True position

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  • True position

    Hi guys,

    I am a rookie with pc-dmis so my "problem" will probably seem ridiculous. I don’t get this true position. I have measured that .437 boss, thread hole, and both lines. I don't understand how machine is doing the math so I am not sure if I am dimensioning this right. I don’t know if it is taking center point of a line for dimensioning because in that case it would depend on first and last point I took when I measured that feature. I am babbling... Anyways, I attached the drawing, so any help on this is more than welcome!

    Thanks!
    Attached Files
    Last edited by Grobar; 04-13-2006, 12:05 PM.

  • #2
    Create a cylinder on the .437 dia boss and align to that cylinder then set zero in both directions to the cylinder. Compare the threaded hole to this alignment as true position (t/p), your theoreticals should be .000 - .000 for the c/l of the threaded hole and your tolerance for the t/p should be .010 at RFS. Think of it as rotating the boss with an indicator on the minor dia of the thread, you are actually measuring runout or T.I.R. from one feature to another. Oh yeah..... just to through in another little twist t/p of a thread is ALWAYS measured to the pitch cylinder, not the major or minor dia ( unless otherwise specified on the drawing ). Have fun.
    sigpic Eye Yam Sofa King We Todd It.

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    • #3
      check out this site for a True position calculator.

      http://www.engineersedge.com/true_position.htm

      Your print is hard to read. But it appears you can translate your origin (alignment) to the measured .437 boss and report the 1/4-20 diameters on both sides of your part. Use your true position for dimensioning. Nominals would be X=0, Y=0 (depands on your working plane). Should calculate it for you.
      You may wish to obtain a book on Geometric Dimensioning and Tolerancing (GD&T).

      Good Luck and welcome to the school of Hard Knocks

      BS
      Windows 7
      Pc-Dmis 2015
      Global Performance 7-10-7


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      • #4
        After a break, we're back on track. This long weekend was too short!
        Thanks guys for your help, but the thing that's giving me a hard time is true position of those notches (see .343 distance between notches). How can I do that?
        Any thoughts?

        Thanks.

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        • #5
          one way is to create a midpoint or symmetry between the .343 notch and check it in relationship to the .437 boss. in y the variation should not exceed +/-.005 and you may also use mmc from the size of the notch.
          sigpic
          Southern Man don't need him around anyhow!

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          • #6
            Would concentricity & true position be the same thing when the datum is circle and the circle which calls out for TP is above that?
            I used to be high on life but I built up a tolerance.

            Brown & Sharpe Global Advantage
            PCDMIS CAD++ v2011mr2
            PH10MQ/SP600M


            sigpic

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            • #7
              post pic of your drawing?
              If your FCF has a position symbol, than it is position. If it had a concentricity symbol, it is concentricity. 2 diff. things.
              RFS Means Really Fussy Stuff

              When all you have is a hammer - everything looks like a nail....
              sigpic

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              • #8
                The part I'm looking at is basically a cap that has an inner cylinder in the center. The print is calling out for the TP of the outer diameters to the inner (datum). I'm questioning because it used to be concentricity, but now there's a new print with the TP called out. Can someone elaborate why? And how it's different?

                <<<< Learning noob....
                I used to be high on life but I built up a tolerance.

                Brown & Sharpe Global Advantage
                PCDMIS CAD++ v2011mr2
                PH10MQ/SP600M


                sigpic

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                • #9
                  think like a gage
                  DR Watson shut me down again !!!! :mad: Smoke break:eek:

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                  • #10
                    Underspec,
                    Check your PM's...

                    It might explain why...
                    RFS Means Really Fussy Stuff

                    When all you have is a hammer - everything looks like a nail....
                    sigpic

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                    • #11
                      New print = new part too. I'm saying the customer usually calls out concentricity on this type of dimension.
                      I used to be high on life but I built up a tolerance.

                      Brown & Sharpe Global Advantage
                      PCDMIS CAD++ v2011mr2
                      PH10MQ/SP600M


                      sigpic

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                      • #12
                        Check your other thread, I uploaded a file from ASME for you...
                        KEV
                        RFS Means Really Fussy Stuff

                        When all you have is a hammer - everything looks like a nail....
                        sigpic

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