A pyramidal broach? Ie, take a 1/4" sq. broach, taper it a little (might
need a grinding house to do this right), drill a 1/4 or 15/64 hole, and
broach away, proly doable on a BP or a drill press.

Greenfield makes a "knockout punch set" for electricians, where you drill a
3/8 or 1/2" starter hole, and thread the male/female halves of a threaded
ball-bearing punch set on either side, and ratchet out your desired pipe
opening--over 2" in many cases.
Maybe you can locate this style of punch for small square holes, altho you
are dealing w/ a substantial thickness for that dimension.

Very fine O/A might could do it also. You can get amazingly smooth cuts w/
O/A, esp. if you get the heat right, and it kind self-rounds the edges--if
you desire. Or it can leave them quite sharp. You'll need some kind of
fixturing guide, for height and dimension. Will take some practice, also.

The 12 ga shotgun suggestion may just be a good bet!
----------------------------
Mr. P.V.'d
formerly Droll Troll
wrote in message
ups.com...
How would I go about cutting small 1/4 inch square holes in 10 gauge
sheet sheet metal?