Cone to Cylinder Concentricity?

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  • Cone to Cylinder Concentricity?

    I'm doing a quick correlation study for an injection-molded part and the company that supplied us their layout, says that the concentricity between of Datum C to Datum A (0.1 max) averages 0.03-0.04. Come to find out they are only taking a circle from the cone and referencing that back to Datum A, which goes against what the print asked for.

    Both datums revolve around the same axis and the whole part is only 50mm long. I'm getting 0.3-0.4 consistently.

    My question is: as I don't have experience with cones in general, is it common for the cone-to-cylinder concentricity to be wonky in PCDMIS (using 2018R1 here)?

    I've checked my alignment, none of the hits seem to be out of place with respect to the CAD... what other things should I be looking at?

    Thank you.

  • #2
    You have to construct the circle, at the right height (constructed circle / cone/height)
    In ISO world, if the features are not in the same plane, a concentricity needs 2 datums. If not, it's a coaxiality (ISO1101).

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    • UKCMM
      UKCMM commented
      Editing a comment
      Would go with coaxiality in this case unless the drawing specifically calls out a height on the cone for the measurement.

    • JEFMAN
      JEFMAN commented
      Editing a comment
      ukcmm : +1 !

  • #3
    My advice:

    If using Xact/GeoTol:
    1) Probe your datums
    2) Define the above referenced features as datums to PC DMIS
    3) Probe the geometry you want to check the concentricity of as a cone.
    4) Use the feature control frame builder to report the GD&T of the cone.


    If using Legacy-->
    1) Level to cylinder, Rotate to whatever work coordinate system of your CMM, XYZ origin to the cylinder & datum structure called out in your concentricity's feature control frame
    2) While recalling your datum alignment, measure the geometry you want to check the concentricity of as a cone.
    3) Report the concentricity of the cone back to your alignment.

    Above being said..
    I disagree with their method of reporting a circle that is constructed on the cone. By only checking the circle, they're not evaluating the entire form of the cone. They could be good at one cross section but bad at another if the part has any form or angular error. I have plenty of parts where I am reporting the concentricity of a cone back to my alignment, one is running on the cmm right now actually.

    Something to look out for...
    There are a lot of prints that will call out a cylinder as a primary datum in a feature control frame. By doing this, this drives you to level through that cylinder. Leveling through the cylinder makes total and complete geometric/logical sense...HOWEVER... in real life...this only works well if you have a long enough cylinder but it can be a SERIOUS pain in the a$s if you're dealing with short cylinders because any form error over that short length gets exacerbated through your alignment and can cause funky readings. I have a gearbox, 1st rev print came to us with one cylinder that has to be concentric to the other within 0.002, they are both only about 0.125" long and they're 13inches apart from one another lmao...had to get their imagineers to change that one for us.



    Hope all of this helped!
    Last edited by DAN_M; 02-11-2021, 07:29 AM.
    SF7107(PCD), SF454(PCD), 152614(Quindos), 9159(Quindos), 7107(Quindos), B&S Manual, M&M Gear Checker

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    • #4
      Turns out, after turning on the graphic arrows for each point associated with the features I'm checking, there were two points that were mishits due to shanking. This issue has been resolved and now I'm seeing good concentricity measurements.

      Many thanks to those that responded. It's appreciated. I'm still new to programming in general, much less PCDMIS. Even after a year, I'm still learning so much from my silly mistakes.

      Comment


      • #5
        Originally posted by ALousyUser View Post
        Turns out, after turning on the graphic arrows for each point associated with the features I'm checking, there were two points that were mishits due to shanking. This issue has been resolved and now I'm seeing good concentricity measurements.

        Many thanks to those that responded. It's appreciated. I'm still new to programming in general, much less PCDMIS. Even after a year, I'm still learning so much from my silly mistakes.
        Are you programming with CAD? If so, maybe collision detection would have caught the shank. Something to think about for your future programs. Glad you're all set!
        SF7107(PCD), SF454(PCD), 152614(Quindos), 9159(Quindos), 7107(Quindos), B&S Manual, M&M Gear Checker

        Comment


        • ALousyUser
          ALousyUser commented
          Editing a comment
          Yes, I'm programming with CAD. I'll keep that in mind, thank you.

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