I had the same issue with my Prusa i3 for a long time, a small bump on every level change. I’m running a Bowden type extruder so a lot of the issue was from the lack of rigidity of the filament between the extruder and hot end. Here are some of the steps I took to remove them, hopefully some may help:
-To double check it is the “z-scar” you are experiencing try switching to slic3r as there is an option to align Z moves, if all your bumps change to a continuous line up your part you know for sure that this is your issue.
-Lower hot end temp
-and slow outer profile speed
-Different filaments seem to be able to have very different flow and ooze characteristics.
-Increase retract distance and speed or use “filament pressure compensation” available in some slicers.
- try releasing the extruder and see if the filament jumps back by itself. your retraction distance will need to be at least this distance to make an effect.
-Some slicers have an “extra length on re-start” option a small negative value should help (I can’t remember if Cura has it)
-I know Slic3r also has a “wipe while retracting” function which starts the retraction before the end of the profile.
-Z-hop by the same distance as your layer height.
-Finally this is a real long shot, I have heard other makers saying that black filament tends to ooze more than others. (I think that it is probably more linked to manufacturer)
Your problem sounds very similar to mine: bumps showing during circular cross sections only of print using black filament. Ive attached a cropped photo of the problem. It seems like it’s on nearly every layer, but never in the same spot. After some observation I think that a print head pause is the problem in my case as well, but I don’t know how to change that! Have you found a solution?
(I’m curious to try the same print in another color, because after hearing a Schnaab’s comment on the black filament I realized that I don’t remember seeing this problem outside of my black filament)
