True Position HELP!!

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  • True Position HELP!!

    This is a tough one, I will try to write this so it makes sense ha ha:

    I am having trouble with a true position spec - I have a 12mm diameter, with a bolt hole pattern of 3.7mm diameters in a 19.05mm diameter around it. The 12mm diameter is lBl. The back wall of the feature thru which the 12mm & bolt hole pattern diameters are located is lAl.

    The true position callout is from each of the (3) 3.7mm diameters, to lBlAl.

    In my alignment, the wall lAl is the Y origin, and the 12mm dia lBl is the X origin.

    Per the engineers in charge, this callout relates lAl to the diameters as perpendicularity of the axis thru the 3.7mm diameters to the plane that is lAl, rather than a linear distance. It appears, however, that PCDMIS (3.7) is calculating this as linear.

    What would I need to do, possibly in the geometry of my constructed features, so that PCDMIS relates, in a TP callout, a line thru the axis of a diameter perpendicular to the plane?

    Thanks for any help on this!

  • #2
    Well, the holes must first be measured as Cylinders. If the datums are properly used as your alignment features, you shouldn't have a problem.
    1) Datum A, level to YPLUS
    2) U need to decide which feature, or feature sets you will use that are perpendicular to DATUM A to establish axis of rotation. Mabey one of the holes in the pattern is daum c?

    oK neXT?

    gABRIEL
    sigpic

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    • #3
      Hi Cumofo, and thanks for the info.

      I have constructed lBl as a cylinder, and used this feature as rotational Y plus around Z plus. The plane for lAl is leveled to Y plus.

      I have constructed one of the 3.7mm diameters as a cylinder. When I dimension this 3.7mm dia as TP to lBlAl, my nominals are showing as X: -4.725 (which is correct) and Y: -.6377 (which would be correct as the center point of the Cylinder, if I were looking for a linear distance.)

      I am still stuck :-(

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      • #4
        shay,

        Wouldn't you consider those to be the nominals for a true position callout for the hole? TP includes perpendiularity because your cylinder has to be within the true position callout top to bottom.

        TK
        sigpicHave a homebrew

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        • #5
          ohh,
          Use the X axis and the Z axis as reported AXIS. Also you may need to use polar coordinates, if you dont have the cad or are lazy with ur trig!

          Gabriel
          sigpic

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          • #6
            ohh,
            Use the X axis and the Z axis as reported AXIS. Also you may need to use polar coordinates, if you dont have the cad or are lazy with ur trig!

            Gabriel
            sigpic

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            • #7
              Thanks for the info guys. I am still working on this one.....

              tking - I understand what you say about the perp being included in true position, but am curious - how is the actual perp value (or deviation) shown in the "results" area of true position in PCDMIS?

              thanks again!!

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              • #8
                Originally posted by shays
                Thanks for the info guys. I am still working on this one.....

                tking - I understand what you say about the perp being included in true position, but am curious - how is the actual perp value (or deviation) shown in the "results" area of true position in PCDMIS?

                thanks again!!
                shays,

                Technically it's not. Simply put if the c/l of the feature is in position from top to bottom it meets the implied perpendicularity requirement. If you want the actual perp deviation from 0 to display you would have to do a perp check and report it, I would report actual only (this is not a 2x calculation as TP is).

                TK
                sigpicHave a homebrew

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                • #9
                  This is what I have suspected, from what I am seeing in my results.
                  Thanks for the explanation, this helps me out a LOT.
                  shays

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