Position of coaxial holes with huge length between them. Please help!

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  • Position of coaxial holes with huge length between them. Please help!

    This is a test part or representation of the actual part.

    We need to measure position of one theoretically coaxial hole to another about 23.125" from face to face

    We consistently got that it was out of position about .0056", we then shifted in the direction X and Y were off and got totally random numbers, or so we thought

    Turns out that the tilt of A axis in our vertical cnc is not accurately rotating to A=90 deg

    Is there a good way to report the position in order to see how much we need to tilt the table and also how much we need to shift in X and Y to get them to be in position to each other?

    If datum A is tilted 0.0035 of a degree over that distance it is around .0014" of movement in Y, if the second hole was perfectly on theoretical position

    Print attached
    Attached Files

  • #2
    You get this when you are dealing with really short features. I always referred to this as " projection error ". What do they look like on a granite ? Level to outside and then use A as X-Y only. How do they look ? Nat saying your getting bad numbers or your process is off but does it agree with the stone ?

    Do multiple circles in each end and then a constructed line. Then dimension the straightness of a line. Whats it look like ?
    Last edited by Schlag; 12-15-2020, 01:16 PM.


    • #3
      The location does seem to match on the stone. We can see the tilt when running an indicator down the length of the bores.
      Creating a line like you said measures straighter than 4 decimal places. We are using a boring bar to create the opposing bores so they are pretty cylindrical


      • #4
        you meant from Datum A to the opposing!

        The straightness measures .0002"


        • Schlag
          Schlag commented
          Editing a comment
          No. 4 circles in each bore. Line made from all 8. This will give a good idea of the TILT between the bores. Allot of times you would see a compound datum using both ends as A-B ..

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