# broken tap in aluminum cranckase



## petertha (Feb 1, 2017)

Dangit! 2 holes away from completion & I broke an M3 tap. I really cant say how, the preceding ones went perfectly fine & I did all the holes & tapping operation identically. It was a brand new, good quality tap, chip ejecting style which I've had excellent good results with in the past. Lots of WD40, controlled tapping....

Anyway, I finished tapping the last 2 holes while it was all set up on the rotary then removed part to examine. I tried heating the CC up to expand a little & gripping the 1mm tap remnant but it just crumbled. Now its now essentially flush. I really don't feel in the mood to start another CC right now. Any successful experience or solutions you can recommend? The hole is 0.300" deep & suspect the tap is 0.250". I can't seem to locate prior threads, Alum or something? And no, I don't have access to EDM nor am I interested in building one.


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## Foozer (Feb 1, 2017)

Aluminum Potassium Sulfate (Alum) A warm saturated solution will dissolve the tap. Broke a 1/4-20, took a couple days. Mixed solution in a glass container set upon one of those coffee cup warmers and changed the solution after 24 hours. Leaves a little soot residue on the part, comes off easy.


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## goldstar31 (Feb 1, 2017)

Probably the easiest way to obtain alum is to buy a styptic pencil. This was the thing that old wearies( me) used to stop bleeding when using old fashioned razors!

Having said that, your breakage  could arise from lack of proper alignment of your tap or - ahem- it was  blunt------or both!

The cure is possibly to follow a lot of my correspondence about such things as Universal Pillar Tools and using a shaped abrasive stone to 'tidy up' the lead on taps. 

I must leave it  for you to ponder.

Norman


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## Cogsy (Feb 1, 2017)

Never tried the Alum myself but I have heard many stories of how well it works, albeit a little slow. Definitely worth a shot before remaking a crankcase.


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## django (Feb 1, 2017)

You could try putting a couple of needles down the flutes and gently rotating the tap back and forth (with a pair of pliers) it works about 60% of the time but you must make sure that any bits of broken tap or swarf are blown out and use plenty of WD40. Remember gently does it. Good Luck!

Paul.


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## Journeyman (Feb 1, 2017)

Alum works, I have used it. It needs to be *hot*, just off boiling, and a saturated solution. It wont work at room temperature I discovered after two days trying!

John


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## mcostello (Feb 1, 2017)

Alum does not always work. I made a saturated solution and left it on a warm wood stove for a week with no result.


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## XD351 (Feb 1, 2017)

You may have to resort to a small carbide end mill .
Being so small using a  2mm carbide mill would be a delicate operation ! 
I have in the past given a broken  tap a few very light taps with  fine pin punch and a small hammer to try to loosen its grip  - works sometimes .
Last ditch effort if all else fails is plunge a 4mm carbide end mill in and machine the whole tap out , then tap the new hole 5mm so you can install and loctite  a threaded plug in then re drill and tap this plug for 3mm .


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## goldstar31 (Feb 1, 2017)

XD351 said:


> You may have to resort to a small carbide end mill .
> Being so small using a 2mm carbide mill would be a delicate operation !
> I have in the past given a broken tap a few very light taps with fine pin punch and a small hammer to try to loosen its grip - works sometimes .
> Last ditch effort if all else fails is plunge a 4mm carbide end mill in and machine the whole tap out , then tap the new hole 5mm so you can install and loctite a threaded plug in then re drill and tap this plug for 3mm .


 
I've answered this SO many times  but the few times that I have been daft enough to break a tap, I've either cracked the carbon steel tap or welded a stud on to the stump. 

N


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## Herbiev (Feb 1, 2017)

Alum has always worked for me


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## ozzie46 (Feb 1, 2017)

I broke 6-32 tap in aluminum piece and the alum trick did it just fine. Went to the grocery store ,bought some alum, it was in the spice section, did a saturated solution heated on the stove at almost boiling point.I had to add some water when it got to thick but it ate the tap in about 2 hours.

Ron


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## ninefinger (Feb 1, 2017)

Alum does work most times, but it needs to be able to get to the tap - if the flutes are all plugged up with aluminum swarf it will take forever as its only going to be working on very top.
As also mentioned, it needs to be 1. Saturated solution and 2. hot - near boiling. 3. stir the part / brush with a toothbrush to help remove the oxides that form.  
If you do this in a pot it either needs to be aluminum or as suggested use a glass coffee decanter and warmer.  Stainless steel pots will be affected by this solution (it will stain it).

If you are lucky it will dissolve it enough that you can get it out without having to wait for the entire tap to dissolve.

