I can't get a good first layer anymore

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aidtopia

(@aidtopia)

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I can't get a good first layer anymore

I'm out of ideas.

I had no problems for hundreds and hundreds of prints over several years with my MKS3+, but now PETG prints always fail and PLA prints almost always fail. Failure takes different forms.

It's usually a first layer problem, but first layer problem doesn't really narrow it down much. Sometimes the bead doesn't stick at all. On other attempts it sticks in most but not all places. Sometimes it sticks everywhere but is of inconsistent thickness.

Most often there are sharp stalactite-like peaks that will catch the nozzle on a later layer. These are more frequent and more pronounced with PETG than with PLA. But PLA also gets large blobs of plastic plopped here and there, which are also likely to catch the nozzle a layer or two later. (Photos below.)

The problems began several months ago about half way through a spool of PETG. Prints would fail hours in, resulting a blob on the nozzle and heater block. After cleaning and retrying, it failed again. And again.

I have tried:

Cleaning the build plate more thoroughly than my usual IPA wipe-down.
Using the other side of the (textured) build plate.
Using a new build plate.
Loading fresh filament.
Re-doing first layer calibration (many times).
Cleaning the nozzle (externally, cold pulls, and using "cleaning" filament).
Cleaning out the extruder and checking the alignment of the gears and the tension.
Repeating all of these above with PLA on a smooth build plate.
Replacing the nozzle (for the first time ever), which led to the discovery that my hot end had been leaking internally. (It was a factory-assembled machine and it had worked for years, so I cannot explain how the heater block was not screwed all the way onto the heat break.)
Replacing the entire hot end, including the PTFE tubing.
Cleaning and lubricating the entire machine. Checking the belt tensions, and rerunning the full calibration.
Checking the heated bed with an IR camera to ensure it heats evenly.
Running first-layer calibration again and again, sometimes getting very different results even when I don't change the z-offset.

I've looked through a visual catalog of printing problems, but I haven't found anything that looks like the sharp peaks of PETG or the random blobs of PLA. Those inevitably catch the nozzle on a later layer, which seems to be the most common cause of print failures.

Flat areas often get spiky, which will catch the nozzle on future layers.