GD&T composite question

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  • GD&T composite question

    Does it make sense to have a composite for a set of holes in a flange that is not the primary datum but are qualified that way on the print (second line of FCF = dia 1 MMC |A|)? I've always taken that to indicate they wanted an alignment from the set of holes rotated around but kept on the given plane and using one of the holes for origin. In other words, the holes are all perp to the given plane and report the distance between them. I'm not getting my head around what it would mean using their callout or how to do it.

    BTW, had problems using V4.1 with the new FCF stuff and composites, so dimensioning this the old way.

    thanks

  • #2
    The surface that the pattern of holes is normal to should be called out as another datum. The composite FCF should be split into a multiple single-segment FCF with the lower FCF referencing the new datum. See ASME y14.5M-1994, fig. 5-28, pg. 129 for an example.
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    • #3
      Originally posted by QCinTN View Post
      Does it make sense to have a composite for a set of holes in a flange that is not the primary datum but are qualified that way on the print (second line of FCF = dia 1 MMC |A|)? I've always taken that to indicate they wanted an alignment from the set of holes rotated around but kept on the given plane and using one of the holes for origin. In other words, the holes are all perp to the given plane and report the distance between them. I'm not getting my head around what it would mean using their callout or how to do it.

      BTW, had problems using V4.1 with the new FCF stuff and composites, so dimensioning this the old way.

      thanks
      Could you post a segment of the drawing?
      tx,
      kb
      RFS Means Really Fussy Stuff

      When all you have is a hammer - everything looks like a nail....
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