The mild steel blocks from earlier.
Drilling for an M3 tap. This drill is intended for aluminium, but was all I had to hand and worked fine.
Tapping M3. This tap is also intended for aluminium.
Drills for a #4-40 tap. Actually correct for steel!
The actually correct tap, or at least what's left of it. I don't know why this broke. Well, I do, it was way too tight in the hole; but I calculated the tap drill size the same way I did for the M3 one.
I flattened the top off with an end mill and tried to get a left-hand drill to bite into it. As expected it just skidded off.
