Incremental Jam while printing with MMU
So I've been using my MMU pretty heavily over the last couple of months, must have racked up a couple of hundred hours with 4-5 10-hour multicolour prints a week, and it's been solid as a rock. The odd unload fail but that's down to one specific filament. All PLA in various colours and flavours.
Last couple of MMU prints I've been starting to get extruder skips. It starts with one or two during the ramming pre-unload, and gradually progresses to 4 or 5, to doing it during normal printing moves, and once I left it running like that for a while in a section with no changes and finished up with nothing coming out at all.
To clarify, while it does seem to be gradually jamming up, it seems to be continuing to swap fine all the way along, things aren't getting properly jammed, and they seem to be OK during short (hour long) single-material prints too. At this point what I'm printing is a mix of prusament and plain PLA (also purchased from the Prusa store), though I have had other filaments .
I've tried all kinds of idler tension in both directions to no effect. I've been doing mid-print cold pulls and they come out clean as a whistle and resolve the problem for a little while, maybe 30-60 minutes before it starts creeping back in again. I've had the idler door off and found a lot of debris in the compartment which I've cleaned out to no effect. The PTFE tube looks like it's seated correctly right under the extruder gears, and the gears themselves look clean. I've even had the 0.3mm accupuncture needle up the nozzle a couple of times and that's seemed pretty clear to me.
Hardware-wise I'm running a slightly modified extruder housing that gets the MMU PTFE closer to the gears and double-spring-screws on the idler door. Other than that the only modification is a 0.4mm E3D nozzle X that's been on the printer longer than the MMU.
At this point I'm out of ideas and it looks like I'm going to have to tear the extruder down to get a look at the PTFE tube and hotend to see what's what, but I thought I'd ask around for any other advice on what to try or to look at before I commit a decent chunk of weekend to doing that.
Any advice appreciated, thanks in advance.
RE: Incremental Jam while printing with MMU
Try as I might to include all relevant details, I missed one of the most important - base printer is a MK3S w/ MMU2S
RE: Incremental Jam while printing with MMU
Dont have a MMU but do have a modified MK3. One thing that happens every year is that the amount of posts where people are having jams increases at this time of year. It coincides with the temperature going up. The hot end is air cooled, its supposed to be ok up to 40 degrees. Supposed. Personally I think anything more than 30 and the chances go way up, especially on longer prints and especially on those with a fair amount of retraction.
I dont think its got anything to do with your mmu. Higher ambient coupled with the heat from the extruder motor creeping along the gears and it reaches a tipping point with PLA. If you cool your extruder motor with either heatsinks or an active fan (piggy backed onto the hotend fan) with something like this - https://www.thingiverse.com/thing:3945830 then theres a good chance the issue will go away.
RE: Incremental Jam while printing with MMU
@neophyl
Thanks for the pointer. My office is indeed fairly warm, particularly so this week with ambient temperature monitoring putting the numbers in the high 20s, right at this minute reading 26 near the printer and 27 just outside the office door, so there's a good chance that's related. I'll look into cooling the extruder motor as suggested.
RE: Incremental Jam while printing with MMU
If you cool your extruder motor with either heatsinks or an active fan (piggy backed onto the hotend fan) with something like this - https://www.thingiverse.com/thing:3945830 then theres a good chance the issue will go away.
Thanks for the link. Ever since I started reading this forum I've been aware of the extruder motor tending to run hot, and I proactively added a small heatsink, since I have various heatsinks lying around plus the thermally-conductive adhesive. (Photo below)
I haven't had any issues, but I will download that item, as it looks like it will fit right in there (I do have the MMU2S) and it should not be difficult to steal 5v for a fan.
The one thing I'm leery about, however, is adding more mass to the extruder assembly. I figured one aluminum heatsink should not add that much, but I held off on adding three due to that consideration.
