Need help..

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  • Need help..

    Can anyone help me out with this.... Datum C & D are the same?.. or am I missing something..

    To align i used the c-d diameter and the big bore that's tilted.. intersected the two lines and origin the intersection point.... my alignment seems good... program repeats.. everything else is in tolerance... its when I go to dimension the true positions using Xact... i get an error stating "secondary, tertiary axes are coincident"...

    I checked the 3 bores basic X, Y dimensions and they are within a few tenths from nominal.. help
    Attached Files
    Last edited by jozey; 01-28-2020, 07:16 PM.

  • #2
    Yes in a fashion. If I was programming it I would level to the C-D cylinder, rotate between C-D and one of the other holes (constructed line between cylinder C-D and another hole and add a rotation offset if needed) and translate to one of the faces. When you go and construct the datums, I would construct two pierce points using the cylinder and a plane on the face at each end, then offset those points to construct a Datum C plane and a Datum D plane.

    I've been through this once or twice before.
    "Do what I want you to do, not what I tell you to do."

    -Me

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    • A-machine-insp
      A-machine-insp commented
      Editing a comment
      I do agree with NinjaBadger below that it is an invalid datum structure. However, in the absence of yelling at the design engineer (possibly beating him over the head with a baseball bat) and having the print redrawn correctly, my example above will get the job done.

  • #3
    Originally posted by A-machine-insp View Post
    Yes in a fashion. If I was programming it I would level to the C-D cylinder, rotate between C-D and one of the other holes (constructed line between cylinder C-D and another hole and add a rotation offset if needed) and translate to one of the faces. When you go and construct the datums, I would construct two pierce points using the cylinder and a plane on the face at each end, then offset those points to construct a Datum C plane and a Datum D plane.

    I've been through this once or twice before.
    ok let me give this a shot... thank you. then entire part is done its just these three true positions I've been struggling with.

    i checked the basics of the diameters and they are dead nuts.... when I go to report it using xact measure is when I get the "secondary, tertiary axes are coicident"
    Last edited by jozey; 01-28-2020, 07:00 PM.

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    • #4
      That's because as it's drawn those are invalid datums. You might know what the datum should be, but those centrelines could be the centre lines for the bore or any of the nominally concentric ODs.

      The designer need to be reeducated on GD&T.

      Automettech - Automated Metrology Technology

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      • Jim Poehler
        Jim Poehler commented
        Editing a comment
        Just like MOST design engineers,

    • #5
      Originally posted by NinjaBadger View Post
      That's because as it's drawn those are invalid datums. You might know what the datum should be, but those centrelines could be the centre lines for the bore or any of the nominally concentric ODs.

      The designer need to be reeducated on GD&T.
      This is exactly what i was thinking.. I really appreciate the response

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      • #6
        I think I see the engineer's intent, it's an incredibly poorly executed datum structure however. They probably want C Datum to be an axis line of the ID's that is horizontal on paper.
        Then for D datum, they want an axis line for the (about 20°) angled cylindrical features that shows horizontal in the bottom view (vertical/angled in top view).

        C datum should be primary
        D datum should be secondary
        and K datum should be tertiary.

        Level Z to C (ID Axis line of tube)
        Rotate X or Y to D datum axis line, about C datum axis
        Origin C datum X/Y
        Origin K datum Z

        this would produce the most robust alignment possible for that part. But obviously won't match the print. Hope this helps you to feed whatever edumacating the ID10T engineer desperately needs.

        Comment


        • #7
          if those drawings are snippets of your drawings designer needs a GD&T lesson--datum on a centerline is not correct unless as a reference back to datum feature for clarity.

          Datum features need to be attached to features or surfaces not centerline on a drawing, somewhere, a feature or surface is supposed to be declared as a datum or datum targets declared to show how part will be measured from or secured to control orientation of part.

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          • #8
            Thank you louisd and rich p your input really helps. I will give that alignment a shot louisd

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