Also, in my case it left the part (a crankcase ) with a dull finish.

Mike


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## portlandron (Feb 1, 2017)

You can get Alum at a will stocked grocery store. It's used for canning.


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## John S (Feb 1, 2017)

Send it for anodising. that will remove the broken tap and any helicoil inserts that are fitted.

Don't Ask.


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## petertha (Feb 1, 2017)

What's an appropriate vessel to simmer the water/alum solution? An aluminum pot? Avoiding glass (don't ask).


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## portlandron (Feb 1, 2017)

Glass container should be used with Alum.


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## XD351 (Feb 2, 2017)

goldstar31 said:


> I've answered this SO many times  but the few times that I have been daft enough to break a tap, I've either cracked the carbon steel tap or welded a stud on to the stump.
> 
> N




I would like to see you weld something on the end of a broken M3 tap without melting the parent metal around it  now it has broken off flush !


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## goldstar31 (Feb 2, 2017)

XD351 said:


> I would like to see you weld something on the end of a broken M3 tap without melting the parent metal around it now it has broken off flush !


 
I confess to being  around with the dodos but the technology then was that it was possible to join metals with friction and again on a more 
 lowly bit of the firmament, people were sticking carbides to parent steel with silver foil. I suspect that they still are.

Again, having been retired for longer than I ever needed to work, my late wife was happily welding stainless steel wires and bracket to children's teeth. My little grandson orthodontic work is no longer routed (rooted?) to welds but is something rather simpler like these fancy glues with an accelerated gel done with UV light.  Actually, someone used it on the dentine of my broken teeth. For a more approachable application, I have seen the stuff on sale to Joe Public and possibly a write up here.

As far as the other alternatives, in the days when I larked about as a manure student, we used Migs to fire wire through niobium steel and also stuck wires into dented metal to correct car bodies.

I thought the answer out which if you look at it rationally, only involves a slug of metal jammed in the wrong place.

Norm


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## XD351 (Feb 2, 2017)

And none of that will help the OP get the broken tap out !
If the alum is not working maybe there is some contamination stopping it like tapping fluid ?
Is the tap carbon  steel , chrome steel or HSS , maybe the composition of the tap itself is inhibiting the chemical process?


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## ozzie46 (Feb 2, 2017)

I used a cheap teflon coated pan from "wally world". The teflon protects the aluminum pan from the alum

Ron


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## petertha (Feb 2, 2017)

I'm going to try the alum route. Just trying to hunt down a suitable glass pot. I'm getting the impression they are kind of going out of favor over metal cookware but looking at something like this, trade name Visions. I've seen pictures where cooks are boiling potatoes so hoping it should be good for this application. Pyrex (or at least the thick glass measuring cup I used) is not suitable for cook top. I'll save that story for another day but as a teaser it ends with Boom 

I don't have a welder nor do I think I have the skill to stick something on the end of a sheared off 3mm dia tap, so that's a non-starter.


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## goldstar31 (Feb 2, 2017)

It seems unfortunate to add more possible difficulties but using a Water Dispersant fluid as a lubricant hardly will have helped. I tend to stick( OucH) with traditional cutting fluids like lard oil and tallow which is where cutting fluids arose. 

Going back to the problem, there is plenty of advice in the past but few workers wrote about aluminium. It just wasn't available- then.

However, it is not only easy to machine but is malleable. Frankly, there hasn't been malleable steel around for decades. 
Realising two things, your offending drill hole is open and the second is that it allows you to deform the bit of thread which is jamming.

So it becomes classical in the old fashioned 'Bob and Aunty' which is how the old blacksmiths  like my father, his brothers and my grandfather and great grandfather described a punch and dolly. If you can get a parallel punch as a dolly below the untapped bit and tap it with a hammer you will start to stretch the cheeks of the tap in one direction, then you need to reverse the tapping from the top.
In effect, you are expanding the original tapping. Repetition should loosen the front end of the tap - because it has a tapered 'lead'
With correct lubrication and inserting and then twisting fairly hard tempered wire- like piano wire, it should wind out.

If it doesn't , use a hollow dolly and knock it through with a hammer and parallel punch.

There doesn't seem much compared with tackling something less forgiving.

Norm


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## John S (Feb 2, 2017)

Norman,
If you can't post a coherent reply why bother.
Nothing you have posted is helpful to the OP.


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## Walsheng (Feb 2, 2017)

Norman:

I for one enjoy reading all your posts.  Just keep on going!

