My first attempt at cutting one to size with a cutting/grinding wheel in my angle grinder didn't turn out very well. For the second attempt, I cut the head off a bolt and used it as a mandrel in my 1/2" drill motor. I clamped the big washer between 2 smaller washers and 2 nuts. After I chucked it in the drill, I put the drill in my vise and locked the trigger down with a zip tie. Then I set the angle grinder to the washer at a 90 degree angle and started grinding a groove all the way around it. When the groove was most of the way through, I shut off the drill and turned the washer a bit at a time, and finished cutting the ring off. Then I used the bench grinder to round and smooth it out while I spun it in the drill. Then I spun the edge against 2 different files and a piece of sandpaper to really smooth out the edge. And finally, I sanded both sides and put some paste wax on it to reduce the chance of rust. I intentionally made it small enough to fit in the can, rather than over top the edge of it, so I can keep it in the can. I should have made it a little bit bigger, but I think it will work okay as is.