I ran across a similar problem to the guy with the aluminum the other day.
During my lathe experiments to make a pivot pin for my knife I discovered I
didn't have any stainless nuts the right size for my pin. No big deal I
thought. I'll just make one. I drilled out a piece of the same stainless
bolt I used to make the pivot pin and then tried to tap it. Holy cow. Talk
about tight. Never could get all the way down to the free spin section on
the tap. I did get far enough to get it on my pin, but it started me
thinking. Is there a best way to drill work hardening materials to minimize
hardening so you can tap it easily?

There are a bunch of little tools and fixtures I have in my gonna build it
when I need it plans that will require drilling and tapping as part of the
assembly.