True position Formula

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  • True position Formula

    Can anyone tell me what the formula is for True Position? For whatever reason this engineer thinks that the true position should have a bilateral tolerance. ( print calls out true position of 12) The engineer thinks that it should be like a profile point and be +/- 6.

  • #2
    hahahaha, DUMB ENGINEERS.
    Last edited by MIKEY; 06-12-2008, 07:28 PM.

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    • #3
      This thread.

      This site.

      Such a helpful answer there Mikey.
      When in doubt, post code. A second set of eyes might see something you missed.
      sigpic

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      • #4
        Originally posted by Shelia Moser View Post
        Can anyone tell me what the formula is for True Position? For whatever reason this engineer thinks that the true position should have a bilateral tolerance. ( print calls out true position of 12) The engineer thinks that it should be like a profile point and be +/- 6.

        Well is it a Diametrical True position? Then no, if it does not have a Diametrical symbol then yes it is plus or minus 6.

        x(dev)^2+y(dev)^2+z(dev)^2

        (x(dev)*x(vector))^2+(y(dev)*y(vector))^2+(z(dev)* z(vector)^2)
        sigpicSummer Time. Gotta Love it!

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        • #5
          Originally posted by John Kingston View Post
          This thread.

          This site.

          Such a helpful answer there Mikey.
          John I thought the same thing, only I think I said " WTF?"
          sigpicSummer Time. Gotta Love it!

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          • #6
            Originally posted by Paul Sarrach View Post
            Well is it a Diametrical True position? Then no, if it does not have a Diametrical symbol then yes it is plus or minus 6.

            SQRT(x(dev)^2+y(dev)^2+z(dev)^2 )

            SQRT((x(dev)*x(vector))^2+(y(dev)*y(vector))^2+(z(dev)* z(vector)^2))

            FIFY, forgot the square root.
            When in doubt, post code. A second set of eyes might see something you missed.
            sigpic

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            • #7
              He's half right. In your case the TP would be a circle with a 6 radius centered at the theoretical center of you feature, per your print. So if your x dim is 100 and you y dim is 100 then you TP circle center would be at x 100 and y 100.
              And the center line of your feature would then have to be inside the circle
              Achieving unverifiable productivity daily

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              • #8
                I like Phil's description. Draw a 6 inch radius circle. Draw a 12 x 12 square using the same center. The square represents a +/- 6 inch tolerance zone. The circle is the 6 inch TP zone. See how much of the square falls out of that zone? Show the engineer.
                When in doubt, post code. A second set of eyes might see something you missed.
                sigpic

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                • #9
                  (squarerootofxdeviationsquaredplusydeviationcripes iwishtheywouldputtheignoreuseroptionbackineffecton thisforum)
                  Lately, it occurs to me
                  What a long, strange trip it's been.

                  2017 R1 (Offline programming)

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                  • #10
                    Originally posted by John Riggins View Post
                    (squarerootofxdeviationsquaredplusydeviationcripes iwishtheywouldputtheignoreuseroptionbackineffecton thisforum)
                    whydoyouwanttoignoremeandithinktheyfixedthatoption

                    edit:theydidifixthatoptionjohn
                    Last edited by John Kingston; 06-12-2008, 08:25 PM.
                    When in doubt, post code. A second set of eyes might see something you missed.
                    sigpic

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                    • #11
                      Originally posted by John Kingston View Post
                      whydoyouwanttoignoremeandithinktheyfixedthatoption

                      edit:theydidifixthatoptionjohn
                      icantseemtofindtheignoreuserfeaturewhereisitexactl y?
                      Lately, it occurs to me
                      What a long, strange trip it's been.

                      2017 R1 (Offline programming)

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                      • #12
                        Originally posted by John Riggins View Post
                        icantseemtofindtheignoreuserfeaturewhereisitexactl y?
                        clickonUserCPtheignoreoptionisintherecheckyourpmIs entyouamessagehthereIamhavingablasttypinglikethisa ndthebeerhasnothingtodowithitdoyourealizehowhardit istotypelikethiswithouthittingspace?
                        When in doubt, post code. A second set of eyes might see something you missed.
                        sigpic

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                        • #13
                          true positionpythagorean

                          If you are measuring something in XY plane for example the formula for true position is: The square root of ("X" deviation from nominal squared * "Y" deviation from nominal squared)*2. It's the pythagorean theorum*2.

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                          • #14
                            Originally posted by Shelia Moser View Post
                            Can anyone tell me what the formula is for True Position? For whatever reason this engineer thinks that the true position should have a bilateral tolerance. ( print calls out true position of 12) The engineer thinks that it should be like a profile point and be +/- 6.
                            I know PC-DMIS still uses TP, but technically as of ASME Y14.5 -1994 it is no longer called true position. It is just position, and it is calculated, as others have said, by taking the square root of the deviation in one axis squared + the deviation in the other axis squared and multiplying that answer by 2.

                            Maybe you need to talk to this kind of engineer:

                            http://i203.photobucket.com/albums/a...ock/rae2-a.jpg

                            Not this kind:

                            http://i203.photobucket.com/albums/a...n_engineer.jpg
                            Marty Dobson
                            Director of Quality
                            http://www.linkedin.com/in/mjdobson

                            PC-DMIS CAD V4.2 MR1 & V2011
                            PH10MQ
                            TP200

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                            • #15
                              Maybe this is the one...?

                              http://www.sliderulemuseum.com/SR_Im...seEngineer.jpg
                              sigpic

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