Other option is a cnc plasma or laser system.

Martin

On 11/3/2011 12:32 AM, David Lesher wrote:
A friend asked:

Need to cut a few (=6) 5.5" holes (actually 140mm, but that
is 5.51", so close enough) in 1mm sheet metal (carbon steel, I
think).

2 side by side holes initially in a roughly 20"x17" piece of 1mm
cold rolled steel with one finished side. May need to put holes
in 2 similar pieces of sheet metal later on.

I thought:
HF has a flycutter with a carbide tip...
http://www.harborfreight.com/carbide-tip-adjustable-circle-cutter-68117.html

That, a longer arm& a drill press...