When I was at ID school in the early '90s the shop didn't have any freaking countersink bits, so we'd have to drill pilot holes with a 3/32" bit then ream it with a 1/4" to make a sort of ghetto countersink. (And this was before keyless chucks.) By necessity we all got pretty good at doing this, but I was never so happy as when I bought my own countersink bit.
Anyways, here's how they make the little things (and plug-cutters to boot). I know it's just a tiny piece of steel, but it's still one of the favored objects in my toolbox.
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