Simulated datum shift

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  • Simulated datum shift

    The EIC of the newest project here wants to include "A possible simulated datum shift" within an inspection program. (Basically, we are allowed to flex the part with X pounds force, thus slightly moving the datum structure.) Can PCDmis replicate this, and if so, how?

  • #2
    I don't think PC-DMIS or the CMM can replicate moving the datum based on X pounds of force. Datum shift isn't the actual datum moving. The feature moves about the datum until it hits the maximum material boundary of the datum. The datum is stationary.

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    • #3
      Originally posted by Sammus72461 View Post
      The EIC of the newest project here wants to include "A possible simulated datum shift" within an inspection program. (Basically, we are allowed to flex the part with X pounds force, thus slightly moving the datum structure.) Can PCDmis replicate this, and if so, how?
      First, it is very important to define whether you are :
      A) actually in real life physically flexing the part with force and then measuring it in this state, or

      B) attempting the incredibly foolish and doom-laden effort of simulating this flexing movement and measuring a part that is NOT flexed with force.

      If A then: no datum shifting is required at all, the datums will be flexed, the CMM will use them, the inspection features will be flexed, and the results will show the skew. This is an incredibly valuable measurement exercise and should be done.

      If B then: you are fooked as the results will be meaningless and misleading.

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      • #4
        EIC - Earned Income Credit?

        As bfire85 says, Datum Shift is a legitimate phenomenon of Maximum Material Boundary applied to Datum Features of Size when said actual features deviate from their Maximum Material Condition. IMNSHFO the purpose of the this control is to give guidance to the design of functional gaging per ASME Y14.43-2011.

        Simulating the part flexing under a given load is an entirely different can of lunar tardigrades. If there is a need to inspect the part in a restrained condition, the details of said constraint must be fully defined. See paragraph 4.20 of ASME Y14.5-2009.

        HTH
        sigpic"Hated by Many, Loved by Few" _ A.B. - Stone brewery

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        • #5
          Originally posted by Ego Murphy View Post

          First, it is very important to define whether you are :
          A) actually in real life physically flexing the part with force and then measuring it in this state, or

          B) attempting the incredibly foolish and doom-laden effort of simulating this flexing movement and measuring a part that is NOT flexed with force.

          If A then: no datum shifting is required at all, the datums will be flexed, the CMM will use them, the inspection features will be flexed, and the results will show the skew. This is an incredibly valuable measurement exercise and should be done.

          If B then: you are fooked as the results will be meaningless and misleading.
          My sentiments exactly

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          • #6
            Originally posted by Wes Cisco View Post
            [COLOR=#008000][SIZE=14px][FONT=lucida sans unicode

            ]EIC - Earned Income Credit?
            EIC = Engineer In Charge

            :P

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            • #7
              You need to use FEA software if you want to simulate the flex, and I would never ever even remotely consider using a combination of actual data and theoretical data to report dimensions under a load. The data you provide your customer needs to be 100% actual and factual. No theoretical nonsense.

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              • #8
                If you can simulate the datum structure, and use a loadcell with an elaborately rigged (or designed) fixture to apply the "flex" your EIC is expecting to apply, it is possible. But at what cost?

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                • #9
                  Originally posted by louisd View Post
                  If you can simulate the datum structure, and use a loadcell with an elaborately rigged (or designed) fixture to apply the "flex" your EIC is expecting to apply, it is possible. But at what cost?
                  I don't know how much it cost them, but the fixture is designed and in use now.

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