"Molly Brown" wrote in message
...
I usually somehow manage to remove a broken bolt but in this instance
that is not an option so I need to drill it out. The bolt is probably
hardened steel and I am using a drill press at 300 RPM, a cobalt bit,
and metal cutting oil. I have had the drill press arm bungee tied for
the past few hours and all I got was about a millimeter. Is this
normal or am I doing something wrong?

Sometimes **** can be spectacularly and anomalously hard. For example, I
was trying to drill/tap some holes in the ends of a dumbbell for an eyebolt.
One drilled fine, the other was like glass, absolutely un-drillable.

A carbide bit might help, but maybe you just have to heat the thing red hot,
and let it cool slowly (cover with sand or sumpn), to anneal.

Also, some stuff is superhard, but just on the surface, as in
case-hardening, while the interior is softer, sometimes very soft. If you
try grinding away 1/16 inch or so, you might find it much easier to drill.

I wonder if they make a "grinding drill", which would basically be a rod
coated with aluminum oxide, to just grind a hole through.... which could be
a very slow process. You could run this idea by the folks at
rec.crafts.metalworking.

I doubt a bungee cord is doing anything but dulling the bit.
--
EA