oops,hardened the blade before drilling for thumb-bob

OK ,I can anneal the blade,drill the hole,reharden and temper,I don't like this option because of the scale clean-up.Or try to drill the hole with carbide bits,very fragile and at $10 per bit this could get expensive.Or silver solder one on,I was thinking of a different sort of thumb-bob anyway,since its a damascus blade,maybe a small piece of the same damascus.Anyone ever try this,and if so how did it work?

Sounds like something I'd do . . .

Actually, I would try to drill a hole in the hardened blade. MSC Industrial has ATRAX solid carbide drills in sizes from 1/32" up. They are spade drills (no flutes) so they're pretty tuff - I use them on hardened liner-lock blades to drill the detent (I like to do this on the hardened steel so I get a good sharp detent form) and they really work well - you should be able to drill through a blade pretty easily. Cost is around $8 for sizes 1/8" and under, so they're pretty reasonable.

Those silicon carbide spade bits can do a great job for you on those thumb bob holes. Actually Iuse two sizes for this job. I use a 3/32 and a 1/8 to counter sink. I do all my thumb bob holes after heat treat and of course the detent hole as well. Frank Niro

If the thumb bob is threaded, that limits the options...

Craig