any chance you could center a 1/4" carbide endmill over it in a mill?
MSC might have c'bores.
can't seem to find a carbide step drill anywhere. I tried drilling through this stuffDoes anyone know where I can buy a carbide step drill or counterbore for 4-40 pan head screws. I need to put some screws into a hardened steel gear. I
with a cobalt drill and it wouldn't touch it. Then I chucked up a carbide drill and
it goes through it nicely. Now I just need to find a supplier...