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Thread: GD&T questions

  1. #1
    Associate Engineer
    Join Date
    Sep 2018

    GD&T questions

    I have the question in regards of the attached print GD&T Spec Diameter 12.7 +-0.3 Position Diameter 3(MMC)/A/B(MMC)/C, see attached. My readings are (if I measured correctly) 12.72 and 12.71 and for the Position, I do have 3.254 and 3.487 (Two holes). The question that I have is the 3.254 and 3.487 still intolerance?
    Attached Files Attached Files

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    1. The PDF attachment is very hard to read.
    2. Datum B, appears to be 74.4 + - 0.5.
    3. Datum B is a feature of size and the MMB (circle M) specifies that additional position tolerance is available which is equal to the as-built datum feature size divergence from the MMB size.
    4. I think the feature in question is an internal FOS, MMC = dia. 12.4. and LMC = dia. 13.
    5. At dia. 12.72, the allowed bonus tolerance is 12.72 - 12.4 = 0.32
    6. At dia. 12.71, the allowed bonus tolerance is 12.71 - 12.4 = 0.31

    Again, Datum B as-built size is unknown therefore an answer is not possible. Moreover, it is unlikely that the effects of the Datum FOS divergence from MMB can be calculated using a simple sum since the relationship to the referenced feature is complex.
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