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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 have also had mixed results filing flats on the screws 180
degrees opposed, and grabbing on with a crescent wrench or vice-grips.
Careful, do not 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:
> fredfighter@spamcop.net wrote:
> > jls wrote:
> > > I am 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've
> > > 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've 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.
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Re: aluminum rib, aluminum spar, holes drilled but screws broken off
