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MMC by hand

Good morning,
We've been asked to report the position and parallelism of a keyway to a bore. It's a simple bore, with a one straight keyway in it. We have also been asked to use the MMC bonus in the calculations. The keyway is shallow enough that we can't get two good planes from the sides, or we would use a width feature. We've tried to make a width feature using two lines constructed from points taken on the sides of the keyway. We either don't understand that process well enough to make it work, or it just doesn't. Anyway, we've decided to do this in legacy, using an alignment. One advantage of this is that we can clearly demonstrate our process to disbelieving minds. We have somewhat figured out how to use assign to do some simple arithmetic. We can assign the value of a letter or something to be the measured value of the bore, minus the smallest (maximum material condition), allowable diameter of the bore. We can subtract that bonus from a reported position or parallelism, and report the result of that using a generic feature. What we haven't been able to figure out is how to keep our report from showing a minus number if the position is really good, and the bonus is large. (we know that pcdmis reports the actual position, but doesn't turn it red if the bonus is large enough) We're sure there is a way. We've looked at the "if then" stuff for pcdmis on the internet, and we're going to try and fumble our way through that on Monday morning.

Can someone possibly direct us to some good "help" information, or maybe provide a simple example of how to correctly do what we are trying to do? Being able to do this kind of "if then" arithmetic is something we could use a lot.

Thanks for your help.
Parents
  • Thanks again for all your help.

    We do use the generic circle thing for keyways. It usually works well for us. This particular drawing asks for bonus from the keyway size, and bonus from the bore, which is datum A. I don't fully understand how, or even if, that method actually uses the datum modifier bonus. Probably just my own ignorance. I click on the use datums button select the A cylinder, and click on the M button for the datum, but it only seems to use the bonus from the keyway. Maybe that's all it's supposed to use. Again, probably my own ignorance. Our engineering dept. thinks it should get a bonus from both.

    Thanks
Reply
  • Thanks again for all your help.

    We do use the generic circle thing for keyways. It usually works well for us. This particular drawing asks for bonus from the keyway size, and bonus from the bore, which is datum A. I don't fully understand how, or even if, that method actually uses the datum modifier bonus. Probably just my own ignorance. I click on the use datums button select the A cylinder, and click on the M button for the datum, but it only seems to use the bonus from the keyway. Maybe that's all it's supposed to use. Again, probably my own ignorance. Our engineering dept. thinks it should get a bonus from both.

    Thanks
Children
  • The (M) on your datum is NOT the same as the (M) for your feature. These bonus values do not work the same. For your datum it is a SHIFT allowance within the confines of itself, for the feature it is a direct add on to the tolerance value set by the print. The example I provided does not account for Datum Shift, you would need to use GEOTOL to gain that bonus.

    I would recommend some time reviewing the difference of Datum Shift vs Bonus Tolerance.