This video explains how to use acetone to remove the clogging in the extruder tube.
WARNING: Acetone is flammable! Pouring acetone into the hot extruder tube while the printer is on can cause ignition or explosion. Do not do it! I take NO responsibility for your actions. Keep the acetone bottle away from any hot parts of the printer, and put the cap on it after use. Proceed at your own risk.
http://www.youtube.com/watch?v=fnXtxdIBsUQ
Couple of points… from what I’ve read, acetone is only going to affect ABS, not PLA. Maybe other materials, but it doesn’t seem to do too much to PLA.
Second, I think it’s worth repeating 1,000 times… acetone is explosively flammable. Using it in close proximity to electronic components probably isn’t wise… and heating elements not so wise either. It’s auto-ignition point is well above the temperature that extruder heads tend to use, but absolute any risk of sparks anywhere near where the vapors could be (and if you have fans blowing but not good ventilation on top of it… like an open window… the vapors could go all over).
Good points Trevor, didn’t realize that acetone is flammable at the time of filming. Will make a warning below the video.
Yeah, it’s like gasoline flammable. Anything used as a solvent tends to be highly flammable. Just wanted to make a note so people could make an informed decision. Obviously we all do potentially dangerous stuff sometimes… 
BTW… I wouldn’t be terribly worried about a small amount of acetone on a hex wrench… it’d probably burn super fast and not cause any damage, but definitely watch the larger container of acetone… keep it away from the electronics and put the cap on it so the fumes don’t get out too much.
Also… I thought of one other minor issue with using acetone. It’ll soften ABS, but if there’s enough acetone, it can make a slurry. Basically a bunch of liquid ABS. This isn’t a huge deal if you’re doing a thorough cleaning, but if you don’t get all the slurry out, once the acetone evaporates, you could have a thin layer of ABS on the inside of your extruder. Not sure how much of an issue that might be.
@TDB_Gryffyn Actually, acetone is much more volatile than gasoline. I’d be more worried about it damaging EVERYTHING, than it igniting at the quantities he’s using though. I use a Replicator 2X at work, and my main problem is the actual Nozzle getting clogged with carbonized plastic/dust. I’ve tried to force it down with toothpicks and allen keys, but I still get the telltale spiral ABS coming out of the nozzle, along with the extruder gear stripping the filament. I’ve tried pulling the nozzle out and soaking in acetone overnight then jamming said allen key in again, still no help. For most clogs, I need to push a piece of wire wrap wire from the outside in. I can see there’s a clog with a microscope. The best thing I’ve found is to use a blowtorch (a stove burner can be used as well) and burn the plastic out. I pretty much allow the nozzle to get lightly red hot, then allow it to cool naturally, as quenching would cause it to warp. Then I “floss” the opening with the piece of wire wrap wire and confirm it’s clean by making sure I see clear light through the hole. I use a microscope to confirm. This works like a charm, but obviously requires a torch of some type
Eric, your approach is quite extreme…
@Eric_Moy my main point about acetones flammability is that it was “more than enough flammable that it should be taken seriously” hah
And yeah, I’ve seen mention of people using torches to basically carbonize all the plastic so you’re just dealing with carbon at that point. Seems not as extreme as it may seem on the surface. Especially when you consider the plastic melts in a nice controlled fashion for extruding around 200C… cleaning with a torch would have to be at least a bit hotter than that to do more than melt it.
Yeah, at first I though it was extreme as well, but after burning my fingertips on the heated extruder parts too many times, I gave it a shot based on a youtube clip I found. Shockingly, it was really effective. The cool thing is, when you hit it with the torch, all the plastic shoots out the large end like a big flaming worm, then fizzles out. That alone is worth the price of admission
@Renat_Z btw, I think the brown filament is actually your filament burning. I have no remnants of brown in my nozzle a I torch it, but i notice if I preheat my nozzles for too long, the filament is brown at the tip. If I preheat for way too long, the nozzle clogs
Makes sense, preheating extruder too long may cause clogging. From now on I’ll only preheat the build plate. Thanks Eric!