How Bonus is applied to the datums-y14.5-94

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  • How Bonus is applied to the datums-y14.5-94

    Hi gang, I have a question here is the callout, Profile .005|A|Bm-Dm|C.

    A - Flat surface
    B and D opposite inside diameters
    C- Flat surface for clocking

    How does material condition applied, when dia. B and D are not the same size? I guess what I am trying to understand how would the Bonus apply per y14.5-94?

    If I were to measure a part not using the MMC, RFS with the profile result being .004, then separately adding the least Bonus of the two diameters to the tolerance, would this method meet the requirement?



    Last edited by WolfMan; 01-29-2019, 09:59 AM.
    B&S One
    PC-DMIS CAD v2014

    Romer Infinity

  • #2
    i think you would need to do a simultaneous evaluation of the profile to ABmC and ADmC. Using this method should account for the datum shift of the combined axis.

    Comment


    • WolfMan
      WolfMan commented
      Editing a comment
      What do you mean by simultaneous eval?

  • #3
    I think I figured it out. Thanks.
    B&S One
    PC-DMIS CAD v2014

    Romer Infinity

    Comment


    • RIDER
      RIDER commented
      Editing a comment
      Insert / Dimension / Simultaneous Evaluation

    • WolfMan
      WolfMan commented
      Editing a comment
      Never seen this until now. WTH is this thing?

  • #4
    Profile .005|A|Bm-Dm|C

    Should point out that the Circle M on Datums is not Maximum Material Condition, it's Maximum Material Boundary (MMB). You can't just simply add tolerance to a MMB. A MMB lets the part move around i.e. Datum Shift. Calculating shift can be quite difficult although building a Go/No Go gage to inspect to it is relatively easy.

    Comment


    • VinniUSMC
      VinniUSMC commented
      Editing a comment
      MMB was introduced in 2009.

    • Schlag
      Schlag commented
      Editing a comment
      Every single post that asks about a circle M next to the DATUM has to go thru the same explanation that its MMB and not MMC !! I cant count how many times I have stated this in a post. I vote that they up the price of DMIS $150.00 per seat and send a copy of Y14.5 with it. Sorry ISO, you're own your own !

    • Kp61dude!
      Kp61dude! commented
      Editing a comment
      "yeah but it's so much better to just treat it as MMC, everyone else does, you get so much more bonus tolerance that way!"

  • #5
    The term was introduced but the concept is much older than that.

    Comment


    • WolfMan
      WolfMan commented
      Editing a comment
      I don't believe this true. the concept of adding BONUS tolerance towards the TP tolerance is allowed per y14.5-94, just not on the Datum modifier. I could swear I saw it in pc-dmis...was I wrong?
      Last edited by WolfMan; 01-29-2019, 09:51 PM.

    • VinniUSMC
      VinniUSMC commented
      Editing a comment
      Yes, that is how I was taught to the 94 standard.

      It doesn't matter how old the concept is, it matters what the standard that you are being held to says.

    • Kp61dude!
      Kp61dude! commented
      Editing a comment
      I agree kingsld1 it has always existed, humans only discovered it a few years ago. Kinda like math... we only discovered it not created it.

  • #6
    Vinni, did that changed in 2009 spec? I know that MMC was renamed to boundary, but other than that I dunno or did I misread kingsld1 statement?
    Last edited by WolfMan; 01-30-2019, 07:21 AM.
    B&S One
    PC-DMIS CAD v2014

    Romer Infinity

    Comment


    • VinniUSMC
      VinniUSMC commented
      Editing a comment
      When I was training to -94, our guru taught me to add datum material condition just like feature material condition, except that when B and C both have material condition, that only the smallest amount of bonus is allowed from 1 of them.

      I think 14.5.1 may have been fixed faster than 14.5 was, so datum shift/MMB/etc was better understood before 2009 came out, but MMB did not "exist" in the 14.5 standard before 2009.

      MMC was not "renamed". MMC as applied to datum features was changed to MMB. And boundary condition was introduced for TP. The concepts do predate 2009, but you can't use 2009 standard language and definitions to apply to 94, because they didn't exist in 94.

  • #7
    Originally posted by VinniUSMC View Post
    When I was training to -94, our guru taught me to add datum material condition just like feature material condition, except that when B and C both have material condition, that only the smallest amount of bonus is allowed from 1 of them.

    I think 14.5.1 may have been fixed faster than 14.5 was, so datum shift/MMB/etc was better understood before 2009 came out, but MMB did not "exist" in the 14.5 standard before 2009.

