It is possible for the filament to get jammed in the hot end of a 3D printer; after all the nozzle in a 3D printer is very tiny. The exit hole is anywhere from .2mm to .5mm in diameter - that's a tiny hole. There a few different reasons as to why this happens. Some of the causes are that the nozzle get's clogged with foreign materials or deteriorated plastic, the nozzle exit was blocked during printing (un-level build platform or 1st layer gap too tiny), the cooling fan stopped working, the filament has expanded in the barrel, or finally, the filament might not be actually jammed or stuck, it could just be stripped at the drive gear. Stripped at the drive gear means that the the filament wasn't moving or feeding through yet the drive gear kept spinning - eventually wearing the filament in the same spot to the point that the drive gear isn't pressing against the filament anymore. Whatever the cause of the filament getting jammed it is something that a 3D printer operator must learn to deal with from time to time.
It is always nice to have an understanding of how something works before you attempt to try and fix it. With that in mind lets take a moment to look at the anatomy of the extruder - both the hot end and cold end. While this article is written specifically for the hot end on a Plastic Scribbler Asterid 1000 and 2000 series, the information within this article may be helpful for other types of 3D printers as well. Please consult with the manufacturer of other 3D printers before attempting to try the suggestions that follow.
The extruder of a 3D printer is made up of two sections. The cold end and the hot end. The cold end is responsible for feeding the filament into the hot end. The hot end melts the material and is where the filament exits or extrudes.
The Asterid 1000 and 2000 series 3D printer use an all metal hot end. This can can be advantageous over other types of 3D printers when removing jams. In particular, the Asterid hot end consists of a barrel, nozzle, heating block, heating element, thermistor, cooling block(s), heat sink, and fan.
When the filament gets stuck or jammed it usually happens in the middle of a print. Most people will start a print, leave, and come back later. In this scenario the user doesn't realize the printer is jammed and the printer doesn't know that it is jammed so it continues to go through the motions of printing. If the filament is jammed and the printer is still printing (or trying to print) first stop the printer.
To remove a jam, the heating element of the 3D printer must be on. Keep in mind that a hot end as the name suggests is HOT, very hot so please be careful when working on the hot end. Set the temperature of the hot end to the appropriate temperature for the filament loaded into the extruder.
First try to reverse the filament out using the controls in Pronterface. Reverse 100mm worth. If the filament isn't moving when reverse is pressed, verify that the drive gear is turning on the motor of the extruder. If the drive gear is spinning then GENTLY and lightly pull up on the filament as it is reversing. If the filament is stripped, pulling up while it reverses will generally be enough to allow the drive gear to get traction on the filament and reverse itself out of the hot end. BE CAREFUL AND TRY NOT TO BREAK THE FILAMENT OFF IN THE EXTRUDER. If the filament does break off, there are further instructions to remove the filament below.
If this doesn't work. The next best thing to do is to try a higher temperature and try the same technique. GENTLY pull up while the filament is reversing. Keep raising the temperature in 5° or 10° increments and keep trying to reverse and pull. If after raising the temperature to 20° past the recommended set point doesn't work, set the temperature back to the recommended settings and move on.
If that still doesn't work the next best course of action is to try and release the filament by inserting a probe into the exit hole of the nozzle. As mentioned above the hole of a nozzle is extremely tiny, but special stock/drill bits can be purchased that fit into the hole. Check to see what size diameter the nozzle is to obtain the appropriate size probe. You must insert the probe into the nozzle while it is hot. Be careful not to burn yourself if you try this technique. After inserting the probe into the hole try the reverse and pull technique again. Sometimes inserting the probe is enough to loosen the jammed filament, but it doesn't always work.
At this point, if the filament is still stuck in the hot end but not broken off you can try unscrewing the tension spring on the bearing arm and pulling up on the filament. Try to pull as hard as you can. If the filament breaks- then DON'T panic, this is why an all metal hot end is advantageous.
Filament broken off in hot end:
First you must remove the hot end from the cold end. Again this procedure must be done with the heating element turned on so be careful not to burn yourself. The hot end on an Asterid 3D printer single extruder is held up via two bolts through the top of the fan. Being that the unit is ON the fan will be spinning. Use the utmost caution not to accidentally break the fan when removing the bolts (don't stick the screwdriver in the fan!). After removing the two bolts please take notes of the orientation of the heat sink and the direction of the fan so that you can reassemble it easily. There is thermal grease between the heat sink and the cooling blocks- try not to wipe it off or replace it if you do wipe it off. If the filament is broken off at the drive gear then there is still some filament protruding from the hot end. With the bolts removed pull the hot end and filament out of the cold end. Use needle nose pliers to grab the filament at the spot nearest to the barrel and pull. The filament will normally pull out after a nice good tug. If the filament breaks off right at the entrance to the barrel and you can't grab it with the pliers then all hope is still not lost!
Drill the filament out:
ONLY do this if you have an all metal hot end. Use a 5/64" drill bit to drill into the barrel of the hot end. Only drill up to 36.5 mm or 1.437" any further and you will drill into the nozzle of the hot end and you will be forced to rebuild the hot end.
After you have drilled out the hot end, cut the filament square and try feeding it into the hot end by hand. It should go through the nozzle very easily. If it doesn't try drilling again. Once you have it feeding through easily reattach the hot end to the cold end of the machine.
If the cooling fan of the extruder is failing or has failed it can cause the hot end cooling system to over heat. If the filament gets stuck because the fan has stopped working, then first cool the machine to room temperature. Wait for the cooling blocks to completely cool. Then reheat the heating element of the hot end to the recommended temperature of the filament you are using. As soon as the temperature hits the set point, use the pull and reverse technique to remove the filament. With the filament removed, replace the fan before attempting to print again.