Just re-read this thread and missed some of it last time. A square, rounded and straight chisel work very efficiently cutting out metal up to about 1/8" thick on a treadle hammer. It takes two passes but it works great. Those patterns on my previous post only represent ideas. If you want to make one from copper, you can take two pieces of plywood and cut out the outline, you can then place bolt holes all the way around and bolt a piece of annealed copper within it. this way you can force it out to give it some depth. You have to create a right and left side then phos-copper or solder them together after trimming the edges. This was demonstrated by a very talented member of the MS Forge Council, I have not done it myself yet but am looking forward to giving it a try.