printing in single mode with 0.25 nozzle
I recently assembled an mmu2s and after solving some initial issues i started having some succesful prints. So i gave a try using 0.25 nozzle on MMU2S single mode. My first print was ok ( a miniature with 0.05 layer height) but after that most of my prints encountered the same problem. About an hour in the print i get under-extrusions that some of them result on jam and other on really bad prints. The one with the jams deform the filament. I tried cold pulls before each print, +/- up to 15 in temps, reducing retractions, reducing volumetric speed down to 8 for PLA, increasing speed, increasing speed only in infill, reducing speeds individually, printing with PETG, printing a stepper motors (extruder) "base" and attaching a fan to reduce creeping heat, printing with 0.07 and 0.1. More or less i get the same results. I printed different stls. When i print lets say a small miniature chest on its own with completion time of <1h it prints successfully so its not the model. When i add another two instances that print longer i get this issue. I was reading about changing the heartbreak but i don't want to cause future problems with the, already finicky, loading/unloading of a mmu print.
Does anyone have a clue to what else it may be?
More often then not when I see results like that, its temperature related. Are you printing in an enclosure? The trapped heat can cause the filament to soften and the extruder teeth will chew that up. The longer the print, the more heat gets trapped.
I have been printing with a 0.25 mm nozzle on my MMU2S in single mode almost exclusively (5-8 hour prints) without any failures like that. I print with the default, official 0.25 mm Single Mode MMU2 profile, through Prusa Slicer with MatterHackers PLA at 210/205 c.
I tried a temperature range between 200 and 225 in increments of 5 for PLA with no noticeable improvement. I tried with prusament and filamentum PLA. After reading a lot of similar problems my hypothesis was the same as yours.. heat creeping and softening pla. But the strange part is that it also happened with PETG. That why i installed a fan and a small hetasink on the motor. The tem was substantially decreased but the problem was still there (i gained a few layers but that was all). I noticed though that with reducing the retraction length the problem worsened so i increased it to 1 from 0.8 which is the default. I got a slight improvement so i went up to 1.2 and this is where i got a successful print. This was also evident from trying to print a miniature using 0.25, PVA and PLA with mmu2 since the multiple retractions/ loading unloading didnt allow for a clog to form . But one successful print doesn't mean that i found the problem. I'll try a few more print during the weekend.
I dont print in an enclosure but is kinda hot here (40C during midday and around 20-25 during nightime). I also used a silicon sock in my hotend. If this print was only an exception i really dont have a clue what to do next. I'm thinking of changing my extruder for a bondtech bmg reducing this way feat creep problems.
Assuming you have checked the habitual options, that it seems you have done that work already (clean nozzle, bondtech door tension and so on), try decreasing a little bit the extrusion multiplier, can be a pressure build up, the thinner the layer you are trying to print more impact has the calibration.
You can also check the z axis and extruder steps, but I think that on the mk3 they are fine as default, but just to try another options.
40C during the day is pushing the upper limit of the extruder cooling, try doing your long prints overnight, at least till the daytime temps are cooler
The heat creep problem was solved after installing a bmg bondtech extruder. i even installed a heatsink and fan on this one too (not needed anyway). Printed 4 miniatures at 0.05 with no layer skips.
Going to one of the geared extruders avoids transfer of extruder motor heat down its shaft and into filament drive chamber.
Heat isolation is an overlooked advantage of the geared and belt drive extruders.
Hello! I am trying to print with the 0.25 nozzle and mmu2s. Something similar happens to me .. after 1 hour or so .. the extruder is as if it gets stuck .. he keeps putting filament but it does not come out through the nozzle .. the printing continues and in the end it makes me a ball in the heat cube. I think it is a configuration problem .. since there is no configuration to use the 0.25 nozzle in multimaterial system. Can you give me an appropriate profile .. for this type of printing?[video width="1280" height="720" mp4="https://forum.prusaprinters.org/wp-content/uploads/2021/02/VID_20210223_054926_043.mp4"][/video]
What i did with mmu2s was to write down the configuration for single 0,25 nozzle and then copy the settings on to the materials of mmu2s and 0.25 nozzle. But one quick change you could do and it may turn out positive results is reduce the flow by 5% directly from the printer. Tune->flow.
Okay, thank you very much .. that's what I did at first .. copy the parameters to the different extruders .. but I don't know why it does that .. it is as if the filament were slightly jamming .. Thank you very much for your contribution. this afternoon I will try.