They happen when lines meet where the width of the feature isn’t an exact multiple of the extruder’s width and the printer has trouble filling in the void. Usually they’re fairly invisible, but when printing white on black, they stand out like a sore thumb.
I’m wondering if there’s a good simple way of avoid this problem in the slicer. The ultimate fix of course is to print a square sheet of white PLA under the white letter, but I’d rather not mess with my model because it’s quite complex already.
Hand code is still used. Most frequently, a sub is hand coded with incremental moves and then called at a point. A lot of probing, weird moves, edge cases all still get hand coded.
Hand editing CAM produced programs constantly occurs at the machine as well.
3D printing gcode is pretty ugly because hobbyists “improved” the language without really understanding why it was so stripped down.
Modern Gcode is really meant to be machine generated and human readable/editable.