MMC bonus

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  • MMC bonus

    I am dimensioning true position of a few holes, the diameters are out of tolerance (to big) so should they still benefit from the MMC and gain that Bonus tolerance?

    or do they not receive bonus since the diameter is out of tolerance?

    I've seen a few situations where the diameters are to big but still receive the full bonus, and situation where the diameter is to big and not receive any bonus.

  • #2
    ok I think I understand MMC correctly, MMC = what your diameter measured minus the smallest possible diameter then that number is added as bonus to position tolerance.

    my question is, what if my hole diameter is over the given tolerance allowed for diameter, should it still receive the MMC bonus?


    • #3
      quick pic.PNG


      • #4
        so you can see the callout, so if my diameter measures 5.2 should it still receive the bonus? the highest possible bonus is .2 so will the true position tolerance be 2.2, even tho the diameter is out?


        • ctw00
          ctw00 commented
          Editing a comment
          If your hole measures as 5.2 it is at the upper limit of the tolerance, not over it!

        • PacMan23
          PacMan23 commented
          Editing a comment
          your right, I meant to say something like 5.3,

      • #5
        I think that might be a bit debatable.

        The feature is non-conforming for size. It certainly is 0.3 departed from MMC and, by it's size tolerance, can receive up to 0.2 bonus tolerance. The question becomes, does a non-conforming feature still allow for MMC? And I'm not entirely sure that there is a definite answer.

        It probably depends on the function of the feature. If the part could still function, then applying the MMC should be ok. If the part would no longer function, then what's the point of worrying about MMC?

        Finally, if you're worrying about 0.2mm of bonus tolerance, when you're already using up 2.0mm of tolerance, surely the concern should be, "why is this hole oversized and off location?" instead of, "can I get 0.2mm of extra tolerance for a hole that is basically completely nonconforming?" IMHO.
        "This is my word... and as such is beyond contestation."


        • PacMan23
          PacMan23 commented
          Editing a comment
          this is true

      • #6
        It has always been my understanding that if the hole size fails or the stud size fails, then NO bonus is allowed. As far as I know, Pcdmis has also always done it this way. Failures can not in any way aid your process.
        Originally posted by AndersI
        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.


        • #7
          The bonus is still applied to position even when the diameter is oversized. It doesn't give you more bonus than the spec allows, it will only give you the max but either way the size is out so Rule #1 applies.


          • #8


            • #9
              I'd say it depends on your customer. If the hole is oversized, and the true position is only because of the 0.2 bonus for the oversized hole, I'd make both perfectly clear when asking for relief from tolerance..

              If you're asking for internal process control reasons, IMHO I wouldn't use bonus tolerance at all. For process control I'd use RFS, the process need be dialed in in case the hole size changes. The part may be acceptable, but I would do that determination separately.


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