Autoleveling with PETG

I’ve started to get good PETG prints - with the one glaring issue that when PETG is in the nozzle, autoleveling on my Mini works incredibly poorly. It’ll make contact, but only after bending the tip up / bed down, so that the resulting calibration is incorrect. It requires me to very carefully watch the sequence, see if any of the 4 don’t hit exactly, and then cancel the print and restart it after scrubbing the nozzle again. If I don’t catch it, it’ll end up dragging the nozzle along the PEI and damaging it.

Autoleveling is quite reliable with PLA.

Has anyone figured out a way around this problem?

PETG seems to be quite “sticky” and doesn’t seem to clean off the way PLA and ABS do… instead of peeling off of the nozzle on the cleaning pad, the PETG seems to just end up smearing all over the tip.

The trick I’ve found is to ensure that the nozzle is thoroughly clean manually, before letting the firmware run the cleaning/probing sequence.
a) Ensure that the tool head is pre-heated, and once at temp, retract a few mm of filament. Skip this step if you’ve just completed a print, because the stock firmware has already retracted the filament a bit. This helps to lessen the chance of filament oozing out.
b) Pre-heat the extruder to the cleaning temperature.
c) Use the tweezers to “snip” off any filament that you can, being very careful to avoid the block and those wires (!).
d) Use a scotch-brite pad (non-metallic) to scrub off the tip of the nozzle. I use the tweezers as a “feeler” to assess the cleanliness of that tip; you can generally feel the difference between a small layer of softened PETG vs the brass nozzle. Again, use care to avoid the wires on the block.
e) Repeat © and (d), until you’re quite sure that it’s clean.
f) Start the print, keeping a close watch on the probe sequence, and abort it (and redo this procedure from (a)) if there’s any visible bounce on the washers when the nozzle retracts from the probe point.

Using this strategy, I’ve had nary a single bed leveling failure with any of the PETG and T-Glase prints I’ve done.

I bought a 3.5 inch concave mirror at the grocery store for less than $5. Combine that with a small LED flashlight and you can examine the nozzle for debris quite easily.

Like said before by mwester I closely watch probing when printing with PETG, retract enough before probing, clean it.
I do it manually with fingernails when PETG is hot (180C), it comes off like gum. it’s hot but doable if done in one swift move :wink:

It turns out my biggest problem was the ooze continuing after I wiped the nozzle. Retracting a lot sorta worked, but I found the most reliable thing was to preheat the nozzle to 240C and let it sit there for 10 minutes to let the ooze finish before wiping and starting the print.