Broken tap solutions

[cr17]

Ok I need help here. I broke off a 4 flute 1/4 tap in the %%##^%# hole - well below the surface in a piece of aluminum. Any recommendations on getting it out? Walton tap extractor? EDM if I can find it, anything else? Anyone tried the old alum method. Did I mention %#^#^##^#

Thanks

[mike in co]

there is a kit sold for this. try a couple of the online machinest stores. emco, grizzley.

or buy a dremel type tool and a couple small carbide bits. cut the tap in pieces.
go slow....

mike

[scb]

Yea, being a 1/4" tap you may be able to cut it out with a carbide burr in a dremel tool. I've done it. But like mike said go sloooow. If you break that carbide burr off in the hole then you are screwed. Done that too. I haven't used it but MSC is selling a carbide drill set specifically to drill out broken taps. If it one of those "must save" parts I think I'd give them a try. steve

[10-x]

How tight is the broken tap in the hole? Were you cutting threads or backing it out? Is it a blind hole or through hole? Blind holes are hard to deal with.If backing it out try the tap extractor using acetone as lube. If cutting try tapping on the broken end of the tap with a small pin punch and a small hammer to loosen it up and then the extractor and acetone.
Another reason to use 3 flute taps.
Good Luck

[johniv]

GO SLOW, I havent used the new tap removal stuff for sale now, but years ago I brok a 1/4 " tap off flush in a hole (blind) and a MASTER welder in the shop TIG welded a small pillar on top of the broken tap and forked the top, it was then removed with a plier. key word here is MASTER welder.
also it was broken in a steel workpiece so this may not be possible for you. Just my 2 cents worth.
I feel yer pain.
John

[Sam]

Get with your dentist and get your hands on some old dental burs.
They are diamond an dcut much better and are easier to control than carbides.
They will easily remove the worst broken taps.
Instead of cutting off the "webs" of the tap cut straight down the center and then cut outward. They break like glass.

Unless you are really really really good at it never use HSS taps.
Broken carbon steel taps are much easier to remove:-D

Sam

[JIMinPHX]

You’re in luck because it’s in aluminum. Put a 5/16 nut over the hole & stick a mig welder down in the center of it & weld the tap to the nut. Don't be shy with the heat. About 5 seconds after the orange glow goes away, turn it out with a wrench. Steel mig wire doesn’t stick to Aluminum & the heat from the weld will expand the aluminum & loosen the tap. Aluminum expands much more than steel does when you heat it. I’ve done this for broken exhaust bolts on Harley shovelheads several times. It works great.

[Lloyd Smale]

you just taught an old dog welder a new trick. thanks!
You’re in luck because it’s in aluminum. Put a 5/16 nut over the hole & stick a mig welder down in the center of it & weld the tap to the nut. Don't be shy with the heat. About 5 seconds after the orange glow goes away, turn it out with a wrench. Steel mig wire doesn’t stick to Aluminum & the heat from the weld will expand the aluminum & loosen the tap. Aluminum expands much more than steel does when you heat it. I’ve done this for broken exhaust bolts on Harley shovelheads several times. It works great.

[Bret4207]

Don't bother with the tap extractors. Do as Jim recommended or go EDM.

[dnepr]

I thought there was a chemical the would attack the steel tap but was safe on aluminum . For the life of me I can't remember what it is called . The idea is that you fill the hole with this stuff and it disolve enough of the tap to make it loose but this stuff doesn't touch the aluminum. It is supposed to be a slow process it takes somthing like a week to get the tap loose enough to come out.I remember hearing about the stuff but I have never tried it myself. The old memory isn't what it used to be.

[fishhawk]

what i have used in the past before i was "wealthy" enough to get the brownells tap extractors was nitric acid takes time but it does eat the steel and iron. it can be found in small quanities know as "aqua fortis stain" many muzzleoaders are stained with it after aplying it then heat. just not sure what it will do with alum.

[leftiye]

Lloyd, .... What do you weld on them dogs? (I know, .... couldn't resist)

[John Taylor]

Have removed many broken taps with a milling machine and a carbide end mill. I use old broken end mills and sharpen them like a cold chisel. Run the RPMs higher than normal and you can drill right through the center of the broken tap and then dump out the pieces.

[cr17]

Well I should give an update. I went for Jim's solution but I can tell you that convincing the local welder was a challenge. (Mind you this was all in French, and my technical welding vocabulary is nil.) Neither he nor his father, an old machinist from the logging/mining camps up north, believed it would work. In fact, he bet a gallon of maple syrup that it would ruin the whole piece. So no I have a gallon of maple syrup coming when the sugaring starts, a piece that I can use ( I buggered the hole in my ham handed attempts to get it out) and a new technique.

Thanks all

[scrapcan]

Sounds like all worked out well. You will ahve a lot of use for the gallon of maple syrup. and best of all I got to learn a new technique also.

[JIMinPHX]

I’ve also got another little broken screw removal trick that involves a cam shaft & a left handed drill bit that a lot of people tell me can’t work, until they see it done. That’s a story for another day. I’m glad that this worked out for you.

In the future, if you’re tapping 1/4" threads in aluminum, you may want to consider a roll tap (Also known as a thread flower, a forming tap or a Ballax tap). Roll taps make threads by displacing material rather than by cutting it. They actually swage the threads into shape. In aluminum, they make stronger threads because of the surface compression. These taps are also much harder to break because they have no flutes cut into them. They just look like a screw. If you use one of these, you need to drill a different size (larger) pilot hole. You also need to use plenty of thread cutting oil. These work great in aluminum, but they are not so good in less ductile & less malleable materials.