John


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## Hopper (Feb 2, 2017)

There is alum and there is alum. It seems the exact chemical formula of what marketers label as "alum" can vary. Had a mate here in town go through all this. He found the "alum" sold as a flocculant at local swimming pool shops was in fact a slightly different chemical from traditional alum but still uses the same generic name. Eventually he bought some off the net that worked better for him. You might have to do a bit of research on that if the first try does not work. Being chemically illiterate i don't remember the exact differences in chemicals but will try to find out for you if I can. It may have been that one was pottasium aluminium sulfate and the other was just plain aluminium sulfate.


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## goldstar31 (Feb 3, 2017)

I doubt that the stuff used in swimming pools would be much use as the stuff would bugger the pump mechanisms. 

I've just sold mine along with the Spanish house. 'Nuff said.


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## petertha (Feb 3, 2017)

What I purchased was called Powdered Alum in the grocery store. Ingredients label says 'potassium aluminum sulphate'. I got 2 tins of 65g each & used both diluted in maybe 2 cups of distilled water. Not sure why I used distilled, just figured it was handy & maybe would mitigate any mineral issues of my hard tap water. I read somewhere the alum is supposed to be added to saturation but I'm not sure what volume that equates to. Tonight I gave it a go in a proper glass pot. 

Well... lots of bubbly-bubbly action & encouraging looking steady stream emanating from the tap hole. I had to call it a day after about 2 hrs. The black color came off reasonably well with light rubbing but the last 20 min or so must have had the top peeking out the liquid through evaporation & that stain is more persistent. I think I should keep it fully submerged. I'm not too worried about color right now. 

Hard to say how much eroding to the tap body has occurred. Under a magnifying glass it looks dull charcoal & the flutes look enlarged a bit? Maybe wishful thinking on my part. I cant move it with tweezers so will require another extended bath. Any idea/experience on time vs. steel volume? is the color a reaction to aluminum alloy & solution or related to steel erosion?

I'll have to find another supply of alum as the store was out. I guess someone else broke a tap recently or a big pickling party underway. I actually don't even know what its used for but the concentration is very low for food preparation, whatever it is.


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## ninefinger (Feb 3, 2017)

Wow - whats in your water out there?  My piece came out a dull grey, nowhere near as black as that!  Maybe lower the heat a bit?  Keep at it - the tap will come out.
Mike


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## petertha (Feb 3, 2017)

Like I mentioned, this was distilled water, so there shouldn't be much of anything in there. Maybe tap water would have been better :/ Found a supplier of larger volumes alum, local food supply place. Will give it a go again here shortly with higher concentration.


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## Cogsy (Feb 3, 2017)

Was it actually distilled water though? I ask because that stuff is reasonably difficult to source except from scientific supply houses. Most 'distilled' water you find off the shelf is actually deionised water and the 'distilled' part is treated as a brand rather than a description. Check the label and it should tell you. If it's deionised it can have all sorts of stuff in it which could potentially be reacting (it just should have relatively few ions compared to tap water).


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## petertha (Feb 4, 2017)

Gosh, you got me on that one. Its off the shelf drugstore brand, label says Distilled ozonated fluoride 0 ppm, 'steam distilled'. I bought bulk alum from a food supplier. Much cheaper than the grocery store tins. I figured try one change at a time, so used the same 'distilled' water FWIW. Reduced the heat to simmer. Actually that's how 90% of first bath went but it was picking up agitation towards end as some of the liquid evaporated off when I took the picture. 

Tonight I still see a steady stream of bubbles emanating from tap. Again, hard to visualize tangible progress along the flutes & but it looks marginally thinner...if I squint my eyes. Another 2 hours into cook time. At this rate I predict sometime in June ha-ha

So far this has been a frustrating & rather ugly looking science experiment. But no regrets, thought it looked like the least onerous solution at the time. I can still see all my machining marks under the black & the tapped threads still engage bolts ok so hoping it will all clean up. 

One thing that might be impeding things is it was a coated tap. I know.. I know.. why did you use a coated tap in aluminum. I even found a bright spiral flute M3 in my supply that was reserved for aluminum but completely forgot. Truth is I've used this one on mild steel & aluminum with fantastic results up until this disaster. It remained razor sharp & makes 2 nice swirly swarf strings as it taps. Maybe alum solution works best on bright conventional HSS & there is some magic ingredients in this tap that's impeding the breakdown? Maybe causing blackening? 

The other thing in back of my mind is I got this log of aluminum from a guy who called it 'aircraft aluminum' from where he works. It machines exactly like some 2024 I have so took it on face value. In all honesty I thought I might be 'practicing' this part a few times & held my 7075 for the real one, but this bugger turned out fine right until the 99.5% point. I can't think that any decent grade of aluminum would blacken like this based on alloy constituents, but its really beyond my pay grade.

