Soo... This will be a long post, but let me share it, and hopefully save some time to the other newbies :) After the usual print / tinkering / print / tinkering I noticed that I started to get these horizontal "bands" in the prints - sometimes the layers were displaced, sometimes they were just wider/narrower on all 4 sides. And because I like to do systematic testing, I tried everything (well... almost everything - as it turned out): - Reduced the speeds (to 30mm/s outer, 40mm inner, etc.) - usually suggested solution for all issues ;) - Didn't get better. A bit worse actually :) - Increased the speeds (to 60-100mm/s) - Tried different layer height (0.2, 0.3) - the issue was not so prominent on 0.3, but it was still there - different values and combinations for some print options (acceleration - 100-400, jerk 5-10, infill 0-20). Printing with infill 20% seems to have helped a bit. - Tried with tighter belts (to the point in which I had to finally print the rear frame brace) - Tried with looser belts (to the point where I got ripples all over the print) - Cleaned the extruder gear (it was clean anyway) - Oiled all rods - Removed the Y-Axis cable chain mod (I thought it might be putting some resistance to the movement) - Temporarily removed the "overhead spool holder" that some hate so much (made ABSOLUTELY no difference) - Measured all axes, everything is "square". On a side note, the pulley on my X axis motor is a liiittle bit excentric from the start (just the pulley, not the motor axis). I ordered a few replacements. - Printed in different (warmer) room. The room in which the printer usually runs is not heated and it's 14C there now :) - printed on different, a lot more rigid table - absolutely no difference. - Printed on different temps (PLA): 185-220 - Tried with my old roll of filament, with which I had printed the same test cubes, and they were perfect back then. Not anymore. - Tried slicing with Simplify3D using the settings from the files section. Oh the horror... NOTHING REALLY HELPED. TLDR; You know what helped? Changing the wall thickness to 1.2 instead of 0.8. And now the cube is (almost) perfect - in reality it looks even better than the photo. FFFFUUUUUU I know that NOW everyone will tell me that the error was obvious, but the other day, when I initially asked about the issue, everyone was sooo quiet... ;) PS: Ignore the bad first layer on the photo. It's not it's fault - small leveling errors correct themselves in the upper layers;)