My second choice would be a two-flute spiral-point gun tap, if you want to stay with a “cut tap”. The gun taps are much stronger than a standard hand tap & take abuse much better. You also don’t need to stop to clear chips because they push the chips ahead in front of them. You just run them straight through in one shot. With a 1/4" gun tap, I usually just put it in the chuck of a cordless drill, dip it in oil & run it right through. The only down side to a gun tap is that they are not the best in a shallow blind hole because the chips that they push in front of them have no where to go. Gun taps can be had for pretty much the same money as a standard hand tap & they use the same pilot hole drills.

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. The other tapped holes in aluminum aircraft parts were usually specified as roll tap only. You can get roll taps, gun taps & a good selection of thread inserts from places like MSC.

[MtGun44]

I have never needed it, and with modern fears about mercury, maybe
nobody would do it, but ---

Brownell's gunsmithing kinks book years ago said you could heat the
broken tap up to red head with a small tip acetylene torch and drop
a drop of mercury on it from an eyedropper to cool it ultrafast. Of course,
this would vaporize some mercury, so do it outdoors, etc., etc. or don't
do it at all.

They claimed it made the tap so glass brittle that you could break it up
into tiny chunks with a pin punch and pick out the pieces.

Never tried it, but it was so interesting that it stuck in my rat trap of
a brain,using a liquid metal to get a cooling rate faster than with water.

Bill

[EMC45]

I have always heard to use a selfloading punch and just pop it and it "should" break!

[Morgan Astorbilt]

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

[JIMinPHX]

I usually just try to use taps that don’t break easily & treat them properly. When I was doing production work that involved tapping a 1/4-20 thread an inch deep in 6061-T6, I would get about 1200-1500 good tapped holes before I’d break a tap. The taps that I was using were not much more expensive than the ones you find at the hardware store. They were just better matched to the job at hand.

[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 (http://gsgindustrial.com/searchresult.aspx?CategoryID=344)

[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

[Sig shooter]

Unless your working a 3 - 4 inch dia. ring , I doubt normal freezing will make a measurable difference with calipers . But what do I know ... I will shut up and stop lighting off the short fused folks .

[miestro_jerry]

I have just asked that people try this method, and it seems nobody will. So maybe it's time I say goodbye to the forum.

Jerry

[Junior1942]

Calm down, Jerry. we don't break taps in aluminum every day.

[No_1]

Hi Jerry,

Just because people who have posted here do not want to try your suggestion does not mean that the rest of the non-posters do not hear you or would not / have not tried it. I am sure there are plenty out here that have listened and marked it down in "the book of things to be remembered". Years ago when I worked in an automotive machine shop we use to weld a pass around the inside of valve seats that were in aluminum heads. The pass on the inside caused the seat to shrink allowing us to just lift it out once it was cooled. There was never any damage to the head. We would then freeze the new seat and drop it in the head. So here we have a case of heat making something smaller then cold doing somewhat of the same thing. That alone was an example of how tempature does things that don't seem right.

Hang in here brother.

R.

[miestro_jerry]

Junior and Robert,

I have dealt with machining most of my life, I own a machine shop out here in BFE. This is one simple method for extracting broken taps. There are many other methods, including special tools to get the piece of the tap out.

If some one states an opinion without the experience behind, it shows a great deal of ignorance to me and the inability to think in the real world. I am not insulting anyone, because many people only think in simple methods and with a lack of experience. I even have people show up to my shop asking me to get a tap out of other materials, things like 4041 steel or Titanium. I use the freezer method with them. I do not recommend the chemical extraction methods because of the chemicals reactiveness and the possible damage to the work piece.

Some of them, I get out an old CO2 fire extingusher and while cooling the metal down, we have a couple of cold ones to sip on while doing this process. Today is a cool drink sipping day here.

I am building Bat Houses this afternoon, no machining involved.

Thanks for putting up with me,

Jerry

[floodgate]

Hey Jerry, my idea was just that - an idea, and I have not tried your solution. I useta be a physicist, and could probably gin up some numbers to support my speculations; but experiment ALWAYS trumps theory! Next time I break a tap in aluminum, I'll give it a shot and see. Stick around; we need your insights!

Floodgate

[Mumblypeg]

I'm no machinist but I think Jerry is right. It's the metal that's shrinking, not the hole. But you know what? All we have to do is try it before we go and say it won't work. Hang in there Jerry is't no big deal. Say, you ain't seen my wife in one of them houses have you?

[JIMinPHX]

Geeze,
I guess that it was me that started all this mess with my doubting words. Please allow me to explain myself a little better.

Based on my experience heating aluminum carriers to remove steel bearings & things like that, I know that aluminum expands & contracts more than steel does when exposed to a temperature change. I also know that when steel gets heat treated, it grows & holes in it shrink. That’s why die taps are slightly oversized. They allow the tapped hole to start out oversized so that after heat treat, it will be what you want it to be. Based on that experience, I said that I didn’t see how the freezer method would work. I was not calling BS on Jerry’s statement as another then posted, but I was expressing my doubt & hoping for more information. More information has since been provided. The freezer trick still seems unlikely to work in my opinion, but not having tried it, I can’t say for sure & I realize that. I don’t feel like sacrificing a tap just to test out the suggestion, but the next time that I do break one, I’ll give the freezer method first shot at solving the problem to see what actually happens.

A lot of people doubted my method of welding a nut to the remains of a tap & that worked out well. That was an example of popular wisdom being incorrect, as was the old wives tale about lead boolits needing to be kept under 1,000fps. This board is full of examples of people bucking the trends of popular wisdom to discover where the difference between fact & fiction really lies.

Jerry, please don’t allow yourself to be driven off by a few nay-sayers. Regardless of whether your trick works or not, it is something new to try that deserves to be explored. I for one appreciate the diversity of options provided by people speaking their thoughts openly. I hope that you will remain here as a contributing member. I apologize if my post seemed like it put you down or inspired others who did. That was not my intention. If your trick actually does end up working when I try it, I will then thank you for it

[JIMinPHX]

Hey Jerry, my idea was just that - an idea, and I have not tried your solution. I useta be a physicist, and could probably gin up some numbers to support my speculations; but experiment ALWAYS trumps theory! Next time I break a tap in aluminum, I'll give it a shot and see. Stick around; we need your insights!

