Datum Shift on Report ? What does this mean ?

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  • Datum Shift on Report ? What does this mean ?

    I was reading through my report and I am wondering what it means by datum shift. I would assume you'd want it to be 0 and not shift whatsoever as that would make all the measurements inaccurate .
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    Last edited by sscandlon; 03-14-2019, 02:49 PM.

  • #2
    Switch fit to datums to off (No modifiers used)
    sigpicIt's corona time!
    737 Xcel Cad++ v2009MR1....SE HABLA ESPAƑOL

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    • sscandlon
      sscandlon commented
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      Where is that located ? Apologies I am quite new to PC-DMIS.

    • Roberto
      Roberto commented
      Editing a comment
      You can place the cursor on the dimension and press F9.
      Click on the advanced tab. There you should see the fit to datums option. Just uncheck.

  • #3
    in the feature output you will see a line that says (fit to datums) yes change to no.
    Time for the Trolls to leave.

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    • sscandlon
      sscandlon commented
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      Thank you !

    • sscandlon
      sscandlon commented
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      What is the benefit of using this versus not . For my purpose I want the accurate reading with no shift since I am using the TP readouts to reprogram our machine. But I just wanted to ensure that by not using it I am not missing out on info I may need.

  • #4
    Datum Shift allows the measured feature to "shift" until the shift hits the max material boundary of the datum. So lets say you are measuring the true position of a feature in the X axis. Your datum has a diameter callout of 6 +/-0.1, and your datum measures at exactly 6. Your datum "bonus" will be 0.1, but the feature can only shift about the datum 0.05 ((6-5.9)/2) until it hits its max material boundary. If the datum measured at 5.95, then your feature would only shift by 0.025. This helps simulate the function of the part. Now, if you feature control frame says, 0.1 | A | B | C |, then you are not allowed any shift. If it says 0.1 | A | B(M) | C, then you are allowed a datum shift. If you don't want to see a datum shift, then shut it off as the others have described above.

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    • A-machine-insp
      A-machine-insp commented
      Editing a comment
      Thanks for the great explanation. Now, maybe I can get the other programmer to quit using Legacy with modifiers. I keep telling them that Legacy doesn't like modifiers but they like to see the dimensional results in the edit window and not have to have the report open.

      I'm not the best at explaining things so hopefully this will help.

  • #5
    Originally posted by sscandlon
    For my purpose I want the accurate reading with no shift since I am using the TP readouts to reprogram our machine.
    Then you don't want a TP. The TP with datum shift is a functional gage - it tells you if the part will work or not. For adjusting the manufacturing process, you use LOCATION.
    AndersI
    SW support - Hexagon Metrology Nordic AB

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    • #6
      The datum planes you use will determine with axis are fixed in the datum shift.
      You use 2 datum's and in datum shift the Y and Z direction are fixed. Looks that you used datum in Z instead of X direction.

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      • #7
        I think I have said this time and time again. When you make an alignment at the very, very beginning You lock the part down in all 6 degrees of freedom. Once the part is locked down, it can no longer move, shift, rotate, nothing!!!!. When you are creating a Program, you are creating the mating part for the Parts (CAD MODEL) you're company is making. The virtual mating part that you made (YOUR DATUM STRUCTURES) they are allowed to move about the part (BEST FIT) Don't be fooled by the CAD model. When your done making your program make your CAD model disappear, and what you have left is your mating part. Then when you get a part from your machinist, you then are holding your part still (your alignment) and moving the virtual MATING part to see if it will fit to the part your machinist has made. Your Cylinders are gage pins, locked in according to your structure (Datum Reference Frame) Plane that you Level Represents the mating Plane (Surface Plate) if your laying it out manually. Except the difference is, when your laying the part out manually, you're moving the part on the surface table, in PC-DMIS you're moving the surface table around the part. That's why you see DATUM SHIFT, because if allowed, the table, pins, or any other feature that we create, is allowed to Rotate, or shift (in the boundary given). NOT THE PART.
        (In Memory of my Loving wife, "Ronda" who I lost March 7, 2016. I love you baby.)
        They say "Nobody's Perfect." I must be Nobody.

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        • thomas pilc
          thomas pilc commented
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          wow that might be the best explanation i have ever heard do you mind if i steal that i got about 10 inspectors and 5 cnc programmers who i have tried to explain this too and i can see about half look at me with a glazed over look at the end of the conversation

        • KIRBSTER269
          KIRBSTER269 commented
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          thomas pilc there's a $5 deposit fee for that info kidding. Of course you can use it if it makes sense for the others.

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