I made a rather agricultural GC making system untill I got a Frechex ll from the US.

I used pieces of scrap steel and used broken drill bits (okay I cut the top of a couple to use) and used the drill pres as a vertical lathe and polished them to the required size. As you can see from the pics I did have a couple of tries till I got it right. I ground a slight cup into the end of the drill bit shank to make slight cutting edge. The discs dropped through into a colector jar under the platform

Then it was a matter of drilling a hole that was equal to twice the thickness of the Al material plus the dia of the gc shank of the boolit with a recessed portion at top to sit the disc of Al in.
Another drill bit shank was polished to size.

They were servicable but I was looking for the velocity past where they were effective so used copper in the Freechex tool and because it is so easy I also do the Al checks with it now as well.

Von Gruff.