true position strikes again

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  • true position strikes again

    I have a callout for a t.p. of a hole of .8mm A,B,C MMC for all datums
    the hole is off 1.2 in the Z, .4 in the X , and .2 mm in the Y
    The T.P says a deviation of 3.2mm? How is this possible?
    Am I using this software right?

  • #2
    First of all, please read this.

    http://www.pcdmisforum.com/showthread.php?t=3139

    Maybe post your program that measures the hole and the TP call.


    Jan.
    ***************************
    PC-DMIS/NC 2010MR3; 15 December 2010; running on 18 machine tools.
    Romer Infinite; PC-DMIS 2010 MR3; 15 December 2010.

    Comment


    • #3
      Originally posted by RClone View Post
      I have a callout for a t.p. of a hole of .8mm A,B,C MMC for all datums
      the hole is off 1.2 in the Z, .4 in the X , and .2 mm in the Y
      The T.P says a deviation of 3.2mm? How is this possible?
      Am I using this software right?
      This is the actual formula:
      2*sqrt(x^2 + Y^2)
      "^2" is the term squared
      Example; 2*sqrt(.4^2 + .2^2) = .89443MM

      You are showing 3 deviations with a result of 3.2MM??????

      You only choose one feature to use the TP (assuming you have your datums set correctly) Datum 1, Datum 2 etc... are used to add positional tolerance if mmc is applied to that paticular datum.
      Robert Horne
      Va.

      Comment


      • #4
        This is because TP is deviation normal to the nominal axis of the feature. In other words, only two axis at one time. Three axis would be a spherical tolerances zone and I don't think that is what you have. post the print
        sigpic GDTPS - 0584

        Comment


        • #5
          Originally posted by inspector212 View Post
          This is because TP is deviation normal to the nominal axis of the feature. In other words, only two axis at one time. Three axis would be a spherical tolerances zone and I don't think that is what you have. post the print
          UNLESS he has marked PERP TO CENTER LINE, it WILL give a 3-D TP value, including all axis deviations.
          sigpic
          Originally posted by AndersI
          I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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          • #6
            But he should only report two for a cylindrical tolerance zone.
            Last edited by inspector212; 09-18-2007, 04:59 PM. Reason: added tolerance zone shape
            sigpic GDTPS - 0584

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            • #7
              true position

              ko.JPG

              By the way this 3.7 MR2
              What is the formula used to figure the standard deviation?
              Sorry about the thumbnail, I have security issues with the print.
              The coordinate is a simple plane,circle,circle with circle 1 the zero point.

              Comment


              • #8
                Originally posted by RClone View Post
                [ATTACH]1916[/ATTACH]

                By the way this 3.7 MR2
                What is the formula used to figure the standard deviation?
                Sorry about the thumbnail, I have security issues with the print.
                The coordinate is a simple plane,circle,circle with circle 1 the zero point.
                Datums B and C are not features of size. So they should not have mmc applied to them. Have an engineer re evaluate the feature control frame.
                Robert Horne
                Va.

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                • #9
                  My issue seems to be I clicked all three datums giving me a sphere of tolerence.
                  The numbers seem alot more reasonable usiing just X,Y.
                  TIME for BEER!
                  I'm going to K.I.!

                  Comment


                  • #10
                    Originally posted by robehor4 View Post
                    Datums B and C are not features of size. So they should not have mmc applied to them. Have an engineer re evaluate the feature control frame.
                    Exactly, good catch.
                    sigpic GDTPS - 0584

                    Comment


                    • #11
                      Originally posted by RClone View Post
                      I'm going to K.I.!
                      Kings Island?
                      sigpic
                      Xcel 15-20-10 - PFXcel 7-6-5 - Merlin 11-11-7 - Romer Absolute 7525SI
                      PCDMIS 2012
                      Windows Office XP

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                      • #12
                        My Engineer say he sees nothing wrong.
                        Location: Mason,Ohio

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                        • #13
                          Originally posted by RClone View Post
                          My Engineer say he sees nothing wrong.
                          Location: Mason,Ohio
                          P&G?
                          When in doubt, post code. A second set of eyes might see something you missed.
                          sigpic

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                          • #14
                            Originally posted by RClone View Post
                            My Engineer say he sees nothing wrong.
                            Location: Mason,Ohio
                            Then your engineer, like many others, has no idea how to use GD&T so he just populates the print with inacurate data.
                            Robert Horne
                            Va.

                            Comment


                            • #15
                              Now I have a print that calls out 2 true position FCF 's for a slot.
                              One tolerence for the width and a larger for the length.
                              Is this legal?
                              Is it needed, Since true position will give you a larger tolerence zone ?

                              Comment

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