This is a tool I developed to cut Pancake dies. There is a commercial one but I was so used to using a piercing saw, I found it easier to control. The original still has the piece of cardboard pushed into the top to shim it to the correct angle. You have to rotate the work rather than the saw,
I found it had a lot more uses and I have developed several variants over the years. The pic below is adjustable, it can be used to cut at right angles, this is useful if you want to cut a stack of silver so that the pieces are all the same size, It can also be used to inlay a complicated shape into a different piece of metal. If you set the angle correctly and glue two different sheets of metal together, the kerf you cut will let the cut out piece of the top sheet fit perfectly into the body of the bottom sheet.