TP Manual Calculation z,y,z

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  • TP Manual Calculation z,y,z

    Hi guys,

    Basically I'm measuring a bunch of parts for a capability study. Long story short I need to get true position on four similar features. For this instance I'm not sure how to accurately pull this off with the feature inside PC-DMIS since I'm trying to get it from 3 midpoints (1 in x, 1 in y, 1 in z). I figure I can use all the deviations and export the numbers into my excel and just formula it out. I would think the formula for a radius of a sphere would be the same for true position where TP would be the same as r. In that case r^2=x^2+y^2+z^2, or TP = SQRT(x*x+y*y+z*z). But on another forum post I saw, TP = SQRT(x^2+y^2++z^2)*2. What gives with the *2? They said that was for a circle? My shape is virtually a rectangular box. I don't understand how the middle of one object could be different from the middle of another object if it's "borders" were arranged differently?


    Would, TP = SQRT(xdev^2+ydev^2+zdev^2), be the correct formula for getting TP on a rectangular box relative to called out datums?


    Thank you guys!

  • #2
    Whoops.. just noticed title typo.

    Comment


    • #3
      True position is a bilateral zone. The formula you give will calculate the deviation in one direction so this is half of the true position value. Multiply by two to get the full width of the bilateral zone.
      2013MR1 SP6
      Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

      Comment


      • #4
        DaSalo, I think you mean it is a bidirectional tolerance zone.

        In frop1's case, each axis should have a bidirectional zone defined (x,y,z).

        Each needs to be reported.
        2*Xdev
        2*Ydev
        2*Zdev

        His formula SQRT(Xdev^2+Ydev^2+Zdev^2) = RADIUS of a spherical tolerance zone.

        B&S CHAMELEON/PCDMIS CAD++ V2011

        There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"

        sigpic

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        • #5
          Yep, what dph51 said.
          2013MR1 SP6
          Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

          Comment


          • #6
            Originally posted by dph51 View Post
            Each needs to be reported.
            2*Xdev
            2*Ydev
            2*Zdev
            Would this mean I should be doing,
            TP = SQRT ( (2*xdev)^2 + .. + .. )


            Thanks for helping. I'm just trying to provide accurate information.

            Comment


            • #7
              Originally posted by dph51 View Post
              DaSalo, I think you mean it is a bidirectional tolerance zone.

              In frop1's case, each axis should have a bidirectional zone defined (x,y,z).

              Each needs to be reported.
              2*Xdev
              2*Ydev
              2*Zdev

              His formula SQRT(Xdev^2+Ydev^2+Zdev^2) = RADIUS of a spherical tolerance zone.
              Maybe you meant to say diametric tolerance zone vs radial tolerance zone.

              Comment


              • #8
                The standard equation for 3D true position is: 2*Sqrt((X2-X1)^2+(Y2-Y1)^2+(Z2-Z1)^2)

                Your initial equation gives you radial deviation while this gives diametric deviation.
                2013MR1 SP6
                Global Frames, Tesastar-M Heads, LSP-X1M/H Probes

                Comment


                • VinniUSMC
                  VinniUSMC commented
                  Editing a comment
                  This gives spherical deviation.

              • #9
                FROP1,

                what does our FCF or DRF callout the tolerance zone?

                DIAMETRICAL
                SPHERICAL
                or bidirectional?

                B&S CHAMELEON/PCDMIS CAD++ V2011

                There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"

                sigpic

                Comment


                • #10
                  Ø is a symbol for dimeter
                  Code:
                  FCFLOC2 =POSITION : DATUM_B
                              FEATCTRLFRAME/SHOWNOMS=NO,SHOWPARAMS=YES,SHOWEXPANDED=YES
                              CADGRAPH=OFF,REPORTGRAPH=OFF,TEXT=OFF,MULT=10.00,ARROWDENSITY=100,OUTPUT=BOTH,UNITS=IN
                              COMPOSITE=NO,FIT TO DATUMS=YES,DEV PERPEN CENTERLINE=ON,OUTPUT ALIGNMENT=Datum Reference Frame
                              CUSTOMIZED DRF=NO
                              STANDARDTYPE=ASME_Y14_5
                                SIZE TOLERANCES/1,DIAMETER,2.0866,0.0018,0
                                PRIMARY DIMENSION/POSITION,[B]DIAMETER[/B],0.01,MMC,<PZ>,<len>,C,A,MMC,<size>,<dat>
                                SECONDARY DIMENSION/<Dim>,<tol>,<MC>,<dat>,<dat>,<dat>
                                NOTE/FCFLOC2
                              FEATURES/DATUM_B,,

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                  • #11
                    My superior, at work, told me what he wanted. I am still confused by all of this but I'll do as instructed. He told me it should apply in one direction only. I don't like bugging that boss. I'll just listen so I can finish by tomorrow.

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                    • #12
                      Frop1
                      Which FCF looks like the callout you are trying to describe.
                      (tp means position)
                      (dia means diameter)
                      (S means spherical)
                      (you might have fewer or different named Datum References)

                      A) |tp| 0.4 | A | B | C |
                      B) |tp| dia 0.4 | A | B | C |
                      C) |tp| S dia 0.4 | A | B | C |

                      B&S CHAMELEON/PCDMIS CAD++ V2011

                      There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"

                      sigpic

                      Comment


                      • #13
                        Originally posted by dph51 View Post
                        Frop1
                        Which FCF looks like the callout you are trying to describe.

                        ...

                        A) |tp| 0.4 | A | B | C |
                        B) |tp| dia 0.4 | A | B | C |
                        C) |tp| S dia 0.4 | A | B | C |
                        A for sure.

                        With different numbers it looks like this,

                        2x 12.5 ± .4
                        |tp|1.3|B|A|C (M)|

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                        • #14
                          The FCF is attached to dimension lines about the feature?

                          If it is in the X direction,

                          tp = 2*Xdev

                          If y direction

                          tp = 2*Ydev

                          If z direction

                          tp = 2*Zdev

                          If the call out is for more than 1 direction, each deviation must be reported separately.

                          If your company has the ASME Y14.5-2009 GDT Standards book or pdf

                          see 7.4.4, bidirectional positional tolerancing of features of size
                          7.4.4.1 rectangular coordinate method

                          Fig 7-28

                          B&S CHAMELEON/PCDMIS CAD++ V2011

                          There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"

                          sigpic

                          Comment


                          • #15
                            I don't have that resource but our engineer might.

                            So could you say TP of .010" is the same as saying the distance +/- .005"? If so this whole thing is starting to make much more sense about the *2 part. But then I wonder why list TP instead of distance.

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