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.
Print Rev 1: Ø.130±.003 T.P. w/in .002|A(LMC)|B(LMC)| (-A- is an OD...Ø.130 is an OD...-B- is an OD)
Us: Hey customer, we're having problems with this feature, can you open the tolerance for us? (The fact that this GDT is really useless is so over their heads that we don't even bother bringing it up...)
Note:
THEY TOLD US to intentionally hold -A- and -B- towards low limit so we can try to get more bonus tolerance elsewhere around the part.....they give us a healthy ±.0010 on diameter size
Print Rev 1: Ø.130±.003 T.P. w/in .002|A(LMC)|B(LMC)| (-A- is an OD...Ø.130 is an OD...-B- is an OD)
Us: Hey customer, we're having problems with this feature, can you open the tolerance for us? (The fact that this GDT is really useless is so over their heads that we don't even bother bringing it up...)
Note:
THEY TOLD US to intentionally hold -A- and -B- towards low limit so we can try to get more bonus tolerance elsewhere around the part.....they give us a healthy ±.0010 on diameter size