Cylinder probe calibration issues

It changed again when I calibrated it. It went back to almost the same #s as before. I knew it wouldn't be good because I could see it going around the sphere above the equator.



Hit "Reset" and cal'd again and got...

Sometimes probe files get corrupted. I would delete the probe and recreate it.  Also it's good practice to always "reset tips" before each calibration.  If you use the probe builder wizard make sure your geometry matches the actual probe.

Rusty91307  As I've mentioned before, there is a 1mm offset being introduced to the length from somewhere.  The THEO length is 13.075mm.  The first time you calibrate after resetting the tip, The MEAS length is set to the same as the THEO and PC-DMIS uses that length to drive the tip around the cal sphere.  It then updates the MEAS length to what was actually recorded during the calibration which is where your 1mm offset gets added in.  The next time you calibrate, PC-DMIS uses the updated MEAS length to drive the probe around the sphere and it tries to take hits 1mm higher up.  Because it is a flat bottomed cylinder, rather than a sphere, the corner of the cylinder hits higher up the sphere and the diameter shows out.

.

This can ONLY happen if one or more of the components making up your probe build has a different physical length than the one that is defined.  You have previously told me that you've measured your cylinder component and that it has the correct length, what about other components - extensions, probe module, indexing head, adaptors between the head and the Z ram?  Have you looked at the results for all of your other probe builds to see if any of those have differences between their THEO and measured lengths?

The clue here is "calibrating ABOVE the equator". What you are seeing is a difference between the RADIUS ground on the end of the stylus versus the diameter of the cylinder. I have three cylinder probes and all have LARGER diameters ground into the RADIUS than that of the cylinder. I was able to confirm this on an optical comparator at 50x. In all three cases the diameter of the radius is about 30 to 50 microns larger than the diameter of the cylinder. In all likelyhood... the center of the radius won't exactly align with the center of the cylinder. I haven't checked it on mine. I only use them on a manual Cordax 1805 with Measuremax. I NEVER use them on our FX7.10.7 under PC-DMIS. The results aren't accurate.

If you are only interested in Z readings, why are you using a cylinder stylus?

N8VES , Regardless of whether the diameter is larger near the end, the underlying problem is as I mentioned above.  When PC-DMIS performs a probe calibration, it is the hot-spot of the probe stylus that is instructed to take points.  For this particular stylus definition, that hot-spot is 1.5mm back from the flat bottom (imagine a sphere that is the same diameter as the cylinder with the bottom of that sphere sitting flush with the flat bottom of the cylinder).  The only way for it to behave in the way Rusty91307 is describing is for the length to be incorrectly defined.

ITEM:TIP3BY13MM_CYL_PART_268 M2
EffectiveWorkingLength 13.0
begintip
ribcount 10
color 80 80 80
cylinder 0 0 0 0 0 -2.5 3
cone 0 0 -2.5 3 0 0 -5.5 2.0
color 80 80 80
cylinder 0 0 -5.5 0 0 -7.5 2.0
cone 0 0 -7.5 2.0 0 0 -9.0 3.0
cylinder 0 0 -9.0 0 0 -12.8 3.0
cone 0 0 -12.8 3.0 0 0 -13 2.8   <-- Why is there a cone here? 
sphere 0 0 -11.5 3.0
hotspot 0 0 -11.5 0 0 1 3.0 3.0 shank
endtip

No Cone?
ITEM:TIP0.5BY15.25MMSHNK M2
begintip
ribcount 10
color 142 142 142
cylinder 0 0 0 0 0 -2.5 3
cone 0 0 -2.5 3 0 0 -7.5 1
cylinder 0 0 -7.5 0 0 -10 1
color 255 0 0
cylinder 0 0 -10 0 0 -15.25 0.5
sphere 0 0 -15.25 0.5
hotspot 0 0 -15.25 0 0 1 0.5 5.25 shank
endtip

Because there is a 0.2mm chamfer at the end of the stylus...

As I said before, the contact points when taking hits with this probe should be the hot spot.  You can only probe straight down (along the axis of the stylus - square to the flat) or radially (90° to the cylinder axis).

...Yup totally missed it went from 3-2-2-3  
I have only every used cylinder probes with a full radius on the tip though.

I checked the shop, there were 2 kinds of cylinder stylus: One with round end ( like a half sphere )and the other not

I also have only used radius tipped probes. That does make it a lot clearer, Neil, Thanks. I'll have to play with mine and see if I can get it to make contact in the hot spot zone. Will be interesting to see the results. I had a cylinder probe similar to the one you have pictured. Ruby instead of carbide. Originally it had a radius ball glued to the end of it and it fell off. If I can find it, I'll try to calibrate it in PC-DMIS.