Need Geo tol explaination with datum and feature both at LMC

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Need Geo tol explaination with datum and feature both at LMC

    Hello,

    We rarely see LMC called out on a drawing and I have never had one with LMC on a datum and a feature. My customer believes that the bonus tolerances from the datum and the feature must be added together to give him the total bonus tolerance for the dimension and I don't have enough experience with this to determine for myself if PC_DMIS is doing this correctly or not.

    I have attached a screen shot of the drawing callout and the PC-DMIS report. Could you explain what PC-DMIS is doing in this case? The bonus tolerance is getting reduced from .0119 to .0024 for the datum and PC-DMIS is reporting 2 deviations. One for the datum and one for the feature.

    Thanks!

    t.
    Global Image 555
    PH10M-TP200
    PC-DMIS Cad ++
    Win7 64 bit
    V2014.1

  • #2
    I should also point out that Datum B is an ID cylinder and the axis of datum B matches the OD as shown on the drawing.
    Last edited by dtmtim; 12-05-2014, 10:19 AM.
    Global Image 555
    PH10M-TP200
    PC-DMIS Cad ++
    Win7 64 bit
    V2014.1

    Comment


    • #3
      In the first picture, below the purple colored cross hairs, is a section titled "Datum Shift". LMB on a datum is used, properly, as Datum Shift in XactMeasure.

      In most cases, simply adding departure from boundary as bonus is incorrect.

      It must have something to do with how the part interfaces, but I can't see enough of the drawing to figure out what that interaction is.

      I say just let XactMeasure do it's job.
      "This is my word... and as such is beyond contestation."

      Comment


      • #4
        Im not an Xact measure user so someone else may want to add on this. Wasnt Xact prone to some serious issues on DMIS version 4 ? Isnt wasnt even recomened to be used because of all the bugs ?

        Comment


        • #5
          Originally posted by Schlag View Post
          Im not an Xact measure user so someone else may want to add on this. Wasnt Xact prone to some serious issues on DMIS version 4 ? Isnt wasnt even recomened to be used because of all the bugs ?
          It was never released here in the UK!

          If you're looking at his sig, he's got other 4.x releases listed above it so I'm assuming he's using some one of those.
          Automettech - Automated Metrology Technology

          Comment


          • #6
            Hello, thank you for reading this post. We are still using 4.3MR2.

            I guess it would help if I knew how to do these calculations manually so I could double-check PC-DMIS.

            I need to know why the bonus tolerance changes from one section to the other on the datum feature and if the final inspection report only allows for one number to be reported for this dimension which one am I supposed to used since PC-DMIS is outputting 2?

            Thanks again for your wisdom.
            Global Image 555
            PH10M-TP200
            PC-DMIS Cad ++
            Win7 64 bit
            V2014.1

            Comment


            • #7
              In XactMeasure, when you have a feature of size datum with material boundary, it always shows the datum also.

              When it comes to Datum Shift, the shift doesn't exactly correlate with the departure from boundary. It is much more complicated than just adding bonus from a datum.
              "This is my word... and as such is beyond contestation."

              Comment


              • #8
                With regard to complexity, I figured as much. It seems like my customer is over simplifying it by just combining the 2 bonus tolerances to give himself extra room. The problem is now I am bearing the burden of proof that the software (or the way I'm using it) is correct.
                Global Image 555
                PH10M-TP200
                PC-DMIS Cad ++
                Win7 64 bit
                V2014.1

                Comment


                • #9
                  Not trying deflect the situation (well all right maybe), but if your customer wants you to use more bonus than PC-DMIS allows then simply do some diametrical calculations and add that to the tolerance to give him his supposed "full" tolerance. Done. No?
                  sigpic

                  James Mannes

                  Comment


                  • #10
                    Thanks James, hope you are well. It's been a long time since we chatted last.

                    I basically told him I'm standing by PC-DMIS. When a material modifier is added to a datum it is a much more complex calculation than simply adding the bonus tolerances together. If he doesn't like it he can find someone else to do his inspection. I'm not going to fudge his numbers for him because if the Navy decides to do an audit I'm the one that's going to have to answer for it.

                    Cheers!
                    Global Image 555
                    PH10M-TP200
                    PC-DMIS Cad ++
                    Win7 64 bit
                    V2014.1

                    Comment

                    Related Topics

                    Collapse

                    Working...
                    X