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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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  • I know how to adjust move speed us using code but shouldn't the machine settings match as well? Like should both be using absolute speed or have the same acceleration speed as well? Can that be adjusted with code instead of messing with the machine settings?

    Yes! Both machines should have all settings identical. "Use absolute speed" is a program setting. (on FDC control with v2014 anyways) So in my experience, if you've checked that box it will be in place for both machines. 5mm/sec is pretty fast for touchspeed, but if you're using it on both this shouldn't matter. Its possible that the machines are defaulting different acceleration ans move speed. You can set this in the program using the ACCELERATION (or is it just ACCEL) command.

    You're absolutely correct in thinking that all machine settings must be the same.
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  • I know how to adjust move speed us using code but shouldn't the machine settings match as well? Like should both be using absolute speed or have the same acceleration speed as well? Can that be adjusted with code instead of messing with the machine settings?

    Yes! Both machines should have all settings identical. "Use absolute speed" is a program setting. (on FDC control with v2014 anyways) So in my experience, if you've checked that box it will be in place for both machines. 5mm/sec is pretty fast for touchspeed, but if you're using it on both this shouldn't matter. Its possible that the machines are defaulting different acceleration ans move speed. You can set this in the program using the ACCELERATION (or is it just ACCEL) command.

    You're absolutely correct in thinking that all machine settings must be the same.
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