If I remember correctly, cast iron is more resistant than steel, to attack
by sulphuric acid. If you can fill the hole with H2SO4, you may find that it
dissolves enough of the drill to remove it. You'll have to keep trying it on
a regular basis though, as I have no idea as to how long it will take. I
could give you the usually boring warnings about strong acids and gloves and
glasses, but if you don't know enough about already, you shouldn't mess with
it at all.

Tom miller
"John" wrote in message
...

"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)



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