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Position without DRF/Datums

Hey all,
Wondering how to best measure and report a pattern position without datums. (See Dim labeled 11 on attached print view). The three holes are properly dimensioned to each other with basics and are the primary datum so the GD&T checks out but I'm not sure how to do it properly on PCDMIS. I've used a constructed feature set for that Datum A made from three cylinders, and it seems to be the centerpoint between the three, but I cannot report position with GeoTol as it says datums are required. Do I have to use Legacy? And can MMC be applied in Legacy? Thanks in advance for any advice!

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  • I would say to get an orientation you are going to have to make a line from A to B , then rotate to that, then do a basic rotation of 120°. This will then " square " it back up to the print. Yes you can use MMC in legacy. The 3 holes for A will just be best fit alignment using those 3 holes.
  • I think that orientation does not really matter. All that is called for is that the holes do not violate the maximum material boundary which is a cylinder 11.9mm in diameter located exactly by the basic dimensions, which also indirectly control the orientation of those tolerance zones. They are only relative to one another so the surface hits won't add anything because I'm already measuring them as 3D features.......I think
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  • I think that orientation does not really matter. All that is called for is that the holes do not violate the maximum material boundary which is a cylinder 11.9mm in diameter located exactly by the basic dimensions, which also indirectly control the orientation of those tolerance zones. They are only relative to one another so the surface hits won't add anything because I'm already measuring them as 3D features.......I think
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