So, I plunge-milled, threaded, and filled a misplaced feature with what appears to be a non-stainless set screw and Loc Tite 271. I milled it flush with the frame, center-drilled at relatively low speed with plenty of coolant, then attempted to start drilling with very small drills. It keeps work-hardening, or at least that's my guess, because very quickly, the drill just stops cutting. I'm able to grind through with a very small diamond-point or tungsten carbide dremel tool, but every time I go back to a drill, center drill, or even a mill, it clears a few chips, then stops. I've varied my speed, feed rate, etc., but still the same outcome. When I milled it flush, it didn't seem like particularly hard material, at least to start with. Any ideas on how to overcome this stalemate? I'm thinking carbide, either a straight-flute, or a carbide end mill?