These are all great ideas that work great but here is another way that is much faster, if not as precise.
Paint on a coat of layout blue and scribe a radius with a protractor. Grind away the excess material with a belt sander using a 3M Cubitron II abrasive. This abrasive literally eats metal! Hacksawing away as much material as possible beforehand helps, too. Quick & easy.
Regards, Neil Tucson, AZ