New to polycarbonate - jams
Trying to gauge what my issue is, my guess is retraction settings, but honestly I'm not sure, it's not something I've had to mess with a lot. I haven't been using wider extrusion widths though I've seen the recommendation - I have an enclosure and a heater for it and haven't gotten far enough along to have any warping/delamination issues yet. I'm using an MK3S with a MMU2S but only a single filament.
I've had a few benchies and another print stop about 30 minutes in with the characteristic extrusion issue of it getting thin, sputtery (in look), and then just stopping extrusion. I'm at the top end of the recommended temp for the filament, 280C, and increasing it hasn't helped yet. Increasing pressure from the idler in the extruder has helped a bit, but ultimately hasn't fixed the problem as the print continues.
Most recently, a print failed about half way through (only about 15 minutes, small parts) in the same way, but when I went to pull the filament out of the extruder it was very stuck. I couldn't manage with the bowden on, so I ended up heating up the nozzle, removing the bowden, and prying against the extruder with my pliers until it gradually released. The strange part was the look of the pull - the part removed was cool to the touch (in the heatbreak, I assume), but it had this little ridged sheath. It seems like some small amount of material is working its way up the side of the filament and depositing around it in the heatbreak, making a very grippy sheath that eventually prevents extrusion. I haven't had this on other materials (PLA, PETG, TPU, ABS). I've attached some pictures of the removed filament end.
So what's the best direction to tackle the problem? Higher heat and just jamming it through faster? Turning off retractions? Tried and true slow it down? Is there some issue with my heatbreak PTFE tube or something? These have been my first attempts with PC, so I don't really know if there's quirks with the particular filament, but I've used several types from the same company without issue.
RE: New to polycarbonate - jams
This is the worst case of heat break jam I have seen, and the most classic example.
But it is curable by replacing the Prusa mod heat break with a stock E3D-V6 heat break.
The jams form like this: retraction pumps melt up the heat break where it cools and forms a stub on the filament. The Prusa heat break is modified to have a 2.2 mm bore down to the neck, and continues on at the nominal 2.0 mm, the same as the nozzles ID. The result is during heavy retraction periods hot material can flow up into the larger diameter where it cools, and when the next long continuous extrusion move is made, the cooled melt jams.
RE: New to polycarbonate - jams
I don't know much about the specially made heatbreak, but I've read it has to do with MMU printing, which I am still interested in... will a standard E3D replacement still be compatible with the MMU2S? My printer was a MK3 from the end of 2018 but has been upgraded to the MK3S/MMU2S.
In discussions of the differences, they mention a ridge on the inside that I think I've seen in some nylon cold pulls I've done for cleaning the nozzle, and it did strike me as odd that it was in there at all.
Otherwise, is there something I can do to get around the issue in the mean time? Would reducing print temperature and reducing print speed lessen the issue, at least? My thought would be that lower temp would mean less melting farther back where the issue is happening and lower speed would mean lower back pressure from the nozzle (though I recognize these two parameters are working against each other for that).
RE: New to polycarbonate - jams
Many have tried to work around the heat break jam, including no retractions, but nothing has worked well enough to call it a solution. In most every case, swapping the heat break was the cure. But, it's usually a PLA print issue, not PC. So you'res is a unique case.
There have been many owners of MK3's with MMU's that have swapped heat breaks and have reported they have no issues. The use case for the 2.2 mm diameter is the MMU unloaded filament forms a thread at the tip, and when reinserted that thread bends back on the filament and may jam in a standard 2.0 mm bore.
It comes down to a jam that is 80% certain (Prusa heat break), or one that is 5% (threading).
If it were me, I'd try the E3D heat break, and if I started having MMU jams traceable to tip threads, I'd carefully bore out the Prusa heat break to 2.2 mm a couple more mm so that the step is well inside the heater block rather than outside it; or even all the way through.
RE: New to polycarbonate - jams
I appreciate the info and I'll give the heatbreak a shot, looks like it won't be expensive and will probably be to me by the end of the week. I actually remember my first PLA prints of any real duration ended up jamming, but with a bit of an increase in temperature it was cleared up. I don't know how peoples' experiences usually go, but I do run into jamming issues with new filaments pretty frequently as part of getting my settings tuned, as well as some jams when working through the new complexity of the MMU - maybe it's played a part.
RE: New to polycarbonate - jams
I have an enclosure and a heater for it and haven't gotten far enough along to have any warping/delamination issues yet.
