Tolerance Zone Modifiers
GD&T
Material Condition Modifier
Maximum Material Condition (MMC)
The Tolerance applies when the part is at its heaviest.
Notice how nice and round the hole is on the real part. That's rule number one at work. (See that there is only a tolerance on size.)
Maximum Material Condition (MMC)
Limits the worst case scenario (in terms of being able to assemble parts).
This "scenario" is called the virtual condition.
On the flip side, it provides a "bonus tolerance" for the machinist.
Additionally, it allows for functional gaging.
MMC Example
In your mind “inflate” the shaft to its largest allowable diameter, them move it to “every” allowable position. This creates the virtual condition.
Virtual Condition & Resultant Condition
Virtual condition (previous) is a way to think about the worst-case mating scenario.
The resultant condition is a way to examine when the feature departs in the other direction (toward LMC). It can be used to determine things like whether or not the hole is too close to the edge of a piece of material.
Bonus Tolerance
If the tolerance applies at MMC, the boundary can be larger than if RFS.
MMC creates a zone that surrounds the feature.
A smaller part has more “wiggle room”
Least Material Condition
Same concept as MMC, but with features at their minimum weight (largest hole, shortest length).
Usually used when a minimum distance must be maintained.
Projected Tolerance Zone
Think of a long dowel that needs to be inserted into a hole. An error in the position of the hole will be amplified. Projected tolerance zones can accommodate this condition.
Projected Tolerance Zone