I'm working on tuning an old Ultimaker 2 Go, and I'm having some weird extrusion issues. The printer uses a Bowden extruder. Extrusion seems to increase and decrease. I don't think it is the filament quality, as I am using Prusament PLA that I am storing in a dark closet inside a sealed bag with silica gel. I also did multiple cold pulls until no debris. I do notice that sometimes the filament appears to bubble. The extruding motor also sometimes slips/snaps back while changing filament, but not during prints.
However, I am using 1.75 mm filament while the printer is designed for 2.85 mm. In order to do this, I followed some steps I found from All3D.
I also have a small PVC jig to hold the filament, but I think it turns pretty well and shouldn't be the issue.
Filament: PLA, Temp: 215 °C, Slicer: Cura
*Update: I calibrated the e-steps and all of the axes, but the problem still remains.
I also printed an XYZ cube, and there is a line right under the letters X and Y. It also appears that the extrusion is more inconsistent outside of the letters. I'm pretty sure this issue is related to the weird first-layer pattern, or this is just a cooling issue due to varying cooling %.
Filament: PLA, Temp: 215 °C, Slicer: PrusaSlicer