On Saturday, April 9, 2016 at 4:18:19 PM UTC-7, John Doe wrote:
I need to cut a 1/2" square through 1/4" aluminum. It doesn't have to be
centered, but the dimensions of the hole need to be correct.

Mark out the 1/2" hole carefully, drill a pilot hole in the center, and file it
to the mark. If you have a well-lit bench and can get the workpiece into
a vise, it's easy. Take ten or twenty minutes.

In mass production, you could broach or drill it.