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.
Does your slicer have Arachne slicing mode? It will use variable extrusion width which will help to prevent most of those gaps.
2 replies pretty much in opposition to each other. So which one is correct? One says Arachne might be the cause, the other says to use that to fix the issue.
Arachne is more cleverer but more susceptible to poorly tuned settings (than the classic slicing engine)
You can set the minimum extrusion width to a small value (20-25%) for better fill. You could also use classic mode with gap fill. You can use ironing for both to improve the results.