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Thread: Is my tolerance stackup correct?

  1. #1

    Is my tolerance stackup correct?

    Uc1mY5U.jpg

    Major questions:


    • Are 0.028 locating tolerances divided by two for left/right shift?
    • Do overall drawing tolerances apply to a thru hole with a locating tolerance of 0.028 (max material condition)?
    • If a part is dimensioned off a theoretical center, does the overall dimension apply to the stackup?

  2. #2
    Principle Engineer
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    Do I see 'B' and 'C' datums as the edge of both a 3" and an 8" square part? Then you call out parts to be centered?

    Why not make two bolt holes a common datum in the x & Y plane?

  3. #3
    Administrator Kelly Bramble's Avatar
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    On the engineering drawing ... are the distance dimensions expressed as +/- tolerances?

    and, no your tolerance analysis is not close and you do not appear to have a basic understanding of the tolerances expressed nor the datums specified and the resultant DRF.

    Sorry, feeling blunt this morning...

    and... google my name, ASME certificate holders, GD&T before you cast doubt on my statement.

    First, datums are derived from a geometric counter part simulator collapsed onto the as-built feature therefore the datum itself is non-variable in your calculations.

    Default tolerance block is only applied when there are not any tolerances specified.

    Positional tolerances and composite tolerances and tolerance analysis - I'm not going to try on this forum, I suggest you seek some formal training as this can be a complex subject, particularly the tolerance analysis part..


    Quote Originally Posted by hsheldon View Post
    Uc1mY5U.jpg

    Major questions:


    • Are 0.028 locating tolerances divided by two for left/right shift?
    • Do overall drawing tolerances apply to a thru hole with a locating tolerance of 0.028 (max material condition)?
    • If a part is dimensioned off a theoretical center, does the overall dimension apply to the stackup?
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  4. #4
    Ideally the whole stackup would be centered around the theoretical center (I'm not sure if this is allowed though)

  5. #5
    Yes, all dimensions are +/-

  6. #6
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by hsheldon View Post
    Ideally the whole stackup would be centered around the theoretical center (I'm not sure if this is allowed though)
    Yes ~ it is assuming that reflects functional requirements and the datums are specified on the right features - which it isn't.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  7. #7
    @Kelly how would you dimension the datums?

  8. #8
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by hsheldon View Post
    Yes, all dimensions are +/-

    Positional tolerances (and composite) with the apparent datums specified would require the distance dimensions be Basic or as Theoectical Exact Dimension (TED) if the standard incorporated is ISO.

    So, they're wrong..

    See:

    Geometric Boundaries III, The Interpretation and Application of Geometric Dimensioning and Tolerancing per ASME Y14.5-2009


    https://www.engineersedge.com/Engine..._iii_14849.htm
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  9. #9
    Ok thanks, made the dimensions basic. Back to my "does this matter" question on the picture, can I eliminate those from my stackup since using that theoretical center is allowed?

  10. #10
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by hsheldon View Post
    Ok thanks, made the dimensions basic. Back to my "does this matter" question on the picture, can I eliminate those from my stackup since using that theoretical center is allowed?
    Seriously, we're not going to train via this forum.. I'll do short answers but not comprehensive training..

    Wish you the best.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  11. #11
    Principle Engineer Cragyon's Avatar
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    Quote Originally Posted by hsheldon View Post
    @Kelly how would you dimension the datums?
    See Geometric Boundaries III, page 7.25 is exactly what your're looking for.

    https://www.engineersedge.com/Engine..._iii_14849.htm

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