Floodgate

From a related field of endeavor –

Engineering: the fine art of obtaining knowledge by observing the unexpected after engaging in lengthy & painstaking calculations to predict the apparently obvious…that was actually wrong.

Anybody that’s ever been involved in new product development will attest to that.

[miestro_jerry]

Engineering is the fine art of turning theory in to a usable reality. I used to teach advanced math, physics and but mostly engineering. I have owned my own machine shop since 1994, and have listened to many old timers and tried their ideas out, most of them do work and very well.

There is an urban legend about the mathematician, the physicist and the engineer trying to say that a Bee can't fly because of, math - the drag to lift ratio, physic says the energy that the Bee has to the weight ratio and the aero dynamic feature prevent the Bee from flying. The engineer observes the Bee, who has go into flight by this time from being bored, the engineer want to know how to make the bee go supersonic despite the math and the science. That one is simple buy the bee a place on the space shuttle. :)

Many of these things I have studied at university even to thru my post doctorate studies, I make engineering practical, so the average person can understand what to do with the situation.

Plus I make some really nice rings on my lathe out of Titanium and Carbide, I tig gold in a fusing process and a whole bunch of other things in my day to day work. Today I need to make some bat houses or bat boxes for the local bat population. Instead of using pesticides or other chemicals to control the mosquito population I use some basic ecological engineering. Get what is known as the Indiana Bat to roost near the mosquito breeding ground. So the boxes becomes their seasonal homes. Each bat eats about a million mosquitoes a season. Currently I have two 50 bat boxes built and will work on a much larger one for breeding bats in. I will install them way up on trees later this week.

In academia this statement is not the norm, but is very true and is common:

Engineering: the fine art of obtaining knowledge by observing the unexpected after engaging in lengthy & painstaking calculations to predict the apparently obvious…that was actually wrong


When I state something, it comes from experience, some times I even say 9 of 10 times it works when such a statement is applicable.

Right now, I am trying to calculate the a Lee 7mm, 130 gr bullet mold, mill of the gas check portion, look into making this a HP mold, trying to get the weight down for my 7TCU barrel and shooting of the 7 TCU cartridge. Other than the cost of the mold, it is my time and experience to do such a thing. I am figuring it will be 110 grains when I get done, give or take a few grains either way. From that I can derive much knowledge on how it is done and what would be the pluses and minuses of doing this, in short, more engineering and machining knowledge to pass on to people.

So when I say try it, it is worth trying. Plus I have digital calipers that are good to 4 digits to the right of the decimal point.These are my HF calipers, I still have a great number of the vernier type of caliper, gages and mics.

If we want to talk about getting the tap out of a block of aluminum cost effectively, recycle the alumnum with the tap still in it and start over again. We seems to waste a lot of time in trying to make something work, when it is easier to replace it. That is good time management, something I took during my masters program.

Jerry

[miestro_jerry]

Oh I forgot to mention the answer to everything is 42. :D

Jerry

[JIMinPHX]

the engineer want to know how to make the bee go supersonic despite the math and the science. That one is simple buy the bee a place on the space shuttle. :)



The shuttle is super sonic? I didn't know that!

;-)

Just breaking your chops in a friendly sort of manner there Jerry...

[JIMinPHX]

I tig gold in a fusing process and a whole bunch of other things in my day to day work.

I fooled around with that a little when I was looking into some processes up at a place called Michael Anthony Jewlers in Mount Vernon NY. Those guys produce a LOT of gold jewelry. They've got their processes just about down pat. The gold fusing with a Tig takes some fine tuning to get set up right, but when it's set up perfect, you can't even see the seem. The big brew ha ha when I was up there was finding a more precise way to control the thickness of the gold foil they extrude. .0002" wasn't good to keep them happy. With the price of gold these days, they're probably back on that kick again.

[miestro_jerry]

JIMinPHX,

To leave the earth, the shuttle has to be going about 17,500 miles an hour or Mach 25.

Besides the machine shop I own a jewelry studio. My website has some of the stuff that I do:

http://anvilsandinkstudios.com/studiopage3.html

http://anvilsandinkstudios.com/studiopage2.html

http://anvilsandinkstudios.com/studiopage4.html

http://anvilsandinkstudios.com/studiopage5.html

You can explore the rest of my webpage at your leisure.

I only do one of a kind pieces these days and make replacement parts for a few different machines. My partner runs the company now, so I can play with my toys.

Jerry

[JIMinPHX]

Looks like you have enough equipment there to be half way dangerous. Looks like you keep a nice clean shop too.

[miestro_jerry]

JIMinPHX,

Thank you, I am working on a .308 Win. barrel that is very heavy at this moment, I am going to flute it and fit is to a Seiko receiver. Last week I repaired the crown gear for a 68 GTO. Tomorrow I will be setting a nice 1/3 carot diamond in a belly ring for a nice looking 30 year old. :o

I keep busy, and if it will stop raining around here, dry out some I will go out and try my new RD TLC311-165-RF boolits. Then tune up my 7 TCU Super 14 contender. I think before then I have to tranfer some low sulfur coal to my new storage area, that can be some hard work, this is about 1,800 pounds of coal.

Have a great one and thanks for the compliment,

Jerry

[Arnie]

I have removed a broken tap from Aluminum by using a powderd form of Aluminum Sulfate .It was years ago but still have the bottle up on a shelf above my lathe .The idea is that this stuff when mixed with water eats away at the hardest metals .It also puts a neat finish on the aluminum.I found this tip when i used to make model steam engines .I think it was a hint in a catalog from a place called Coles Power Models .Arnie

[M-Tecs]

Freezing a steel tap in aluminum does seem to work. I can not explain it.

