This is a variation on Aaron Gough’s sanding block (at least that is where I saw this first). The idea behind it is that you have a block with three flat sides that you can use as backing for your sandpaper, and the fourth side of the block serves to hold the edges of the sandpaper. This is achieved by clever use of o-rings and some round stock.
I made a small run of these as a way of role-playing a machinist. Thank Christ this was just a roleplay, because I would starve to death if I had to do it for a living. Nevertheless, an interesting experience.
English