MK3S stopped pulling filament toward hotend after load
My MK3S MMU2S has been printing fine for over a year with little trouble. Today after a successful print I initiated a second print but the MMU refused to load the filament to the hotend. Basically, when the motor is told to go to high speed to move the filament toward the hotend after loading, it is not happening.
For testing I switched to using 'load to hotend' to see if I could get the filament to get there.
It loads and unloads all filament fine at the MMU. The bondtech gears turn to move the filament into position. Normally after it loads the filament it will then pull it on toward the hotend in one smooth movement. However, after it loads the filament, it pauses and stops the bondtech gears instead of pulling it on to the hotend. During the time it should be loading it triggers the bondtech gears in the hotend to move but of course there is nothing there. If I stick some filament into the hotend manually it will eject it at the beginning of the process as expected.
I've upgraded the firmware and verified the sensors toggle from 0/1 appropriately and cleaned everything.
Any ideas or suggestions?
Best Answer by HikerGlenn:
I solved the issue today after spotting a bit of gunk built up on the setscrew of the extruder bondtech gear. This can only be seen by taking sensor door off.
While the sensor behaved normally for test purposes I surmise the following failure mode:
- Firmware detects no filament in the extruder via sensor
- Filament successfully loads on the MMU
- The Firmware then fires up the bondtech gears in the extruder in prep for the fast load procedure
- With gunk on the bondtech gears, it barely triggers the sensor when it begins rotating which aborts the fast load of the filament
- It then stops, thinking it loaded to the extruder. When the gears stop and the sensor reports no filament present so it starts over again loading on the MMU...
So, while it looked like an MMU issue due to no fast load procedure the cause was the gunk in the extruder triggering the sensor when the gears rotated.
RE: Fixed - gunk on extruder bondtech set screw
I solved the issue today after spotting a bit of gunk built up on the setscrew of the extruder bondtech gear. This can only be seen by taking sensor door off.
While the sensor behaved normally for test purposes I surmise the following failure mode:
- Firmware detects no filament in the extruder via sensor
- Filament successfully loads on the MMU
- The Firmware then fires up the bondtech gears in the extruder in prep for the fast load procedure
- With gunk on the bondtech gears, it barely triggers the sensor when it begins rotating which aborts the fast load of the filament
- It then stops, thinking it loaded to the extruder. When the gears stop and the sensor reports no filament present so it starts over again loading on the MMU...
So, while it looked like an MMU issue due to no fast load procedure the cause was the gunk in the extruder triggering the sensor when the gears rotated.
RE: Fixed - gunk on extruder bondtech set screw
I am new to this, but in searching for help I found this entry and it seems to mirror my problem to some extent. I had a crash while printing a stencil insert that was off center and I aborted after it was scraping the top of the failed print. The i3 mk3 was still trying to print it for a while. Now it doens't let the filament go all the way into the gears, I thought it was a nozzle clog, but the needle tool has no problem going to within 1/2 inch of the length. So problem is above that. I opened the extruder door but havent a clue as to what it SHOULD look like. I find references to what clogs or filament blockages look like but not what it should look like in pristine working order. I see no color that I have printed recently.
I have disabled the steppers, filament autoload, and let it set at 285 for 5 minutes. Filament or 1.5mm could get to the gears, but not though. I am ok to dismantle further, but hoped for experienced user to advise.
I've got some notes on clearing jams here that might be helpful.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
...Clearing jams, follow up
That's a lot to absorb! Thanks, I am going to go through your notes carefully. I have ordered extra nozzles just in case, and picked up the tools that may be needed... metric, which I didn't have on hand. This is the most challenging hobby I've had... Loving it!
RE: Perhaps too much spring tension
This is a different issue so you might find it helpful to create your own topic. In my case the filament was never leaving the MMU but in your case it sounds like it's reaching the top of the extruder but not getting pulled in.
My guess would be the tension screw for the extruder bondtech is too tight such that the filament cannot be pulled thru easily. You should be able to loosen the screw on the left of the extruder that has the spring pulling the bondtech door closed on the right. In my case it is just tight enough so the end of the screw is even with the nut on the right side. Too loose and it won't grip the filament enough, too tight and the filament cannot force its way in due to the spring tension.