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Thread: Positional Tolerance on Common

  1. #1
    Associate Engineer
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    Positional Tolerance on Common Axis

    Hi All,

    A quick question on simplifying a drawing I've picked up for checking.

    See attached concerning a counter-bore thru hole. My view is that I can replace all of that with a single positional tolerance of a common axis, much like ASME 2009 Fig: 7-24.

    I simply want to ensure the co-axial holes align and are perpendicular to the back face. Datum A is the back face but its not shown in the image - again it would be the same as ASME 2009 Fig: 7-24.

    I feel I might get some resistance as my company seem to enjoy adding concentric and circularity requirements to holes. My view is that is adds to inspection costs and doesn't add much, if any functional value to the part.

    What do you guys think?

    Thanks.




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    Last edited by rich_c; 07-26-2016 at 05:45 AM.

  2. #2
    Administrator Kelly Bramble's Avatar
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    First question... please verify which dimensioning and tolerancing standard this has been specified to..

    Second.. is this the entire specification? Is there only one hole feature intended to be controlled?

    Three, What does Delta Note 3 indicate?
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Associate Engineer
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    Quote Originally Posted by Kelly Bramble View Post
    First question... please verify which dimensioning and tolerancing standard this has been specified to..

    Second.. is this the entire specification? Is there only one hole feature intended to be controlled?

    Three, What does Delta Note 3 indicate?

    1. None. I have a copy of ASME so that's what I refer to.

    2. Yes, just this hole.

    3. The delta is a revision change symbol. At Rev.03 the GD&T was added.

    And yes, the drawings are a mess...

  4. #4
    Project Engineer
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    Kelly seems to be on to something ... I too suspect that this is not meant to be an ASME Y14.5 drawing, but rather the ISO system. Two clues make me think that:
    -- the print uses commas rather than decimal points
    -- there is a "G7" tolerance, which ASME allows but it's more common in Europe

    So first check on the tolerancing standard (in a note or maybe in the title block?). If it is ISO, then the concentricity symbol has a different interpretation that ASME's interpretation of concentricity.

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