Below are a couple of metal cutting drill bits for a brace, and the holes they bored in a 1/8″ thick brass plate. Also shown is an 18th century style countersink. I ground and sharpened the drill bits to form approximately 3/16″ and 1/4″ holes. The countersunk hole fits a #10 tang screw.
The bits are ground to a basic “V” shape with a slight backward rake (cutting clockwise) on the two cutting edges. You also must grind the flat side down to a point at the tip. If you don’t grind the tip to a small point, then you will end up with an uneven hole and a little pip at the center like you often get turning inside a piece of wood. I ground my tool bits to shape with a 2″x72″ belt sander, and then honed them with 2″x8″ Diamond stones mounted on my bench. I use Diamond stones, with 260 and 600 grit, to shape (the main bevel) and sharpen all my edged tools; and I use them often.
Sharpened as above, the bits and countersink shown, cut out big thick chips of brass,just like it was cutting wax. It didn’t take more than two minutes each to drill those holes. I rarely have anything thicker than about 1/8″ to drill. About the only thing thicker, would be the lock nail hole through the lock bolster, at about 1/4.” A fine grain wrought iron lock plate isn’t much harder than brass.
I plan to make three tap drills for the internal lock screws, the lock nails, and the top jaw screw. The 3/16″ bit and countersink shown will handle all the clear holes.