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Thread: tolerance with MMC

  1. #1
    Associate Engineer
    Join Date
    Mar 2014

    tolerance with MMC

    I am machining a part where the threads are datum A. At the top of the part is a radius that comes down straight to a width of .700 -.03 it calls out a .01 true position to datum a MMC. If the length is running at .682 how much tolerance do I have?

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    MMC is that size of a "feature of size" (FOS) where the most amount of material is present for the stated limits of size.

    So, the length of the radius feature has nothing to with the allowed position tolerance as the tolerance by default applies to the entire length, depth, width, etc. of the feature.

    Without an image showing the feature and the size/tolerance specification a full evaluation cannot be given. I'm not sure from the description that the position tolerance specification is even most-correct. I suspect that a Profile of Line or Surface may be more appropriate.
    Last edited by Kelly_Bramble; 03-21-2014 at 07:29 AM.

  3. #3
    Project Engineer
    Join Date
    May 2011
    Upon re-reading the OP, it sounds like the "M" symbol is after the datum reference rather than the 0.1 tolerance itself. Is that true, Philray?
    Since your datum is taken from the threads, the MMC/MMB idea could make a world of difference in the answer. (Difficult to take a pitch diameter RFS/RMB!)
    If you're able to include a sketch/scan, that will help.

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