Under extrusion & cold pull
Hi there!
I am experiencing what I believe is under extrusion, with PETG and TPU, nozzle sizes 0.8 and 0.4.
First with 0.8 nozzle, I did a few cold pulls. They looked clean. Then I switch back to 0.4 nozzle. Noticed under extrusion again, with TPU. Did a few cold pulls.
I think the nozzle is correctly mounted, see picture for the 0.4:
For the cold pulls I am a bit uncertain. There is a bulge both with 0.8 nozzle and 0.4 nozzle:
They were performed with PLA. I wonder whether the bulging is normal. The picture on Prusa support pages also shows some bulging: https://help.prusa3d.com/article/cold-pull-mini_126399
The extruder gears are otherwise clean.
So before I dig deeper into the problem, can someone please confirm whether the cold pulls look OK or indicate a nozzle issue?
Best regards,
Jerome.
RE: Under extrusion & cold pull
I switched back to PLA. Here is the _second_ layer of a print:
To me it is under-extrusion. I do not know what is going on. Default settings in PrusaSlicer. I never had that before, the printer has just been left unused in a box for 6 months.
RE: Under extrusion & cold pull
Problem solved!
I disassembled the extruder and it was clean.
Then disassembled the print head. It was clean too. There was a very thin layer of plastic on the heatbreak where it makes contact with the nozzle. I removed it and also:
* changed the PTFE tube inside the heatbreak: the spare one was 2mm longer than the original one
* screwed the heatbreak a little more in the heatblock so that the nozzle points outward a little more, in order to be absolutely positive there is a firm contact between the heatbreak and the nozzle
After reassembly print quality was back to normal, so I believe this came from the print head. I just do not know why the problem appeared "suddenly". I last printed around Christmas and everything was fine at that time.
Actually I also damaged my extruder. Before all that I played with the idler tension. Seeing no effect I turned the screw to the maximum tension. When I reloaded the filament this must have bent the screw. It was impossible to undo the screw afterwards. The sunk bolt began to turn in its housing. I cut the plastic in order to grip it, not no amount of force would make the bolt and screw turn relative to each other! In the end the hex head rounded. I finally cut the screw with a Dremel, melting plastic ...
Somehow it still works after this repair. I'll have to print new parts sometime.
I am sad this took me so much time. I bought a Prusa in order not to have to tinker with the printer. I regret my Dagoma whose extruder never caused any issue. It had a manual clutch so the filament could be loaded/unloaded manually, it could be actuated even with a cold extruder, would work with any filament with no adjustment at all.
RE: Under extrusion & cold pull
Oh and the screws holding the heatbreak in the heatsink could not be undone too, had to Dremel them.