On Nov 16, 1:52*pm, "Pete C." wrote:
I have a 3/32" HSS bit broken off ~1" deep in a blind hole in a 7075 AL
part, only a tiny stub of the bit is sticking out. Suggestions on how to
remove it without damaging the part?

Thanks,

* * * * Pete C.

I have had some luck using a small high speed tool like Harbor
Freight item 47869 and dental drills. It is not too fast, and I
would not recommend it on any tap bigger than 3/32 ". The tap gets
hot and loses its hardness to some extent.

i have also kludged up a electric discharge machine using a drill
press to hold the electrode. It was pretty simple. An isolation
transformer to a voltage doubler. Then through a light bulb to a oil
filled capacitor and on to a finishing nail in a dowel in the drill
press. The light bulb acts as a resistor that increases in resistance
if there is a short. The distance is critical . We ( I did this for
and with a friend. ) set the stop on the drill press and could get a
very slight movement by leaning on the down feed. We used kerosene
and had the part immersed in it. Since the sparks all occurred in the
liquid below the surface we did not have any fires. I do not
recommend this unless you have a reasonable background in doing stuff
like this. Lots of ways to get shocked or cause a fire. This is also
not very fast. My friend had broken a tap off in a .45 slide. After
doing all the playing, he took the slide to a machine shop and had
them burn out the tap.


Dan