Need some pointers for my first advanced/complicated alignment please!

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  • Need some pointers for my first advanced/complicated alignment please!

    So I've been using basic 3-2-1 alignments or working with parts that only have 1 datum. Today, however, I have a part that has 3 datums, a flat surface on the top of the part and two through holes. And then there's two diameters around the through holes that are recessed but not through, if that makes sense, and these holes have run out to ABC on them. What kind of alignment do I need to do to be able to get run out to all 3 datums? I've attached a rough picture to hopefully help explain better.

    This is how far I've gotten: level to A, construct diameters for B and C and then create a line to use for a rotation line. But then do I use one circle as my XY origin or the rotation line? And then how do I recall all 3 datums for my runouts? If I just set each of them as a datum will PCDMIS understand or do I need to do something special?

    Attached Files

  • #2
    Well first off that's an odd (if not illegal) callout - runout is usually used for rotating parts - i.e. you'd expect one or two datums (which established a datum reference frame nominally central to the considered feature.)

    Your alignment is pretty much right to establish ABC (the datums should lock any degrees of freedom they can, in the order they appear in the control frame)

    So A is your level (on origin in one axis), B is origin in remaining two axis, and rotation is locked by C.

    However I think if you ask for the runout of the cbore around Datum C, PC-Dmis will give a very high value.

    I think you need to speak to the designer to see what they really want.

    I suspect that either Position or Profile to ABC for the cbore on the left and Position or Profile to ACB for the cbore on the right might be more what they're looking for.

    Automettech - Automated Metrology Technology


    • gt143744
      gt143744 commented
      Editing a comment
      Thank you for confirming my suspicions,I thought the runout was a little weird but I thought I just didn't understand correctly. Position would make the most sense considering it's a relief for a screw I believe. I'll have my boss reach out to the customer. Thanks for the alignment tips!

  • #3
    I would think that Profile would come closer to what the designer is struggling to say. Position generally refers to an axis while profile generally refers to a surface.


    • #4
      What NinjaBadger said. That runout makes absolutely no sense at all. Hard to tell if the runout is connected to the hole or the recessed/counterbore surface though... Regardless, the datums are wrong anyway.
      Last edited by; 09-10-2020, 09:34 AM.
      PC-DMIS CAD++ 2o19 R1 SP11


      • gt143744
        gt143744 commented
        Editing a comment
        I think the counterbore, but according to a higher up the customer only cares about the depth and hole and counterbore size. So I'm not sure why they'd even put all that extra stuff on the blueprint if they didn't want it. I'm still going to program it the way that makes sense.

    • #5
      I think the cbore around -B- should be position or runout to -B- and the cbore around -C- should be position or runout to -C-


      • #6
        Total Runout is not appropriate here. I would get clarification from the designer and not guess at what they are after.
        CMMXYZ Applications Specialist: PC-DMIS Support and Training. Check out my PC-DMIS tutorial videos...


        • #7
          Runout dimensions can only have 1 or 2 datums, never 3. One of the datums needs to be an axial feature that is concentric to the feature with the callout, and if there are two datums, the other one needs to be a planar surface normal to the axis of the other datum.


          • gt143744
            gt143744 commented
            Editing a comment
            *Technically* datums B and C *could* be cylindrical, but they'd be hard to pick up. I'd never seen a call out to 3 datums before so that was my first flag. I need to talk to the customer but what I'm going to suggest is keeping all the datums but having it set up as True Position relative to B or C and then A. Makes more sense to me and would be easier to program and get reliable results from.

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