Filament grinding arises when the filament cannot move forwards, the extruder is still spinning, and his sharp teeth grind away enough plastic from the filament, so that there is nothing left for the gear teeth to grab on to. You will identify the typical small bits in the filament as you see in the picture. Sometimes you hear clicking noises of the extruder.
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.
Adjust nozzle temperature
If you recognize that the extruder sometimes has a hard time to push the filament through the hotend, it´s maybe because your nozzle is too cold, try to rise the temperature by 5-10 degrees so that the plastic flows easier.
If you are printing too fast, it can cause filament grinding. By reducing the printing speed, the extruder motor will not need to spin that fast, since the filament is heated up over a longer period. The slower rotation of the extruder motor can help avoid grinding issues. The same thing happens with the different axis, if the printing speed is too high, the motors must accelerate and decelerate much quicker, this can cause vibrations and bad looking details. If you were printing at 3600 mm/min or 60 mm/s (the most common printing speed), try decreasing that value by 50% to 1800 mm/min or 30mm/s to see if the filament grinding goes away or print quality increases. If not, it´s very likely that the problem is a different one. If the it works out, try to increase the printing speed in small steps till you find the best balance of a good quality and printing speed.
Too powerful retraction settings can cause filament grinding. Try out to reduce retraction speed by 50% and monitor if that influences filament grinding. If yes, we have some recommendations:
The retraction speed is an important setting that influences your print. If you retract the filament too fast, this may cause filament grinding or the filament may separate from the melted part. Otherwise, if you retract too slow, the nozzle may leak before starts printing at the new position. For most printers, the retraction speed should be between 20-100 mm/s or 1200-6000 mm/min.
Try it out by printing two cubes which are 40mm away from each other and increase retraction speed by 20mm/s or 1200mm/min steps and monitor the best performance.
The distance defines how much the filament is pulled back of the nozzle. It depends on your printer what the best distance will be. Try it out by printing two cubes which are 40mm away from each other and increase retraction distance by 0,5mm and monitor the best performance. For most printers, the retraction distance should be between 1 and 5mm.
Retraction is the pulling backwards of your filament during the printing process. When the hotend of your 3D printer is moving to a new location (extruder moves without extruding) strings may occur, because the melted filament is oozing out of the nozzle. This can be improved by pulling back the filament in the moment your hotend stops extruding.
Retraction settings are important to get good results, so we recommend optimizing retraction settings!
Check if the nozzle is clogged
There are two common methods to fix this problem:
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.