Shop Press--Sheet metal Punch attachment.
This attachment slides on the horizontal shop press bar, and has a slider for the forward and backward movement. the slider is made up of 1/2 inch crs with a 3/4 hole drilled in the middle for a dowel that sticks up
1/8 of an inch for the bottom die to rest in. The upper die is threaded into the ram rod.
All that is left to do is to center the bottom die with the upper die now you can cut your hole in the sheet metal.
I made sure my ram rod is square to the punch or bad things will happen.