I'm late to this discussion, but holy cow, an EDM to remove a broken dropout screw? I've done this plenty of times using the method Scott describes below. If the screw is broken flush with the d.o. get your self a standard spring punch and very carefully punch a divot in the middle of the screw. Then start with a small drill, lot's o' high sulphur content oil, a LOT of patience and drill a hole through the screw. Step up to larger drills until most of the material is removed and it's likely you can then get the tap in there to clear out the rest. I would suggest first soak that screw with Kroil or your favorite rust breaker. Let it sit a day or two if you can before going at it with the drill. I find a Dremel motor works well for this application. It's light and easy to keep straight while drilling.
If the screw is broken below the surface of the d.o., very very carefully start with the smallest drill you can manage to keep from bending and breaking and drill the straightest and most centered hole possible. Then, as with the above method, step up to larger drills and remove as much material as you can without drilling into the tapped threads of the d.o. You can either use a tap to remove the waste or pick at it with a sharp dental pick or some such tool and pull the shards out.
Good luck.
Jay Sexton Sebastopol, CA
(snipped)
Message: 14 Date: Mon, 15 Mar 2010 23:28:44 -0700 (PDT) From: minneman@onomy.com Subject: Re: [CR] Snapped ajustment screw To: "John D Proch" <johnprochss@yahoo.com> Cc: classicrendezvous@bikelist.org Message-ID: 1577.99.157.205.104.1268720924.squirrel@www.onomy.com Content-Type: text/plain;charset=iso-8859-1
John,
.......
I've drilled them out before, without much fuss. The trick is getting a
> good (centered) start and staying on line. I'm assuming this is an M3
> fastener. If it's an M4 (uncommon...very early Campagnolo, for instance),
> the drill sizes below are wrong, but the job is much easier and less
> stressful.
>
> Getting a good start is helped by a good divot in the old screw, which you
> can do with a quality punch or, better, with a tiny carbide or stone bit
> in
> a Dremel (think dentist).
>
> After that, drilling isn't really all that difficult. A good quality bit
> really helps minimize the chances of breakage. Either make yourself a jig
> and do it in a drill press, use human spotters for when you're off of
> straight, or make yourself a guide or two so that the desired direction is
> visually obvious (I've used the first and last of these techniques, and
> have
> never messed up a frame). You want a drill bit in the neighborhood of a
> #45...the bigger you have the nerve to use, the less chance you have of it
> breaking. If you're happy with where the bit emerges on the far side, you
> can enlarge that hole even further...up to a #39 or so.
>
> Then, chase the crap out of the threads with a good tap. Again, don't
> economize on the tool. I use a gun tap on through holes like this, so the
> chips get pushed out the far side and don't cause the tap to jam.