I just had a very strange failure. The coupler that holds the PTFE tube in the top of the Extruder Filament Sensor failed, so the PTFE tube to the extruder became disconnected during a print. After 1020 hours, the PTFE coupler in the Filament Extruder Sensor was just worn out from twisting back and forth. Since the PTFE tube to the extruder was disconnected, the hub on the back of the Printer told the AMS that it needed more filament. The problem was that since the PTFE tube to the extruder was floating, the spring in the Hub never triggered a full condition, so the AMS just kept pumping out filament. I had about 20 meters of filament inside the print chamber by the time I finally stopped it.
I was out to dinner when I checked my print and saw filament everwhere. I used Handy to stop the print, and the Print Head stopped moving, but the AMS kept pushing filament into the build chamber. Then I used Handy to Unload the filament, and it finally stopped the AMS. If I had not happened to check the print, the AMS would have dumped the whole spool into the printer chamber…
Here is what I saw after I hit Stop, but before I “Unloaded” the filament. Filament was still being pumped into the chamber at this point.
And here is a micro-photograph of the bottom of the failed Extruder Filament Sensor, with pieces of the PTFE couple clip stuck to the filament sensing magnet. On the right is the hall effect device that detects the magnet position.
The magnet was able to capture the shards of the failed clip, and once I got all the filament out of the chamber and replaced the Extruder Filament Sensor the printer worked fine.
I was also able to salvage the filament that I removed from the chamber. But I had to spread it across a couple of spools, because it had gotten some kinks in it, which broke when I tried to straighten them.
Now I keep a spare Extruder Filament Sensor so my printer won’t be down for a week if this happens again.