![]() No tolerance of position or orientation is allowed if the feature is produced at its MMC limit of size and in this case, it must be located at true position or be perfect in orientation, as applicable. Where a tolerance of position or orientation is applied on a zero tolerance at MMC basis, the tolerance is totally dependant on the actual mating size of the considered feature. Effect of Zero Tolerance at MMC Maximum Material Condition Where the actual mating size envelope has departed from MMC, a deviation is allowed between its axis or center plane and the axis or center plane of the datum. Likewise, referencing a datum feature on an MMC basis means the datum is the axis or center plane of the feature at the MMC limit. The total permissible variation in the specific geometric characteristic is maximum when the feature is at LMC. Where the actual mating size of the feature has departed from MMC, an increase in the tolerance is allowed equal to the amount of such departure. The tolerance is limited to the specified value if the feature is produced at its MMC limit of size. Where a geometric tolerance is applied on an MMC basis, the allowed tolerance is dependent on the actual mating size of the considered feature. Effect of MMC Maximum Material Condition MMC Maximum Material Condition is defined as the condition of a feature which contains the maximum amount of material, that is, the smallest hole or largest pin, within the stated limits of size. Material Modifiers provide one of three callouts that describe whether a feature contains the maximum or minimum amount of material when fabricated, thus affecting the overall tolerance of the feature.ĭefinitions: MMC - Maximum Material Condition LMC is primarily used when concerned with wall thickness.When LMC or MMC are applied the total tolerance is DEPENDENT on the feature size.When RFS is applied the geometrical tolerance is independent of the feature size.–Internal Feature - Feature MMC - Geo Tol –External Feature - Feature MMC + Geo Tol Virtual Condition - Collective effects of a feature at MMC and the applied geometrical tolerance.Rule #2 - Unless otherwise specified, RFS applies to features of size.Bonus Tolerance - As the actual size of a feature departs from MMC, the departure value can be added to the geometric tolerance.Material modifiers help the designer to better describe what is dimensionally acceptable by providing insight into additional tolerances caused by the presence or absence of material on a part or feature. Understanding Material Modifiers - Conditions ![]()
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