I have used a 1 1/2" diameter bimetal hole saw in a drill press to cut
hundreds of lightening holes in 1x2x1/16" wall rectangular aluminum
tubing. Makes noise and chips like you wouldn't believe, but it's
faster and cheaper than a fly cutter or just about any other metal.
Another aspect not mentioned above is that as the cutter heats up from
friction it will expand and bind in the hole. It is necessary to keep
the cutter fairly cool to prevent this from happening. I had another
person squirting oil and compressed air on the cutter to remove chips
and help hold the long piece of tubing while I aligned the hole saw for
each hole and ran the drill press. The compressed air helped cool the
tubing and remove chips.