You can drill hardened Tangs by heating the tang up with a torch to RED color and drilling the tang while its hot, using ordinary drill bits. The heat makes the tang so soft its like drilling soft pine wood. You might want to draft SWMBO to hold the propane torch while you use both hands to control the drill and bit. A wet rag slapped onto the tang after the hole is drilled, and the torch withdrawn restores the hardness to the tang, altho it doesn't make the tang brittle, in my experience.
Clamp the blade in a bench vise to hold the blade while you heat the tang, and drill the holes.The jaws should be set where the tang and the blade meet. The steel jaws of the vise will serve as a Heat Sink. This protects the blade from BOTH softening, and discoloring. If you have aluminum, brass, or copper " Soft Jaws" that you use over the steel jaws, these metals conduct the heat away from the blade even faster than steel does, so leave the "soft jaws" on the vise to grip the blade. The soft jaws insure that you don't mar the blade while doing this work.
I agree that drilling the holes for the pins in the tang before you do the hardening and tempering processes is the SMART thing to do. However, Life doesn't always work out quite the way we plan :shocked2: :blah: :rotf: :idunno: :surrender: sometimes.
If you have to drill another hole, and only figure that out AFTER you have hardened the blade and tempered it, All is NOT LOST. And, this way, you don't even have to think about buying some expensive, Carbide-tipped drill bit to drill one Stinking HOLE! :cursing: :haha: :grin: :v :thumbsup:
Please don't ask how I learned this piece of wisdom. Thank you, kindly. :bow: :wink: