True Position vs Location

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  • True Position vs Location

    Can anyone tell me why when reporting true position the "location" of a hole is different than if I report location?

    DIM LOC1= TRUE POSITION OF CIRCLE DATUM_C1 UNITS=MM ,$
    GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH FIT TO DATUMS=ON DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
    AX MEAS +TOL -TOL BONUS NOMINAL DEV OUTTOL
    X -75.696 -75.000 -0.696
    Z -122.497 -122.500 0.003
    DF 12.682 0.010 0.003 0.000 12.690 -0.008 0.005
    D1 LINE LINE_B AT RFS
    D2 PLANE DATUM_D AT RFS
    TP 0.120 0.000 MMC 1.392 1.272
    END OF DIMENSION LOC1


    DIM LOC6= LOCATION OF CIRCLE DATUM_C1 UNITS=MM ,$
    GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH
    AX MEAS +TOL -TOL NOMINAL DEV OUTTOL
    X -75.002 0.010 0.010 -75.000 -0.002 0.000
    Z -122.496 0.010 0.010 -122.500 0.004 0.000
    END OF DIMENSION LOC6


    Which is correct? Thanks for the help.

    John

  • #2
    They are different because you are using DATUMS with the TP dimension, LOCATION does not. Do the TP without datums, it will match.
    sigpic
    Originally posted by AndersI
    I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

    Comment


    • #3
      Thanks for the ultra-fast reply! When should you 'Use Datums'?

      Comment


      • #4
        ONLY when:
        1) You absolutly need the BONUS (MMC) from the datums (and I would still prefer not to)
        2) When you are NOT aligned to the datums in the FCF (Feature control frame)

        IF you are aligned to the datums in teh FCF already, then you are already set to the datums, no need to call them out. IF you are NOT aligned to the datums, I would align to them anyway, then if you are unsure of what is happening, you can do a LOC of the hole and see what is up.

        Remember, Pcdmis will (depending on the version) use MMC on the datums to simulate a hard gage, and will "move" the part around as much as it can on the simulate datum pins to get the object hole as close to ZERO as it can, so it will quite possibly report ZERO deviations for the OBJECT hole when using datums/mmc.
        sigpic
        Originally posted by AndersI
        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

        Comment


        • #5
          Thank you very much, Matthew!

          (bowing as I exit...)

          Comment


          • #6
            Originally posted by jszanto View Post
            Thank you very much, Matthew!

            (bowing as I exit...)
            ROLF.gif

            Someone is actually reading the signatures!
            sigpic
            Originally posted by AndersI
            I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

            Comment


            • #7
              Well, with those big bright red letters, how can you miss it?

              Show off.
              B & S Global Performance 7-10-7
              PC DMIS CAD ++ V4.2 MR1
              PH10MQ SP25M

              Comment


              • #8
                Originally posted by Matthew D. Hoedeman View Post
                They are different because you are using DATUMS with the TP dimension, LOCATION does not. Do the TP without datums, it will match.
                I need a little more education Sir Matt of Gurus....
                sigpic

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                • #9
                  Originally posted by AuRules View Post
                  I need a little more education Sir Matt of Gurus....
                  OK, come to BBS, we will teach you, or do you really mean you do need some help (more info) with this?
                  sigpic
                  Originally posted by AndersI
                  I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

                  Comment


                  • #10
                    What mat said, plus it looks like your datum selection is incomplete. You only have a line and a plane selected. You need another to make the "use datums" function kosher.
                    Last edited by DBHMAN; 06-26-2008, 10:35 AM.

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                    • #11
                      Originally posted by DBHMAN View Post
                      What mat said, plus it looks like your datum selection is incomplete. You only have a line and a plane selected. You need another to make the "use datums" function kosher.
                      Looks ok to me?

                      Adding a third datum would just decrease the level of movement for the PC-DMIS 'virtual gage', right?
                      PC-DMIS CAD++ 2o19 R1 SP11

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                      • #12
                        Originally posted by vpt.se View Post
                        Looks ok to me?

                        Adding a third datum would just decrease the level of movement for the PC-DMIS 'virtual gage', right?
                        HOWEVER, it WOULD explain the difference in TP vs NON-TP, the VIRTUAL GAGE thing slides the part around to make the subject hole as close to zero as it can, based on the MMC of the datums chosen, thus the difference in the XY deviations from nominal.

                        That is what the OP is all about, WHY are the individual axis deviations different from TP to LOC. It is ALL in the use of the datums in the TP dimension. Leave them out, the axial deviations will (should) be the same.
                        sigpic
                        Originally posted by AndersI
                        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

                        Comment

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