Positional Tolerancing for Coaxial Holes of Different Sizes

[Trevor McLaughlin]

I was hoping to get some help on this. See image below from the Standard. As far as I know, PC-DMIS cannot do this as per the callout since the holes are different sizes.

The closest workaround I can come up with is to dimension Coaxiality of one cylinder to the other, but you need to assign one of them as the datum axis (second selected feature) when using coaxiality. The callout doesn’t specify which is the “datum” axis when comparing one to the other.

I searched recent posts but was unable to find a clear answer. My question is: does PC-DMIS support this specific callout? If not, what is the best workaround? Coaxial Position.jpghttps://www.pcdmisforum.com/image/gif;base64,R0lGODlhAQABAPABAP///wAAACH5BAEKAAAALAAAAAABAAEAAAICRAEAOw==

[bfire85]

Create the holes as a 3D line. Insert the 3D line into the composite position callout without the MMC. Then output the two segments as individual measurements as variables and insert those measurements into a generic with the tolerance being the smallest allowable bonus between both of them?

[Trevor McLaughlin]

bfire85 thanks for the suggestions. I'll play around with the 3D line and see how that goes.

[Rob Jensen]

Trevor,

Create a single segment Position FCF (no datum reference) for each feature, then create a Simultaneous Tolerance command and select the two FCF's. This method will support different size nominal and tolerance values such that the bonus tolerance can be reported for each feature and provide the correct Position results.

[Schlag]

Rob, I just mentioned you in another post 2 minutes ago and added your paper on Use of datums in legacy mode. Long time to see your name here. Thanks for all you have done for everyone on here behind the scenes and without any credit !!!

[Trevor McLaughlin]

Thanks for the clarification Rob Jensen This doesn't come up often, but I need to be able to provide the best solution when it does. How far back is this math supported in PC-DMIS?

[Woody S]

We get this frequently for inline bores. I'll dimension the upper section on it's own and then align to one of the coaxial holes, and set it as a datum, and then dimension the composite section as position to the 1st hole that is the datum, which now is 0,0,0 to the hole I'm positioning. Doesn't match the print, but the theory is the same, just requires some explaining sometimes. It would be easier if PC-DMIS supported, as I'm sure there are millions of prints using a composite with holes of different sizes / size tolerances.