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The Hermit
I'm not currently at work, so I can't recall the exact model of my probe. I think I'm using the HSPX (?), with the large, magnetic base, maybe 1.75" diameter? I'm sure many, if not all of you have had this happen at least one time, if not many, many more. When you rotate, your probe catches the part, the fixture, or even the side column on the cmm and knocks the probe off. Here's my question. Do you automatically recalibrate, or do you kind of base it off the tolerance of whatever you're checking? I'm just curious how others approach this.

Thank you
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  • well, if it is opinions you want, the internet is definitely the right place to come...

    So that I'm not working with a probe that bends or fractures, I use primarily ceramic, so it doesn't survive hitting something when rotating the head.

    If it was steel, and would survive, I would clear the results for the entire build and requalify. If it bends, not only will it be off when you use it, but it won't relate to the other probes at all. Every measurement you take between probes will be wrong.
    Are they enough "wrong" to matter with your tolerance? I couldn't tell you, but I'd requalify the entire probe build if I had a probe survive that.

    I don't requalify more than every couple months.
    I know a lot of people are going to scream I'm a heretic and want to burn me at the stake as a witch. Sorry.
    Going in to that decision is the fact the CMM is next to me, and no one uses it without my supervision. Ever.
    That doesn't mean I micromanage what they are doing, it means I know if they crash or spin the head and knock the probe off.

    I have far more problems letting them requalify, where they don't qualify the master probe first saying the sphere moved and then say no on every other qualification, so the ****ed rack doesn't relate between probes and it takes me an hour to prove that to them. Then I have to clear the results from the rack, which costs me time. A lot of time. We have nine probes in the racks. It is painful to qualify.

    That said, we also compare results between different machines.
    Sure, not qualifying can cost you accuracy, but three machines aren't all going to lose qual in the same vectors as each other, so when the results match, you are safe.

    If people from the floor ran the machines, or if we had a night shift or something, I'd qualify a lot more since I wouldn't know what was happening with my machines all the time.

    To your question about tolerance, going down that road means you are allowing uncertainty, due to a large tolerance. This is acceptable to me.
    If you are allowed .020, and you measure .0199 are you saying the part is "bad" and verifying with something that has the uncertainty required to report a value that close to the limit?
    If you are going down this road, you should either review EVERY output and remeasure anything close to the limit, or adjust the limit. Allow .016 instead of .020. If you get .0159, you're in. If you are over .0161, adjustments need to be made, or you need to measure with another tool for correlation.

    As you calibrate once a month, it likely would have a much greater impact if you didn't recalibrate after dropping a probe. We calibrate per part, per shift, only calibrating the angles for that part. So though a probe may occasionally get knocked off, it's specific to the part it's being used on. I have not given my opinion, but it is that you don't "have" to recalibrate, unless it's a tight tolerance part. In twenty years, I've never actually seen a steel probe bend from a 6" or 7" drop. If it happens to fall on the floor however, that's quite a distance and would get recalibrated. If we're looking at features with a 0.020" positional tolerance, and dropping a probe makes the difference between 0.010 or 0.015, the part is still in tolerance, and I save calibration time. No foul, no harm. It will be calibrated again the next time it comes in. If it's out of tolerance, then that would require a recalibration and recheck. I'm speaking production parts, not PPAP's.
  • in reply to The Hermit
    When a TP20 gets knocked loose, it is often no issue what-so-ever. Sometimes, even with the ceramic, it doesn't matter (if the probe is close to the table).

    The HP-S-X1H probe on the two new machines, the magnets are SOOO much stronger. The ceramic sometimes shatters without the holder even popping off the probe.

    But, no, a short drop is also a deciding factor, I've had the head up and dropped the probe 25-30 inches, which ends badly more often than the short drops.

    So, height of drop is another area where a little common sense can go a long way on determining your actual risks.
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  • in reply to The Hermit
    When a TP20 gets knocked loose, it is often no issue what-so-ever. Sometimes, even with the ceramic, it doesn't matter (if the probe is close to the table).

    The HP-S-X1H probe on the two new machines, the magnets are SOOO much stronger. The ceramic sometimes shatters without the holder even popping off the probe.

    But, no, a short drop is also a deciding factor, I've had the head up and dropped the probe 25-30 inches, which ends badly more often than the short drops.

    So, height of drop is another area where a little common sense can go a long way on determining your actual risks.
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