Tolerance is the acceptable range of deviation from a nominal dimension. It is the single most important factor driving the cost and difficulty of a machined part — and the one most commonly over-specified.
Standard vs Tight Tolerances
A typical CNC shop holds ±0.05 mm as standard and ±0.01 mm as precision. Tighter tolerances such as ±0.005 mm are possible on critical features but require slower cutting and more inspection.
How Tolerance Affects Cost
Every step toward tighter tolerance adds slower feed rates, specialized tooling, more set-ups and additional inspection. A ±0.01 mm part can cost several times more than a ±0.05 mm part of the same shape.
Avoid Over-Tolerancing
Only critical, mating features need tight tolerances. Loose tolerances elsewhere keep the part economical. Over-specifying tolerance on non-critical surfaces is the most common design mistake we see.
Geometric Tolerancing
Beyond size, GD&T controls flatness, position, concentricity, parallelism and run-out. Use it to communicate how features must relate to each other, not just their size.
Specifying Tolerance Correctly
State a general tolerance in the title block, then flag only critical dimensions with tighter values. This keeps drawings clean and quotes accurate.
Need a tight-tolerance part? Send your drawing for a free DFM review and a quote within 24 hours.