Cutting (perfect) circles out of paper or cardboard are not easy if you use scissors. With this rather simple construction, it is a piece of cake. I used 5.2 mm pertinax (phenolic paper) I got from a donor. It's very hard, still good to work with a cnc if you have a single flute end mill. Parameters are small depth per cut and fast cutting speed. Don't forget to engage a dust collection as the fine dust is not exactly healthy.