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Understanding Calibration Results

TheBradish
I don't usually look at the probe calibration results because I don't really understand what I'm looking at. I'd really like to gain a firm understanding of the data and what it should mean to me.

I've been digging through old threads, and I'm getting closer. What I think I get is that StdDev is the standard deviation of single-point error of the measured sphere for each tip angle. (I was told by another inspector here that that number should be .0002 or less.) I also understand that the MEAS D determines the effective probe diameter for each tip, and is used for probe size compensation.

I don't fully understand the THEO/MEAS XYZ (where the THEO comes from, what the MEAS means), or what is a maximum permissible error. What do you guys look for when you read your calibration results? What do you hope to learn from the numbers? What do you consider to be a red flag?
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  • Looks like you're right about that. I just compared the difference in THEO Z for two of my probes (A0B0) and the difference in Z matches the difference in stylus length. I also compared the THEO Z of my master probe to the total length of my Renishaw hardware (using nominals from the Renishaw site) and they match within a couple mm.

    From looking at my results, it looks like my probe head might be slightly out of square. But if the qualification routine compensates for that, will it really make a difference? How much is too much? Here are some of my results for a 1x30 tip:

    .....


    Bolded above are questions that I wish I knew the answer to also. Slight smile

    One of my machines was retrofitted to Renishaw hardware and then upgraded again sometime later (several years before me). The PH10 shaft fits in a hole that is several thousandths larger than it, with a single set screw in the back to hold it in place. The part that holds it is a modified bracket attached to the Z-Rail. Between the two pieces, there is a crapton of slop with how the probe head actually fits. It is definitely not quite square, and I had to add a custom spacer in the probe build before the PH10 to get the height approximately right...

    I used the THEO/MEAS values to try to fine tune it. A0B0, and A90B(0, 90,180, -90) are enough to try to fine tune any skewing. But again, how close is close enough? If I only knew.
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  • Looks like you're right about that. I just compared the difference in THEO Z for two of my probes (A0B0) and the difference in Z matches the difference in stylus length. I also compared the THEO Z of my master probe to the total length of my Renishaw hardware (using nominals from the Renishaw site) and they match within a couple mm.

    From looking at my results, it looks like my probe head might be slightly out of square. But if the qualification routine compensates for that, will it really make a difference? How much is too much? Here are some of my results for a 1x30 tip:

    .....


    Bolded above are questions that I wish I knew the answer to also. Slight smile

    One of my machines was retrofitted to Renishaw hardware and then upgraded again sometime later (several years before me). The PH10 shaft fits in a hole that is several thousandths larger than it, with a single set screw in the back to hold it in place. The part that holds it is a modified bracket attached to the Z-Rail. Between the two pieces, there is a crapton of slop with how the probe head actually fits. It is definitely not quite square, and I had to add a custom spacer in the probe build before the PH10 to get the height approximately right...

    I used the THEO/MEAS values to try to fine tune it. A0B0, and A90B(0, 90,180, -90) are enough to try to fine tune any skewing. But again, how close is close enough? If I only knew.
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