Oh,no! Not unless you want to jerk your wrists out of their sockets.
Two straight lines and a half circle, yes? The edge of a 4" grinder will cut like a cutoff tool. It just takes a little longer because you are cutting a 1/4" swath and not an 1/8" or 1/32" swath. Then, hole saw, hog out or V cut in to your half circle. Again using the edge of the disc against the edge of the steel, carefully grind up to your line. If you sweep back and forth as you grind, you will have a smooth radius.
Same thing I do with the cutoff wheel in extremely tight corners, especially when those corners need to be square.
It all depends on what tools you have on hand. Charlie went with a saber saw and time. It worked great for him.
