Originally Posted by
modelmartin
A lot of repliers (replicants?)got bits of this right. I am a trained professional machinist and here is what I think. Once you get past the case hardening you get to the soft, chewy center and you can buzz away with a HSS drill. Carbide is not required here. Carbide drills are expensive and brittle. Since you are drilling through the tapped hole you would likely be away from the hardened area anyway. I would do this with an electric drill in a vise! Drill half way from each side.
You're probably right about not needing a carbide bit, but you never know how tough these grades of hardenable steels are. Alternatively, I would not expect the case hardening to be anywhere near the tapped hole bore. FWIW, I am an engineer with over 30 years working with steels, mostly surgical stuff, though. I've worked on lines using carbide tipped gun drills for boring titanium about this size.