Run out issue

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  • Run out issue

    PCDMIS 2019 R1 - The Xact will not let me add another datum for my runout in my FCF. I have Datum A (OD cylinder) and Datum B (OD plane that is perpendicular to Datum A). Typically this runout is performed by a gage fixture but I am being instructed to write a program as a back up. The FCF is Runout 0.05 to A B. I have 2 interior features that need measured to this Datum structure. One is a ID circle and the other is an ID plane. In the past if I had 2 datums they were usually constructed into a line, etc (example: 2 cone chamfers at either end of the part). I am clueless as what to construct to make this a singular datum or how to proceed. Generally, I don't like to use the CMM for runouts. Thanks for any help!

  • #2
    Can you even do runout to two datums that are perpendicular to each other?


    • #3
      Please clarify: Is A datum the cylinder or the plane?

      -If A datum is the cylinder, then the GD&T is wrong, and B datum is irrelevant.
      Level Z and origin XY to A datum, origin Z to B datum, but it doesn't make any difference for your runout measurement.

      -If B datum is the cylinder, then runout is relative to the plane, centered at the intersection of the B datum.
      Level Z to A datum. Origin XY to B datum, origin Z to A datum. It's essentially checking perpendicularity to A.


      • #4
        As above, in this instance, Datum B has no effect on the axis of rotation for the considered cylinder, or the considered plane. Just use Datum A.
        Automettech - Automated Metrology Technology


        • #5
          ^ +1

          B&S CHAMELEON/PCDMIS CAD++ V2011

          There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"



          • #6
            You can do runout to two datums but only when the first datum is a plane. In this case, the first datum controls the orientation and translation along it's surface direction and the second datum controls the remaining translations. Think of it like sitting the part on a surface plate (the plane) and sliding the OD up against a V-block then rotating the part whilst reading off deviations from an indicator touching the feature you are checking for run-out.

            When the first datum is an axis, no other datums are allowed.
            Neil Challinor
            PC-DMIS Product Owner

            T: +44 870 446 2667 (Hexagon UK office)
            E: [email protected]


            • neil.challinor
              neil.challinor commented
              Editing a comment
              louisd beat me to it. That post must have landed whilst I was typing.

          • #7
            Everything you guys are saying makes sense. The only thing that I can think of is that they included the Datum B (plane) because it rests on this surface in the run out fixture. I've included a section of the print. The blue arrows point to the ID bore (feature #34) and the interior plane (sorry it's on back of print) to be measured. example1.png Can this still be done with PCDMIS as called out? Thanks so much!


            • louisd
              louisd commented
              Editing a comment
              Since datum A is a cylinder, technically no.

              If you switch datums (making plane datum A and cylinder datum B, you will not be evaluating the part correctly at all. PC DMIS will evaluate perpendicularity of datum a plane to your ID bore, instead of cylindrical runout to the true A Datum cylinder.

              You can origin your alignment to the B datum and then construct your cylinder bore. check total runout of od cyl to id cyl. dont use datum b plane

          • #8
            If you swap the datum order (as per the explanation by neil.challinor above) then yes.
            PC-DMIS CAD++ 2o19 R1 SP11


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