Just out of curiosity... you actively heat your enclosure? What temperature do you have in there when printing?
RE: New to polycarbonate - jams
I'm going to guess Gizmo Dorks is the brand given it is a blue polycarbonate. If so, you may have another problem beyond jamming to solve.
I've yet to get Gizmo Dorks polycarbonate to work well yet.
Priline black polycarbonate, Priline CF polycarbonate, and Polymaker PC-Max all have been successfully tuned for excellent fusion and low stringing. I can print entire extruders with any of those three. They stick well to a layer of Elmer's Ultra glue stick, but Gizmo Dorks simply won't stick well enough to complete a print job.
RE: New to polycarbonate - jams
In my case, this was HobbyKing brand PC, maybe a similar issue in the end, but I've been using their ABS, PETG, and PLA for a while now to good results.
I heat my enclosure because it's large enough internally that I can't get temperatures I need for ABS with the printer's heat alone (it's also not especially insulated), only around 35C with my normal ABS profile. So I use heat lamps on a temperature controller to get it up to 50C or so where I've been able to avoid warping/delamination issues printing ABS. I wasn't heating the chamber for PC, but there's a chance it will be beneficial when I can get the stuff to actually come out of the nozzle....
RE: New to polycarbonate - jams
I don't know much about the specially made heatbreak, but I've read it has to do with MMU printing, which I am still interested in... will a standard E3D replacement still be compatible with the MMU2S? My printer was a MK3 from the end of 2018 but has been upgraded to the MK3S/MMU2S.
A standard E3D heat break is NOT compatible with the MMU2. Part of the reason for the custom heat break on the MK3 is to allow for different tolerances required by the constant loading/unloading of filament with the MMU2.
RE: New to polycarbonate - jams
I don't know much about the specially made heatbreak, but I've read it has to do with MMU printing, which I am still interested in... will a standard E3D replacement still be compatible with the MMU2S? My printer was a MK3 from the end of 2018 but has been upgraded to the MK3S/MMU2S.
A standard E3D heat break is NOT compatible with the MMU2. Part of the reason for the custom heat break on the MK3 is to allow for different tolerances required by the constant loading/unloading of filament with the MMU2.
There have been posts by more than one that say their change to the E3D heat break has not affected their MMU operations.
That said, if I owned an MMU, and I started having this difficulty, and that extra 0.2 mm diameter was important to prevent reloading used filament jams, I'd drill out the stock heat break another millimeter so the step is completely inside the heater block.
RE: New to polycarbonate - jams
I ordered the standard heatbreak and it arrived a couple days ago, got around to disassembling the extruder enough to get at the hotend (and the MK3S is easier than before, I didn't have to remove much!), but I was greeted with a nasty little surprise, first, a continuation from last time.
My efforts to print PC slightly warped those PETG parts near the nozzle, so I went to reprint the extruder in ABS in an overnight print and came back to half a print plus a ball of ABS stuck to the warped fan shroud. Removed it, corrected for more PINDA sag, and tried to reprint the parts since ABS doesn't use the part cooling fan anyways.... but several attempts later I'm actually running into the same issue as with PC described above - the print stops partway through because of a filament jam on settings that have been fine before. On the most recent jam, I was unable to pull the filament from the hotend, even when fully heated, without breaking the filament. All the way jammed, I waited until I planned on installing the new heatbreak before dealing with it.
Back to present time, I pulled the PTFE tube in the heatsink and saw this:
The source of my jam was a little wad of ABS that melted, was retracted into the PTFE tube past the heatbreak, and managed to cool and sort of stick to it. I did a little surgery to see if the filament inside could provide any detail and when I cut near the blockage, I could see it release from the walls of the tube.
Given that other previously working filaments are now showing the same issue as PC, I think I'm going to try another go with the stock heatbreak and a fresh PTFE tube. I still do have the E3D standard one if needed, but I'm suspecting that it's not that now. I've noticed there was some ABS.... frosting? on the heatsink (the condensate of the particulate it produces, I think) that I'm cleaning off and there will be a fresh application of thermal grease to the heatbreak interface. Also saw a very small amount of stringing of plastic on the inside grille of the hotend cooling fan - probably not significantly impeding performance, but a bit concerning. I wonder if this is primarily degredation of the PTFE or if there's some part of it that's also a hotend cooling issue, or if it's actually the heatbreak geometry as originally expected.