Strange behaviour on one extruder only (4 way MM)
Hi all,
My Mk2 with MM is all built but I seem to be having a consistent and repeatable problem with one of the extruders (no. 3).
All the extruders load filament correctly - pushing it down into the bowden tubes, up to the splitter. Extruders 1, 2 and 4 all print fine, but when the printer tries to use extruder #3, it doesn't actually push the filament forward at all. Putting my hand on the filament, I can feel it doing retractions just fine, but it never even seems to try to push it forward (not like it clicks, or anything). All the retractions mean that the end of the filament is half way back up the bowden tube by the time it changes to the next filament.
1. If there was a block in the splitter, then I could understand this, however it would expect any retractions to be pushed back down, and not end up with the end of the filament halfway back up the tube.
2. If there was a problem with the extruder itself then I'd expect it not to even load the filament in the first place. I can see in the bowden tube that it has pushed the filament all the way down to the splitter when the load has been done. I've removed the bowden tube for #3 and checked the steel sheath - it looks the same as all others.
3. I looked at the ejected filament - there is no grinding that would suggest a blockage.
I'm printing a sample MM model gcode from the Prusa installation (took the .gcode file from the models directory and stuck it on the memory card). It's the 4 colour gear model.
Anyone got any bright ideas, or has seen this sort of behaviour before?
Thanks!
Paul.
Re: Strange behaviour on one extruder only (4 way MM)
Paul
For each extruder the following sequence occurs:
Move filament from cooling tube to extruder
Carry out the print for that extruder
Move filament from extruder to cooling tube.
If there is a blockage below the cooling tube, the printer will not know about it, so on each unload the filament will be filament will be moved further back into the bowden tube.
With all filaments either unloaded or in cooling tubes, can you please remove the festo on the MUX for extruder 3 heat the nozzle and push some filament through the cooling tube and into the extruder. Make sure that the filament is able to extrude. If not, then you may have a blockage below the cooling tube.
Another common cause of this problem is a bulge in the filament which will prevent the filament passing through the cooling tube. Discard about 50cm and check the filament diameter.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Strange behaviour on one extruder only (4 way MM)
Thanks Peter. I did as you suggested; removed the festo from the splitter and manually pushed filament through the metal pipe into the mixer and it extruded just fine. I replaced the splitter festo and removed the festo from the extruder and tried pushing the filament all the way down the bowden, through the splitter and it came out of the nozzle just fine, so I guessed that the issue was somewhere in the extruder.
I took it apart and checked the alignment, which seemed perfect - with the tensioner released I was able to push filament through, rotating the extruder motor and out of the other side. I stripped it all down to component parts and rebuilt it (just extruder #3) and now it seems to work! Very strange - can't identify what the problem was as I believe I put everything back just as it was, but it is chugging away, having done 15 levels just fine!
Thanks for the advice!
Paul.