Rhino 3D Tip: Robust Filleting Workflow: Scale, Tolerances, and Topology

Fillets fail less because of the FilletEdge tool and more because of scale, tolerances, and topology. Here’s a reliable workflow to get robust, clean fillets every time.

Prepare the model

• Work near the world origin to avoid numeric instability; move the part so its pivot is close to 0,0,0.
• Set realistic units and absolute tolerance before modeling. As a rule of thumb, tolerance should be 10–100x smaller than your smallest fillet radius.
• Run Check on imported geometry. If the object isn’t a closed solid, fix issues first; naked or non-manifold edges often derail fillets.

Pick the right fillet approach

• FilletEdge (solid-level): Fast for prismatic parts; supports ChainEdges, Variable radius, and Setback corners (R7+).
• FilletSrf (surface-level): Best when solids fail. Use Extend=Yes and Trim=Yes to build robust rolling-ball fillets on cleaner surface pairs.
• When aesthetics matter at tight corners, consider BlendSrf to handcraft transition patches after surface-level filleting.

Simplify topology first

• Use MergeAllFaces to collapse co-planar or co-cylindrical patchwork into single faces—fewer edges mean more reliable fillets.
• Eliminate tiny edges with SplitEdge (to localize) followed by topology cleanup, or remodel problematic details slightly larger than your radius.
• Repair trim issues with RebuildEdges on suspect faces; don’t rely on JoinEdge to “force” joins—it hides problems.

Corner strategy matters

• Select edges in logical chains. For 3+ edge corners, use Setback options in FilletEdge to avoid self-intersections at the pole.
• If a corner fails, fillet two edges first, then build or blend the remaining corner patch manually—more control, fewer surprises.
• Avoid radii larger than available space. Use Distance, DraftAngleAnalysis, or simple measurements to verify room for the chosen radius.

Surface-first rescue workflow (when solids fail)

• ExtractSrf (Copy=Yes) the faces you need, Untrim and ExtendSrf to create “runways.”
• Run FilletSrf between extended faces; Trim and Join the result.
• Finish the corner with BlendSrf or additional fillets, then cap/close as needed.

Troubleshooting quick hits

• If preview fails, try a slightly smaller radius, or increase modeling tolerance modestly (save/restore your default afterward).
• Switch display to Arctic or use Zebra to spot kinks or broken continuity before filleting.
• Watch for overlapping fillet surfaces; reduce radius or simplify neighboring features to remove conflicts.

Validate the result

• Run ShowEdges (Naked/Non-manifold) on the finished part; resolve any strays before moving on.
• Use ShrinkTrimmedSrf on edited faces to clean trims and stabilize downstream operations.
• For planar end caps, use Cap to re-close solids cleanly.

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