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   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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