Broken tap solutions

[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.

[pjh421]

Universal appeal

Paul

[badgeredd]

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.

Totally agree and the use of a GOOD tapping fluid is esential. I've noticed that many people seem to think aluminum taps easily so no lube is needed. Not true. A tap fluid (I like Tap Magic) sure helps to not create grief for ones self.

[miestro_jerry]

Throw it in your freezer for a couple of days. The tap will shrink and then be easy to get out. We break a tap once in a while and I have tried many methods to extractions. An old machinist in the Bay area told me how to get it out, it was simple make it really vold, the tape will shrink away.

Jerry

[nighthunter]

I haven't seen Premier Thread mentioned here. If the tapped hole is buggered you drill it larger and tap to a larger size then screw in a Premier Thread insert . The Premier Thread has hardened steel inserts that are set into the original material. The chosen Premier Thread is pre threaded for your original thread and you are good to go. They are not very expensive.
Nighthunter

[Sig shooter]

We just did a few on a turbine engine gear box " as recommended " by the overhaul facility . These are staked in place with a built in lock ,were a helicoil will unwind at the start of the thread over time . These are much stouter .

Link to site

[JIMinPHX]

Throw it in your freezer for a couple of days. The tap will shrink and then be easy to get out. We break a tap once in a while and I have tried many methods to extractions. An old machinist in the Bay area told me how to get it out, it was simple make it really vold, the tape will shrink away.

Jerry

Yes the tap will shrink when it gets cold, but the aluminum will shrink twice as much with the same temperature change. I don’t see how this would work.

[Sig shooter]

One of the acids will dissolve steel while not hurting aluminum . I did it years ago to get broken drill bits out .

+ 1 on the BS shrinking tap story . Maybe heat the aluminum , I would try that .

[miestro_jerry]

JIMinPHX,

If the aluminum was 2D, instead of 3D you may be right, but since 3D blocks shink in all directions, the hole will get a little larger and the tap will shrink some, if you doubt this, try it. If the hole was to get smaller, the block would be expanding instead of shrinking. The last time I did this, I threw the block in to my deep freeze over night (next to the deer steaks) and the tap nearly fell out on it's own.

Like I said try it.

Jerry

[Sig shooter]

If the aluminum was 2D, instead of 3D you may be right, but since 3D blocks shink in all directions, the hole will get a little larger and the tap will shrink some, if you doubt this, try it. If the hole was to get smaller, the block would be expanding instead of shrinking. The last time I did this, I threw the block in to my deep freeze over night (next to the deer steaks) and the tap nearly fell out on it's own.

Like I said try it.

Jerry

I Respectfully disagree , the expansion rate is higher on aluminum than steel . Heating will make every dimension larger - hole diameter and length if its heated evenly / completely .

Freezing is 50 -80 degrees cooler than room temp , not much is going to change .
Imagine heating a ring / bearing or pipe , the hole gets larger to slide over the shaft - sleeve - fitting .

[floodgate]

Jerry, JIM, SIG:

I believe that what is happening is that on freezing, the Al shrinks more than the steel in all dimensions, the hardened tap compresses the softer Al, so that when it warms up, the hole expands more than the tap, leaving the tap loose.

Fg

[miestro_jerry]

Floogate,

You are right on one point,

the Al shrinks more than the steel in all dimensions

Instead of talking about it, and giving theory, try this process. If the Al shrinks in all dimensions then the hole will get larger. The only way the hole will get smaller is for the Al to expand and that is done with heat.

If you don't believe me, take a pieces of aluminum tubing, use a good set of calipers or mics on it and record the measurement in the X, Y and Z plains, put it in a deep freeze over night, so the metal will loose what ever residual heat to the temp of the freezer, before it warms up measure it in the same locations. The wall of the tubing will have lost some of it's thickness, so everything has shrunk in all dimensions. Try it. Then realize that the hole thru the tubing got wider.

So go out and try this methods, I have used this method as with many machinist over the years.

If every one wants to meet at my place, I have two large CO2 fire extinguishers, we can use to cool the tubing down quickly, then measure the tubing and chill some beers at the same time, we can measure the beer cans, but I would rather drink them.

Jerry

[miestro_jerry]

If you want to try the inverse of this process, take a block of aluminum, drill a hole thru it, again measure all dimensions, but it in your oven on bake until its about 400 dgree F. The measure the hole and all of the other dimensions, the hole will have gotten smaller and the block will have gotten larger.

Jerry