In the need of cutting a round hole (really round!) into a piece of polystyrene foam (in europe we call it styropor), this tool was designed. Whit it, it is possible to cut a round hole (guided by the 4mm drill) into any foam-like (or other soft...) material.
It was designed for minimal material use and printing time (made mine on a prusa with a 0.35mm nozzle within less than 15mins.