Z Calibration Drifting?  

Drift

A slow drift can be normal but it should slow to near nill change.  

drift

So a drift of half a mm in between prints is atypical?

Not normal, but may not be PINDA failure

Posted by: @ke88

So a drift of half a mm in between prints is atypical?

Definitely not normal. I'd make sure the PINDA probe isn't loose or moving before making too many replacements. Also check to make sure the support arm holding it is aligned properly and not sagging. Depending on the age of your printer, some of the earlier design revisions were prone to sagging.

R: Not normal, but may not be PINDA failure

Interesting.  I attempted to wiggle it after the first shift and it was very secure, however I will double check.  As for the age:  I purchased it around April or so.  Not sure if that pre-data any major design changes.

push

I would gently push it from the bottom and not pull on the wires.  

Posted by: @ke88

Interesting.  I attempted to wiggle it after the first shift and it was very secure, however I will double check.  As for the age:  I purchased it around April or so.  Not sure if that pre-data any major design changes.

Similar problem here

Hi, it is interesting, I have a similar problem here ( https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/first-layer-flow-problem/ ) but in the opposite way : Z-Axis seems too high each new print (?!)

SuperPINDA or PINDA?

Is yours a PINDA or SuperPINDA probe? Just to confirm: If you let the printer cool off completely between prints, do you still get the same problem? Conversely, if you lower the nozzle close to the bed and warm it before a print, do you still experience drift? The PINDA v2.1 and SuperPINDA were supposed to eliminate temperature variability, but I've been contacted by owners of both asking for help modifying the 2-step warmup procedure I've documented here. 

If the behavior of yours has changed, it's most likely a failing probe, but this is worth a check.

I've seen this a few times. Each time it was the PINDA loose in its holder. Didn't feel like it when I wiggled it but a quarter turn of the screw that holds it in place fixed it every time.

A few leads

Hi All,

I checked the holder and apparently the screw has wiggled out.  I resecured the probe and will run a recalibration.  If this solves the problem I will feel quite foolish 🙂  The only thing is that if the sensor was loose I would expect it to slip downwards which would result in sensing the bed higher up which would result in the first layer being higher not lower... More testing needed to see if it fixes the problem.

I'm pretty sure it's the SuperPINDA. 

Thanks for all the help so far guys!

Doesn't cost anything to just make sure it's tightly screwed in.

Makes total sense that it would drift closer - or further with a loose probe.  Imagine the probe slipping down enough to hit your print late in the print - it will knock the sensor higher.  Then it slips down and hits at another time... up and down we go.  Just tighten the screw and don't over-think it.

Great diagnostic check!

Posted by: @dan-rogers

Makes total sense that it would drift closer - or further with a loose probe.  Imagine the probe slipping down enough to hit your print late in the print - it will knock the sensor higher.  Then it slips down and hits at another time... up and down we go.  Just tighten the screw and don't over-think it.

That's a great explanation and a good diagnostic check. If it only goes lower and is not random, check out mechanical issues.

So far so good...

Hello all,

I reset the PINDA height and re-ran all calibration steps and am printing fine now.  I will watch for this behavior in subsequent prints and report back if it crops up again.  Thanks again all 🙂