It however, it is not from the aluminum hole expanding. When material with a hole in it is heated the hole expands. When material with a hole in it is cooled it shrinks. In engineering terms, “Every linear dimension increases by the same percentage with a change in temperature, including holes” This link explains it very well http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html

Joel

[remy3424]

Wow Jerry, nice digs there...Keep throwing out the ideas and solutions to our problems and quandaries. There is such a diverse bunch here, someone almost always seems to have a solution for ones issues. What a great resource to casters and shooters.

[Heavy lead]

Freezing a steel tap in aluminum does seem to work. I can not explain it.

It however, it is not from the aluminum hole expanding. When material with a hole in it is heated the hole expands. When material with a hole in it is cooled it shrinks. In engineering terms, “Every linear dimension increases by the same percentage with a change in temperature, including holes” This link explains it very well http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html

Joel

"When a solid expands (or contracts) it does so in all directions however for simplicity only length increase is considered in your book" the linear expansion/contraction calculations are simply done because whomever is teaching this lesson isn't calculating the expansion ratio's in three dimensions so the argument doesn't apply here. I agree with Jerry on this 100%. The hole is a hole and will actually expand rather than contract as the aluminum (or whatever solid is surrounding the hole) contracts. Also remember you don't cool anything. You remove heat. Essentially this is all theory. If the man says it'll work, try it I'm sure in will.

[Heavy lead]

JIMinPHX,

To leave the earth, the shuttle has to be going about 17,500 miles an hour or Mach 25.

Besides the machine shop I own a jewelry studio. My website has some of the stuff that I do:

http://anvilsandinkstudios.com/studiopage3.html

http://anvilsandinkstudios.com/studiopage2.html

http://anvilsandinkstudios.com/studiopage4.html

http://anvilsandinkstudios.com/studiopage5.html

You can explore the rest of my webpage at your leisure.

I only do one of a kind pieces these days and make replacement parts for a few different machines. My partner runs the company now, so I can play with my toys.

Jerry

Absolutely awsome, is there anything you don't do. That copper leaf work is fabulous.

[Duce]

I have dealt with removing taps from alum. all my years as being a machinist but looks like it has been covered in all the areas through argument and I will set back and watch (or read) how it all works out. Many years working as a tool and die man with Cincinnati Gear Company and R.A. Jones company I would know a little about how to go about it but my mouth is shut.


Lou

[M-Tecs]

"When a solid expands (or contracts) it does so in all directions however for simplicity only length increase is considered in your book" the linear expansion/contraction calculations are simply done because whomever is teaching this lesson isn't calculating the expansion ratio's in three dimensions so the argument doesn't apply here. I agree with Jerry on this 100%. The hole is a hole and will actually expand rather than contract as the aluminum (or whatever solid is surrounding the hole) contracts. Also remember you don't cool anything. You remove heat. Essentially this is all theory. If the man says it'll work, try it I'm sure in will.

You are correct that a hole is a hole, however you are incorrect when you state that the laws of physics change from a two dimension to a three dimension part. We can argue theory and physics until the cows come home with no resolution. Essentially this is all not theory it’s all solid physics used by assemblers, machinists and tool makers every day.

I concur with Jerry that this method does work. I do it somewhat differently since I have access to liquid nitrogen that is normally used for installing bushings. I do disagree with why it works. I have no explanation other than it does work.

Let’s turn the discussion to practical examples. Before we do a little out my background. I have been a machinist or Toolmaker since 1978. When I was running Jig Bores at one company .00005” (50 millionths) size and location on holes was not uncommon. In thirty year of high precision work I have never seen anything other the when a hole (material around hole) is heated it expansions and the opposite when it is cooled. Nor have I ever seen any engineering or physics data stating anything different.

My first experience with holes expanding when heated came in 1977 when I assisted the installation of a 12 foot diameter gear on a 3 ½ foot in diameter drive shaft (for a dragline used in coal mining). The gear was heated to 350 degrees to allow the hole to expand for the shaft insertion.

My next experience was also in 1977. I was changing a ring gear on my welding tuck(work as a pipe welder while going to Tool and Die school). Ring gears are held on to the flywheel by friction only. To install a new one you simple heat the ring gear to allow both the ID and OD to expand so it can be dropped onto the flywheel.

Next came installing bearing races on shafts. This I still do. I currently manage a machine shop for aircraft repairs. Depending on what the tech data states the bearing race that goes on the shaft is heated from 250 degrees to as high as 345 degrees. What was a heavy press fit know drops on under its own weight. The other side is cooled in liquid nitrogen to allow it to drop into the seat.

The point of the examples was that to get the holes to expand the material had to be heated. Under Jerry’s theory they would need to be cooled.

I gave three very easily verifiable examples of a hole expanding when heated.

Does anybody have a verifiable example a hole expanding when cooled?

[leftiye]

I think the example of the ring gear makes this clearer, as you can in that instance see the whole ring expanding as a long piece of steel rather than as a hole in a piece of steel. The steel around a hole expands in all directions. The steel at the edge of the hole expands as the ring would and the hole gets larger.

[Heavy lead]

We've about beaten this subject to death. My background is in mechanical refrigeration. Here's what I want to throw out there:
The aluminum and steel tap are at the same (room) temperature.
But they don't contain the same amount of heat.
The steel tap contains more heat (measured in btu or joule for the international folks)
The cooling process doesn't cool, but rather, removes heat.
Therefore even though the temperature of the aluminum and steel will be the same temperature after the cooling process (removal of heat) the steel will have lost more heat (measured in btu or joule) even though they are the same temperature, because the steel is a denser material.
The absorbtion of heat is not a constant. The warmer the material, the less heat it can absorb.
I think what we need here is a double blind study supported by dollars from congress to help with this dilema.:mrgreen:
My head hurts:confused:
FYI, I hope everyone understands all of this is just my opinions of reading everyone else's opinions and some peoples actual experiences. I have broken taps, but luckily always have been able to get them out without too much grief. The science of this is interesting to me, and I'm half temped to take some blocks of aluminum, brass and steel and drill and leave taps in them and put them in the deep freeze, just too see. I don't have any liquid nitrogen, but I do have some R-22 and some R-410a, but epa regs forbid releasing any into the atmospere.[smilie=1:
Time for a :coffee:break!

