jls wrote:
I'm rebuilding a Super Cub wing and the flanges on the ribs and the
spar caps have been drilled perfectly so the #4 steel screws go right
in, that is, if a screw has not been broken off. In which case I have
the option of redrilling and turning the spars into Swiss cheese and
losing ac43-13 edge distance on the rib flanges, or drilling out the
broken, embedded screws. Trouble is that when I try to drill the damn
broken screws out they harden and the drill bit becomes useless.

Looks like I need a #45 drill bit made of diamond or carbide. Ideas?
Thanks.

I have a set of silicon carbide tipped drills. The guy
I bought them from used to go around to woodworking
shows demoing them by drilling holes in files and bricks,
glass blocks, all sorts of things, all with the same bit.

Yes, silicon carbide, not tungsten carbide.

Altavista has lots of hits on "diamond drill bit'".

But a #4 screw is tiny. Good Luck.

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FF