[sanddrag]

I've always had the Renishaw probe in our machine, and it's offset has always been 5.5149. To the best of my knowledge, it's never been crashed. We've never ever replaced the tip on it. After making several parts that were coming out about .016 low in the Z, I checked the spindle probe offset, and it was indeed off. I recalibrated to the OTS on the table, and wouldn't you know it, the spindle probe offset is now 5.4995.

What would or could cause the spindle probe offset to become less all of a sudden?

[haastec]

I've always had the Renishaw probe in our machine, and it's offset has always been 5.5149. To the best of my knowledge, it's never been crashed. We've never ever replaced the tip on it. After making several parts that were coming out about .016 low in the Z, I checked the spindle probe offset, and it was indeed off. I recalibrated to the OTS on the table, and wouldn't you know it, the spindle probe offset is now 5.4995.

What would or could cause the spindle probe offset to become less all of a sudden?

You said that you recalibrated the OTS. Did you verify that the stylus of the OTS was flat? Is the center of the stylus pitted from use? Did you verify that the gauge length of the calibration tool is correct?
If none of these questions are an issue, then run your calibration sequence again, making sure that the machine is adequately warmed up.

Good luck!

[sanddrag]

I did not recalibrate the OTS. I used the VQC routine for calibrate spindle probe length, where it takes the Renishaw work probe and touches it to the OTS. I'll sweep the OTS with an indicator and verify that it is still flat.

[haastec]

I did not recalibrate the OTS. I used the VQC routine for calibrate spindle probe length, where it takes the Renishaw work probe and touches it to the OTS. I'll sweep the OTS with an indicator and verify that it is still flat.

You need to recalibrate the OTS, not just sweep it.

[sanddrag]

Ok, I recalibrated both through IPS, and now my work probe length offset is 5.6189. Substantially different from where it was originally, but perhaps it's because I'm referencing the spindle housing nose where the sunken socket head cap screws are, and perhaps when it was set up they referenced the part of the spindle that turns with the drive lugs on it. Would that be a difference between now and then?

Still not sure why it ever changed by about .016 but, when I probe the work probe to the OTS through VQC, the offset is within .0002 of what it was when calibrating through IPS. Also, when I probe a tool, and I probe a known surface, the tool goes to the proper height of that surface within .0002, so I think I'm good.

Could anything a technician may have done during a Preventative Maintenance procedure caused the spindle probe calibration to be off?

[haastec]

Sometimes a probe system will go years without any issue and other systems seem to require calibration on a more regular basis. What causes it? There could probably be a whole physics lesson on why, but my opinion is that it is just due to the many various machine vibrations. I wouldn't dwell to much on it.

Just remember that anytime you have something odd happening with the system with regards to it's accuracy, the first thing you should do is recalibrate and see if the problem is fixed.

[erikfriesen]

Are your tools measuring the same as they were? It's easy to move the ots top if you are working around it and not paying attention, and it's slightly loose.

[HFO Tech]

You have to recalibrate both systems. IPS and VQC

[erikfriesen]

@HFOtech I'm not sure that is right, I rather think both use the same underlying renishaw routines.

[HFO Tech]

In theory yes you're right, but I've seen on some rare occasions that you have to do calibrate both systems because it doesn't transfer over.

[erikfriesen]

They both use 9802 and 9803 as near as I can tell.

[HFO Tech]

Also, do you keep the probe in the tool changer or do you hand load it? If you hand load it are you calling up the right tool number before you start the probing process? I've seen some people calibrate the probe as the last tool in the carousel, but leave it out of the machine. Next thing you know you run tool 1 through whatever and you complete your part. So you still have the wrong tool in the spindle, but you take that one out and load the spindle probe. Which is looking at the wrong tool offsets for the probe. Just throwing that out there just in case.

[erikfriesen]

I figured out the other day that my OTS was moving slightly. IMO the renishaw way of tightening the OTS to the base is faulty. To get the thing to quit moving with an indicator on it, I had to tighten the setscrews way beyond what the designers should ever have thought acceptable.