> 1. There is a machine called a "tap disintegrator" that uses an
> electrical
> discharge through a consumable electrode to destroy a hard part
> in a hole.
> Usually a stationary machine, but there are a few portable ones on the
> market. Disintegrating a tap, or in this case a broken bolt, does not
> damage the threads in the part. If you can find a shop that has a
> portable
> rig, or if you want to disassemble the engine and take the crank in, this
> is one way.
FWIW, there are also plans running around to build one of these on your own.
It's called Electrical Discharge Machining, or EDM for short, and I've seen
several articles published in Home Shop Machinist. I believe you can still
buy the back issues with the various articles, and they also sell reprints
of one of the more detailed articles.
http://www.homeshopmachinist.net/
One of the articles talked about using the unit to machine out a broken and
corroded steel stud in an aluminum engine block, made it sound easy
(although slow).
Randall
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