Straightness at MMC May Keep Stock
Flat.
A size
tolerance on a flat part, when checked correctly, will
automatically control the flatness and straightness of the
surfaces as well as the size. This is true unless the feature
is stock, left in the "as furnished" condition. The gasket
below is made of a metal plate with rubber seals molded in
place. Since the plate is made of stock left in the "as
furnished" condition, Rule #1 does not apply. The company
wanted to assure that the plate was somewhat flat. A flatness
control would work but may be time consuming to check. A
better approach was to apply a straightness tolerance at MMC
to the plate. In this case, the plate must fit through an
envelope not greater than 3+0.05+0.1=3.15mm. By setting one
side of the plate on a flat surface and mastering an indicator
3.15mm above the plate, the straightness may be verified. This
will restrict the amount the flatness may be out but is often
easier to inspect.
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