You may be able to back the tap out by reaching down into one of the flutes
with a small punch, screwdriver, whatever and rap on it with a little
hammer, turning it backwards in small increments. Barring that, I'd try a
tap extractror - the fact that you can move it back and forth 10 degrees
suggests a tap extractor might work. If you go for it with a solid carbide
drill, position the drill in a drill press or milling machine exactly over
the center of hole.

Bob Swinney
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