    MMC was not "renamed". MMC as applied to datum features was changed to MMB. And boundary condition was introduced for TP. The concepts do predate 2009, but you can't use 2009 standard language and definitions to apply to 94, because they didn't exist in 94.

    True the language of MMB was not in the 1994 standard, but even before the 2009 version was released, the most knowledgeable GD&T folks were cautioning that when a material condition modifier is applied to a datum feature in the datum reference frame the result is datum shift not additional bonus to the tolerance for the feature itself. There was a paper issued about how this impacted Legacy evaluations in Pc-Dmis circa v3.7. In legacy, when you tick the boxes to apply material condition modifiers to datum features in a true position dimension, the result is a Go/NoGo evaluation that is meant to imitate a functional gage check as opposed to resulting in valid variable data.
    Last edited by Wes Cisco; 01-31-2019, 11:10 AM. Reason: clarify the material condition modifiers are applied to datum features
    sigpic"Hated by Many, Loved by Few" _ A.B. - Stone brewery

    Comment


    • #8
      ASME y14.5 1994 clearly defines Simultaneous requirements for MMC (section 5.3.6.2). Additionally, MMC is and always has been synonymous with MMB.
      MMC, as it applies to a datum feature has ALWAYS been axis shift as the part's measured size departs from the Maximum Material (Boundary/Condition, tomato tomoto whatever). This has been in place since ANSI Y14.5 release rev 1973. The only thing that makes all rev's of GD&T different regarding MMC, is pre 1982 MMC is IMPLIED, even if it's not on print. After 1982 rev, RFS is implied, and MMC has to be explicitly defined in order to apply.

      Here's the whole except for that section.
      5.3.6.1, Simultaneous Requirement - RFS. Where multiple patterns of features are located relative to common datum features not subject to size tolerances, or to common datum features of size specified on an RFS basis, they are considered to be a single pattern.
      5.3.6.2, Simultaneous Requirement - MMC. Where any of the common datums in multiple patterns of features is specified on an MMC basis, there is an option whether the patterns are to be considered as a single pattern, or as having separate requirements. If no note is added under the feature control frames (FCF), the patterns are to be treated as a single pattern. Where it is desired to permit the patterns to be treated as separate patterns a notation such as SEP REQT is placed beneath each FCF. This allows the datum features of size to establish a separate datum reference frame (DRF) for each pattern of features, as a group. These DRF's may shift independently of each other, resulting in an in independent relationship between the patterns."

      5.3.2.2 also clarifies MMC applied to datums, as being "axis displacement relative to the true locationof the datum axis" IE: Datum SHIFT.

      Comment


      • #9
        How it applies to the original post: Any size delta from MMB of each datum feature, will result in allowable datum axis shift that is 1/2 the value of the diameter delta from MMB (radial shift).
        So if datum B measures 0.998" and MMB for datum B is 1.000", you get to shift that B axis centroid point for B-D line by 0.001" any way that benefits your simultaneity-applied dimensional results which utilize the same DRF's ([A][B-D][C]).

        Then, if datum D is 1.497" and MMB for D is 1.500" you get to shift that D axis centroid point for B-D line by 0.0015", any way that benefits simultaneity-applied dimensional results which utilize the same DRF's ([A][B-D][C]).

        Yeah?

        Comment


        • RIDER
          RIDER commented
          Editing a comment
          Yes sir. +1

      • #10
        My understanding is that the term boundary was added in an attempt to distinguish between bonus tolerance and datum shift. With the symbols the same though, I don't think they fully succeeded. Maybe there should be a circle to or some other symbol to fully distinguish between the two concepts. As long as there are two definitions for the same symbol then people will be confused.
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        • #11
          So A datum is level plane, didn't really catch that until just now... whoops

          I think WolfMan 's concern is how do you apply bonus shift to B-D axis, and remain level to A and rotated to C?
          To me, the only relevant shift that could be permissible, and would translate the x/y axis, would be applicable to whichever datum is farthest away from datum A (implying B-D is perpendicular to A).

          If B-D isn't perpendicular to A, it gets significantly more complex. I would think the projected pierce point of B-D axis into A would be what you'd have to use to establish B-D datum shift in this instance.

          Comment


          • WolfMan
            WolfMan commented
            Editing a comment
            B-D is perpendicular to -A-. So, I guess my conclusion is that datum modifier per Y14.5-94 can only be used as datum shift (per each datum individually), and does NOT used as a Feature Bonus tolerance does. Did I say this right?

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