True Position Explanation

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  • True Position Explanation

    Does anyone know where I can find a definition as to how PC Dmis Calculates true position?

    An engineer is asking for it...of course.
    2B1ASK1

  • #2
    For single axis, 2 axis or 3 axis Position?
    sigpic...engineering

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    • #3
      TP = 2x sq root of the sum of 1st axis dev squared and 2nd axis dev squared. Nothing new here!

      TK
      sigpicHave a homebrew

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      • #4
        Is he asking how True position is calculated in general (i.e. He doesn't understand it) or how PC-Dmis specifically calculates it?
        Automettech - Automated Metrology Technology

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        • #5
          That will depend on HOW you report the TP.

          1) Straight up TP, hypotenuse of the triangle times 2 (hypotenuse = radius, TP = diameter, so doubled). If all 3 axis are reported, then it is the formula for the radius of a sphere times 2

          2) PERP-TO-CL turned on is a little more 'advanced' as in Pcdmis basically 'levels' to the nominal centerline axis and reports the hypotenuse and doubles it.

          3) Xact measure with datums(M), no way to tell you since this is WAY up there on the math skill pyramid, as there is datum shift, which you pretty much can't do by hand with a pencil & paper

          4) Xact measure without datums(M), should be the same as 1 or 2
          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
            Originally posted by Matthew D. Hoedeman View Post
            That will depend on HOW you report the TP.

            1) Straight up TP, hypotenuse of the triangle times 2 (hypotenuse = radius, TP = diameter, so doubled). If all 3 axis are reported, then it is the formula for the radius of a sphere times 2
            ...
            For 3 axis is exactly the same as for 2 axis, except that under the square root are the sum of the square of 3 axis deviations instead of 2.
            "This is my word... and as such is beyond contestation."

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            • #7
              Originally posted by VinniUSMC View Post
              For 3 axis is exactly the same as for 2 axis, except that under the square root are the sum of the square of 3 axis deviations instead of 2.
              Which is the formula for the radius of a sphere.......
              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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              • #8
                Originally posted by Matthew D. Hoedeman View Post
                Which is the formula for the radius of a sphere.......
                In common parlance, that is not true. If you look up the radius of a sphere, you will not directly find that as an equation. You have to derive it from the equation for a cartesian sphere with a known center (Xsub0, Yxub0, Zsub0) and a known radius, R.

                If someone were to Google the radius of a sphere, the equation they are most likely to find is the derivation from the volume of a sphere, which includes pi.

                FWIW, I wasn't correcting you, I was expanding on what you said for clarity, for the above reason.
                "This is my word... and as such is beyond contestation."

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                • #9
                  Originally posted by VinniUSMC View Post
                  In common parlance, that is not true. If you look up the radius of a sphere, you will not directly find that as an equation. You have to derive it from the equation for a cartesian sphere with a known center (Xsub0, Yxub0, Zsub0) and a known radius, R.

                  If someone were to Google the radius of a sphere, the equation they are most likely to find is the derivation from the volume of a sphere, which includes pi.

                  FWIW, I wasn't correcting you, I was expanding on what you said for clarity, for the above reason.
                  There are many formulas for the radius of a sphere (or a circle) and they are all derived from some other formula. In this case it is a sphere with a known center and a point on its surface.
                  Therefor, the most basic equation used by PC-DMIS to calculate POSITION (and many other things like T-value) is Pythagorean theorem:

                  a^2+b^2=c^2.

                  Ken,
                  you should tell your engineer that PC-DMIS calculates POSITION the way that the ASME Y14.5 explains it. As he is an engineer, he should know the standard well.
                  Last edited by Nano Vujkovic; 04-28-2015, 01:14 PM.

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                  • #10
                    Originally posted by VinniUSMC View Post
                    In common parlance, that is not true. If you look up the radius of a sphere, you will not directly find that as an equation. You have to derive it from the equation for a cartesian sphere with a known center (Xsub0, Yxub0, Zsub0) and a known radius, R.

                    If someone were to Google the radius of a sphere, the equation they are most likely to find is the derivation from the volume of a sphere, which includes pi.

                    FWIW, I wasn't correcting you, I was expanding on what you said for clarity, for the above reason.
                    sqrt(Xdev^2+Ydev^2+Zdev^2)= radius of the sphere broken down to the very basics.

                    It matters not where the center of the sphere is (Xsub0, etc.), from the 'given' center of the sphere (nominal) when you have a point on the surface of the sphere (actual), and you know the difference (deviation) from that point to the center (theo), you can calculate the radius of the sphere with that formula.
                    sigpic
                    Originally posted by AndersI
                    I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

                    Comment


                    • #11
                      Originally posted by Matthew D. Hoedeman View Post
                      sqrt(Xdev^2+Ydev^2+Zdev^2)= radius of the sphere broken down to the very basics.

                      It matters not where the center of the sphere is (Xsub0, etc.), from the 'given' center of the sphere (nominal) when you have a point on the surface of the sphere (actual), and you know the difference (deviation) from that point to the center (theo), you can calculate the radius of the sphere with that formula.
                      It certainly does. How do you think you know the deviation? Xdev = Xactual - Xsub0. (Xsub0 is X subscript 0, or X naught)

                      Knowing this comes from knowing the XYZ nominal, which is the center of the deviation sphere. If you didn't know the nominal(aka center), you couldn't know the deviation. It is the same for TP or for 'T' values.
                      "This is my word... and as such is beyond contestation."

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                      • #12
                        Originally posted by VinniUSMC View Post
                        It certainly does. How do you think you know the deviation? Xdev = Xactual - Xsub0. (Xsub0 is X subscript 0, or X naught)

                        Knowing this comes from knowing the XYZ nominal, which is the center of the deviation sphere. If you didn't know the nominal(aka center), you couldn't know the deviation. It is the same for TP or for 'T' values.
                        What you won't find by Google searching is R=sqrt(Xdev^2+Ydev^2+Zdev^2).
                        Actually

                        http://www.wikihow.com/Find-the-Radi...ere-Step-9.jpg

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                        • #13
                          Originally posted by NinjaBadger View Post
                          Is he asking how True position is calculated in general (i.e. He doesn't understand it) or how PC-Dmis specifically calculates it?

                          HE is asking how PC-Dmis Calculates it.
                          2B1ASK1

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                          • #14
                            Originally posted by Ken8282 View Post
                            HE is asking how PC-Dmis Calculates it.
                            Just like ASME Y14.5 defines it.

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                            • #15
                              Originally posted by Nano Vujkovic View Post
                              Whatcha refuting there Nano?

                              You can't prove I deleted anything! /hide

                              Originally posted by Nano Vujkovic View Post
                              Just like ASME Y14.5 defines it.
                              +1
                              "This is my word... and as such is beyond contestation."

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