DIYbanter - View Single Post - creating (square) carriage head bolt holes

In article ,
says...
I am in the midst of fixing some farm machinery with new sheetmetal. The
metal I am using is 14 gauge, and the proximity to moving parts requires
carriage head bolts. The previous metal used 1/4" carriage head bolts, and
I would like to do the same. I don't have any idea how to create the square
holes. Each piece of metal is roughly 3 feet by 2 feet, and the holes will
be within 2 inches of one side of the metal.

Any help would be appreciated.

Drill a 1/4" hole, heat the area around the hole to red
with a torch, drive a carriage bolt or a tapered square
punch into the hole. You could probably do it cold with the
punch, but I think you'll get less distortion with the
heat, if that's important to you.

Ned Simmons