I've been scroll sawing for a few years, I mostly do wood-cut version of old video game sprites. I've been gradually having an issue with pieces from my scroll saw that I don't have with my jigsaw. After I paint the sides, no matter how much I sand, and how smooth they feel before painting, they start getting frayed. In the first pic from a Halloween decoration, the black-painted piece, this is off my jigsaw. I barely had to sand it. In the second pic, from my scroll saw, I sanded this edge down and it felt smooth, then I painted it and it frayed, sanded again, re-painted. After every painting, it frays.
When you step back and look at the whole piece you don't notice and it's fine, but this feels like it's getting worse. I mostly use 1/2 inch sande plywood from Home Depot, but I will also sometimes use a baltic birch from a lumber yard. Sometimes I mix in 1/4 inch pieces for 3D effect. The issue is not as bad from the baltic but it still happens. I use the Behr interior paints from Home Depot for the colors. Just looking to try and improve my skills.