In hindsight I think it was either chips in the bottom of the hole that prematurely bottomed out the tap. Or maybe I had my (Tapmatic head) stop set too close to bottom. It was at least 0.050" high but now I'm reading about more generous allowance recommended. The clutch was set for M3 & that's supposed to be conservative insurance against tap breakage. On all the preceding holes I could watch the tap come to a slow stop as the clutch engaged. As soon as that point occurred I backed off down feed pressure, it auto reversed & out she came. Time after time. This one hole just locked & broke tap without warning. Maybe the tap just failed. Guess I'll never know. To be continued....


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## Cogsy (Feb 4, 2017)

If it's steam distilled then it is properly distilled so that shouldn't be the issue. Now guessing entirely but I'd say the coating on your tap is probably both the cause of the blackening and the slow progress of the alum. Fingers crossed for you it works out in the end.


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## petertha (Feb 4, 2017)

This is the tap I used (for better or worse). I had to terminate tonight's Alum Soup vII for bedtime. But I'm happy to say 90% of the black came off with soft brush & dish detergent except in some nooks & crannies. So that's encouraging.

I'm hopeful its making progress. The tap break point is for sure a couple mm below surface now, but many mm to go. The flute area seem to be opened up (again maybe wishful thing). If this was aluminum packed it would explain slow progress but it feels clear now with a toothpick probe. Tomorrow I will blast air in there & maybe spot a Dremel on the end of tap to give it exposed metal to begin again.

Question. If the alum broth goes back into solid-ish state next day from liquid cooling, is it just a matter of reheating again to go back into solution & go at I again?


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## goldstar31 (Feb 4, 2017)

As this problem is 'the remains of a coated tap' it is arguable that what has been said about the possibility of dissolving it with alum is questionable. ALL and I repeat ALL the information about using alum seems to be pointed at iron, in whatever stage it is at- but not coated with a metal that is highly resistant to attack from both acids and alkalis. 

I suggested a possible mechanical alternative which 'went down ' criticised by people who I believe have done little but to be armchair critics. 

What appears to be happening is that the otherwise excellent craftsmanship is being damaged by unnecessary immersion instead of simply blanking off the open end, building a dam to contain the liquid and classically agitate and replace spent solution.

Frankly, it is NOT what I would have done. I would have 'blasted' the broken bit out with brute force and bloody ignorance and low temperature aluminium soldered the damage, drilled and re-tapped it and gone on my merry way in what for me in what I regard as nothing more than a diversion from the important things in  what remains of my life.

Thank you 

Norman Atkinson


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## petertha (Feb 4, 2017)

The drill-out option is still there, Norman. Like I said, I went into this alum adventure heads up thinking (hoping) it might be a simple 2 hour simmer, tap gets eaten & carry on based on others experience who did this successfully. The special coated tap was a bit of curveball even I didn't recognize as potentially important to the outcome. So right now its just full disclosure providing info in case someone else has this issue one day & can learn from it. 

The tap coating may well be contributing to the blackening because apparently nobody else has experienced this & doesn't seem related to the water or my choice in alum supplier. And it might be slowing the erosion process down if only the end core is exposed. But I think I can see progress along the flutes, which would suggest it must be through the coating. The tap engaged with aluminum is another matter, logically it will be the last to go.

I'm not exactly how I would build a dam around the offending hole, but it crossed my mind. I guess the dam would have to be aluminum to be 'alum solution proof' but my question was more about the liquid seal/adhesive. Would that then eat away (yet another rabbit hole). Then assuming I had a dam, how would I maintain temperature? Most people who did this successfully mentioned 'near boiling' & maybe related agitation is required. The dam route seemed more difficult.

I did a complete clean last night & all the black coloration seems to be removable. All the tapped threads fit M3 bolts nicely so I don't think the aluminum is being adversely affected by alum bath. I did some spot checks on the facet dimensions & cylinder skirt bores which should be within 0.0005". So far that is looking like no distortion which was my fear. I'm not sure if alum saturated water raises boiling point but lets call it sub 100C bath temp. I'm hoping that would have no adverse effect on aluminum itself tempering wise, but not sure there. I don't want to touch anything with fine wet-o-dry until final cleanup because its just going to darken again with every bath treatment.

If I have to drill it out, contemplating a carbide EM (its a blind hole), then tap it with say a M5, insert aluminum bolt as a plug with permanent Locktite, then tap that with M3. If that M3 tap breaks I will jump off a cliff 

..to be continued


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## goldstar31 (Feb 4, 2017)

Peter, my chemistry is a one day affair before my science master went off to navigate a Lancaster bomber- and didn't come back!
So I am merely guessing that the black stuff is either an alloy salt or a compound of the steel. I don't know. GHT writes about this but uses nitric acid but is answering a matter of iron or steel. and certainly not aluminium. 

