fcf and datums

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  • fcf and datums

    Profile .002 B-D C

    Was trying to paste in a fcf but nothings working for me today. I need some help understanding the above callout. Its asking for profile of a surface to datums B, D and C.
    The fcf had B and D in one box and C in the next. What is the purpose of grouping the datums like this and does it affect how I apply my tolerance, I know datum C will be form and location of +/- .001 but will the tolerance be the same for B and D.

    Thanks in advance ( My head still hurts from Paddy's weekend )
    To the Brave and the Faithful nothing is impossible

  • #2
    Are -B- and -D- diameters in line with each other? I've seen this kind of callout on shafts before. Just create a line between the 2 diameters, level to the line, and set origin to the line. Then set the 3rd origin to -C-.

    In that alignment callout form and location of the feature being toleranced.
    PC-DMIS 2016.0 SP8



    • #3

      Usually when I see two datums in one section of the fcf as you describe it is because the part is a cylinder and each of the two datums is a diameter on opposite ends of the part. Essentially what they are asking for is the two datums to be connected into a cylinder whose centerline is then treated as a datum. HTH
      sigpic"Hated by Many, Loved by Few" _ A.B. - Stone brewery


      • #4
        How can you level to a line? Thought you had to have a plane to level to.
        David Monroe
        Is there any way to stop the infernal beeping!?

        3.5 MR2
        Dual Arm Vento



        • #5
          You can level to a line or a cylinder as well. When you have the alignment window open and select the line (or cylinder ) it will turn red and show an arrowhead indicating the vector of the feature. Just be sure to select the axis in the Level dropdown that most closely matches the vector of the feature (if you don't want to flip your axes around). The default axis in the dropdown will match your current working plane.
          Jonathan S
          pcdmis 2009
          G&L CORDAX RS-150 DCC
          B&S global 15-30-10
          DEA Delta Slant 30-100-15


          • #6
            When leveling to a line, make sure that it is a 3-d line, and you vectors match


            • #7
              That would be what is known as a "combined" datum feature.
              RFS Means Really Fussy Stuff

              When all you have is a hammer - everything looks like a nail....


              • #8
                As usual ye are spot on.
                B is a 7" rad and D is a 6.9" rad, both have the same center. I use an iterative alignment to level to B and D, rotate to A and origin to C. From what you've said its form and location of +/-.001" for B, D and C.
                Thanks again
                To the Brave and the Faithful nothing is impossible


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