material condition modifiers on datum reference frames

[Tenkan]

Help me understand the use of, and when to use material condition modifiers on datum reference frames.

Is it because the material condition of the DRF needs to accommodate parts as produced at their limits of size? Otherwise in the case of RFS, some parts that are produced within their size limits might not fit into the simulated DRF failing inspection when in reality they are good?

To clarify, attached is an example drawing where datum reference B has a MMC modifier, why?


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[powerhound]

It just so happens that the latest tip on datum shift has a figure that looks like yours.

Link

This should help your understanding.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Tenkan]

Thank you Powerhound, this is a good start. So this means the modifier affects the location of the pattern, not the pattern elements to each other?


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[powerhound]

Yes. The amount that the pattern can shift depends on the actual produced size of the datum feature. The tolerance zones are still the same size and located in the same place relative to each other but as datum feature B departs from its MMC size then the pattern can shift away from its center by the same amount.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Tenkan]

Thanks powerhound, pretty straight forward. Ironically, not covered in detail in my 101 class.



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