[floodgate]

leftiye:

OK, as a retired physicist who has thought this through, but never actually tried the freezing method for removing a broken tap in aluminum (no, I'm NOT gonna break a tap just to prove the point), here's what my "intuition" tells me:

Chill the piece; the steel tap shrinks a little bit (thermal expansion coefficient 0.000010 inch per inch per degree C); the aluminum shrinks quite a lot more (0.000024 inch per inch per degree C, or about 2-1/2 times as much); the tap being hard, the aluminum around the tap can't shrink enough, so - being much more malleable than the tap, it is distorted to the diameter of the chilled tap, with the strain being distributed plastically into the surrounding metal.

Let it all warm up; the metals expand again, hole and all, the Al more than the steel, leaving the tap loose in the aluminum.

Just what is called a "thought experiment" in the physics trade; no guarantees until I try it.

Floodgate

[leftiye]

Good explanation. I was only dealing with why holes in pieces of metal don't shrink when the surrounding metal expands.

[Nueces]

Second the motion for floodgate's thought experiment (I'm also a retired physicist).

There are a bunch of guys here who have a great deal of shop experience. I propose a thought experiment that taps into that body of knowledge.

What say we consider shrinking a bearing onto a shaft. If heating a piece with a hole in it causes the hole to shrink, then we'd cool the bearing to increase the ID so it could be driven onto the shaft. What say y'all, is that how it's done?

Mark

[10-x]

You've got to be kidding!
Any 1st year shop student in any mechanical study knows HEAT Expands, Cold Contracts.
I would like to see the proponents of any other theory try cooling a ~35" I.D. combination taper roller/thrust bearing that cost around $100K and fitting it to it's "stump" that also measures within 0.0001" of the bearing's I.D. on a 108" Bullard VTL.
Perhaps they are part of the "Get a Bigger Hammer" crowd?

[miestro_jerry]

When the saturated heat is removed metalic items, the expansion/contraction is in all directions, but the hole doesn't contracted when cooled, it widens. Try the inverse and you will find that to be true also.

I have been doing metal at various levels, from Blacksmithing to exotic metal machining for many years, plus being a retired engineer gives me the ability to research concepts, but some times just trying it out is the best teacher.

Jerry

[docone31]

Ah, the I broke the daggoned tap in there trick!
I was tapping the reciever of my O3-A3. Dang, they are hard! Well, there it was, not enough to grap with anything, stuck in the metal, and I was screwed, blued, and tattooed.
I am a jewler. I have lots of ball burrs, both HSS, and diamond.
Simple, I used a diamond burr with an high speed hand piece. A Dremel at high speed does the same thing. The diamond burr was small enough to fit into the space between the flutes of the tap.
At high speed, with cutting oil, the burr made short work of the broken tap. I cut off two flutes. The space left from the burr allowed the flutes to fall out. I could then turn the tap untill it fell out.
I got another 4-44 tap and finished the tapping.
Took ten minutes.
I have also found, I can drift to center with a ball burr any center holes I slightly miss on.
Those diamond burrs can be found on the 'net, and most Dollar stores. They do not last long unless High Speed is used, and very light pressure. That is how diamond bits work anyway.
With cutting oil, no heat.

[Nueces]

You've got to be kidding!

No, not kidding, just asking a question intended to provoke some analysis. I figured, as you said, that many shop guys would have some experience of using heat to expand a hole to fit a shaft. I thought that would help advance this discussion.

To remove all doubt resulting from my attempts at subtlety, I’m convinced that holes expand with heat, just like all other linear dimensions. The tensor that denotes the volume coefficient of thermal expansion for metals can, for all practical (that is, our) purposes be approximated by a scalar equal to three times the linear coefficient. The predicted difference resulting from this simplification amounts to much less than one-millionth of an inch for a 1” bore and a temperature change of 100 degrees Celsius.

This means that calling upon volume effects to explain a proposed heat contraction of a hole are not tenable. And the theoretical prediction is for an expansion of the hole ID.

Meistro, you have a great deal more hands-on experience than I do. I do not doubt that you have observed things that cause you to propose the idea that volume heating will result in the contraction of a hole ID. It does sound reasonable and my first thoughts about this issue were in line with yours. The mental picture seems right. Just ain’t so, however. The mathematics predict another outcome.

As you so rightly say, the best way to test this is by trying it. That makes it science. Communicating like this makes that sort of hard, so I located some sites that can be investigated instead. I found both engineering and physics sites, some of them talking about shrink fits. Nowhere did I find a recommendation that a shrink fit be accomplished by cooling the outside member. In each case, heat is applied to grow the hole.

http://eb-cat.ds-navi.co.jp/enu/jtekt/tech/eb/info/12/12_2_2.htm

http://www.alliedpipefreezing.co.uk/shrink-fitting.htm

http://www.ameritherm.com/overview_shrinkfit.php

http://www.accessscience.com/abstract.aspx?id=621400&referURL=http%3a%2f%2fwww.accessscience.com%2fcont ent.aspx%3fid%3d621400

http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/thexp.html

As some others have said, I’m not addressing the issue of how to remove a busted tap. I agree with floodgate about how heat is likely to work there. My words are just about what happens when heat is added to a bit with a hole in it and which has a positive coefficient of thermal expansion.

