Problem with underextrusion on UM2

[gr5 2,027]

Swapping from ABS to PLA takes lots of experience and practice but usually results in clogged nozzles. You might want to remove your nozzle and burn out all the plastic and then soak in acetone.

Certainly you want to get all that ABS out of the bowden and out of the feeder before you start a print. ABS, if kept hot for too many minutes slowly cooks into a very difficult gunk that will require special effort to remove from the nozzle.

 

[leon-grossman 0]

I'm back for a status update.

I didn't expect this problem since I swap between ABS and PLA on my home printer all the time. As a result, it never occurred to me that it could be material remaining in the nozzle that was my primary problem. My clue came when I noticed that t-glas print on my home printer had a dark shading on the bottom half due to residual black ABS in the nozzle.

Since that discovery, I just let the PLA feed through the nozzle for about a minute after ABS to PLA material change on my UM2 and I haven't had clogging issues since.

 

[eldrick 64]

ABS does not cook in the nozzle - it's PLA that breaks down and turns to brownish stuff like crystalized sugar if you leave it in a hot nozzle.

That said, when I change from ABS to PLA, in the future, I will definitely use the nuclear option to get as much ABS as possible out of the nozzle.

BTW, is there any long-term risk in doing the nuclear cleaning? I've had to do this repeatedly to get clean extrusion without slowdowns.

 

[leon-grossman 0]

I've been playing with 3D printing for about 1.5 years now. Four different printers. I've only ever had to go for a full disassembly cleaning once. I don't count the trials I had figuring out the UM2 issues as it was never actually a clogged nozzle.

My current belief is that my problems have been 99% because of ABS clinging to the walls of the nozzle a little longer than expected. When running PLA, the temps are not high enough to get this residue off the nozzle walls but it does seem to handle the flakes of ABS coming up the bowden tube.

FWIW, it should be an *exceedingly* rare case where you should need to go full disassembly and then it was probably because of cheap filament with metal shavings or running PLA way too hot and causing it to crystallize.

 

[illuminarti 18]

I'm with Leon. In over two years, with two generations of Ultimakers (and taking no particular special care to keep the filament clean) I've still *never* had a clogged nozzle that required disassembly. I think that a lot of the disassembly that people do is a knee jerk reaction to damaged filament, or problems at the cold end. By the same token, I've never printed ABS on my UM's - although I have printed Nylon, Laywood, and LayBrick quite a bit.

PLA does become very liquid at high temps and has a much more brittle texture upon solidifying again. But it seems to keep flowing ok. Whereas ABS (I've printed that on a QU-BD RXL) definitely *does* get burnt if left sitting at high temps.