There are several reasons you may need to clean out your nozzle. Foreign particles, filament contaminants, accumulated dust, overheated and scorched plastic can all become lodged in your nozzle and prevent smooth extrusion. Scorched plastic can also stick to the sides, creating resistance for the plastic traveling past without actually blocking the nozzle. This procedure for clearing your nozzle should be performed any time you are unable to extrude plastic, and periodic cleaning by this method is not a bad idea.
In the early days of home 3d printing, it was much more difficult to clear nozzles. It often required disassembling them and heating with a torch to remove plastic to get obstructions out, but this results in more scorched plastic and risks damaging some of the parts if improper force is applied (stripped threads, nozzles breaking at the narrow point between the threads and the inner bore, etc.) or nozzles being reinstalled without a proper seal. Some people also soak their nozzles in a solvent, but it can take some time for solvents to completely penetrate the plastic inside the nozzle, and even once saturated with a solvent, the plastic can be viscous and difficult to remove entirely.
The safest and most effective way to completely clear the plastic from a nozzle, taking any contaminants with it, is what I call a “cold pull”. The idea behind the cold pull is to pull the filament out of a nozzle at a temperature cool enough to keep it in one piece (rather than leaving molten plastic in the hot zone), but still warm enough to allow the plastic to stretch enough to pull away from the sides of the barrel so that it doesn’t seize up entirely. This is easiest to perform with a polished-smooth stainless steel barrel, with those that have a PTFE liner all the way to the end coming in second, because nozzle pressure can slightly compress the softer PTFE and create a plug that will be difficult to pull out.
The cold pull technique has been successfully done with both ABS (this was the best material to use for a long time, with a cold-pull temperature of about 160-180C) and PLA (much more difficult due to its thermal transition properties, but a cold-pull temperature of 80-100C will sometimes work), but Nylon 618 from Taulman (pull temperature of 140C) is far easier and more reliable to use for this purpose due to its strength, flexibility, and low friction. These are generally maximum temperatures (temperatures above which the plastic is unlikely to come out solid). For best results, you should always pull the plastic at the lowest possible temperature, and it may help to cool the nozzle well below this temperature and then continually attempt to pull it as the nozzle heats up again.
|Successful cold-pull with ABS. Air was pulled in through the tip leaving the sample hollow and likely to break while being pulled.||Successful cold-pull with PLA. Air entered around the filament as it stretched. Too much stretching leaves the filament too thin, and the stretching concentrates at the (weaker) thin section until it breaks.||Successful cold-pulls with 618. The strength and low friction allow it to be pulled at a temperature low enough to prevent deformation that will cause the filament to break.|
The first thing you want to do is remove as much of the plastic that you’ve been using as possible. To do this, you can attempt a cold pull with ABS or PLA with the temperatures listed above. Next, you will want to heat your nozzle to 240C so that it can thoroughly melt the nylon and push the nylon filament in. Attempt to extrude the Nylon slowly (If your printer has a bowden extruder, like the Bukito, you may find it easier to remove the tube and push the filament directly into the hot end by hand). Most clogs (especially those caused by accumulated dust) will not actually block the nozzle entirely, but will be pushed into the nozzle and stop it when the nozzle pressure increases, then float up out of the way when left to sit. If you don’t have a hard clog (usually a solid foreign particle lodged in the nozzle) a slow, pausing extrusion should allow you to purge the old printing material. Once nylon starts coming out of the tip, you can begin cooling your nozzle to the pull temperature.
|A tip that is rough and or colored indicates that the old plastic wasn’t completely purged, and you may want to try again to make sure the nozzle is completely clear.|
If you have a hard clog that prevents you from extruding at all, you will have to dislodge it before proceeding. The best way to do this is to find a thin steel or brass wire (electrical wires like aluminum and copper are usually too soft) that will fit up through the nozzle (bristles pulled from small wire brushes work well, thin music wire works too). An even better solution is to buy some acupuncture needles in a diameter that is at least .05mm smaller than your nozzle bore, but you should never use a drill bit to unclog a nozzle (some suppliers have begun selling these specifically for this purpose, but microdrills are brittle and likely to break off in your nozzle, and even if they don't, they will alter the shape of the soft brass used to make the nozzle). Push the wire or needle up through the nozzle to dislodge the clog, then continue attempting to extrude. Really nasty foreign particles may need to be dislodged repeatedly. Once the clog is dislodged, you can push the nylon in to try to purge the old material.
|Wire pulled from wire brush.||Pushing wire into the nozzle to dislodge a hard clog.||Nylon pulled with hard foreign particles visible in the tip.|
If you pull the nylon out and the surface is rough, dark/discolored, or has black spots around the sides, this indicates that there is residue of overheated or carbonized burnt plastic in the nozzle, usually from sitting hot for extended periods without flowing (Deezmaker printers use a feature called “extruder runnout prevention” to avoid this by periodically extruding a few millimeters of filament if the machine is idling with the nozzle hot, but a clogged nozzle will prevent it from working) or from attempting to clear a clog using fire. If you see this, you should clip off the end and repeat the process until all of this residue is removed and the nylon comes out smooth, clean and mostly white.