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Measuring the same part on 2 CMMs, Different Results

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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  • , i must agree with you and all what you write above, but I just disagree with the word"uncertainty" that you use in MPEe first term. The MPE is a tolerance, not an uncertainty. It's only the deviation value that you mustn't exceed on a calibrated standard measurement.


    Jeffman, you are entirely correct.
    I employ the first term as a means to introduce the idea that the measurement device has a measurable amount of uncertainty in it's results.
    As I pointed out the effective uncertainty comes from many other factors like long styli, etc, but we begin with the tolerance the machine is supposed to hit when making beeps on a standard.

    I don't think I'll be able to submit anything else today.

    I'm in south texas and under hurricane warning. We'll be closed tomorrow and possibly Monday.

    Gonna spend the rest of the day backing up cmm stuff.


    Hey you're in my territory!

    Yep, looks like that "tropical depression" is picking up speed... good luck!

    Hit me up if you need to get this sorted out, I work with the Service guys all the time.

  • Have you been to the JSF assembly line in FW?
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