I’ve now experienced this issue at least three times now with my K2 with CFS, and I’m wondering if anybody has any idea what could be happening and how to stop it from happening.
The issue is that when I run out of filament, I end up in a state where the filament is beyond the reach of the CFS motor, but apparently also out of reach of the extruder motor, and the printer starts printing air. The runout sensor doesn’t trigger.
If I then disconnect the hose from the buffer, I see that there was maybe a foot of filament beyond the buffer. I’ve tried tugging on it, and it will not tug. As soon as I stop printing, it magically manages to extrude the remainder of the filament in an endless loop. So it acts like maybe the tail end of the filament is exhibiting drag on the tube sufficient to stop extrusion, but by pulling it past the buffer, it is able to use up the last tail as though nothing went wrong.
This occurred twice with Creality Hyper PLA, and I think once with PETG.
The fact that this has happened twice in just a couple of weeks is alarming, because it means the filament runout sensor is borderline useless, because the end of the filament is likely to never actually reach the sensor.
What could possibly be going on here? Between these two incidents alone, I’ve wasted almost an entire spool of PLA.