Fillets and chamfers are the two standard methods for treating sharp corners in CNC machined components. Both remove the sharp corner — but they produce different geometry, require different tooling, and have different applications.
What Is a Fillet?
A fillet is a rounded arc that replaces a sharp corner. It is defined by a radius — the radius of the arc that blends the two adjacent surfaces.
Fillets are used when:
- Stress concentration must be minimised — sharp corners are stress risers
- The component will be handled — sharp corners are a safety hazard
- The design requires a smooth, continuous surface
- The mating component has a corresponding radius
In XyzPilot, fillets are created with the Fillet/L,L,R operator. The operator creates the arc and automatically trims the adjacent lines — no separate trim step required.
What Is a Chamfer?
A chamfer is a straight angled cut that replaces a sharp corner. It is defined by setback distances — how far back from the corner the chamfer starts on each adjacent surface.
Chamfers are used when:
- A component must be inserted into a hole — the chamfer guides the insertion
- A bolt or screw must be seated — the chamfer provides clearance
- The design requires a defined angular break edge
- The machining process makes a fillet impractical
In XyzPilot, chamfers are created with the Chamfer/L,L,D1,D2 operator. Chamfer lines are stored as Line entities (L-prefix) and behave exactly like any other line.
Fillet vs Chamfer: The Decision
| Consideration | Fillet | Chamfer |
|---|---|---|
| Stress concentration | Better — distributes stress | Worse — still a stress riser |
| Tooling | Ball-nose or radius cutter | Chamfer cutter or angled pass |
| Insertion guidance | Poor | Good |
| Appearance | Smooth, continuous | Defined angular break |
| Drawing specification | R value (e.g. R5) | Angle × depth (e.g. 45° × 2mm) |
Corner Radius in CNC Pockets
In CNC pocket machining, the corner radius is determined by the tool radius — the cutter cannot produce a sharper internal corner than its own radius. The pocket corner radius must be specified on the drawing and must be ≥ the cutter radius.
In XyzPilot, pocket corner fillets are created with Fillet/L,L,R using a radius equal to or slightly larger than the cutter radius.
Programming in XyzPilot
Both fillets and chamfers are created in the geometry stage — before CAM setup. The CAM module then generates the toolpath to machine the profile, including the fillet arcs and chamfer lines.
For fillets: Fillet/L3, L0, R=10 — creates the arc and trims the lines automatically.
For chamfers: Chamfer/L3, L0, D1=5, D2=5 — creates the chamfer line. Trim the adjacent lines separately.