Query on true position geometric tolerance

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  • Query on true position geometric tolerance

    I have just been trying to get my head around a true position geometric tolerance for some holes that references 4 (yes 4) Datum features.
    These holes are machined perpendicular to a face (Datum A) and
    positioned to centrelines (Datums B and C)

    Datum Description
    A Face
    B Centreline of main bore
    C Centreline of main bore @ 90° to B

    No problems so far, but the then the geometric tolerance calls up Datum D which is a group of 4 holes machined in the same face

    I think the draughtsman has got it wrong and there should be 2 seperate geometric tolerances.

    The first one referencing Datums A B C
    The second on referencing Datum D

    Then I would report the holes twice, first time to Datums A B C, second time to Datum D.

    Any thoughts?

    Bob Fairbrother

  • #2
    is this an extruder barrel? I have seen this in the past and I reported the true position to each datum ABC then to D
    sigpicTHE TASK AHEAD OF YOU, IS NEVER AS GREAT AS THE POWER BEHIND YOU. I Fight for Freedom and Pray For Peace..

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    • #3
      Originally posted by Bob Fairbrother
      I have just been trying to get my head around a true position geometric tolerance for some holes that references 4 (yes 4) Datum features.
      These holes are machined perpendicular to a face (Datum A) and
      positioned to centrelines (Datums B and C)

      Datum Description
      A Face
      B Centreline of main bore
      C Centreline of main bore @ 90° to B

      No problems so far, but the then the geometric tolerance calls up Datum D which is a group of 4 holes machined in the same face

      I think the draughtsman has got it wrong and there should be 2 seperate geometric tolerances.

      The first one referencing Datums A B C
      The second on referencing Datum D

      Then I would report the holes twice, first time to Datums A B C, second time to Datum D.

      Any thoughts?

      Bob Fairbrother
      Bob,

      Any basics from -D- to the holes? Wondering if the A/B/C is for alignment and maybe the center of the -D- pattern is origin.

      Just thinking. Kbotta can help on this, my bet.

      TK
      sigpicHave a homebrew

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      • #4
        Possibly look at it this way.

        The boss says, "Mount the durn wheel, I don't care if it had to be 1 inch off position to balance the deck."

        So, hence, the TP to the bolt pattern is greatly important, while the position to A/B/C is not so inflexible.




        Remember, if it doesn't fit, FORCE IT. If it breaks, it needed replacing anyway.
        http://baggy3.info/signani3.gif
        Excercise your mind,..... muscle works better than fat!!

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        • #5
          Normally there is a tighter tolerance to D
          Would the part be good to D if its ok to ABC using the same tolerance?
          DR Watson shut me down again !!!! :mad: Smoke break:eek:

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