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Problem with CAD/RPS Alignment

Davcom
Hello, I'm fairly new to CMM programming with CAD models, I just started a month ago and I haven't had any major problems until now. I have to say that I never had a proper formation on CMM programming at all, I learned everything I know by my own.

My problem is that I have to measure a part which it's datums are given in car body coordinates (2 circles and a slot) and I've never aligned a part like this before. I tried doing a 3-2-1 iterative alignment and then a best fit as I always did, but I can't get it to work because the deviations of the real part from the CAD are so big that whenever I try to measure a hole the probe bumps into the part like 3 or 4 mm away from the hole and as much as I try to do a better best fit alignment it doesn't seem to work. so after plenty of time of trial and error I gave up and asked for help to my co-workers, but they use different CMM machines and software (Metrolog XG), so they don't know how to use PC-DMIS. They suggested me to perform a RPS alignment to try to get around this problem, but I have no clue on how to do it in PC-DMIS. Anyone who knows how can I get this to work?

Any help I could get would be highly appreciated.

Please, be aware that i'm a newbie in CMM programming, so try to be as clear as you can.
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  • 2 circles and slot does not sound like much of a datum structure. I am guessing that there is more to it than that.

    Iterative works great, unless your part is egregiously out of tolerance.

    What feature(s) make the primary? What feature(s) make the secondary? What feature(s) is the tertiary?

    As I said, the blueprint shows 2 circles and a slot with their coordinates for the alignment. Also, I used many time 3 circles as datum for the alignment, 3 circles to level the plane, 2 to rotate an axis and 1 as the origin.

    In the blueprint there is:

    1st circle A1, B1 and it's coordinates XYZ.
    2nd circle A2, B2, C1 and it's coordinates XYZ.
    Slot A3 and it's coordinates XYZ.

    And yes, part is egregiously out of tolerance, I never had to measure such a deformed part like this one.
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  • 2 circles and slot does not sound like much of a datum structure. I am guessing that there is more to it than that.

    Iterative works great, unless your part is egregiously out of tolerance.

    What feature(s) make the primary? What feature(s) make the secondary? What feature(s) is the tertiary?

    As I said, the blueprint shows 2 circles and a slot with their coordinates for the alignment. Also, I used many time 3 circles as datum for the alignment, 3 circles to level the plane, 2 to rotate an axis and 1 as the origin.

    In the blueprint there is:

    1st circle A1, B1 and it's coordinates XYZ.
    2nd circle A2, B2, C1 and it's coordinates XYZ.
    Slot A3 and it's coordinates XYZ.

    And yes, part is egregiously out of tolerance, I never had to measure such a deformed part like this one.
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