We have to be able to disagree about stuff like this and talk about it and offer evidence. If it’s not plain from my words, I’d like to say that I offer these comments only in the spirit of gentlemanly scientific debate. For any shortcomings in attaining that tone, I apologize and hope all will give me the benefit of the doubt.

Mark

[Red River Rick]

As a Journeyman Machinist/Tool & Die Maker with over 25 years of experience, it simply blows me away at how much time could be expended dealing with such a small problem. The part could have been replicated a hundred times already with all the time that's been spent trying to figure out "How Too", wouldn't you agree?

The comments posted vary. Seems to me the most logical method would be to "SCRAP" the part and start over if its simple and cheap. However; if the parts of value and somewhat expensive, then the most effective method of removal would be to EDM the remainder of the tap from the hole. If the hole is a "Thru" hole, then the wire EDM would work great. If the hole is a "Blind" hole, then a RAM type with an electrode will suffice.

I have to add that I agree to what Nueces said in his last paragraph. That's what make this place such a great site.



RRR

[M-Tecs]

Earlier today a machined a part out 3” diameter 7075 T651 aluminum. The portion that I chucked on is not used and about 1’ thick. I bored this piece to an ID of 1.0002” checked with a 1” ring standard and a .0001 dial bore gauge. I placed the part in liquid nitrogen (minus 321 Fahrenheit). The shop is about 80 degrees today. This means the part was cooled about 400 degrees. The dial bore gauge reading was .9971 as best I could tell.
We have very high humidity today and frosting was a problem in getting an accurate reading. The hole contracted .0031. The linear expansion of aluminum per inch per degree Fahrenheit is .00001244. The calculations show that the hole should be .00496 smaller. The part may not have cooled to -321. The liquid nitrogen had stopped boiling off the part so I had to be close. The point is the hole shrank

[10-x]

Gentlemen,
I have to agree with RRR, scrap the piece and start over if it can't be fixed with EDM.
On the other hand the other posts address issues of heating / cooling different materials and how they react.
Removing a broken tap really should not be such a big deal, the real problem is why did the tap break in the first place?[smilie=1:
Center punch, center drill, drill to CORRECT size for tap, countersink hole, then tap using a #1, then #2 and then #3 tap with plenty of tapping oil/fluid with each tap.
nuf sed:drinks:

[Nueces]

Good info, M-Tecs. Thanks for taking the time to try it and to post it.

My sources agree with yours on the coefficient for aluminum, but are for temperatures above 32. The coefficient is monotonic (goes up and down with) with the heat capacity, which goes to zero at absolute zero, so the value of the coefficient should fall at low temperatures. Ignoring any structural phase transitions or quantum effects, that probably accounts for your results.

Sorry for the non-boolit content, guys. I'm home with a lawyer, high school daughter and a really smart dog, none of whom are interested in this stuff in the slightest. Maybe you're not either, but, here at least, I get an occasional bite. Besides, I figure it's compensation for my having to listen to Glock talk. :drinks:

Mark

[M-Tecs]

Mark

Thanks for the info, I truly love learning new things and I learned two things today. I did not know that coefficients of expansion are monotonic and I learned what monotonic means!!!!!!!!!!:drinks:

Joel

[Tom Herman]

I have never needed it, and with modern fears about mercury, maybe
nobody would do it, but ---

Brownell's gunsmithing kinks book years ago said you could heat the
broken tap up to red head with a small tip acetylene torch and drop
a drop of mercury on it from an eyedropper to cool it ultrafast. Of course,
this would vaporize some mercury, so do it outdoors, etc., etc. or don't
do it at all.

They claimed it made the tap so glass brittle that you could break it up
into tiny chunks with a pin punch and pick out the pieces.

Never tried it, but it was so interesting that it stuck in my rat trap of
a brain,using a liquid metal to get a cooling rate faster than with water.

Bill

Hi Bill,

This is one trick I wouldn't do! And it's not because of any alleged harzard of using Mercury (I've played with all sorts of acids, bases, alkali metals, Phosphorus, Mercury, Uranium, etc. for over 30 years).
The problem is that Aluminum is a very reactive metal, and that the only reason it doesn't oxidize and quickly turn into a lump of white powder is that it is what is called a "self protective metal".
This means that a very thin coat of Oxide forms on the surface of the metal when exposed to air, and this layer keeps the rest of the metal from quickly rusting.
Mercury, unfortunately, will amalgamate itself to most metals, Aluminum included.
If you're unfortunate enough to try this trick, you will probably have a layer of Mercury that continually brings a fresh layer of Aluminum to the surface of this amalgam, and that will react with the Oxygen in the air to form Aluminum Oxide.
Unless you can drive all the Mercury off, the process stops only when all of the Aluminum is consumed.
A classic experiment is to drop a piece of Aluminum in hot water. Nothing happens.
Rub a bit of Mercury onto the same piece, drop it into the same hot water, and the Aluminum quickly begins to bubble giving off Hydrogen gas as it reacts with the water, generates lots of heat and forms all sorts of nasty crud (Aluminum Oxide and Hydroxide).
Put a drop of Mercury onto some Aluminum work? Not me!

Happy Shootin'! -Tom

[scrapcan]

All right good stuff all around. I had to dro in to ease the old mind, and now we get to drop in some good info to talk about when that uninterested person least expects it. Thanks guys.

Nueces,

Thanks for thinking of the rest of us when the lawyer, the daughter and the smart dog don't care. We do, or at least I do.

Floodgate and Nueces,

You guys might be retired but I see the good stuff is not forgotten or kept to yourselves. Thanks.

[arclight]

I haven't seen this trick mentioned yet, so here goes:

If you're going to scrap the part anyway, try burning the tap out with a cutting torch. The "Smoke Wrench" will preferentially eat the steel and for the most part leave the Aluminum alone. You have to watch that it doesn't get hot enough to slump the Al, but that's pretty easy since Aluminum sucks heat away so quickly.