What he does mention is the dam construction. Provided that you don't want to heat things up, child's modelling clay will suffice. 

It's perfectly normal sort of thing but I tend to use BluTack to hold things that I can no longer safely hold. 
So you and other readers can play about with problems in iron/steel with alum or nitric or even a mixture of sulphuric and nitric.
It will NOT remove that slug in aluminium and provided that you have a few pennorth of a decent aluminium soft solder, you could drill the threads away, leaving the slug which can then be unscrewed and fall out- or be waggled out! You can as an alternative complete the drilling underneath and bash the lot into submission.

As I wrote elsewhere, I've just started to tackle a broken alloy bracket on my lathe which has half a1/4"BSF tapped hole left 
I 've had to add a stump of alli which will eventually be drilled and tapped to take the detent. As I said elsewhere, I did all the soldering on the gas cooker. As a preliminary, I did exactly what I am advising, I drilled a hole by hand in a spare bit of alli and heated it up on one of the gas rings and once hot enough fed my wire solder rod in, puddling my way to scratch the parent metal until it was slightly overfull.

This afternoon, I milled the excess solder with a 1/2" slot drill.

Not surprisingly, it has taken me longer to scribble these notes than to do it.

Nevertheless, I hope that the notes have been useful

Regards

Norman


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## petertha (Feb 4, 2017)

My folly realized? Recall I mentioned leaving 0.050" clearance between bottom of tap & hole depth. I think I grabbed that number out of the ether based only on my prior M3 tapping experience. Well the answer was laying out there in internet land for me all along. Tapmatic provides a little formula that lays it out very clearly
http://www.tapmatic.com/tapping_questions_drill_depth_clearance.ydev

I'm not 100% sure what plug form my particular tap corresponds to but guessed 4 threads just as an average based on their description. When I compute & tally the remaining parameters I get recommended 0.138" standoff, much higher than my 0.050". IOW the tap was allowed to penetrate too deep by Tapmatic guidance.

So... notwithstanding other variables, I probably had this coming. Live & learn. What made me suspicious is I was seeing threads pretty much right down to the bottom of 0.300" pilot hole. I'm not entirely up to speed on tapping head mechanics of when the clutch engages, but it has both top & bottom float from the resting position. 

If anyone knows about tapping head setup in this regard, would love to hear your input


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## petertha (Feb 4, 2017)

Well tonight I'm throwing in the towel. Whatever that tap was made of is space age stuff. After an estimated 10-12 hours of cumulative alum bath time, the tap has eroded about 0.070" from edge of CC. That means another 0.230" to go at this snails pace. After another de-blackening cleanup the CC is now looking rather ugly, grain etching & now some porosity pocks showing up. Maybe if it was straight HSS tap, the story would have ended better, but it is what it is.

I'll clean it up & keep it as a tester for subsequent operations. There is value in having a practice piece. There are still many M3 tapped holes remaining on front & rear face so this operation needs to be bulletproof. Maybe I'll take a crack at drill out + plug + re-tap operation just to see. But at this point I think its wiser to move on & make a clean start on a fresh piece. 

Thanks for the comments & suggestions. We tried! I'm now also going to spend some quality time with my tapping head on scrap pieces with various blind hole setups so I'm smarter next time. I now suspect the error was on my part with too deep a bottoming set point. If the tapping head method still feels iffy I can come up with a hand method with more sensitive feel.


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## mcostello (Feb 5, 2017)

The tap I used was not a coated tap, just plain HSS. The bath time was a solid week, I put the failure down to different materials used in different taps. Many have said it works, some have said it has not.


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## keith5700 (Feb 5, 2017)

Peter, I know you said the part is just about scrap now, but if you wanted to experiment further, just out of interest, then could you set up a lash up anodising tank?
Plastic bowl, battery acid, bit of lead sheet and 12 volt supply. I would be surprised if the tap wasn't out in under 2 hours. You'd only have to put part of the block in the acid, so you wouldn't need much.
If you leave the part in the acid after anodising, with no power on, then the anodising should dissolve.
I've done a couple of broken taps this way, but then I'm  already set up for anodising.
Keith.


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## John S (Feb 5, 2017)

keith5700 said:


> Peter, I know you said the part is just about scrap now, but if you wanted to experiment further, just out of interest, then could you set up a lash up anodising tank?
> Plastic bowl, battery acid, bit of lead sheet and 12 volt supply. I would be surprised if the tap wasn't out in under 2 hours. You'd only have to put part of the block in the acid, so you wouldn't need much.
> If you leave the part in the acid after anodising, with no power on, then the anodising should dissolve.
> I've done a couple of broken taps this way, but then I'm  already set up for anodising.
> Keith.



