Many modern 3D-Printing extruders use a technique called “dual-drive”, which refers to two coupled gears that grab the filament from both sides. It aims to increase torque and reduce slippage at faster volumetric flow rates. If the grub screw on the shaft-gear comes loose, the gear still rotates because it is held by the D-cut shaft, but it can move vertically along the shaft. Unfortunately, that makes it hard to detect it preliminary. Single-drive extruders can also have the same issue, however, they often have no rounded tooth profile, making the problem less severe.
Printers affected by this issue:
Nearly all printers can have this happen. Only press-fit drive gears are less likely to become loose. In my case, it happened on a Voron M4 extruder.
How to detect?
Poor retraction quality (stringing) and difficult filament feeding might be a sign for a misaligned drive gear. If you don’t detect this issue, a failed print is likely to happen after a short time. In my case, my printer simply continues to print, while the extruder grinds through the filament.
Dangers imposed by this problem:
- Extruder motor can get very hot, because there is a higher load on the shaft, potentially melting the extruder parts
- Long prints can fail, resulting in wasted time and material
- Filament in the hotend can degrade, clogging up the hotend and potentially releasing fumes
- Check gear alignment regularly (~150 print hours)
- Apply thread locker to the grub screws
- Properly tighten them (Attention: the tiny screw head might break!)
Bonus tip: Add some grease to the spur gear side of the drive gears, for a smoother operation!