MMC and LMC 

Maximum material requirement (MMR) at the maximum material condition (MMC) is a brilliant modifier used in gd&t that you can use to save manufacturing costs while still satisfying the function.  

As the name suggests, maximum material condition MMC means that the Geometric tolerance is only valid when the size dimension is at its limit which results in the part having the maximum possible mass of material. In other words, the tolerance limit results in the heaviest part.  

So, for a shaft with an outer diameter of 10 + - 0.1, the maximum material condition is 10+0.1 = 10.1, this is the size that results in the shaft being at its heaviest condition.  

But for a part with a hole with a diameter of 10+-0.1, the maximum material condition is when we have the smallest hole.

That is when the part is in its heaviest condition. So, 10 – 0.1 = 9.9  

The least material condition (LMC) is just the opposite of (MMC).  

Was that simple?  ,, yes? ,, good, because somehow there is a lot of confusion about MMC and LMC.  

MMC and LMC Calculator

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Let's look at how we can use these conditions to save some money.  

By adding the letter M in a circle after the geometric tolerance, for example, the position tolerance, we are saying that the value of the tolerance is only valid when the part is at its MMC, if the part did not reach this limit, then the manufacturer can add the unused tolerance to the value of the geometric tolerance.  

If I have a part with these two holes, both have the diameter 5 + - 0.1.  

And the distance between the holes is 10. And I add a position tolerance on the diameter of this hole of 0.1, to Datum A, while A is the diameter of the other hole. 

This would mean, that the value of the position tolerance zone is 0.1.  

But if I add the M in a circle modifier to the Feature control frame next to the tolerance value, then this means that the 0.1. is only valid when the hole size is at its MMC of 5-0.1 which is 4.9.  

But if the hole was actually 5., then I can use this extra 0.1 and add it to the value of the position tolerance. So, I actually am allowed a position tolerance of 0.2.  

And if the hole was 5.1, then I can use the 0.2 difference between the real measurement and the MMC and add it to the position tolerance. So, I got 0.1 + 0.2 = 0.3

By doing so, we can allow the manufacturing to have more deviations in one tolerance if the other tolerance is precise.  

The MMC can also be applied to the size of the datum feature.  by adding the “M” symbol to the feature control frame 

This way, the dimension that has to be at its Maximum material condition in order for the geometric tolerance to be valid, is the size of the datum feature.  

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