Broken tap

[bushka]

the best tapping fluid I ever used being a machinist was "tapmagic" with that cance causing stuff triclorethene

[grumpy one]

This will work with carbon steel taps. HSS will just peen over. That's why I always use carbon steel in the small sizes, if available. These are sold by Brownells for this reason.
If in a bind, you can have it shattered, I think ultrasonically(some scope mount companies used to offer this service), or cut out with an EDM(this may be what they used).
Morgan

I don't know whether HSS is brittle at low temperatures - many alloy steels are. If so, a liberal dose of liquid nitrogen followed by a smack with a punch would work wonders.

My method for removing broken HSS taps is very slow and fairly destructive of the original thread. I make a punch and use it to tap gently on the flutes in the unscrewing direction, rotating around the flutes in sequence so I don't cause the tap to dig in radially. The biggest problem is when you've backed it up about 30 degrees and have to break the chip. If I were a much more patient fellow I'd make an extractor out of alloy steel, designed to slide down the recesses between the flutes of the broken tap. Then I could apply a pure torque in the unscrewing direction, instead of a series of tangential forces (which is all I can apply with the punch).

As often as not, I end up having to break the tap to pieces, which I do by applying a punch axially. I don't have any particular problem breaking the tap - in my experience HSS is extremely brittle. Of course the pieces then won't screw out: they jostle each other and dig in radially. The next step is to break the pieces into pieces, and lever those out individually. Takes hours, and leaves the thread pretty hopeless so it has to be drilled and tapped oversize.

[floodgate]

Geoff:

"If I were a much more patient fellow I'd make an extractor out of alloy steel, designed to slide down the recesses between the flutes of the broken tap. Then I could apply a pure torque in the unscrewing direction, instead of a series of tangential forces (which is all I can apply with the punch). "

You can buy exactly what you describe; IIRC, they are called "Walton(?) Tap Extractors", and you can get spare fingers for them, which are oval in cross-section to match the flute and the curve of the threaded hole . Trouble is, you need different sets for 2-, 3- and 4-flute taps, and for each size tap you use - I started getting them, and found they add up in $$ (US, AU or NZ) pretty fast; and they still aren't perfect, if you shear one of the "fingers" off and have to extract it too.

My experience is altogether pretty much like yours.

Floodgate

[No_1]

Floodgate and Gentlemen,

RIDGID makes the same thing you just discribed.

R.

Geoff:

"If I were a much more patient fellow I'd make an extractor out of alloy steel, designed to slide down the recesses between the flutes of the broken tap. Then I could apply a pure torque in the unscrewing direction, instead of a series of tangential forces (which is all I can apply with the punch). "

You can buy exactly what you describe; IIRC, they are called "Walton(?) Tap Extractors", and you can get spare fingers for them, which are oval in cross-section to match the flute and the curve of the threaded hole . Trouble is, you need different sets for 2-, 3- and 4-flute taps, and for each size tap you use - I started getting them, and found they add up in $$ (US, AU or NZ) pretty fast; and they still aren't perfect, if you shear one of the "fingers" off and have to extract it too.

My experience is altogether pretty much like yours.

Floodgate

[JIMinPHX]

This will work with carbon steel taps. HSS will just peen over. That's why I always use carbon steel in the small sizes, if available. These are sold by Brownells for this reason.
If in a bind, you can have it shattered, I think ultrasonically(some scope mount companies used to offer this service), or cut out with an EDM(this may be what they used).
Morgan

I don’t know about the ultrasonic deal, but an EDM or it’s little brother, the spark eroder, will both eat through either HSS or Carbon steel & not wreck the tapped hole in the process.

[deltaenterprizes]

I have read that ALUM will eat the steel and not harm the aluminum.

[Newtire]

Since you have a half buggered hole already, you may want to go with a heli-coil or thread insert collar to fix up your current piece. These are not hack & slash repairs. Some of the aluminum aircraft parts, that I used to make, specified heli-coils in the original design because they provide a more robust thread than a straight tapped hole.

Just my 2-cents. We use Time-Serts instead of Heli-coils as they give a better hold on the work. Cadillac is using these to screw head bolts into. We did the heli-coil route on torpedo motor casings on one now-obsolete model when I was in the USN. These Time-Serts have Heli-coil beat hands down. You can even get them in oversize called "Big-Serts".

[monadnock#5]

This is an extremely interesting and informative thread. Great stuff from pros and advanced hobbyists. I do believe this thread belongs in the "Sticky" Hall of Fame.

The only tip I can offer is a front end suggestion. When you're into a project that you only have one chance to do right the first time, always, always, always use a brand new tap.

[cr17]

I agree with monadnock -- and I'm always amazed at the wealth of information on this site. Quick note though, don't bother with the alum. I tried various strengths for up to 10 days, and at moderate heat ( sat it on the furnace). The only result was that the aluminum turned black.

[uncle joe]

you just taught an old dog welder a new trick. thanks!

I had a guy remove a stuck and broken setscrew that was in a 4 foot diameter sprocket. It was about a half inch setscrew and the top of it was about 2.5 inches down in a hole. He took a stick welder and welded a little and chiped flux a little over and over til he could weld a nut on top of the hole and wrenched it out. My mechanic I sent with it said it was the coolist thing he ever saw. He also learned a valuable lession that we all have used many times.
I removed a broken quarter inch tap from a hole with an air arc tool once, removed the tap and left all the threads in the hole in tact. Thought I was hot S#*$ till I stuck another tap in the hole to chase the threads. The air arc rod had coated the hole with carbon, can't cut it with a tap, had to move the hole.

it might not be easy to teach an old dog new tricks but if he's a smart dog you can learn new tricks from HIM