It even works on a steel tap broken off in a steel part, as the pre-heat mostly hits the part you concentrated the torch on.

This technique requires a steady hand, but I have personally tried it.

As an aside, I fixed some stripped out allen bolts on an old Ponsness Warren 12GA reloader by TIG welding an old hex to them. The bolts were threaded into Aluminum. When I unscrewed them, the screws were almost cool to the touch. Guess that casting was a pretty good heat sink!


Arclight

[miestro_jerry]

I will have to try my Smith's Micro Torch with this trechnique. Thanks for posting it.

Jerry

[miestro_jerry]

Also, I agree with RRR, scrap the piece, it's salvage value maybe enough to pocket, but if I spend more than 10 to 15 minutes on an aluminum and steel situation, my time is wasted and I am not getting younger so my time is getting more valuable.

Jerry

[JIMinPHX]

I would like to see the proponents of any other theory try cooling a ~35" I.D. combination taper roller/thrust bearing that cost around $100K and fitting it to it's "stump" that also measures within 0.0001" of the bearing's I.D. on a 108" Bullard VTL.
Perhaps they are part of the "Get a Bigger Hammer" crowd?

That's a pretty big machine to be kicking around. Those things scare me a little.

[725]

For the first time ever, I broke a tap off inside a hole. !!!! Hanson 8-40 from Brownells. !!!! Had visions of a Winchester holding that tap forever. Took a long, slender punch and tapped the tap back out. It was deep enough to make it a pain but just shallow enough that I got a slight purchase on one flute. Kroil, prayers, and a gentle touch got it out.

[Nueces]

It's Miller Time!

Mark

[725]

You're not kinding.

[briang]

I find this topic very interesting, so interesting that I am going to run a tap into a piece of scrap AL and see if it gets any looser after a night in the freezer. Off to the shop I go.

[briang]

Alright, I decided it didn't need to be over night and 6 hours would be fine. I used I piece of unknown alloy but definitely AL .25 inches in thickness, that was the thickest I could find. I used a 12-26 tap going in and a .25-20 tap going out. I could wiggle both taps but could back neither out without tools. After freezing I still couldn't remove either tap by hand but I could wiggle both more than before. The freezing does seem to have loosened the hole to tap fit but I do not know if it as the hole growing or the tap shrinking. I guess I didn't really prove much of anything huh?

[jmorris]

http://www.electroarc.com/?gclid=CNaDxe_C25oCFQIWFQodcirt3A

It will even take out carbide.

[yekcim]

If anyone (briang) who has changed steel cylinder liners in motorcycle blocks knows you put the block into a home kitchen oven for a a few minutes after you have the new liner into the refrigerator freezer compartment for a while. Take block out of oven, tap liner out of block. Replace block into oven for a few minutes and remove the new liner out of freezer, remove block from oven and quickly place the new liner into the block. You have a minute or two before the hole in the block shrinks back too small for liner to go in all the way. Like miestro jerry said politely a few times.Try it you will like it. Just like the tap. Just do it. Works for me. Don't know the scientific reason & don't care. Works for every mechanic I ever worked around, even me at home.

[longbow]

Well, recently I had some troubles along this line with a broken off tap in an engine block. It was awkward to get at for many of the solutions here, at least without removing the engine.

In the end, I decided to try a carbide bit in my Dremel. To top it off the only carbide bit I could find locally was for cutting ceramic tile.

It cost about $20.00 but considering the options I figured if it worked, it was a cheap solution and if it didn't well, it was a pretty cheap failure.

Short story is, much to my surprise it ate right through that tap. No acid, no heating, no welding, no freezing, just a few minutes with a Dremel held carefully and the broken tap was little bits.

So, I agree with John Taylor in post #13 ~ a carbide cutter, end mill or whatever is up to the task.

Not saying this is the best or only solution for all situations, just that it does work and does not require any special equipment.

Longbow

[jimkim]

Dang I'm low tech. The last one I broke was removed with a hairpin. I slid the hairpin in the flutes, stuck a long nail in the loop, and backed it out. I heated it with a small torch first.

[Heavy lead]

Dang I'm low tech. The last one I broke was removed with a hairpin. I slid the hairpin in the flutes, stuck a long nail in the loop, and back it out. I heated it with a small torch first.

Man, that's a deceivingly simple good idea, never thought about that.

[longbow]

I tried the hair pin idea only it was a bent loop of old bicycle spoke. If the tap isn't jammed that can work. Mine was jammed in a blind hole as well though.

Long skinny needle nose pliers can sometimes do it as well it the tips are small enough to get into the flutes.

[jimkim]

Did you heat it first? Use the largest hairpin that will fit. The large flat ones don't flex as much. I guess to be accurate I should call them Bobby pins.

[longbow]

Man you must be as old as I am to know what a Bobby pin is!

Yes, I did try heating but no go. She was jammed badly. I couldn't get it to budge. I honestly didn't think the carbide bit would survive but it did. I guess if you don't have a Dremel it isn't such a simple solution but then I don't have a TIG welder, couldn't put the engine in a freezer, didn't have a bottle of liquid nitrogen, no mercury on hand ~ what did I miss?

Necessity is the mother of invention and it is interesting to see how many different solutions there are to a problem like this.

Longbow

[Boz330]

I broke a 6-48 off in a blind hole for a scope in a brand new barrel couple months back and couldn't budge it with a broken tap extractor. Put the barrel in the freezer for a couple days and the extractor took it out. I was right at the point that I thought it might break but it let go. I had a box of dental burrs and a Dremel but that hole was so small that I was concerned about buggering the hole for good. At this point the gun hadn't even been fired yet.
+1 on the freezer method.

Bob

[dominicfortune00]

I haven't seen this trick mentioned yet, so here goes:

If you're going to scrap the part anyway, try burning the tap out with a cutting torch. The "Smoke Wrench" will preferentially eat the steel and for the most part leave the Aluminum alone.

