CNC Tolerances and Cost

A tolerance is a promise to spend money. Every decimal place of precision costs exponentially more, because it demands slower feeds, better tools, and more inspection.

A practical rule

• Plus/minus 0.1 mm — standard, cheap
• Plus/minus 0.025 mm — precision, roughly 2–3x cost
• Plus/minus 0.005 mm — grinding territory, roughly 5–10x cost

Most features do not need plus/minus 0.025 mm. Apply precision only where function demands it — a bearing seat, a locating diameter — and leave everything else generous. The part works identically and costs half as much.