Under extrusion can have some different causes. A clogged nozzle, slipping extruder gear, the wrong filament diameter / extrusion multiplier settings in your slicer program.
A cold pull works best with slippery, soft materials – like Nylon filament.
Again, heat up your hotend to the working temperature of your Nylon or Polyamide filament, push it through the hotend as far as possible, ideally, until your previous material is cleaned out, which obviously is going to be somewhat hard if your nozzle is completely clogged. Then have the hotend cool down.
What we recommend is to set the hotend to 110, 120°C and just keep on pulling on the filament while the hotend is heating until the filament plops out in one piece. Then cut off the impure end of the filament, fully heat the hotend again and repeat the process until the pulled end of your filament comes out clean and you’ve restored good flow through the nozzle. Usually, two or three passes should be enough.
The most common filament diameters are 1.75 mm and 2.85 mm but there exist many more. But these measurements have different tolerances which can vary from 0.01 mm to 0.1 mm.
So, make sure you measure your Filament with a calliper on 4 to 5 points on the first meters and calculate the average diameter, before you use it. (Sum of measurements divided my number of measurements)
Use the calculated result, to set either the filament diameter or the extrusion multiplier to the correct value.
The most common method is to set the filament diameter to the standard measurement (1.75 mm, 2.85 mm etc.) and change the amount of extruded material over the extrusion multiplier.
(Attention: The extrusion multiplier is the percentage of extrusion for the specific diameter.)
For this method, you need an acupuncture or hypodermic needle, so that you can try to remove the blockage. Obviously, you’ll need a needle or wire that is small enough to fit into your nozzle bore, typically 0.4 mm.
We don’t recommend using a drill bit instead, because they break more easily than solid needles and worst of all, can permanently damage the nozzle if you are not careful.
Preheat the nozzle to your regular printing temperature for each material and start poking with the needle. Be careful not to burn yourself. The goal is to break the blockage so that it slips through the nozzle. The next time you push filament through the blockage will slip through the nozzle together with the filament.
You might have to go through the cycle a few times and push through a bit of filament by hand to check if you have managed to break up the blockage sufficiently. If this method does not work for you try the cold pull method.
Slipping extruder gear
All FDM 3D printers use a small drive gear which grabs the filament and presses it against a bearing or another drive gear. This drive gear has sharp teeth that allow it to grip the filament. If the filament is unable to move, the drive gear keeps spinning and it can grind away enough plastic from the filament so that there is nothing left for the gear teeth to grab on to.
If this happens on your printer, you will usually see lots of small plastic chippings from the filament that have been shredded away. You may also notice that the extruder motor is spinning, but the filament is not being pushed in the hot end.
To solve this problem, you can try:
- to increase the nozzle temperature by 5-10 degrees so that the plastic flows easier.
- to change the printing speed, if the extruder tries to push the filament faster trough the nozzle than the hot end can melt it. Reduce it by 30% to see if the problem is resolved.
If the extruder slipped, make sure that the drive gear of the extruder is clean, because the plastic shreds can fill in the teeth of the drive gear. If this happens it is more likely that the drive gear slips again.