True Position- Legacy vs Xact on v4.2

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  • True Position- Legacy vs Xact on v4.2

    I searched the forum already but could not find something similar. I use v4.2, I have a part with -A- as a plane, -B- as a cyl, and -C- as a circle. For my alignment, I leveled ZPLUS to -A-, rotated XPLUS to -B- and -C-, -A- is my Z origin, and -B- is my X and Y origin. There is a True Position callout on the print of Ø.12mm -A- -B- -C- for a hole that would be in the ZMINUS workplane on the back of the part. When I dimension this with XactMeasure (as a cylinder with two levels), it says my X-dev is -.02 and Y-dev is +.09, but when I measure it with location or legacy, it say X-dev is -.09 and Y-dev is +.09. I cannot figure out why the two are different. I toggled fit to datums on and off, switched between DRF and current alignment, I made two circles that hit in the exact same spots as the cylinder and constructed a cylinder from those thinking maybe it was the axis of the cylinder throwing it off. I also dimensioned these cirlces with legacy and XactMeasure, but no matter what I did, legacy stayed at -.09 and XactMeasure stayed at -.02. Does anyone know why these X values are so different? The datum shift on the report is all zeros. I don't know which value is correct. But I'm leaning towards Xact being wrong...

  • #2
    Read all of this thread!
    link.jpg
    smarty%u00252520britches.gif
    From the link
    Originally posted by Smartybritches View Post
    2) Perhaps the biggest single thing I took away is the knowledge that in Xactmeasure Pc-Dmis takes the first datum in the FCF you build in Xactmeasure andlevels Z+, then the second datum in the FCF is used to rotate X+ to.
    "People demand freedom of speech as a compensation for the freedom of thought, which they seldom use." ~ Soren Kierkegaard

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    • #3
      Thanks for the link, there was some useful stuff in there. However, my questions still stands. Why does legacy measure differently than XactMeasure? It can't be the alignment because Xact Measure calculated it the same when I used current alignment as when I used the DRF. We have PCDMIS Vision on another computer running 2011 MR1 Release and I opened the program in there and it gets the same results as in v4.2. Is this due to a datum shift or something? Why does my X deviation become so much less with Xact Measure?

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      • #4
        Cylinders you say?

        What reporting options do you have set in the legacy evaluation calculation (worst axis, start, end, etc.)?
        Maybe it is those that differs between Xact/legacy making the result differ?
        PC-DMIS CAD++ 2o19 R1 SP4

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        • #5
          Originally posted by Mike Ruff View Post
          It can't be the alignment because Xact Measure calculated it the same when I used current alignment as when I used the DRF.
          Please note that the alignment in Xact is only used for presenting the result, the calculation is always done against the refs.

          Also note that the ref elements are recalculated with the restriction that they should be at right angles - this may affect your secondary.

          Also note that Xact grabs as much alignment info as it can from each of the refs, which means that the secondary will take its direction from B (unless it's the same as A), not necessarily B-C unless you write it like that.
          AndersI
          SW support - Hexagon Metrology Nordic AB

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          • #6
            For Xact Measure you need correct nominals and vectors on your datums and feature you are trying to report.
            sigpic...engineering

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            • #7
              Originally posted by vpt.se View Post
              What reporting options do you have set in the legacy evaluation calculation (worst axis, start, end, etc.)?
              Maybe it is those that differs between Xact/legacy making the result differ?
              I tried it with all of the different options and the legacy never came close to matching XactMeasure values even when they were both on the same setting :/

              Originally posted by AndersI View Post
              Please note that the alignment in Xact is only used for presenting the result, the calculation is always done against the refs.

              Also note that the ref elements are recalculated with the restriction that they should be at right angles - this may affect your secondary.

              Also note that Xact grabs as much alignment info as it can from each of the refs, which means that the secondary will take its direction from B (unless it's the same as A), not necessarily B-C unless you write it like that.
              I didn't know this. Thank you for the clarification!

              Originally posted by Obelix View Post
              For Xact Measure you need correct nominals and vectors on your datums and feature you are trying to report.
              I'm using autofeatures from the CAD model so all nominals should be correct. I also double checked that the legacy and Xact nominals were the same

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              • #8
                Do you have datum modifiers on Datum -B- and -C-?
                Post some code, maybe we can see something there.
                sigpic...engineering

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                • #9
                  So I was looking through the code copying and pasting it in here and I found the error- I had a line constructed from datums -B- to -C- and I had that set as a datum from when I was troubleshooting something else earlier. I switched it back and the values still don't match but they are way closer now. Thanks for the help guys! I really appreciate it

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