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Measuring the same part on 2 CMMs, Different Results

acgarcia
We have 2 4.5.4 SFs. I ran a part 5 times on CMM A and then ran the exact same part on CMM B. Got different and same results.

CMM A runs 2016 and CMM B runs 2017. Both use the same star probe build. Both checked the same features with the same parameter... number hits, prehit retract, etc..

One CMM seems to read a little larger than the other. CMM B measures one feature 0.002" smaller than CMM A and CMM A measure a feature 0.0006" smaller than CMM B. One feature was exact on both CMMS, exact nominal and deviation, 0.000.

Essentially I copied the program from CMM A to CMM B and just adjusted some movespeeds.

Is this something normal? Operators at night sometimes will fail parts on one cmm and then take them to the other cmm and it pass so they pass the part through. I know they CMM will not match perfectly but they should be closer than 0.002". I'm trying to build confidence in the CMMs for the operators as its only be a few years of having CMMS.

Any advice or ideas on this?
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  • Sorry if some of this seems way too obvious, but when trying to get "tenths" out of comparisons, we should not assume anything.
    One thing I just thought of that I don't see specifically answered anywhere above: Are the two programs exactly the same?
    If not, then it could cause some of the problems.
    For instance, on a production part (not a ring gage) if the start points and end points on a circle are not in exactly the same place you could get very different results. Chatter, out-of-round, etc....
    Same goes for vector points.
    A production part is not like a ring gage or jo-block.

    Oh, one more thing...
    Could the two fixtures be different enough to cause issues?
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  • Sorry if some of this seems way too obvious, but when trying to get "tenths" out of comparisons, we should not assume anything.
    One thing I just thought of that I don't see specifically answered anywhere above: Are the two programs exactly the same?
    If not, then it could cause some of the problems.
    For instance, on a production part (not a ring gage) if the start points and end points on a circle are not in exactly the same place you could get very different results. Chatter, out-of-round, etc....
    Same goes for vector points.
    A production part is not like a ring gage or jo-block.

    Oh, one more thing...
    Could the two fixtures be different enough to cause issues?
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