Rhino 3D Tip: BlendSrf Workflow for Smooth Surface Transitions

For silky transitions between surface patches, BlendSrf with the right continuity controls delivers production-quality results fast.

When to use it:

• Bridging two trimmed surfaces where simple fillets or blends fail to preserve form quality.
• Upgrading a positional seam to tangent or curvature continuity for better reflections and highlights.
• Creating editable transition patches that can be refined without rebuilding the entire model.

Preparation (small investments, big payoffs):

• Clean edges: use RebuildEdges if needed, and remove tiny sliver trims before blending.
• Unify surface directions: run Dir and make normals consistent to avoid flipped handles.
• Diagnose first: use Zebra and CurvatureGraph to understand the existing surface flow and target continuity level.

Command flow:

• Run BlendSrf and select the first and second surface edges. Use ChainEdges when working across multiple joined segments.
• Set continuity per side: Position (G0), Tangency (G1), or Curvature (G2). Match each side according to adjacent surface quality, not habit.
• Place and move section handles. Add more sections where the shape changes rapidly; fewer where the form is calm.
• Adjust bulge and bias sliders to tune volume without breaking continuity.
• Use Trim inputs when you want a clean, production-ready join without manual trimming afterward.

Continuity guidance (choose deliberately):

• G0: Position – Fast and light. Use for hard-break seams or when downstream fillets will control the transition.
• G1: Tangency – Default for most product blends. Keeps shading continuous while preserving edge intent.
• G2: Curvature – Best for highlight-critical surfaces (automotive, consumer electronics). Demands cleaner inputs; rewards with superior reflections.

Shaping strategies:

• Balance continuity with control: overusing G2 on noisy inputs can introduce ripples—clean curves or rebuild surfaces first.
• Distribute section handles evenly; dense clusters create bumps. Add sections only where needed.
• Leverage RecordHistory so upstream edge edits update the blend. Toggle off when finalizing to keep files lean.

Evaluation and refinement:

• Run Zebra before and after to confirm smooth highlights across the seam.
• Use MatchSrf if adjacent surfaces were edited post-blend or to promote a G1 blend to G2 without rebuilding.
• If BlendSrf struggles on complex trims, BlendCrv between edge curves, then Sweep2 using the blend curves as sections for added control.

Common pitfalls and fixes:

• Broken continuity at edge kinks: simplify edges or insert a transitional surface to remove corner singularities.
• Over-tight bulge causing self-intersections: reduce bulge, relax handles, or increase continuity only where the form supports it.
• Heavy control structures: if the blend is overly dense, rebuild inputs or reduce section count and iterate.

Workflow accelerators:

• Create aliases for faster access, e.g., bs = BlendSrf with your preferred defaults.
• Save analysis display modes (Zebra, Curvature) as toolbar buttons to audit continuity in one click.

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