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Flatness Tolerance on a Resting Face

Flatness is a Form tolerance. By default, Form tolerances refine size tolerances, and are consumed within the envelopes of size. Hence once the size tolerances are accounted for, a separate accounting of a Form tolerance is not required in DVA. The following 3 special cases of Form tolerances however, require a separate accounting of the tolerance towards DVA.

  • Flatness on a resting face
  • Flatness on a Feature of Size median plane expressed with a Modifier or expressed RFS.
  • Straightness on a Feature of Size median plane/ axis expressed with a Modifier or expressed RFS.
This case shows the impact of Flatness tolerance on a Resting face for two blocks. The impact of the Resting Face flatness can be seen on the gap variation.