Is this datum callout legit?

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  • Is this datum callout legit?

    I am about to inspect these parts, but the -B- and -C- datums have me scratching my head.
    Last edited by d.evans; 01-29-2009, 06:13 PM.
    ** "Well, ain't this place a geographical oddity. Two weeks from everywhere!"~ Ulysses Everett McGill **

  • #2
    That is a little strange.

    Level A, rotate to the centerline of B, transfer axis to A, transfer axis to centerline of B, transfer axis to centerline of C.

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    • #3
      This is odd. Level to A, but what to do with B and C?

      Can you get the fixture from manufacturing in which they make this part? See how they hold it. What are the hard points, where are the clamps. Follow what they do in mfg. This may not be right, but in this case I think you are better off to just do what they did.

      This is very ambiguous. I have never seen this before.


      Jan.
      ***************************
      PC-DMIS/NC 2010MR3; 15 December 2010; running on 18 machine tools.
      Romer Infinite; PC-DMIS 2010 MR3; 15 December 2010.

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      • #4
        Setting up the part per the Datum callout does not look to hard. Holding or fixturing the part so you can measure looks like fun. Not a very big part. Enjoy
        sigpic.....Its called golf because all the other 4 letter words were taken

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        • #5
          pretty common callout here in wafer valley

          they want the center of the part as your datums B & C
          you can do this easily with pcdmis

          create a mid-line between the two sides
          create a mid-point between the two arcs

          this will now be your center
          with the mid-line also being your rotation of your alignment

          so your alignment would be something like this

          level to top surface
          rotate to mid-line
          topsurface is z zero
          mid-line is x zero
          mid-point is y zero

          good luck
          Last edited by bob mappes; 01-08-2007, 05:13 PM.
          Which one gets ridden today? MPH vs MPG..tough choice, both are FUN
          sigpic

          Starrett RGDC 4028-24 :alien:
          Demon vintages 3.7, 4.1, 4.2, 4.3, 2009

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          • #6
            Basically the centers of OD of the part as a slot width B datum and length C datum
            B and D center points become your origin

            Bobs way will do it

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            • #7
              Thanks all.

              I went to the engineer, and he agreed with what you all have said. It is tiny though. Looks like it has an appointment with Mr. Sticky Tape. That will be the only option I have and still get to the features.

              Bye.
              ** "Well, ain't this place a geographical oddity. Two weeks from everywhere!"~ Ulysses Everett McGill **

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              • #8
                try using hot glue to hold it

                put a dab on a 1-2-3 block and press it on it while still hot

                you want the datum a to be up so you can check most of it from there
                Which one gets ridden today? MPH vs MPG..tough choice, both are FUN
                sigpic

                Starrett RGDC 4028-24 :alien:
                Demon vintages 3.7, 4.1, 4.2, 4.3, 2009

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                • #9
                  I know this is an old post but it applies to part I just checked. My question is WHY dimension it this way? I'm obviously not an engineer so I can't "think" the way they do.
                  CMM Programmer
                  Jackson Michigan
                  Mistral 7.7.5
                  4.3MR2

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                  • #10
                    Easy money I do agree datum B is used as a 2way in this datum scheme Ull have that. Good luck JC
                    sigpic
                    Jeremy Cavender
                    CMM Metrology Engineer
                    PC-Dmis 3.2/2010/MR2

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                    • #11
                      Originally posted by Sl33stak View Post
                      I know this is an old post but it applies to part I just checked. My question is WHY dimension it this way? I'm obviously not an engineer so I can't "think" the way they do.
                      That's exactly why, they don't think the way everyone else does.

                      As a programer, I would probably either, one, sent the print back to them and asked for a updated print, or submitted an Engineering change order, if that's what it is called there, or checked it to the functional/critical features, and marked up a print. Then submitted all the information to them.

                      I would also check it my marked way, and their way, just to see any differance.
                      But yeah, i have seen some pretty messed up callouts, and I have to stop and ask the same question, why?

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                      • #12
                        It needs to fit in/on the counterpart, perhaps?

                        Would probably be better to use a profile tolerance and use the holes as datums, though.
                        PC-DMIS CAD++ 2o19 R1 SP11

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                        • #13
                          Looks fine to me. The only thing is for datum -C- I would use tangent points on the 2 radii (tangent to datum -B- midline), and use a midpoint of these 2 points as my origin. So level to -A-, rotate to -B-, set origin xy to -C- and z to -A-.
                          sigpic
                          Global Advantage 12-22-10
                          TESASTAR M SP25 4.3mr2

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                          • #14
                            It looks legit to me due to the simplicity of the part.
                            Normally, major machined datum(s) tied to raw material/casting as your starting point(s), in this case almost all of the machined features on this part are used to establish part coordinate.
                            You can either dimension casting features to the part coordinate or machined features to casting coordinate, the sketch is simple, easy to understand, it’s symmetrical all around and everything is covered, it’s a smart way to dimension it (IMO).

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