They make metal hole saws. That metal is likely too thick for a nibbler, IIRC. Sometimes a cone reamer will work well. They make some large ones for pipe up to 2" that I have seen.
Do NOT use a fly cutter with a hand drill. (:oops: ).
I have used an air die grinder also.
Often, your local full service welding or machine shop has a punch capability.
(Talk to them. You might be able to get it done for a 6 pk. left by their back door.)
