True Postion problem

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  • True Postion problem

    I am having a problem with the true position in version 4.1. I am using legacy dimension settings. I have measured this part with a smartscope and it is very good but when I true position a hole feature I am getting a 4.5mm error in the y direction. There is MMC for hole and datum C. Datum C would be my Y direction datum. I have read some posts where it is not recommended to use MMC to datum features. I saved the part program as version 3.6 and opened it in 3.7MR2. I did not change the TP settings in the dimensioning but did change the workplane from X to Y. This fixed the problem and the data looks great. the 4.5mm error isn't likely since the holes are only 3mm in size and on the smartscope the distance is good. Why does this work in 3.7 and not 4.1? I went back to 4.1 and tried the same thing with the workplane and it didn't work. I do not understand the workplane issue either. is there some documentation explaining workplanes.

  • #2
    You have explained your circumstance rather well except some info would be necessary to make an informed response. Can you, 1. post a print of your datum structure/area of problem, and 2. can you zip your program up and post it to the forum? I would like to see this issue and try to understand what is going on, but until more information is provided it is rather hard to make that informed response.
    sigpic

    James Mannes

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    • #3
      I will attempt to do this when I get back to work on Monday.
      Thanks,

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      • #4
        program and image upload

        I have uploaed the program with image of datum structure. I really appreciate any help with this.
        Attached Files
        Last edited by calbritton; 03-26-2007, 09:07 AM. Reason: to upload image

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        • #5
          It is in the way you have called out your datums when using "use datums" check box. What you need to do is call it out just like an alignment, primary (DAT_A), secondary(DAT_C), and then tertiary(DAT_B). See my example below...

          DIM LOC27= TRUE POSITION OF CIRCLE DAT_D UNITS=MM ,$
          GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH FIT TO DATUMS=ON DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
          AX NOMINAL +TOL -TOL BONUS MEAS DEV OUTTOL
          Y 63.302 63.302 0.000
          Z -8.620 -8.667 -0.047
          DF 5.000 0.100 0.010 0.027 5.017 0.017 0.000 ----#-------------
          D1 PLANE DAT_A AT RFS
          D2 5.380 0.100 0.010 0.110 5.551 CIRCLE DAT_C AT MMC
          D3 LINE DAT_B AT RFS
          TP MMC 0.100 0.096 0.094 0.000 --------#---------
          END OF DIMENSION LOC27
          Last edited by JamesMannes; 03-26-2007, 09:22 AM. Reason: Change datum names
          sigpic

          James Mannes

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          • #6
            That's not how I would work this call-out.

            Originally posted by JamesMannes View Post
            It is in the way you have called out your datums when using "use datums" check box. What you need to do is call it out just like an alignment, primary (DAT_A), secondary(DAT_C), and then tertiary(DAT_B). See my example below...

            DIM LOC27= TRUE POSITION OF CIRCLE DAT_D UNITS=MM ,$
            GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH FIT TO DATUMS=ON DEV PERPEN CENTERLINE=OFF DISPLAY=DIAMETER
            AX NOMINAL +TOL -TOL BONUS MEAS DEV OUTTOL
            Y 63.302 63.302 0.000
            Z -8.620 -8.667 -0.047
            DF 5.000 0.100 0.010 0.027 5.017 0.017 0.000 ----#-------------
            D1 PLANE DAT_A AT RFS
            D2 5.380 0.100 0.010 0.110 5.551 CIRCLE DAT_C AT MMC
            D3 LINE DAT_B AT RFS
            TP MMC 0.100 0.096 0.094 0.000 --------#---------
            END OF DIMENSION LOC27
            True Position to -A- with Max to it's self. I would say that in this call-out -B- and -C- are not to be used as Datums at all. Only -A-.

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            • #7
              ok!

              I understand what you are saying but I believe my alignment is A (primary), B(Secondary), and C(Tertiary). Does that mean that they have be in that order in the part program. Currently I am measuring A first, C second, and B third but the alignment is A, B, and C. Maybe I just didn't do the alignment correctly.

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              • #8
                Originally posted by Tested View Post
                True Position to -A- with Max to it's self. I would say that in this call-out -B- and -C- are not to be used as Datums at all. Only -A-.
                I am making the assumption that the callout he is referring to is not the same one found on the provided print. He said the print provided explains his datum structure not that it was the feature control frame he was talking about in the original post.
                sigpic

                James Mannes

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                • #9
                  DUMP the datums out of the TP dimension. Align to the FCF datums, then do the TP of the feature. IF I have read all this right, the hole you are trying to dimension IS the b-datum (or 4-way locator in automotive slang) and if it is, then you can't use the b-datum feature as one of the datums in the TP datum list, if ya follow me. You can't TP a feature to itself, that is like dividing by zero, you will get an error.
                  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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                  • #10
                    Originally posted by calbritton View Post
                    I understand what you are saying but I believe my alignment is A (primary), B(Secondary), and C(Tertiary). Does that mean that they have be in that order in the part program. Currently I am measuring A first, C second, and B third but the alignment is A, B, and C. Maybe I just didn't do the alignment correctly.
                    I'm running something right now so I can't open your program at this time, but you used your DAT_B as a rotation feature, that to me says tertiary. I will look at the program a little more in depth when I can. Provide a print of the hole being called out?
                    sigpic

                    James Mannes

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                    • #11
                      Because the call-out is only back to -A-, and not to -B-, or -C-; it is looking more for a "perpendicularity" I just guessing here but does this pin go thru the part? If so then check it on one side and report the other side to it just from -A-. If it does not go thru the part measure it at the 2 extreams and report it one from the other, again aligned only to -A-.
                      Thats my take on the call-out.

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                      • #12
                        Matt

                        Originally posted by Matthew D. Hoedeman View Post
                        DUMP the datums out of the TP dimension. Align to the FCF datums, then do the TP of the feature. IF I have read all this right, the hole you are trying to dimension IS the b-datum (or 4-way locator in automotive slang) and if it is, then you can't use the b-datum feature as one of the datums in the TP datum list, if ya follow me. You can't TP a feature to itself, that is like dividing by zero, you will get an error.
                        I believe this is a common call-out And is too it's self. Please refer to GD&T book.

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                        • #13
                          calbritton,

                          Have I miss understud? What is the call - out you are look ing for?

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                          • #14
                            My CS is leveled to A, = Z+, rotated to B, =X+, and located to C =Y+. the holes on the part, five of them have different specs. TP = 0.1, 0.15 or 0.2. an example is /(TP) 0.1 (M)/A/B/C (M)/.

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                            • #15
                              Sorry I missed that. I thought you were asking about the call-out on the drawing you posted.

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