A drawing that says ±0.05 mm everywhere is often a drawing written by fear rather than by function. Real machining cost scales non-linearly with tolerance because tighter work needs more setups, slower feeds and more frequent inspection.

The good news is that only a handful of features on most castings actually need the tight callout — locating bores, sealing faces and press-fit diameters. Everything else can stay at a standard tolerance and keep the part affordable.

Key Points

  • Cost reality: a feature tightened from ±0.1 mm to ±0.05 mm typically adds 3–5× machining cost on that feature; below ±0.02 mm it can require grinding or wire EDM.
  • What 3-axis CNC holds easily: ±0.1 mm; 4/5-axis with care: ±0.05 mm; grinding: ±0.005–0.01 mm.
  • Write tolerances only where function demands them, and let the drawing note say 'unspecified ±0.1 mm' — your supplier will quote a much better price.
  • Share your GD&T with us before quoting; we flag over-tightened features that add cost without adding performance.