Another Poker Kitty find. Next day, reading glasses on, beer goggles off, easier to tell just someone with too much time on hand. Still wonder how they did it...............
You hold it in one hand with your thumb in the middle stabilizing it on your first finger. Then file strokes to the side of your finger, rotating the quarter before each file stroke again.
Bad pic guys, and, the relief hides how uniform the INNER perimeter damage / filing is. Pretty certain it was machine-done. Just can't tell how it was mounted - reeding is unblemished, obverse is intact too