Datum Shifts?

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  • Datum Shifts?

    Does anyone have a problem with Datum Shifts in PCDMIS 2013 MR1? Sometimes there will be shifts/rotations in the profiles then sometimes not. The program has been run several times on multiple parts. Some have a shift and some don't. Please explain to me what the actual purpose of Datum Shifts is? Also, I understand the requirement for Datum Shifts when holes are involved especially Composite True Position.


  • #2
    can you post some code/screen shots? that would help a ton


    • #3
      Datum shift is when you have datums that have the circled M that used to be called MMC, but has since been updated to MMB.

      Max Material Condition vs Max Material Boundary:

      MMC is for feature size and adds bonus tolerance.

      MMB is for datum size and adds potential for datum shift.

      Bonus tolerance is straightforward, it is addition to the original tolerance. Datum shift, OTOH, is the amount the part can be shifted, based on the departure of the datum from MMB.

      Datum shift should only be calculated if it is necessary to produce a passing result (Wes, chime in here please, this is my (imperfect) understanding of Xact).

      So, it is not necessarily anything to fret over.
      "This is my word... and as such is beyond contestation."


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