If you are experiencing extruder jams, here are the basic steps to follow to reduce or, as in my case, completely eliminate them! Jams can be cause by incorrect temperature settings, trash in your nozzle, incorrect extruder grip, long melt zones, poor spooling and any number of other causes. Here are some solutions to those problems and some additional tips.
Fix temperature settings
Almost every supplier of filament has slightly different datasheets for their plastic. You need to set your temperature high enough to melt it and get an even flow. In my case this involved two things, the first was to mount the thermistor very close to the nozzle tip tightly wrapped with kapton to get a more accurate reading. The second was to crank the temp up to 243°C for ABS. I've read multiple documents indicating anywhere from 220°C to 245°C, with varying conditions. In my case I do have a heated bed, and most people seem to get away with the lower end, but I just couldn't get even flow so I had to move up to the upper end. If you start getting pops, hisses and steam from your extruder, its probably too hot and you should lower it. It the flow is uneven, try increasing the temperature.
Clean your filament
This one is easy. Take a lint free cloth, cut a 1" x 4" strip and wrap it around your filament before it gets to your extruder. Take a zip tie and secure it around the filament, and then use another zip tie to hold it to the frame or some fixture to keep the cloth in place. This will also act as a guide for your filament so be sure to put it in a place that your filament normally feeds through. The cloth will wipe any hair, dust or other trash off the filament before it feeds into your extruder.
Clean your nozzle
If your extruder is shooting out plastic sideways, in an oval shape or thinner than you expect there may be trash inside the barrel. To clean your nozzle, disassemble your extruder while cool. If you use kapton/nichrome to heat it you may have to redo the heater section. If you have a removable heater this is much easier. Once you have the barrel/nozzle out of the PTFE thermal barrier, you will need to secure the barrel to remove the nozzle. I recommend using a chuck in a hand drill or drill press, as a vice will crush the sides and probably tear the barrel in half.
Before wrenching off the nozzle, hit it with a torch for a few seconds to melt and plastic inside or melted into the threads. If you have the barrel secure in a chuck, use a wrench to slowly turn the nozzle off. If it doesn't come off easily, hit it with the torch again. Be very careful here, especially if your barrel is thin. If you use too much force you will tear a hole in the barrel which is bad news.
Once disassembled soak the barrel and nozzle in acetone overnight, or at least for a few hours. Afterward you should be able to use some filament to push all the old dirty plastic out of the barrel and a small wire to scrape out the nozzle. If you can't push a pin or wire through your nozzle you may have to redrill the tip. I recommend securing the tip in a vice and using a dremel drill press or something similar with a 0.5mm bit to redrill it.
You can also redrill the inside of the nozzle with a 5mm bit while you are at it. Be very careful if you decide to do this as you can go all the way through quite easily. If you redrill with a 5mm bit you might want to retap the threads. You can also put the barrel in a hand drill and file the tip down to 118° (so it is the same angle as your drill bit). This will help the seal and prevent leaking around the nozzle threads.
Before reassembling, run a die over the threads of the nozzle to clean up any burrs caused by the chuck.
Align your extruder
If you have a pinch wheel extruder, be sure it is adjusted properly. If you have too much grip you will deform the filament, which will cause it to jam. If you don't have enough it won't feed and will cut an C out of the side of the filament. Makerbot recommends a space of 2.0mm between the idler wheel and gripping gear. [Makerbot Extruder Assembly Guide] RepRap.org reccomends 2.5mm between the motor shaft and idler bearing for a Mendel extruder. [RepRap.org Extruder Assembly Guide] Use the one that is appropriate for you filament. I use a drill bit to align the space, have your motor bolted in firm but loose enough it can slide a little. To expand the gap, run a drill bit down the filament shaft by turning the motor to feed it in. It should space the motor to the size of the bit. If you want to decrease the gap, just stick a smaller bit in the shaft and slide the motor against it. Once aligned, tighten up the bolts to keep it in place. You may find that you have to realign your motor every 30 or so hours of use, depending on the type of mount you use.
Spool your filament...tightly!
If you don't have a spool make one! [Thingiverse: Cardboard Spool by charlespax] This one is cardboard easy to make, I made 4 in a couple hours with a weed-eater box, tin snips and a cardboard cutter. When you put the filament on the spool, wind it on tightly. This is easier with two people, so you can help keep the tension up. If you don't you may end up with one of these:
Shorten Your Melt Zone!
Done all the above and still having problems? Perhaps the melt zone of your extruder barrel is too long. When feeding filament slowly (230PWM or less), the entrance to the barrel is often hot enough to soften the filament. This makes the plunger effect of the filament ineffective and pushes melted plastic back up the nozzle in reverse. This melted plastic would form a plug and leak out the PTFE barrier. The PTFE barrier would be deformed and unusable afterward, as the threaded section would be stretched out and the middle bulging. There are two steps to fixing this problem, but you may only need the first. Buy or machine a barrel like this:
The thin section in the middle will cut down on heat flowing from the hot tip up to the PTFE barrier. The other step is to switch to a PTFE sleeved PEEK thermal barrier instead of PTFE. I have found that PEEK does not deform under the stress and heat like PTFE, and the PTFE sleeve allows PLA to feed without sticking.
Still having problems?
If you did all this and are still having problems, you might try some different filament, leave some comments, or post on the forums [forums.reprap.org]!
