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.
What should I try or check next?
RE: I can't get a good first layer anymore
I've had my Mk3S for 6 years, the pinda probe would move over time until I finally used purple thread locker. Had to reestablish my z offest too many times. Thier zip tie method to get the generic placement, but you need then run live z tests to dial it back in in. I used a different file to get the live Z, never found the built in very good. See below.
Setting the live z too low will create build up on the nozzle, which will then drop off onto your print, not so much PLA, but very much PETG.
Wet PETG will also not stick properly.
When swapping from PLA to PETG, need to purge alot. Saw that often, 1st layer would fail on next print and then be fine for following prints.
Also to aid in the blob issue.
Nozzle getting overloaded and then dumping the plastic in a single spot. This was common on printer, keep your nozzle clean before all prints, sit and wait, grab the ooze with tweezers just before the nozzle hits the build plate to probe. I also found a 1 layer skirt for all prints helped.
Also this one speed change on the start g code helped alot.
G1 X60.0 E9.5 F850.0 ; intro line X Position E Material extruded F (was 1000) Speed
RE: I can't get a good first layer anymore
The PINDA is rock solid. After installing the new hotend, I tried to follow the steps to set the height of the PINDA. I couldn't adjust it at all. Even if I completely remove the M3 screw that clamps it into place, I cannot get it to budge. It feels like it was glued in place at the factory. Fortunately, it seems it's at the suggested height. I can just barely push a zip tie under it, and its height relative to the nozzle appears exactly like the reference photo in the instructions.
The first-layer calibration pattern could've been designed a lot better. I never thought to use Live-Z with a better pattern. I'll try that. Thanks.
I have suspected that part of the problem is the mesh leveling, since there are two places that never seem to adhere well: the front left corner, and the extreme right edge about halfway back (regardless of build plate or filament type). I've wondered whether the auto-leveling is under- or overcorrecting in those areas. There's no warping I can detect visually or with a straight edge. I tried switching the auto-leveling to 7x7, but that made no difference. I'd love to see the actual measurements the sensor is reporting for each point in the sampling grid. It surprised me to learn an inductive sensor can precisely measure the build plate height in the vicinity of the magnets that hold it in place.
But a mesh leveling problem wouldn't explain those sharp peaks that are especially prominent with PETG. If they occurred where the head changes directions or the extruder retracts, I could understand them. But they are all toward the middle of straight segments used to cover an area. It's like there are localized bubbles of air trapped between the plate and the filament that expand from the heat until they burst free.
I don't frequently change materials. Since replacing the hotend, I switched to PLA (and then back to PETG) only to rule out possible causes of the problem. I do purge generously when I switch materials.
You said wet PETG doesn't stick well. By "wet," I assume you mean PETG that has absorbed moisture from the air. I considered that, which is why I switched to a fresh spool.
RE: I can't get a good first layer anymore
Fresh spools may not be dry either, to limit variables, dry the spool. But that is not likely the cause.
In both your pics, looks to me, you don't have the z offset set correctly, nozzle is too high, therefore it doens't stick to the plate and pulls up, and some sticking to the nozzle, which then blobs off. Use the Live Z file I linked, you may have to print many of them, you'll learn alot, may feel like reading tea leaves at 1st, but it is a skill worth mastering. Take the nozzle so low to the point it starts making micro groves into the squares, then bring the nozzle up until you have smooth to rough squares. You can feel each square with a finger while it is going, and make live adjustemnts, save alot of time. Then once you have it close start doing to full review of the print like I show in close-up pics, especially using the light.
RE: I can't get a good first layer anymore
Also your z offset will change with each plate you use if they are different thickness. Also a textured plate will always require a lower nozzle than a smooth plate to get enough surface contact. I kept a list with all of my live z adjustments per plate type. You can change it in the printer directly each time you swap plates or you can adjust by creating a new printer profile for each plate type in the slicer and adjusting the offset there.
the pinda probe would move over time until I finally used purple thread locker.
The OP's first layer doesn't look too far off ... a loose pinda seems unlikely; with ordinary filaments Z recalibration will be needed every two or three months as the nozzle wears, it's only if it's more frequent that the pinda is suspect.
Whilst I agree with @ruebarb in that the first layer squish isn't perfect I don't think it's far enough off to cause the issues here ... and it's not the blobbing that concerns me.
There is an odd, regular, judder in the surface of the first layer perimeters that I've not seen before; there are hints, 'though out of focus, that the first layer fill might show the same symptom.
I don't know what might cause this but my first thought would be to check the bearings in the extruder idler and make sure the extruder motor turns smoothly (if turned by hand you should feel gentle 'cogging' - the steps of the motor, but nothing sharp or grating) - this is only a guess.
I would like to see the pattern from the built-in first layer calibration, *on the print sheet* as it's the diagnostic we are most familiar with.
Cheerio,