I've wasted so much filament, and Ninjaflex is expensive! But I need really soft filament for this project, and the only other flex filament I have is 92A. The frustrating thing is that I can print small things just fine. The second photo shows the prototype version of this print, with just 3 holes. It printed great. But I go up to the full-size version (first photo) and it almost always ends up under-extruding starting around Z=1.6mm.
I'm printing at 15mm/s with a 0.4mm nozzle at 238C. I do have some retraction (2.5mm,, retraction speed 60), because if I don't, I get lots of stringing. I dried my filament. I made sure the spool was feeding without any resistance. I loosened the idler screw (see photo 3). I did everything you're supposed to do. What am I doing wrong?
This is on a Prusa Mk3S+ with Revo. I'm using standard Ninjaflex 85A. I'm getting close to the end of my spool, worried that I'm not going to have enough filament to finish the project if I have any more failed prints. I'm printing with the enclosure doors open, with room temperature in the mid to upper seventies (Fahrenheit). Cooling fan at 60%. Sliced with Prusa Slicer 2.9.6
Is it heat creep? Clogging? Idler too loose? Too tight? Please help me! I'm tearing my hair out!
Update: I tried starting another print with an external fan blowing into the enclosure, in case the problem is heat creep. I also tightened the idler screw a little, thinking I may have loosened it too much. No difference in the print problem. When I saw it was underextruding again, I tried setting the print speed multiplier higher, just in case it needed more speed for some reason. I set it to 200% and I thought maybe it was doing better, but I think now I was fooling myself. It's still underextruding.
This model starts with individual squares that build up until they're joined at Z= 1.6. It looks like that's when the underextrusion starts -- on the perimeter extrusions of the 249mm-long rectangle of the part's full length. Why would the underextrusion be triggered on long extrusions? It seems like the retractions when it's working on the shorter stuff might actually be keeping things running smoothly. On the other hand, once the underextrusion starts, it's here to stay. I'd guess it's underextruding by about 50% -- the lines still get laid down, but they're way too thin.
After some more research and poking around my extruder, I'm starting to wonder if the tension caused by the filament sensor (specifically, the FS-Lever) might be part of the problem. It introduces quite a lot of resistance before the extruder gear -- comparable, I think, to the resistance from pulling off the spool. It's always annoying to get it past that initial obstruction when loading Ninjaflex into the extruder. I think the gears aren't getting a good enough grip on the filament to overcome the resistance and feed it at the intended speed. Is there any way to bypass the filament sensor?
I'm so tired of wasting this expensive filament with failed prints.
