Distortion budget: how it propagates through the build

Allocating dimensional change across rough machining, heat treat, finish, EDM, and nitriding so the cavity tolerance survives the build.

6 min readLesson 6 of 13

A 500 mm by 500 mm H13 closed-die cavity comes back from the vacuum heat treater. The cert reads 48 HRC, double tempered at 580°C, NADCA #207. The toolmaker sets the block on the surface plate, sweeps the cavity face, and reads 0.18 mm of out-of-flat across the diagonal. The print called for 0.05 mm. Nothing on the cert is wrong. The heat treat ran to spec. The block moved, because every block moves, and the build did not budget for it.