MMC on a radius

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  • MMC on a radius

    This is the first time I've tried to attach a file so I hope this works :-)

    I’m trying to figure out how to measure a radius correctly with MMC in PCDMIS (see attachment) I use legacy dimensions

    This is the first time I've seen MMC applied to a profile tolerance and I may be way off on my interpretation but here is my take on it:

    To create the nominal position for feature R75.05, alignment is leveled through the B-D axis and pitched to the rad centre from datum [A] point (where B-D axis pierces datum [A] plane)

    The profile surface tolerance of 0.1 would then have to be equally disposed bilaterally about the theoretical surface or perfect form of the surface being R75.05.

    The MMC condition is placed after the tolerance value which refers to the feature being measured (R75.05)

    Without MMC I would simply measure the R75.05 to +/- 0.05 to be held to the constraints of 0.1 surface profile coming from the theoretical rad centre created from datum [A][B-D]

    My question is:

    What is the customer asking for here? Where is the bonus tolerance coming from for MMC?

    If the rad measures 75 (bottom limit within the constraints) does this allow a bonus of 0.1 making a profile limit of 0.2, and if it measure 75.1 no bonus is given leaving an overall profile of 0.1 seeing it would be at MMC?

    I'm totally confused by this, any help or advice would be greatly appreciated


  • #2
    I may be wrong and will stand corrected, But i didnt think MMC on a profile tolerance was allowed.


    • #3
      It would make things a lot easier if it wasn't allowed thanks for your input.


      • #4
        On ISO2692, it seems that it's possible to dimension it. The real surface mustn't go away than the virtual surface at the MMC (it's my translation, I can't find the english text !!!!!).
        I read it quickly, they don't say what you do with the bonus !!!!! I believe it only define the passage of a rotating part in an assembly...
        Don't know about ASME for the instant (I hope I will know soon... )


        • #5
          From Tec-Ease

          The Y14.5 Standard tells us that we cannot apply the MMC modifier to a profile tolerance because it is a surface control. We can, however, apply MMC or LMC to the datum references of a profile tolerance where the datum features are features of size.

          Don't know about ISO Standards.

          B&S CHAMELEON/PCDMIS CAD++ V2011

          There are no bugs, only "UNDOCUMENTED ENHANCEMENTS!"



          • #6
            Originally posted by JEFMAN View Post
            Don't know about ASME for the instant
            Originally posted by dph51 View Post
            Don't know about ISO Standards.
            Between us, we might be able to answer ...


            • #7
              From contents table :

              In examples, they talk about location, straightness, parallelism, perpendicularity (...) They don't talk about surface, they don't say if you can use it or not...
              Last edited by JEFMAN; 07-06-2015, 08:25 AM.


              • #8
                In my opinion MMC on profile is wrong.
                The modifiers (MMC, LMC) are used where a tolerance is applied to a feature's center point. axis or center plane.

                Did you ask the customer what is the intent?
                sigpicIt's corona time!
                737 Xcel Cad++ v2009MR1....SE HABLA ESPAÑOL


                • #9
                  Thanks dph51 and JEFMAN, I'm struggling to find information on this in ISO. I'm starting to think it's poor draftsmanship

                  Thank's Roberto, that's a good brief explanation of how the modifiers work. The job is quite far on and as usual inspection are trying to keep up, we are at that stage of production where we feel it might be too late to ask. I'll send an e-mail up the hierarchy and see what they say.

                  Thanks for all the advice


                  • #10
                    Just some feedback for anyone that is interested. We have spoke to the customer and their design intent was to hold the rad size to +/- 0.3 (ISO 2768-m) and then from the rad size measured, all form must be within the 0.1 profile limit relative, no mention of where MMC bonus would come from. Anyway, I have a method to achieve what they are looking for so all good

                    Thanks again..


                    • #11
                      Thx for the explanation !


                      • #12
                        Modifiers may only be applied to features of size. The call out is illegal.


                        • #13
                          NP JEFMAN and thanks for your input KevRok after some sound advice and research I happen to agree with you..


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