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Master Probe

Scott Brown
Good Afternoon

I have read a number of posts regarding probe calibration and using a Master probe to relate multiple probes. I have a few questions that I did not find the answers in the posts.
Question #1 - If you are using the Master probe for measurement does it affect the relationship of the other probes if you re-calibrate A0/B0 of the Master Probe after answering "N0" to the calibration sphere move. For example - Start of shift the Master probe is calibrated at A0 / B0 and you answer "Yes" the tooling sphere has moved. Now you open a program that uses the master probe for measurement. You want to perform a calibration on the angles that are used in the program. Perform a Marked Used which includes A0/B0. You answer "No" the tool has not moved and perform calibration. Is the relationship of the other probes and angles lost???

Question #2 - Is it necessary to calibrate Master Probe every time the machine is homed??

PC-DMIS 2014.1

Thanks for your help
Scott
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  • #1
    What are you expecting to gain by re-calibrating the master probe as a 'normal' probe? The only effect I can imagine is that you add one level of uncertainty to the relation between master probe and the other probes, making everything worse. First you create a relation between master, datum and other tips, then you change the master - why should that make anything 'better'?

    Probe calibration is not some magic that makes the probe (or machine) 'better' - it is the way to have a consistently known relation between everything that is used during the measurement, and that means that any change somewhere in the middle of the calibration chain breaks the chain at that point. Depending on your tolerance needs, the break may be insignificant, but it is still a break.

    It might be a good idea not to use the physical master probe too much for daily work, to minimize the risk of damaging it. And always reset it to THEO before locating the datum sphere!

    #2
    As for the question about homing, it might differ between different CMM:s. If the CMM claims 'absolute scales' it shouldn't be necessary; if it's a homing CMM it depends on the quality of the 'home detectors'. It's easy to do a little experimentation and find out what goes for your particular CMM(s), or you take the easy way out and treat all CMM:s the same and say "yes, it is necessary". Depending on your tolerance needs, the deviation may be insignificant, but there is probably still a deviation.
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  • #1
    What are you expecting to gain by re-calibrating the master probe as a 'normal' probe? The only effect I can imagine is that you add one level of uncertainty to the relation between master probe and the other probes, making everything worse. First you create a relation between master, datum and other tips, then you change the master - why should that make anything 'better'?

    Probe calibration is not some magic that makes the probe (or machine) 'better' - it is the way to have a consistently known relation between everything that is used during the measurement, and that means that any change somewhere in the middle of the calibration chain breaks the chain at that point. Depending on your tolerance needs, the break may be insignificant, but it is still a break.

    It might be a good idea not to use the physical master probe too much for daily work, to minimize the risk of damaging it. And always reset it to THEO before locating the datum sphere!

    #2
    As for the question about homing, it might differ between different CMM:s. If the CMM claims 'absolute scales' it shouldn't be necessary; if it's a homing CMM it depends on the quality of the 'home detectors'. It's easy to do a little experimentation and find out what goes for your particular CMM(s), or you take the easy way out and treat all CMM:s the same and say "yes, it is necessary". Depending on your tolerance needs, the deviation may be insignificant, but there is probably still a deviation.
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