Single datum Upper and Lower segments in a Composite FCF?

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  • Single datum Upper and Lower segments in a Composite FCF?

    If Datum A is a plane to which my pattern of 8 dimensioned holes is perpendicular, will a composite FCF with only datum A in the upper and lower segments not yield the same deviation for both segments? My QE's think I have the dimensioning setup incorrectly in PC-DMIS as they are reporting the same deviations and just wanted to double check I'm not missing something before "going to bat" for myself.

    Single Datum Composite.jpg

  • #2
    The Ø0.010 to A out-tolerances the Ø0.020. So everything will be based on a 0.010 tolerance. Yes, they will be the same deviation because the feature is measured against the same datum structure.

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    • PantsFreeProbing
      PantsFreeProbing commented
      Editing a comment
      Matthew,

      If the upper segment applied to each hold individually, but only reference the plane the holes are in as datum A, wouldn’t that result in zero deviation? I’m assuming the holes are 2d features (circles). Am I missing the mark here?

      Sincerely,
      PFP

    • sealevel
      sealevel commented
      Editing a comment
      This GD&T callout is from the government/IRS tax table of the current administration. I totally get it.

    • oddam
      oddam commented
      Editing a comment
      I agree with Matthew, individually each hole is reported Ø .020 constrained in rotation to -A- within the pattern size. Then as a group Ø .010 to -A-. That's how I would interpret the composite positional tolerance frame that calls the group -B-.
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