According to print specifications should I use datum shift?

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  • According to print specifications should I use datum shift?

    http://drive.google.com/open?id=1oXM...bRDYFjdY9PNV_u

    http://drive.google.com/file/d/1Gqjp...ew?usp=sharing

    Should Datum shift be enabled according to the print also how do I display the X and Y tolerance on the report for the position dimensions.
    Last edited by sscandlon; 04-03-2019, 11:35 AM.

  • #2
    No datum shift. No bonus on size. Your FCF (Feature Control Frame) does not have MMC modifier affixed to the datums or the part.
    You can display X/Y variation from basic if you (and your organization/customer) see fit, I do it as a report comment, so no dimensions are presented to apply to the basics.

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    • sscandlon
      sscandlon commented
      Editing a comment
      ok so would this be a correct way to display the X&Y , my boss wants to be able to see the + and - tolerance for each X and Y

      https://drive.google.com/open?id=1Gq...Mc7h40qIi67CK7
      Last edited by sscandlon; 04-03-2019, 12:47 PM.

    • louisd
      louisd commented
      Editing a comment
      Linear resultant values do not correlate with positional tolerance, so no ± 0.003" linear does not encompass pass/fail of true position.
      (0.003" TP is a circular tolerance zone, x/y ±0.003" is square)

      That's why you shouldn't apply tolerances to the basic, because the linear position has capability of (appearing to) accept a bad part. (EX if your variation in X is 0.0025 and your variation in Y is 0.001", your TP result is 0.0054" out of spec.)
      Last edited by louisd; 04-03-2019, 02:01 PM.

    • sscandlon
      sscandlon commented
      Editing a comment
      ok so how do I ensure I am take the dimension of the true position correctly. Attached are my FCF for 3 of the pin holes of the same size as well as the report

      https://drive.google.com/open?id=16S...LT5lzbvaBbEJpb

      https://drive.google.com/file/d/1zuf...ew?usp=sharing

  • #3
    As long as your nominal value for the pin holes match the X and Y BASIC dimensions on the print, and your datums are defined, setup, and referenced properly, it's accurate.
    --Double check on a rock with an indicator, or put part on a comparator if you don't trust the results.

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    • #4
      Need to know where to manually correct your nominals? read what I suggested to you the other day. I mean, you can do it in summary mode, it's just buried.

      one last thing. switch your edit window layout from "Summary mode" to "Command Mode" now (at bottom of "View" dropdown), and stick with learning in command mode. It is just so much easier to read and understand.

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