This came about from a need for a school project for my daughter and I realized that it could apply to our hobby for gasket making.
This punch can be used at any location on a sheet of cardboard. It was "whipped up" in around five minutes from scrap "off the top of my head". No formal dimensions, just "that looks about right".
The cone in the center is for picking up punch marks for locational purposes. The punch is used by simply laying the cardboard on block of wood and stricking the punch with a hammer.
It has a .020 wall thickness with a slight internal chamfer on the id. It was quickly deburred/honed with a stone while still in the lathe.
The cardboard in the picture is .020 thick. Being, "whipped up", the punch is not perfect. The punched slug has to be picked out with an Exacto knife. With some refinements I believe that it could be developed into a useful tool.
-Bob