Create a Watchmaker's Blend

+++ title = “Watchmaker Blend Workflow (Rhino 9 WIP)” +++

In this exercise, you’ll learn a workflow for creating high-quality corner blends using the new Patch Multi-Blend method in Rhino 9.
This technique improves highlight flow and avoids messy fillet corners — often called a watchmaker blend.

What You’ll Learn

  • Evaluating fillet quality with highlights
  • Preparing edges for patching
  • Creating a proxy surface
  • Building a multi-directional blend with Patch
  • Verifying continuity with Zebra

Exercise — Creating a Watchmaker Blend

Initial fillet result with uneven highlight flow.

Initial fillet result with uneven highlight flow.

1. Create the Base Fillet (0:18)

  1. Run FilletEdge.
  2. Set radius to 0.5 units.
  3. Accept default (no setback).
  4. Inspect the corner result.

👉 Rhino 9 produces a valid corner, but highlight flow may appear uneven.

2. Evaluate the Surface (1:12)

  1. Switch viewport to Rendered mode.
  2. Apply a simple material.
  3. Observe highlight behavior in the corner.

If highlights bounce or break, refinement is needed.

3. Remove the Corner Surfaces (1:41)

  1. Ctrl+Shift-click the fillet corner faces.
  2. Delete them.

You should now see the surrounding boundary edges.

4. Repair Edges with MergeEdge (1:58)

  1. Run MergeEdge.
  2. Merge edge segments where continuity should be smooth.
  3. Leave key transition edges split.

This simplifies the boundary for patching.

5. Create a Proxy Surface (2:13)

  1. Run BlendSrf.
  2. Pick the two opposing edges.
  3. Accept defaults (curvature is fine).

The surface does not need to fit perfectly — it only guides the patch.

Proxy blend surface used as a guide.

Proxy blend surface used as a guide.

6. Build the Multi-Blend Patch (2:38)

  1. Run Patch.
  2. Select all surrounding edges.
  3. Set continuity to G1 for each edge.
  4. Enable Multi-Blend.
  5. Click Preview.

You should see a smooth multi-directional blend forming.

7. Finalize the Blend (3:03)

  1. Accept the patch.
  2. Delete the proxy surface.
  3. Mirror the result if needed.
  4. Run Join.

You should now have a closed polysurface.

Final multi-blend corner.

Final multi-blend corner.

8. Inspect Highlights (3:25)

  1. Switch to an environment with strong reflections (e.g., automotive).
  2. Compare highlight flow between the original and new blend.

The new surface should show smooth, continuous reflections.

9. Verify with Zebra Analysis (3:57)

  1. Run Zebra.
  2. Inspect stripe continuity across the blend.

Clean, uninterrupted stripes confirm a high-quality transition.

Zebra analysis showing smooth continuity.

Zebra analysis showing smooth continuity.

Understanding Continuity Feedback (4:46)

When running Patch:

  • Each edge displays its assigned continuity
  • The command reports whether G0 and G1 are achieved
  • If continuity passes, the surface will join successfully

Rebuilding the Blend (Optional Practice) (5:02)

  1. Repair edges again with MergeEdge if needed.
  2. Recreate the proxy surface.
  3. Run Patch → Multi-Blend.
  4. Confirm continuity readout.

This repetition helps reinforce the workflow.

Result

You now have a high-quality corner blend with:

  • Smooth highlight flow
  • Verified G1 continuity
  • Clean zebra stripes
  • A fully closed polysurface

Summary

  1. Create a standard fillet
  2. Remove problematic corner faces
  3. Merge and prepare edges
  4. Add a proxy blend surface
  5. Use Patch Multi-Blend
  6. Validate with Zebra
Finished
You’ve created a production-quality multi-directional blend using Rhino 9’s new patch workflow.