Sharp edges are rare in the real world — they're fragile, uncomfortable, and hard to manufacture. Fillets (rounds) and chamfers (bevels) finish your model's edges, and they're usually the last features you add.
Fillet vs. chamfer
- Fillet: a smooth, constant-radius round. Use for comfort in hand, stress reduction at inside corners, and a finished look.
- Chamfer: a flat angled cut. Use for lead-ins on holes and shafts, breaking edges cheaply, and 3D-printing overhangs (a 45° chamfer prints where a fillet's overhang may droop).
The workflow
- Open the Modify toolset and choose Fillet (or Chamfer).
- Tap the edges to round — in OpenShape3D you can keep tapping to build a set, and tapping a face grabs its whole edge loop.
- Drag on the model for a live-preview radius, or type it exactly (e.g. 1 mm to "break" an edge, 3–5 mm for grips).
- Apply. The kernel rolls a precise ball along each edge and stitches the result.
Choosing radii
- 0.5–1 mm: edge breaks — removes sharpness without changing the look.
- 2–5 mm: handheld comfort on enclosures and handles.
- Match your tooling: inside corners cut by a CNC end mill need a radius ≥ the tool radius anyway — design it in.
Why fillets fail (and fixes)
Filleting is famously the hardest operation in solid modeling. Typical failure causes:
- Radius too large for the geometry — the round would consume a neighboring face. Reduce the radius or fillet the big edges first.
- Adjacent fillets colliding — order matters; try filleting the connected chain in one operation instead of separately.
- Tiny slivers of face left by earlier operations — clean up the model before rounding.
Because OpenShape3D uses the OpenCASCADE B-rep kernel, fillets are exact surfaces (rolling-ball blends), not mesh approximations — so a 2 mm fillet measures 2.000 mm and exports cleanly for printing or machining.
Pro habits
- Fillet late: rounds complicate every subsequent boolean and sketch-on-face.
- Big fillets before small ones.
- Keep functional surfaces (mating faces, datum faces) unfilleted.