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MMC May Be Applied to Datum References in a Profile Tolerance Callout - But Not to the Profile Tolerance
(In accordance with Y14.5M-1994 standard)

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The Y14.5 Standard tells us that we cannot apply the MMC modifier to a profile tolerance because it is a surface control. We can, however, apply MMC or LMC to the datum references of a profile tolerance where the datum features are features of size. Here the secondary and tertiary datum features are features of size. Applying MMC to these features means that the part may be shifted on the datum feature virtual conditions in order to bring the features into their profile tolerances. The lower illustration is of a possible overlay chart that could be used if the part is inspected on an optical comparator. You can see that the part has been shifted on the datum feature virtual conditions in order to bring the features into their profile tolerances. If the datums had applied RFS, this part would not pass inspection. This is easy to do with an optical comparator. This is not easy to do in an open set-up and on most coordinate measuring machines. It is important to know what inspection method will be used when assigning geometric tolerances and material condition modifiers.

Back to Tips Tip added Jan 2007