Inconsistent Extrusion

Good results in 3D printing are coupled with a very consistent amount of extruded plastic. This issue is visible especially at fine lines on your print and will affect the final print quality. Watching your printer closely as it prints is the best way to detect bumpy extrusion, which varies in size. Inconsistent extrusion can be affected by many causes, including a clogged nozzle, very low layer height, incorrect extrusion width, poor filament quality, filament is getting stuck or tangled and mechanical extruder issues.

Adjust the layer height

If your printer is not able to perform a very low layer height this might be a source of error. In that case set your layer height higher and check if the problem is fixed now. As a rule of thumb, take 75% of the diameter of your nozzle as maximum layer height.

Change extrusion width

One possibility for inconsistent extrusion is the wrong extrusion width. Try to fix the problem by changing the extrusion width. As a rule of thumb, the extrusion width should be between 100 and 150% of the nozzle diameter. If the extrusion width is under the nozzle diameter, no consistent flow of filament would be able.

Cold Pull Method

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.

Needle or wire method

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.