Broken tap solutions

[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.
My head hurts
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.
Time for a 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/jtek.../12/12_2_2.htm

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

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

http://www.accessscience.com/abstrac...%3fid%3d621400

http://hyperphysics.phy-astr.gsu.edu...rmo/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?
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

[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.

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!!!!!!!!!!

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