Tertiary axis/plane is parallel to primary axis

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  • Tertiary axis/plane is parallel to primary axis

    So I have been having a problem with this part. I have been trying to get the position dimension on the 0.266 holes (in the middle holes compared to Dat D, Dat B, and Dat C) but I have been getting the "Tertiary axis/plane is parallel to primary axis" error. I am using one alignment for all the measurements with all 6 degrees constrained and marked all the work plains for the different sides.

    Anyone see anything obvious that I missed or have anything I should try?

  • #2
    This DRF is invalid. PCD will never let you use -C- in XACT Measure because all 6 degrees of freedom are already constrained by your primary & secondary.

    DBC interpreted literally would mean Level Z+ (or Z- depending on vector to Cyl_D, rotate Plane_B to Y+ about the direction of -D-, make -D- X AND Y origin, and make a plane or point on top face to set your Z origin. -C- would get entirely ignored as tertiary.
    Last edited by DAN_M; 06-15-2020, 02:56 PM.


    • dph51
      dph51 commented
      Editing a comment
      Don’t the counter sinks in Datum D control the up and down?

      The part needs to conform to EU standards and maybe the part needs to be ISO compliant, not ASME.

      Just a thought.

    • Darius11
      Darius11 commented
      Editing a comment
      Datum D can't be primary because then it will conflict with datum B. I think should be A/B/C or so.

    • DAN_M
      DAN_M commented
      Editing a comment
      He asked about DBC so I gave a correct explanation of what that DRF means. My advise was not specific to a certain spec, or telling him how I THINK he should do it..just explaining basic "can-may-must".

      If he measures the part the way I said, he'll get BLUEPRINT CORRECT dimensions off of the part. That may be different then the Engineer's "design intent" for the part but that's their mistake, not his. I run into this issue a lot. When this happens, open and respectful dialogue with the designer is key. If you're 22, don't be foolish enough to tell anyone they're wrong for at least the next 10 years def go about that one a different way my friend!

      In THIS scenario, I would defer to the Engineers & do what they say. You need to get along with them. They have history on the part and it sounds like they know how they want it done.

      Going forward, get some GD&T training. After that happens you'll be able to speak from an educated standpoint when things don't make sense. I work with BRILLIANT engineers who quite commonly mess up their GD&T. They're doing their best but they're human too. If the CMM programmers at our company weren't as well versed in GD&T as we are, there would be a lot of bad parts up there right now lol.

      With all due respect, you're incorrect. -D- can be, and is, the primary datum. The engineer put it first in the DRF, that makes it so. Regardless of how much it may not make sense to us, it is mathematically acceptable. It also would not conflict with -B- (as they have perpendicular surface vectors).
      Last edited by DAN_M; 06-16-2020, 02:11 PM.

  • #3
    (In Memory of my Loving wife, "Ronda" who I lost March 7, 2016. I love you baby.)
    They say "Nobody's Perfect." I must be Nobody.


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