On Monday, July 15, 2019 at 7:59:29 PM UTC-7, John Doe wrote:
I have one regular and one heavy-duty "flying parts" or whatever
they are called hole cutters. The heavy duty is too big to cut a 40
mm hole. The small one probably won't cut 1/4"+ thick 6061 aluminum.

If the hole saw cuts, it will cut a quarter inch just fine.
But, a hole saw in a drill press (vertical downward press)
doesn't clear chips from the cut, you have to back out and apply
suction, or a brush, or otherwise get the junk out of the
kerf. Hole saws work better with horizontal boring, or an active
flood of coolant, or lots of back-off-and-clear-waste.