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GD&T Question
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Posted by: arul

10/14/2004, 06:30:20

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Friends,

Can Anyone Explain Maximum Material condition (MMC) in GD&T Concepts.

I need an Example to be used for Explaining.

Thanks

Arul

 







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Re: GD&T
Re: GD&T -- arul Post Reply Top of thread Forum
Posted by: Cragyon
Bart
10/14/2004, 14:27:56

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Maximum Material Condition is the condition of a feature of size where the maximum amount of material is present on the feature for the stated limits of size.

Example #1:  A hole feature, with a stated limits of size,  dia. 1.000 +/- .005 has a maximum material condition of  dia. .995.  The least material condition for the same hole is dia. 1.005.

Example #2:  For a cylindrical boss feature, with a stated limit of size, dia. .500 +/- .010 has a maximum material condition of dia. .510, and a least material condition size dia. .495.







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Re: GD&T
Re: Re: GD&T -- Cragyon Post Reply Top of thread Forum
Posted by: traingdt

10/14/2004, 23:05:56

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I agree completey with the definition given for MMC. We can then take it one step further.
In GD&T usage, the MMC idea is often invoked with the MMC modifier, symbolized by a circled M. When that symbol appears after a geometric tolerance number, it means that the given tolerance only applies when the feature is made at its MMC. So if a hole is given a size of 1.000 +/- .005, and also a position tolerance of .004, it means that the position of .004 is to be held if the hole is made to a size of .995 (its MMC)!
But suppose that we make a hole of .996. This is not the MMC size, but it is still within legal range. So here's where it gets interesting -- a hole of .996 has deviated from MMC by .001 inch. So we can adjust the position tolerance by .001 also! The print said position of .004, but our part really gets a position tolerance of .005! This trend continues until the hole reaches its LMC (1.005); at that size the position tolerance would be .014. This is the original .004 plus a "bonus" of .010, which comes from the deviation in hole size.
Essentially, it boils down to this: the small hole has to be positioned pretty accurately. But as the hole gets bigger, its center may deviate more from the true position. This is often helpful if the hole is simply a clearance hole.






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