One of the guys at work used to be a mechanic on bulldozers and other big equipment, and he said he used a torch to burn a hole through the middle of those long pins that were galled in, like on the track of a bulldozer. He said that the heat would loosen up the pin and then it could be tapped out.



As an aside, I fixed some stripped out allen bolts on an old Ponsness Warren 12GA reloader by TIG welding an old hex to them.

To get out stripped head allens, I just tap a Torx bit in that is a little bit bigger in diameter than the allen recess in the bolt head. The six ribs of the Torx cut into the allen bolt head and have enough gripping power to allow the bolt to be turned out of the hole. Works very well on those button head allens, the head of which strips out if you look at them funny.

[Morrison Machine Shop]

I use a carbide end mill on the mill, cuts like butter.

[BeeMan]

Since I broke a tap in aluminum last week I'll bite. Remaking the workpiece wasn't practical.

Chips may interfere with backing out a tap if they lock it in place. No joy here for my project as the tap was firmly jammed and too small for an extractor.

Shattering a carbon steel tap has worked before but this was a high speed steel tap so shattering was out. The machinists at work use a carbide end mill but I did not have one, nor a burr for a Dremel. No liquid nitrogen or CO2 was available so I tried chemical removal.

Make a saturated solution of alum in hot water. Alum is used for making old fashioned pickles and is potassium aluminum sulfate. A Google search will explain why the steel is etched away, but aluminum is not affected.

Soak the aluminum work piece until enough of the steel tap dissolves to remove the remainder of the tap. This may take several hours to more than a day, depending on the concentration of alum and the temperature. No paid machinist is likely to consider this method. It is slow but it works well for a home project without damaging the aluminum workpiece.

Floodgate nailed why relative thermal expansion of aluminum and steel loosens a steel tap in an aluminum part. Restrain a material from dimensional changes it normally makes with a change in temperature and it will yield in the restrained axis but grow in another direction.

In this case the aluminum yields when the steel in the hole prevents the aluminum (and the hole in it) from shrinking. When the workpiece warms back up, both expand. The aluminum expands more and is now loose around the steel.

Last, someone mentioned special size taps for features machined before heat treat so that dimensions are correct in the hardened part. This is not a co-efficient of expansion effect. The part is machined at room temperature and the dimension after all is done is measured at room temperature.

The post heat treat dimension change is due to the various forms of compounds formed by the alloying elements in the steel. Quenching, normalizing, annealing, and tempering all have differing effects on which compounds are formed and when. Find a good explanation of steel heat treat - I don't recall for sure but Machinery's Handbook may cover this.

BeeMan

[JIMinPHX]

The post heat treat dimension change is due to the various forms of compounds formed by the alloying elements in the steel. Quenching, normalizing, annealing, and tempering all have differing effects on which compounds are formed and when. Find a good explanation of steel heat treat - I don't recall for sure but Machinery's Handbook may cover this.

BeeMan

I don't think it is due to a change in compound. I think that it is due to a change in the geometric structure of the molecules in the metal. There are different terms for the same material with different internal geometric molecular structures. Austentite & Martensite are two of the common ones in steels.

[David2011]

+1 on the Tap Magic. That is some really good thread cutting fluid. In gunsmithing class tonight I found a newbie trying to thread a block of aluminum deep (1/4 x 20 threads over 1" deep) and dry. He was amazed at the immediate difference with the addition of thread cutting fluid.

David

[Jim_Fleming]

add me to the Tap Magic list...

Only thing I despise about that dang stuff is that it stinks to high heaven...

UGH!

[JIMinPHX]

add me to the Tap Magic list...

Only thing I despise about that dang stuff is that it stinks to high heaven...

UGH!

If I try to blow the chips out of a blind hole with compressed air after having used that stuff, it goes aerosol & makes me choke. The stuff works, but it's not my preferred substance for all applications.

[j23]

I broke a tap off in a rifle tang once, tapping for a tang sight.. I took a steel punch and hammer and smacked the punch which was resting on the broken tap. The tap, being made of extremely hard, yet brittle steel 'shattered' out. The threads I had been cutting were finished with a second tap, no harm no foul, the screw went in smooth as butter.

YMMV of course.

[Russel Nash]

Another trick I have heard was to use a carbide tipped drill bit in a hammer drill, yeah, like what you would normally use to drill concrete. Chuck that into a hammer drill where you can turn it to just plain hammer mode (some of the better hammer drills have a switch that allows them to be regular drills drills, hammer drills or hammer only).

Then gingerly set the the carbide tipped bit on the end of the tap and hit the trigger on the hammer drill.

That supposedly will cause the tap to shatter.

I haven't tried it myself...just heard about it.

[BeeMan]

I don't think it is due to a change in compound. I think that it is due to a change in the geometric structure of the molecules in the metal. There are different terms for the same material with different internal geometric molecular structures. Austentite & Martensite are two of the common ones in steels.

Jim,
My point was that the change in dimension from pre- to post-heat treat is caused by volume changes due to phase transformations within the alloy. The dimensional change is a not a function of thermal expansion, as was inferred by someone earlier in this thread.

My memory of the particular terms involved in steel phase transformations was / is fuzzy so I suggested a good reference. For a brief summary see the short paragraph Volume Changes here:

http://books.google.com/books?id=_a9UEHk4cOwC&pg=PA252&lpg=PA252&dq=steel+phase+transformation+dimensions&source=bl&ots=mf9cttvw8o&sig=6PAozgGg8smUkh6IsPwCGxB367M&hl=en&ei=DU7LSpKtDJGsMe3hpM0D&sa=X&oi=book_result&ct=result&resnum=7#v=onepage&q=steel%20phase%20transformation%20dimensions&f=false

I think we are trying to say the same thing re: the volume change. Have a good day!

BeeMan