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Position without DRF/Datums

edw.jack23
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.
  • in reply to Schlag
    I don't think that's a valid statement. Pretend its thin stamped sheet metal. How would you make cylinders in that ? The callout is just making the sure the 3 holes are in position to each other. Think of it as the bottom segment of a composite position callout. If it was that thin you would rally have to use surface hits next to each of the 3 holes. Then in reality your leveling to the " face " of the part and not A. Sometimes theory and how you actually have to do it don't quite match up.
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  • in reply to Schlag
    I don't think that's a valid statement. Pretend its thin stamped sheet metal. How would you make cylinders in that ? The callout is just making the sure the 3 holes are in position to each other. Think of it as the bottom segment of a composite position callout. If it was that thin you would rally have to use surface hits next to each of the 3 holes. Then in reality your leveling to the " face " of the part and not A. Sometimes theory and how you actually have to do it don't quite match up.
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