PETG printing perfectly for weeks, overnight switches to failing 100% of the time
I got my new MK3S a few weeks ago. When I received it I immediately switched it over to Prusament black PETG to make spare parts for it, and I finished all the black parts with perfect quality. I started making parts for the Ikea Lack enclosure v2 about a week ago, and immediately got an X axis crash problem. This was solved solved by lubricating the rods with a thin coating of 3-in-1 oil which I've been very careful to avoid getting near anything except the rods, and it's been running perfectly again. Until 2 days ago. I set a part running for 4 hours in the evening, finishing at midnight. It printed perfectly. I tried to print another part the morning after, and it failed the first layer dismally. And so has every other print attempt since. I have changed nothing. The filament is the same, the settings are the same, the files were sliced at the same time, the ambient temperature is the same within a few degrees, but it keeps failing.
It does the pressure stabilisation sweep at the start, and then starts laying down the skirt. At random points, only about half the filament sticks to the plate. The rest just globs up onto the nozzle until it gets dragged off onto the print. As the nozzle continues around the plate, the filament is at best 50% adhered to the plate, but where it is adhering it is firmly down with perfect print quality.
The Prusament PETG reel says on the side 250°C. The default setting for that filament in PrusaSlicer is 240°C for the first layer only but that's not concerned me because every print has been perfect at this setting up until now. I clean the textured plate with 90%+ isopropanol on kitchen roll before every run, and allow it to dry. I make sure the nozzle is clear of debris (which there is now a lot of after every failed run) by heating it and gently removing it with a brass wire brush and a small pair of needle nose pliers beforehand. Whether I start a run cold or get it preheated using the interface to 230°C (default PETG preheat) or 240°C (manually set) before starting, the result is the same. If I do preheat it, filament starts to slowly extrude out of the nozzle by itself. It often develops a curl about 1mm in radius and tries to stick to the nozzle but if I guide it down then the extruded filament runs smoothly if I manually increment the extruder value. When I start the run, it does the 9-point bed level check. Sometimes the extruder is still oozing a little bit and it squishes the excess filament onto the nozzle, but even if I wait for the pressure to equalise and remove the excess filament up to the tip so it starts the bed level check with a completely clean nozzle, it still fails at the first layer.
I have no idea what could affect print quality so dramatically like this overnight. Does anyone have any troubleshooting tips to try track down the problem?
Best Answer by --:
With the powder coated sheet - soap and water is often needed in the initial weeks of use. Something in the PEI spatter comes to the surface and contaminates the surface; soap and hot water seem to work well to remove it. Alcohol, not so much.
Prusa advises against washing with water due to rust: but many have found it to be the only way to get material to stick reliably. So after washing, it is important to heat dry the sheet to remove all moisture; bake it at 80c for 30 minutes to ensure the texture is completely dry. Also, once cleaned this way, subsequent cleans with alcohol seem to work well enough.
RE: PETG printing perfectly for weeks, overnight switches to failing 100% of the time
Hello Mathew
I had the same situation when i first started with my mk3.
Turns out what worked for me was every so often a light scrub and wash of the pei build plate with dish soap.
It seems i must have touched the build surface to much with my hands and the ipa only was not enough.
Good Luck
RE: PETG printing perfectly for weeks, overnight switches to failing 100% of the time
Your Z-level appears to be too high, so the filament "rolls" up and sticks to the nozzle. So you should slightly adjust the Z level down.
If this does not help, clean the steel plate from grease stains (fingerprints) with detergent and warm water.
Isopropanol can be used between the prints, but it is not so good at removing greasy fingerprints.
Bear MK3 with Bondtech extruder
RE: PETG printing perfectly for weeks, overnight switches to failing 100% of the time
With the powder coated sheet - soap and water is often needed in the initial weeks of use. Something in the PEI spatter comes to the surface and contaminates the surface; soap and hot water seem to work well to remove it. Alcohol, not so much.
Prusa advises against washing with water due to rust: but many have found it to be the only way to get material to stick reliably. So after washing, it is important to heat dry the sheet to remove all moisture; bake it at 80c for 30 minutes to ensure the texture is completely dry. Also, once cleaned this way, subsequent cleans with alcohol seem to work well enough.
RE: PETG printing perfectly for weeks, overnight switches to failing 100% of the time
It wasn't entirely apparent from the image I posted (I've now figured out how to post images at a reasonable size!) so I've reposted it larger - The Z-level looked okay on the part at the back where it adhered, and the section in front of it where it looks like poor Z-level alignment is actually support structure that is adhered correctly as well. It's supposed to have mirror symmetry left-to-right so you can see the second part was a complete failure.
As such, I assumed Z-level was not the problem so put some gloves on and washed the steel sheet gently with a tiny bit of diluted washing up liquid and a very soft brush, then dried it with kitchen roll, and it's working fine again - I assume the surface was beyond the capacity of isopropyl alcohol to clean. Or I put the sheet on the other way up and the flip side is still dirty (I completely forgot it was double-sided until I removed it to clean 😓). In either case, it's working fine again on the first print attempt afterwards. Thanks for the help, everyone 😊
RE: PETG printing perfectly for weeks, overnight switches to failing 100% of the time
You are more gentle than me. I scrub it with lots of Dawn and copious water - and my bare hand.
Then lots more water to flush off the soap, and scrub dry with a fresh paper towel.
I only wash immediately before a print, so final dry is on hot bed.
For all their sins - these sheets are pretty tough.