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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
  • I'll also add (speaking from a fair bit of experience) that if the keyway is too small to measure planes on each side, it is too small to reliably check with a CMM. This is especially true for internal/broached keyways.

    A milled keyway on a shaft you might be able to do.

    The CMM is not always the best tool for the job!
Reply
  • I'll also add (speaking from a fair bit of experience) that if the keyway is too small to measure planes on each side, it is too small to reliably check with a CMM. This is especially true for internal/broached keyways.

    A milled keyway on a shaft you might be able to do.

    The CMM is not always the best tool for the job!
Children
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