2 Nov
2007
2 Nov
'07
4:23 p.m.
I've come to the conclusion that most people who
have success with
tap extractors buy really cheap taps that break if you look at them
crosseyed. A good tap, when it breaks is impossible to remove with a
tap extractor.
Good tapes are, of course, hard and thus brittle.
Most of the time tape break for one of 4 reasons :
1) Applying a sideways force (not just a torque) to the tap. Often by
using a ppoor tap wrench
2) Not clearing ou the swarf often enough. The old rule was '1 turn
forwards, them half a turn back (to clear the swarf)' With practice you
can feel when it's gettign too stiff, I normally remove the tap
completely every few turns (peaticularly on blind holes) to clear the
hole out/
3) Using a blunt tap
4) Haivng too small a hole to tap.
I suspect a tap extractor would work for case (1), but the sort of person
to have a tap extractor is also the sort of person to use the right tap
wrench and apply an even torque to it.
A very slick way to remove a steel bolt or tap that's sheared off in
an aluminum casting (e.g. a hard disk body) is to use nitric acid
and a little heat--the acid doesn't bother the aluminum but eats
enough of the steel to loosen it for removal. I've heard that alum
(I don't know what sort, probably amonium) also works.
I've heard EDM can work for this, but I've never tried it. The though of
discharing large capacitors charged to 50V or so is a little 'interesting'
-tony