Sheet-metal drill
The sketch in Fig. 1 shows a modified high-speed twist drill that will make clean round holes even in very thin metal stock. This type of drill, which was brought to my attention by Sgt. L. W. Atkins of the RCAF, can be made from discarded, worn-out drills. First, grind a wedge on the tip of the drill as shown in the sketch at the right in Fig. 1. Then rotate the drill 90 degrees and grind the drill to resemble the sketch to the left in Fig. 1. Grind a small rake on the cutting edge of the drill to insure clean chip removal. Drills down to inch can be modified this way without much trouble.
Fig. 1. Sheet-metal drill.
R.R. Sopczak, VE3ABL.