I mentioned this in post #14.
Whay anyone would want to mess about with Alum, even if they can get the right grade seeing as Alum is a generic name, puzzles me.
Same for all the weird and wild guess but never do brigade who advocate welding a stud to a M3 tap inside a hole with not welding equipment or skill.

As Keith says. two hours tops and the job is done.


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## petertha (Feb 5, 2017)

keith5700 said:


> Peter, I know you said the part is just about scrap now, but if you wanted to experiment further, just out of interest, then could you set up a lash up anodising tank?


 
Hi Keith. Anodizing is for sure on my long term to-do list. But after de-blackening after this extended bath, I think you'll agree its belongs alongside some artifacts from the Titanic. I think the folks who were able to remove HSS after a couple hours soak time suffering only a dulled finish is about as good as can be expected. But my tap refused to decay & the process took its toll for this duration. I'll keep it as a guinea pig for subsequent operations. 

I've put this behind me & already have a new piece in the lathe. CC-1 taught me the importance of a better setup on the RT now with a better fixture & 4-jaw chuck. CC-2 taught me to pay special attention to tapping operations & some more proficiency required. Its a radial engine, multiple parts are required. Just not this part!  I've got some experiments in mind for my tapping head on scrap aluminum to become as proficient as possible. I will also try some simulation fixes because wishing this will never happen again is probably naïve. If I evolve to more complex engines one day than I have to be able to deal with this.


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## petertha (Feb 5, 2017)

Pictures of CC-2


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## petertha (Feb 5, 2017)

I never showed the tapping head & tap, here it is.


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## xpylonracer (Feb 6, 2017)

Seems we have discovered a new aluminium blackening product, that part looks good in it's new colour.

xpylonracer


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## Blogwitch (Feb 6, 2017)

Peter,

If you had your Tapmaster adjusted correctly on the clutch it should never have been able to break the tap.

I have a very old (from the 60's or 70's) tiny tapping head that actually uses a fibre type washer for the slipping clutch. Yours is most probably the same method of clutch control but hidden inside the unit at the top. Mine is underneath the head before the holding chuck.







The way I set it up with something like a 2mm tap, is with the correct sized hole drilled, I start off with hardly any clutch pressure at all, then try to tap the hole, usually it just starts to slip, a bit more pressure and try again. Eventually it will start to cut the thread, but if anything goes tight the clutch again starts to slip. Eventually the tap will cut to depth and then the head reverses and the tap is withdrawn. Even if the tap bottoms out, there is no way it should break because the clutch starts to slip before it can happen, maybe your problem is that the clutch isn't slipping soon enough.


John


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## petertha (Feb 6, 2017)

Thanks John. I want to delve into this with some further testing. I may even call Tapmatic, I recall they were pretty helpful when I was first deciding on the unit. The unit is new & lightly used thus far. I guess its possible its not quite (factory) calibrated, but I'm leaning more towards the my depth boo-boo. But like you I was thinking if the clutch stops under whatever safety margin is correlated into tap size setting then it shouldn't really matter what the source of sticking is? All the holes were positioned with DRO & depth stop. Even though the tapping head uses rubberized collet & is somewhat forgiving on positioning, all my tapped holes were re-positioned exactly to same prior drill XY DRO position. The pilot holes were 2.5mm, 0.300" depth. One thing crossed my mind as I was rotating CC on RT, same operation on each of 5 facets - maybe some neighbor chips migrated in & clogged it? I'm not sure if this would be enough to catch the tap off guard as it screwed in. But my 0.050" cellar probably didn't help matters. My new procedure is have my compressed air handy to give it a mild blast before tapping fluid & tapping operation.

If you look at my  pic under the knurled ring, Tapmatic clutch setting is performed by rotating body to desired setting along progressive sizes. I set mine 1/2 stop under M3, meaning theoretically clutch should slip out on the conservative side of their rec. Now the secret sauce behind what that's based on is what I don't know but will find out. I cant see my tap being weaker than a typical off the shelf one of same size. They use it in cnc environment. Now whether there further allowances to be made based on material or whatever I cant say. I mentioned in hindsight maybe this wasn't the best tap for my aluminum (although in recommended materials I think they say cast aluminum). It works killer in mild steel & has remained razor sharp. I intend to test with a HSS version of same chip ejecting style.


