Designing for CNC: five rules that cut your unit cost

Most of what a CNC part costs is decided before it reaches a machine. The geometry you hand over sets the tool paths, the number of setups and how long a spindle has to run — and machine time is the bill.

1. Respect internal corner radii

A tool can't cut a perfectly sharp internal corner. Designing in a radius at least one-third of the cavity depth lets a larger cutter clear the pocket in fewer passes.

2. Keep wall thickness sane

Thin walls chatter and deflect. For metals, stay above 0.8 mm; for plastics, above 1.5 mm — or expect a finishing pass that adds time.

3. Limit the number of setups

Every reorientation of the part is another setup, another fixture, another chance for error. Features on fewer faces machine faster and cheaper.

4. Loosen tolerances you don't need

Tight tolerances mean slower cuts and more inspection. Call out precision only where the part actually needs it.

5. Pick a stock-friendly size

Designing around standard bar and plate sizes cuts material waste and the time spent roughing down to your envelope.