When wall & switch plates are manufactured, they are put through a stamping machine, which cuts out the holes, and the shape of the plate. Then the "blanks are put through another machine that forms the shape of the plate, which is the final product.
In order to replicate the process used during the manufacturing of the final product that you see in the stores, you will have to take time to do it, but may not look the same without some sort of jig to produce a somewhat reasonable product.
oh okay, I understood that is how they're produced, wasn't really sure what you were saying that for though. I wasn't trying to manufacture a plate, just mod an existing decora plate for a coax, but it's all good and done now!