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## John S (Feb 6, 2017)

Going back over the replies to this thread it splits between Alum, welding a stud on, trepanning out oversize and plugging and drilling out with a carbide cutter.
What many have not read is the size of this broken tap at 3mm.

Alum whilst working for many is a bit hap hazard as it's sold under many names and for may uses so Alum from one place isn't the same as Alum from another place so no one actually states a trading name.

Welding unless you have a bit sticking out is pie in the shy. In this case the tap was buried and the OP said he only had basic workshop gear. A TiG welder isn't basic workshop gear.

Removing with a carbide cutter as a method does work but not on this scale.
I personally wouldn't try it on anything less than 6mm.
The reasons being and we will take this example of a 3mm tap is the tapping size should be 2.5mm minimum so to get in there without it deflecting and damaging the parent metal you need a 2mm carbide cutter.

Now carbide by virtue of it's manufacture has no grain or tensile strength, end of the day is a powder that has been heated and pressed into shape and is very, very friable. Now the tap has broken to no standard at all, chances are some of the top surface of the tap is made up of smaller broken bits jammed into position and nothing is flat.

So our 2mm cutter which indecently has to be mounted very rigid and no bench drill is god enough for this job is fed into the work and one flute hits the first peak which will either remove the cutting edge of a very brittle and fine tool or it will tip the bit of broken tap so the next flute hits it and snaps that. Result is we now have a cutting tool with no cutting edges which is about as much use as a left hand lollipop stick,

If you have a big enough broken tap then a carbide cutter 'can' work but be aware that the cutter isn't going to come out of the meeting with a piece of loose HSS unscathed, it may even take 2 or 3 cutters to complete the job and if you are talking quality cutters here as the cheap Chinese ones can't cut it, literally, then you can be talking upwards of 30 pounds or even more.

The problem is the internet.

Someone reads what one person posts and then repeats this ad hoc, never actually having done this but hey it was on the internet.

Trepanning will work and work well in this situation and is not out of the realms of a simple home workshop.

In this case take a short length of silver steel or drill rod, 5mm, 6mm or even larger and drill a hole up the centre12mm or so, not critical and drill at 3.2mm.
Then turn the outside down to 4.2mm and then file 4, 5 or 6 deepish teeth on the basically make a hole saw, get the teeth pointing the right way.

A tool this small can be hardened off on just the teeth on a kitchen gas stove.
Then set up in the mill as you need rigidity and absolute position and drill down carefully over the hole, using lubrication, WD40 is good for alloy, and go as deep as the original hole.

Once drilled you can then prise the core side to side with a screwdriver until it breaks off. That gives you a nice clean hole to tap to M5, screw a stud in, cut off, clean the top surface and then drill and retap.

Yes OK you have read this on the internet but it works.


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## petertha (Feb 6, 2017)

I called Tapmatic today & got some good information (paraphrasing)

The dial clutch setting on the unit is indeed a ballpark starting point. For most through holes this 'should be ok'. But the usual caveats, material type, tap type, tap condition, speed, lubrications...

Blind holes are a different animal. 

- The tapping head allows the spindle to continue tapping for another 3mm (0.118") extra travel on my model after the tap down feed has completely stopped. You can actually pull the arbor down from resting position, its kind of under spring tension. This is part of the allowance calculation I mentioned above. In my case it was evident I was set too close to bottom at 0.050". So now its a dog race of which problem arises first but bottoming the tap is likely what was going on & I can see full threads to bottom in my good holes. 

- He also mentioned its best (as I think Blogwitch John is saying) to start conservative clutch setting & see how the tap progresses & how/where stops. In other words tune the setting on a practice piece or at least base it something comparable which I didn't do. So I was likely at too high a torque setting for this particular operation.

- Even though a tap is a chip ejecting style, that doesn't mean 100% of chips are coming out. I saw nice swarf stringers come out during tapping but I also saw a little pile of mini chips when tapping was complete. The flutes could still be getting bunged up to some degree. 

Well, it makes me feel a bit better to have some likely answers. Now I'm going to tap a bunch of test holes in scrap & carefully observe things until this becomes second nature.

ps - I like that core drill-out idea. Kind of like a mini annulur cutter. May as well mess with that as well. I know that just making the tool in preparation will help ward of evil tapping spirits!


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## RonGinger (Feb 7, 2017)

There is a device sold to wood workers to remove broken off screws. It is simply a roll pin of the right size, with a few saw like teeth ground on the end. The important part is the teeth are ground to cut in the revers direction, so the cutter will likely catch on the screw and turn it out. 

These are the roll pins made of a hard steel, rolled into a cylinder.  In use as a pin the spring compresses so the pin is a force fit  into a hole. I have made the teeth free hand with a dremel cutoff wheel.

