“I started with a 1” square piece of double-sided copper-clad PC board. I drilled it in the middle to fit the shaft of the soldering iron, plus a bit so it’s a loose fit. I then used a file to make the square into a disk. While I was at it, I tapered the edges of the hole so the copper surfaces wouldn’t touch the iron shaft and short. I should have tapered the outside edges as well - more on that in a moment.”