You might also try a left-hand (that is the reverse of standard,
right?) drill bit. HF sells 'em, and you may also find them packaged
with a set of EZ-outs at the BLUE or ORANGE stores. That might work if
the screws aren't corroded into the holes. If there's enough of a screw
left, I've also had mixed results filing flats on the screws 180
degrees opposed, and grabbing on with a crescent wrench or vice-grips.
Careful, don't break the screw off a second time like I did.

You might also try drilling with cutting fluid. I had a similar
experience trying to drill out a set of rivets holding the ball joints
into my Dodge. (Wadda they make those damn rivets out of anyway?) With
the hand-electric drill it took 27 broken bits and 4 days. When I did
the other side, I pulled the a-arm out of the truck, mounted in a vise
on the drill press, and then drilled down using a 1/64" cobalt bit and
cutting fluid. It only took about 5 minutes per hole using 7 different
sized bits to achieve the same results. I wasn't using any more
pressure or speed with the drill press. So maybe the cutting fluid is a
semi-magic bullet?


jls wrote:
wrote:
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.

--

FF

Thanks, Fred. All these ribs I bought from Northland in Dakota
Territory @ $50 apiece were already drilled for screw holes-- eight per
rib and two for each nose rib. They matched up perfectly to the holes
drilled in the spars when this aircraft was built at the factory in the
fifties, so when I began fastening new ribs to the old spars I began
finding holes that were stopped up, i. e., holes where screws had been
broken off.

So a guy in the Supercub Club from the Cleveland area has advised me to
buy a pencil die grinder, i. e., a carbide tipped tool--- like the
dentists use--- to drill out the embedded screws.

Thanks for your very informative post.