"Jeff Wisnia" wrote in message
...
John wrote:
"Jeff Wisnia" wrote in message
...

John wrote:

I'm trying to determine which of the acids we used to use, in the old
days, to disintegrate broken taps or drills. I remember when that was
done occasionally, but don't remember which acid was used. I have a
friend who has a broken drill in cast iron and I thought this might be
a
possibility before we start chopping at it with carbide tools and make
matters worse. It might at least loosen it up enough to remove by hand.
It's a 1/8" dia. drill and not in too deep, about 3/16", but it's bound
pretty tight.

Thanks
John


If you find something which will disolve tool steel out of cast iron
without eating up the cast iron too, please let me know.

Think EDM...

Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)




You're right Jeff, it might eat up a small amount of the C.I., but in
this
particular case that's not to important. The part is too odd shaped to
mount to a machine table to mill out. If we could loosen the drill
slightly
I think we might be able to get it out.

I just remember that in the past there have been occasions where we
removed
broken cutting tools from a base material with an acid. I don't recall
which specific acid or base material worked the best. Obviously if it
eats
up your part it wouldn't be too good. I wouldn't propose doing it on a
precision machined part, that's why I thought this group might have a
suggestion or two. I've removed many broken tools over the years with
left
hand drills and left hand carbide end mills, but that won't work too
well in
this case.

73,
John (W7JDA)



Try putting a little light oil or Kroil in the hole and then try tapping
against the flutes of the busted drill tip with a sharp punch and a
light hammer.

If it's only in 3/16" deep, I bet you can wiggle it enough to let the
oil get down into the crevices and help you make it easier to back it out.

Ay least that's what I'd try first, you can alway go on to more exotic
methods if my suggestion fails.

Jeff
-
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

Expanding on that idea, if you heat it up first (propane torch should be
adequate, if you use OA, be conservative with it...) and then squirt some
WD-40 into it, it should loosen. A part of the problem is that the broken
drill is tight against the sides and it makes it difficult for the oil to
penetrate. But, if you heat the whole mess up a little, then squirt it, the
oil will cool the drill and it will contract enough that the oil can
penetrate the gap. Then proceed as Jeff suggested.

Jerry