I got two new rolls of filament for christmas (Both PLA), and decided to build a dry box for them. The first print with the new filament was a small red eagle statue, to see if everything was working correctly. It wasn't. There were weird diagonal lines on the print surface, that I had never seen before. I found images of strong underextrusion, that seemed to match my print surface, but increasing the extrusion multiplier didn't help much. Even at over 300% flow there were still lines. I thought that the dry box might be the fault, and took the filament rolls out. It changed nothing. I thought it might be the new filament, and tried one of my old rolls, but once again the lines were still there. I tried changing the heat, I ran some cleaning filament through it, I changed the nozzle, I looked for loose screws, but nothing. When I printed a Benchie, there were no more diagonal lines, but there were still strong signs of underextrusion and especially on the thin parts like the chimney there were still many imperfections. I printed two more benchies with slightly different settings, and surprisingly the imperfections were the same on all of them.
My nozzle size is 0.5mm, and both filaments used in the images are filamentum PLA. For slicing I used Cura
I think I found the source of the problem.
It wasn't the extruder or loose screws, but the slicer software. My current theory is, that I accidently changed one of the settings without noticing, and that was enough to ruin all my prints. I found out by downloading another slicer, and trying that one.
Maybe everything isnt tight enough, maybe the extruder isnt gripping the filament enough, maybe the throat inbetween the extruder and heater block needs to be replaced. Id suggest looking into buying a new extruder and hotend like the E3D Titan extruder and V6 Hotend.