I had a business removing broken taps and bolts for 18 years. And I think
you might be able to use a Dremel slitting wheel to put a slot like a screw
slot in the end of the tap and then use a screw driver. If you use a carbide
drill I would try a .125 dia. Carbide does not like interrupted cuts and if
you go bigger the cut will be breaking into the flutes. Then break tap out
with a punch. If you use carbide be sure the broken tap is not moving
around in the hole .Because if it moves under load it can break the drill.
And drill from the bottom and the drilling may unscrew the tap. So leave
room for the tap to go if it does unscrew. Jim
wrote in message
...
I have a broket 1/4-20 tap in some 1/2 in steel plate.
(Last hole of 8, of course)

I can access both sides of the tap, the tap is a 4 flute tap
and has a dimple in the end
(Looks like it was setup to drill it out.)

My HSS drill bit does not even touch it.

So my thought is to go to the local machinist supply store on monday
and buy a carbide drill of the apropriate size and drill out the tap
on the drill press.

Should I drill undersize and work my way up to the proper size?
Or should I drill at the apropriate size all at once.

The part is simple and not worth taking to to an EDM shop etc.. I'll
just make another one if I have to.


I can rotate the tap back and forth abut 10 degrees with some small
needle nose. In general I've never had any luck with tap extractors,
alas if one was ever going to work at all now is the time.

Paul