True Position Call Out

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  • True Position Call Out

    Hi guys. I'm back. I haven't done a true position in so long. I was hoping I could pick the collective hive mind and get some pointers on the best way of doing it. No one I work with has a great understanding of GD&T and I'm stumped. So I have 2 posts on a ~2.20 basic with a true position call out of .005. I don't know how to build my basic diameter or what I'm actually doing with that call out. PC DMIS is telling me that I need datums for that callout, which makes sense to me, but I see online you can have a true position with no datums. Besides that basic circle, there's no other dimensions to relate them back to. Am I misunderstanding the blue print or is the call out where?

    I've attached a rough sketch of the part/call out.
    Attached Files

  • #2
    It is not a cylindrical tolerance zone, so you probably have just a TP callout using the one basic dim. I've personally not seen to no datums, but I'd make the assumption of the primary datum as the surface the TPs are on if I was doing it.

    Comment


    • gt143744
      gt143744 commented
      Editing a comment
      That makes sense. I'll fiddle around with the planes and such and see what I come up with.

  • #3
    It looks to me like you have 2 x Ø.33 - .34 circles/cylinders with a 2.20 basic between them. Position of the pattern with no datums. That would just be position of one to the other, essentially. You can make one the datum and position the other, or, if using 2020 R2, just request the pattern position with no datum references.

    I would also question the intent of the tolerance zone shape. If these are cylinders and it isn't sheet metal, the zone should be diametral.

    Comment


    • gt143744
      gt143744 commented
      Editing a comment
      How do I get the pattern position without datums? Google isn't helping much and if I call 1 post my datum I get a .0000 answer (either with circle 1 as a datum or circle 2).

      Edit: OK I got them as a feature set and I'm still getting .0000. I'm seeing a circle diameter of 2.19ish which I'm assuming is my basic diameter but I have no idea why I'm getting 0 for my results.
      Last edited by gt143744; 12-09-2020, 07:51 AM.

    • JacobCheverie
      JacobCheverie commented
      Editing a comment
      gt143744 Measure each post as a cylinder individually. You should have CYL1 and CYL2. Now, define CYL1 as Datum A and CYL2 as Datum B. Now, request the position of CYL1 to B and/or the position of CYL2 to A.

      Which version of PC-DMIS are you using?

    • gt143744
      gt143744 commented
      Editing a comment
      I have 2020 R1. I see now what I was doing. I don't have much room so I was just measuring circles, but I'll try to squeeze some cylinders on those posts. Thanks!

  • #4
    Can you plane to something flat? rotate to the 2 small dia's and set to the large dia od or id. and then check small diameters and see what you get.
    A pretty bad print.
    Last edited by Randy P; 12-08-2020, 02:15 PM.

    Comment


    • gt143744
      gt143744 commented
      Editing a comment
      A pretty bad print sums up all this company's prints. I'll try that approach thanks.

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