Maximum Material Condition (MMC)

The maximum material condition is used when designing two mating parts.
Taking a shaft designed to fit into a bore as an example, this specification ensures that the shaft actually fits into the bore under the maximum material condition (MMC), while also preventing excessively strict size tolerance from being applied in order to avoid cases where the shaft does not fit into the bore.

What Is ?

To apply the maximum material requirement to a dimension, you write after the size tolerance in the feature control frame. “M” stands for “maximum material condition" (MMC). This symbol indicates the application of maximum material requirement.

What Is M?
The axis with a diameter of 20 mm (0–0.2) must be between two planes separated from each other by 0.3 mm and parallel to datum A.

Handling Size Tolerances

Size tolerance is always followed when the maximum material condition is used. However, if a size tolerance is deviated from the maximum material size, the difference can be added to a geometric tolerance to make a virtual size.

  1. Maximum material condition

    Maximum material condition
  2. Virtual condition

    Virtual condition
    a
    Virtual size

Expressing Maximum Material Condition Using a Dynamic Tolerance Diagram

The dynamic tolerance diagram is a tool that visually expresses the changes in the tolerance zone of size tolerance and geometric tolerance. By marking geometric tolerance on the vertical axis and size tolerance on the horizontal axis, the variations in both size tolerance and geometric tolerance can be presented at the same time. The application of the maximum material condition also clarifies the bonus tolerance that occurs when the geometric tolerance increases.

Drawing indication
Shaft and housing
a
Shaft
b
Housing
Dynamic tolerance diagram
Dynamic tolerance diagram
a
Straightness
b
Shaft size tolerance
c
Bore size tolerance

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