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Bonus tolerance calculation for virtual condition

Jimmest
I have a true position call out for a hole of T.P.ø.028(M)/A/B(M)/C(M).
The datums are as follows:
A - plane perpendicular to hole axis
B - Hole in the same plane as the hole we are dimensioning
C - Different hole in the same plane as the hole we are dimensioning

I am having trouble understanding how PCDMIS calculates the bonus tolerance for this true position. Both Use datums and Fit to datums are turned on. Please see the attachment below for more information.



As you can see, the top dimension has a total bonus of .0086, while the bottom dimension has a total bonus of .0094. It's also perplexing that the bonus for D2 is so large (.0355) compared to it's deviation from nominal (.0075).

Any ideas?
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  • R2 is pretty much spot-on.

    But, to help you understand a little better -

    The actual DF values in the top and bottom are different. That's why the bonus is different.

    I'm pretty sure when the feature is so far out that the bonus will not bring it in tolerance (as in the top example) PCDMIS reports it OOT and reports the actual OOT values without adding the bonus.

    Plus there's this - MMB on datum features does not equal bonus Position tolerance. In some circles it is argued whether the software evaluates Datum Bonus correctly. Right or wrong, that evaluation is largely based on whether the alignment is 100% correct.
Reply
  • R2 is pretty much spot-on.

    But, to help you understand a little better -

    The actual DF values in the top and bottom are different. That's why the bonus is different.

    I'm pretty sure when the feature is so far out that the bonus will not bring it in tolerance (as in the top example) PCDMIS reports it OOT and reports the actual OOT values without adding the bonus.

    Plus there's this - MMB on datum features does not equal bonus Position tolerance. In some circles it is argued whether the software evaluates Datum Bonus correctly. Right or wrong, that evaluation is largely based on whether the alignment is 100% correct.
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