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Mmc

Geoff P
Can’t believe most inspectors and especially engineers don’t know this!

On a hole diameter MMC = Actual measured hole size minus the smallest allowable size which is the MMC condition… max material.

So for TP .5 on a 10.0 +/- .5 hole that measures 10.1
You get .6 Bonus (actual size 10.1 minus the smallest size 9.5 = .6) this .6 extra tolerance is then added to the given .5 TP tolerance for a grand total of 1.1 tolerance.

For a solid pin or outside cylinder it’s outside diameter, same concept. Largest allowable size minus the actual = Bonus Tolerance.

BONUS TOLERANCE =
DIFFERENCE BETWEEN MMC SIZE AND ACTUAL SIZE! ADDED TO GIVEN TP TOLERANCE IN THE FEATURE CONTROL FRAME.​
Parents
  • I had a few engineers from our customer tell me that a CMM does not have the accuracy to measure the part in question and they recommended using a scanner instead. Tolerances were +/- .005"

    I had just had my machine calibrated so I gave them in depth results of the calibration. They still said it wasn't going to be accurate enough. Finally, I told them I would be willing to scan the part as long as they paid for the software, scanner and annual calibrations.

    Turns out a CMM will work....Astonished
Reply
  • I had a few engineers from our customer tell me that a CMM does not have the accuracy to measure the part in question and they recommended using a scanner instead. Tolerances were +/- .005"

    I had just had my machine calibrated so I gave them in depth results of the calibration. They still said it wasn't going to be accurate enough. Finally, I told them I would be willing to scan the part as long as they paid for the software, scanner and annual calibrations.

    Turns out a CMM will work....Astonished
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