Well guys, this is a new one for me.
I'm modding a production knife, and need to put a 2-56 screw through the bolster, into the hardened steel liner.
I've tapped 1/4" ti with EASE on MANY occasions. This is a whole different game here.

While I have never purchased any, I figure they probably make carbide taps, or something that will tap this steel. They probably cost $30 or more a piece, I would think.

My other guess would be to anneal the liners in the small spot where I need to tap the 2-56 hole.
I have never done this. Do I just put an acetylene torch with a neutral flame up to the spot, and get it red hot, and then let it cool?
I did a search on three knifemaking forums for "tapping hardened" and "tap hardened" and didn't find much. I think I saw one post, but they decided to put a softer metal in the hole to tap. This is not an option for me.

BTW, I have plenty of Cool Tool II and Tapmagic, as I know that always gets brought up/recommended, no matter what material is to be tapped...
Thanks for any help.

Could be quite a trick.

What about threading the bolster and putting the head of the screw on the inside of the liner, inside out so to speak?

Difficult to say without knowing just how hard the steel is you want to tap. If George's method will work for you, then you should give it serious consideration. If you must tap the steel, then I think I would recommend drilling an oversized hole so that the tap cuts very light threads. This is often done with titanium. Also, I think I'd stay with the HSS taps. They will probably be ruined by tapping the hard steel but they are less llikely to snap off than a thin carbide tap would be (depending on how you support your taps)....

I think you'd be lucky to even get the tap to start cutting. It kinda depends on what steel and how hard it is, but I wouldn't even try it. What kind of steel is it and how hardened? I've burned out broken taps from parts for that exact reason. HSS will almost always self destruct with hardened steel. Carbide can cut hardened steel, but it needs to meet a few conditions. It has to be rigid and continuous. If the pressure is on, then off, then on, etc... it will probably snap.

I burn threads in hardened steel all the time at work with a sinker edm machine. It would be a piece of cake with that. I routinely burn threads in carbide parts.

Otherwise, I'd go with George's suggestion.

Jamie

Well George, Thank you very much sir.
At first, I didn't think this was possible, as I would have still had to countersink the head of the screw in the hardened liner.
However, a tiny little 0-80 pan head screw head, is slim enough to work perfectly. Great suggestion George. Thanks fellas.