Hot End / Filament Feed Problem
My MK2.5S (MMU) was printing pretty well until recently. I replaced the PTFE tube and the nozzle - in that process, disassembled the heaterblock, heatbreak, and heatsink to put all back together again. Got it to start printing again but soon found out I had left a gap and there burnt filament oozing out of the heaterblock.
So I took the hotend apart again and put back together. Now I'm getting a new problem. When trying to print, when the filament gets intially fed, the melted filament will start to come through the nozzle onto the bed. But it just pools there around the nozzle - the printing head never moves. And you can hear some grinding like it's trying to get the filament through the hotend. Doesn't seem to be a blockage since the PLA seems to flow through pretty easily.
I've disassembled and reassembled the hotend several times, following the Prusa instructions, but the problem persists.
Has anyone seen a problem like this before? Any thoughts on a fix? See the attached video.
-Mike Ogilvie
USA - Richmond, Virginia
RE:
It seems that your nozzle is very close to the bed during filament feeding, does it do the same thing if the Z height is maybe 50mm? I'm thinking it probably does.
It sounds like the filament starts feeding ok, then the extruder start skipping. This can be caused by a clog between the nozzle and the Bondtech gears of the extruder but it can also be caused by high friction of the filament path. I would look for a mis-aligned Bondtech gear, that is to say the toothed groove that drives the filament must line up with the PTFE tube with the extruder fully assembled. A small allen key can be used to check the groove is aligned with the PTFE tube. Also, the drive gear setscrew must be tight on the stepper motor shaft.
It could also be a pinched or distorted PTFE tube or maybe a dragging / sticking Bondtech idler (driven) gear. If you have the extruder apart, see if the PTFE tube is being pinched, perhaps at the top if it is cut too long? Also, the bottom end has to seat fully into the heatsink.
Oh, wait! It's an MMU? could something be acting up in that? Perhaps unrelated to the extruder itself?
Good luck!
¡no entiendo Español!
Nein! Nicht Versteh!
Я немного говорю по-руÑÑки но не очень хорошо, и...
I'm not very good at English either! Maybe someday I'll find a language I'm good at?
RE: Hot End / Filament Feed Problem
Thanks for the feedback Chicago Keri!
It's normal for the nozzle to be up against the bed when feeding the filament - I think that's just how the MMU does it when first starting a print.
I will check out the Bondtech gear alignment. I'll do the allen key check (I vaguely remember doing that way back when assembling the printer). Not sure how else to check the alignment though. I'll search around a bit.
The PTFE tube is almost certainly not the problem. It's a brand new tube from the Prusa kit. Definitely the right size, and I've triple checked to make sure the right end is up.
The MMU is picking the correct filament without a problem and sending it down to the extruder just like normal, so I don't think it has to do with that.
I'm a little skeptical about filament feeding issues because there is definitely molten filament coming out, so it seems like everything is aligned. Also, if it was just feeding issues, wouldn't the whole unit start to move like it does with a normal print? But I don't pretend to fully understand the inner workings. 🙂
-Mike Ogilvie
USA - Richmond, Virginia
RE: Hot End / Filament Feed Problem
So it seems to feed ok but the X and Y axis don't move?
Maybe something isn't plugged in at the Rambo board or the MMU board?
¡no entiendo Español!
Nein! Nicht Versteh!
Я немного говорю по-руÑÑки но не очень хорошо, и...
I'm not very good at English either! Maybe someday I'll find a language I'm good at?