Recently had to make some rectangular cut outs in 2 mm aluminium sheet with a hand held nibbler which is always a pain to get neat, so I was casting about for easier methods.
There are 'Throatless nibblers' where the die pokes out of a table and cuts on the down stroke - very handy, but not cheap and they take up floor space.
There are punch and die sets for Fly Presses, but the depth of sheet is very limited by the upright of the structure and again they take up much floor space for the arm to swing.
Then I cast eyes on my Richmond 3 foot radial arm drill. Very heavy construction, lots of room for biggish panels, perhaps I could make some sort of reciprocating punch holder, and rig the corresponding die on the table with guides for the sheet.
Then I thought - don't be daft - you've got precisely that hung on the back of the Bridgeport in the form of a slotting head.

Crank woggles a cutter up and down at a rate set by change gearing, and again masses of room for a biggish sheet of metal. Only issue that I can see is arranging some form of 'stripper' to stop the sheet being pulled back up by the punch as it withdraws.
Anyone been there and done this? Or have any comments on the strength of 'push' of the standard Bridgeport slotting head. How much force does it take to ram (say) a 3 mm circular punch through 2 mm aluminium sheet or 1.6 mm galvanised sheet?