This is my first time seeing a call out like this. What is the benefit of dimensioning this way?
I feel like it would be more beneficial for tolerance stack to increase the perpendicularity to .002 - .010, remove bonus tolerance, and decrease the width allowance.
Unit is inch
The call out is for the width of the part, not a hole
I understand how to apply the GD&T and how the bonus tolerance works, I just don't know the benefit of toleranceing it this way or why they would tolerance this way.
LaserJay It makes sense then at least to me. At MMC the part has to be perfectly perpendicular due to the mating part. Any bit undersize allows for movement so the perpendicularity can increase as overall size decreases. That would be why they use MMC instead of a blanket tolerance w/o MMC. The tolerance is allowed to grow as size decreases. Say they called .005 perpendicularity with no modifier, the mating part may not fit if the perpendicularity is .005 if the part in question is at MMC but it will fit if perp is at .005 and the part is .005 undersize. What I'm trying to say is that the designers may not have a problem with the part being loose but if the part is at MMC, it has to be perfect. Any smaller than that and the tolerance can grow as the size shrinks.
I hope I am explaining this in a way you can understand. I can see it in my head but sometimes typing it out isn't my strong suit.
Traditionally, a designer will split tolerance between size and form. Often the parts do not meet the stated tolerances of one or the other but they still assembly and function as intended. So the designer will change size or form tolerances while still retaining the 'virtual condition' of the part. What zero tolerance at MMC does is say I don't care that much about size or form just so the part mates to the next assembly.
One other nice thing is that if you make a hard gage for hole locations is that the pins in the gage will do double duty to verify both location and GO size
