Filament Jams on Slow/Low Layer Height Prints
I've found that if I slow a 0.2mm layer height print down to about 75% of a 45mm/s print speed, the extruder will start clicking and clogs. I do this because when printing small object with sharp corners, those corners tend to get pulled up on the first layer if the print speed is too high.
The clogging also occurs if I try to print 0.1mm layer heights at 100% of a 45mm/s print speed. It will go fine for a while and eventually start clicking and I have to kill the print and unload the filament. I've never had to clean out the nozzle and just reloading the filament seems to clear any issue until the next print.
Clogging does not occur when printing 0.2mm layer heights fast, during the filament load step, or if manually extruding from the LCD. There's no curling of the filament at the nozzle tip and everything seems to flow nicely out of the nozzle. It appears that it's low extrusion rates that are causing the problem. Chat support tells me that I should print at 0.15mm as my minimum, but I don't find that solution acceptable on a printer that's supposed to be able to print at much lower layer heights. Any ideas?
In case anyone else in the future has the same problem, what ended up working for me is applying some thermal compound to the threads on the heat break. I found this solution mentioned in a couple different places from people who seemed like they were having the exact same issue as me: clogged prints at low layer heights or slow speeds. From what I've read, heat creep causes a blob of filament to occur at the end and it stops feeding into the nozzle. This blog is something I've noticed since I received the printer and it's gotten stuck a few times when removing filament.
Talking with the Prusa chat support before I took my hot end apart, I was told that they apply thermal compound at the factory, and that I shouldn't need to do that. When I took my hot end apart, I didn't see any evidence of it. Maybe they don't put much on or clean off the excess really well, but the threads looked pretty bare to me. After I applied some compound I had as directed in the E3D assembly instructions, the problem seems to have gone away and I have a 0.1 mm print running right now, hours after previous prints would have already failed.
I am so glad I found your post. I am printing with the Prusa MK3 for months with the same PLA Filament, same G-Code files and all of a sudden the prints stuck when there where small details and also on the top surface sometimes. Basically everything printed slow and with lots of retracts.
And exactly as you described I could unload and reload the Filament and it worked for a while. The nozzle was never blocked.
First I replaced the Nozzle, then the heat brake and also the complete hot end. Nothing seemed to fix the issue. Then I replaced the extruder motor as it got very hot compared to the other stepper motors. I also replaced the bond tech gears. Everything that has to do with the extrusion.
Nothing fixed the issue and I was really desperate.
I would have a question to the thermal compound you used. What type was it and did you apply it on the end in the heat block to the heat sink, or both?
I have to admit that I am a little disappointed that the new hot end that I ordered from Prusa did not have the Thermal Compound applied. As it apparently did not fix my issue.
I will defently give it a try with the thermal compound and report if it fixed my issue.
Thermal compound gets applied to the longer part of the heatbreak i.e. in the heatsink only
If you need pictures to know where to apply thermal grease, here is one: https://help.prusa3d.com/en/article/extrusion-stopped-mid-print-heat-creep_1948
Having the same problems since printing with automatically generated layer heights.