifyMeshNormals before exporting.

Best practices and pitfalls

• Don’t over-weld: seams needed for UV islands or deliberate hard edges should remain unwelded.
• Before welding heavy scans, run CullDegenerateMeshFaces and CheckMesh or MeshRepair to eliminate zero-area faces and non-manifold issues.
• For performance, welding reduces drawn edge counts and can improve viewport smoothness on dense models.
• In Grasshopper, pair Weld and Unify Normals components after mesh generation or remeshing to standardize outputs for rendering or simulation.

Angle selection cheat sheet

• Organic/characters/industrial clay: 180°
• Consumer product casings: 45°
• Mechanical with chamfers: 20°–30°
• Architectural faceting: 10°–20° to preserve panel breaks

Small, consistent cleanup routines pay off across the pipeline—viewport previews, render engines, and game/AR platforms all benefit from welded vertices and unified normals. If you’re outfitting a team or standardizing workflows, explore Rhino licenses, training, and compatible plugins at NOVEDGE. Their specialists can help match add-ons like remeshing and repair utilities to your production needs. Learn more and compare options at NOVEDGE.