LMC as Related to Positional Toleranc

ing. Where positional tolerancing at LMC is specified, the stated positional tolerance applies where the feature contains the least amount of material permitted by its toleranced size dimension. Specification of LMC requires perfect form at LMC. Perfect form at MMC is not required. Where the feature departs from its LMC limit of size, an increase in positional tolerance is allowed, equal to the amount of such departure. See Fig. 5-12. LMC may be specified in positional tolerancing applications where MMC does not provide the desired control and RFS is too restrictive. See Figs. 5-13 through 5-15. LMC is used to maintain a desired relationship between the surface of a feature and its true position at tolerance extremes. Considerations critical to the design are usually involved.

5.3.5.1 LMC to Protect Wall Thickness. Figure 5-13 illustrates a boss and hole combination located by basic dimensions. Wall thickness is mini-

Rfs Mmc Zero Tolerance Mmc
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