Maximum material condition MMC

MMC is that condition of a part or feature which contains the maximum amount of material, e.g. minimum size hole, or a maximum size shaft. In certain cases its use allows an increase in the specified tolerance if it is indicated that the tolerance applies to the feature at its maximum material condition.

The maximum material principle takes into account the mutual dependence of tolerances of size, form, orientation and/or location and permits additional tolerance as the considered feature departs from its maximum material condition.

The free assembly of components depends on the combined effect of the actual finished sizes and the errors of form or position of the parts.

Any errors of form or position between two mating parts have the effect of virtually altering their respective sizes. The tightest condition of assembly between two mating parts occurs when each feature is at the MMC, plus the maximum errors permitted by any required geometrical tolerance.

Assembly clearance is increased if the actual sizes of the mating features are finished away from their MMC, and if any errors of form or position are less than that called for by any geometrical control. Also, if either part is finished away from its MMC, the clearance gained could allow for an increased error of form or position to be accepted. Any increase of tolerance gained this way, provided it is functionally acceptable for the design, is advantageous during the process of manufacture.

Straightness error

Actual diameter

Actual diameter

Actual diameter

Virtual size being the effective assembly diameter

The symbol for maximum material condition is the letter M enclosed by a circle, M . The symbol is positioned in the tolerance frame as follows:

0 0.05 (M)

X

0 0.05

0 0.05 M

Refers to the tolerance only. Refers to the datum only. Refers to both tolerance and datum.

Refers to the tolerance only. Refers to the datum only. Refers to both tolerance and datum.

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Responses

  • wayne
    How to interpret maximum material condition eng drawing?
    8 years ago
  • shishay
    Who draw the maximum material and energy from the environment?
    2 years ago

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