I just learned a new lesson.
When you unload filament, if you are not at the ready when the extruder starts ejecting it then you will hear a clicking noise. This is just the end of the filament touching the extruder gears as they spin trying to push it up. This does not cause a problem.
A strange thing i wonder if anyone else has noticed, is that when the tool head gets to the home position and just before it starts pushing the filament up, it actually pulls the filament in slightly. Just an odd observation.
Now for the problem. Many of us have created a post talking about printing air. This happens if for some reason the extruder cannot move the filament. Because the filament sensor still sees filament, the extruder keeps trying to push filament through the nozzle.
I have had this happen for several reasons.
- the spool runs out, but the end of the filament was anchored to the spool so securely that it will not come loose.
- the end of the filament comes loose from the spool, but it has a very severe kink at the end and cannot be pulled through the guide tube.
- somehow the filament gets tangled and the extruder just cannot pull any more filament from the spool.
I would guess there are some additional cases caused by the AMS.
The problem is, as long as the filament run-out sensor sees filament going in to the extruder it does not care if it is not moving. I have had the printer print the first 5 minutes of a 2 hour print and then keep grinding for the next two hours while printing air.
When the extruder is grind away on some filaments the filament is soft enough to just shred. This causes a mess in the extruder that needs to be cleaned up.
In other cases, such as the one that just happened to me, the yellow extruder gear is the weak point and starts skipping. The drive gear is steel and it will slowly abrade the teeth of the yellow gear. This is the clicking that you do not want to hear.
It took me quite some time to find the problem. I disassembled the extruder at least three times. What made it so hard to find is that the damaged teeth on the yellow gear are barely shaved and it only affects the tooth at the slipping point. You can unload and reload new filament and it seems to work fine, but when the yellow gear gets to that tooth the filament stops moving and you hear the clicking.
My suggestion is when you hear a clicking and the filament is not extruding look at the yellow gear through the window in the side of the tool head and see if it is turning. If not then you have the problem.
I also notices when cleaning the extruder during the early part of troubleshooting, there was a tiny piece of filament stuck down in the steel gear that drives the yellow gear.
I am waiting for a new extruder and a new gear set (double redundancy) and I thought maybe I could help someone recognize the problem before parts got to damaged and needed replacement.