A roll pin will be easier to make and is already hard.


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## petertha (Mar 3, 2017)

Just some added FYI on this saga. For kicks I tried over-milling on the stuck tap in junker crankcase. First with Tin coated endmill. It met resistance. I pecked at it for 0.025" or so, but figured maybe it wasn't ground quite correctly for that kind of center cutting. Then I switched to brand new 4.5mm center cutting carbide ball end mill. Almost same result. I need to use these tools so didn't want to bugger them up experimenting. But the tap seems to be tough stuff. One day maybe I'll try a carbide drill.


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## petertha (Mar 4, 2017)

I ended up making a new crankcase. They get better with practice . After trying all kinds of different setup variations & tap types & fluids... this time I offset tap from bottom of hole the proper amount & it everything went smooth & predictable. Concluding that the broken tap arose by a combination slightly shallow hole (drawing interpretation error) and insufficient bottom clearance (my fault).

I'm going turn up some little dedicated (hand) tapping knobs as I have some M2.5 threads into even shallower blind holes in my future. I think I want to do these by hand. But anyway I'm much more confident of my tapping head operation now when the need arises.


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## Ropetangler (Mar 16, 2017)

One way which will succeed is to use a hot sodium hydroxide (Caustic soda and lye are other names) solution. Your crankcase will go into solution, and the tap will be lying in the bottom of the container. As an added bonus there will be copious amounts of hydrogen released as well;D. The new one looks great by the way:thumbup:


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## stackerjack (Mar 16, 2017)

I haven't trolled through all the replies here, so forgive me if this idea is already there somewhere.
The basic idea is to weld a steel rod to the tap. I know this is not always possible, but now and again, it is. If the welding is successful, it will almost certainly get the broken tap out.


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## werowance (Mar 17, 2017)

i have had great success with removing broken drills from aluminum with alum powder.  i am actually removing a #50 drill now.   

here is what i use,  mason jar with a bottle of alum in it and water. i have spring water at my house.  sort of a double boiler setup because i don't have a pyrex or glass pot and don't want to ruin my wifes good pot.  anyway i het on the simmer burner on the stove.  you can see the little white dots in the picture,  those are actually bubbles that the flash made look white.  those bubbles are coming from the hole the drill is in.  

the drill is just a cheap black oxide coated drill.   when its done the aluminum will look dull gray in color but will rub right off with some fine steel wool or hit it with the buffer for a second.   once done ill show what it looks like


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## madmachinist (Mar 26, 2017)

You're going to be very lucky in getting it out with all these suggestions.  I would take it to a shop that has an E.D.M. -- and hopefully they will be sympathetic and do it for free.  It's the only way of getting it out without making a mess, and ruining your crankcase and doing more damage.  Good luck!


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## petertha (Mar 26, 2017)

The 'mess' is behind me & a new crankcase successfully machined. I learned some important lessons about blind hole tapping. Good thing, radials have a lot of these. I am going to turn myself some knurled style mini tap holders 'knobs' so I can feel the hole & tap progression by hand. I have some even smaller M2.5 & M2.0 ones to do. Stay tuned. Right now I am doing some lathe repairs / upgrades. It coughed a fur ball half way through my crankshaft.

BTW, this fellow is building an homebrew EDM
http://www.****************.com/threads/building-a-pulse-edm-machine.55621/


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## Blogwitch (Mar 27, 2017)

Peter,

I uploaded a cheap and easy spark eroder to make a few moons ago.

http://www.homemodelenginemachinist.com/downloads/cheap-and-easy-to-make-spark-eroder-240.html

Instead of making finger turners for your taps, where they can still go in not square, what you really need is a tapping stand.
I made mine from an old cast iron surface plate but almost anything can be used as long as the column is truly vertical to the base.

Just search for tapping stand and look at the images, they will give you enough info to easily make your own.

There are even a few shown on here. This is a basic one, I fitted a small chuck to mine so that it is a lot easier to fit different sized taps.

http://www.homemodelenginemachinist.com/downloads/mini-hand-tapper-166.html


John


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## goldstar31 (Mar 27, 2017)

Greetings John.
Unfortunately, I'm getting precisely nowhere with both projects mentioned..
Cheers

Norman


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## petertha (Mar 27, 2017)

Thanks John, appreciate the plans links.

For this specific part I wanted to preserve the indexing setup on RT & mill. Each of 5 cylinders needs to be facet cut, cylinder skirt bored and the 4 M3 blind tapped holes on a pattern. It was easier to set the XY hole coordinate & then repeat for all 5 facets vs. tapping off the mill or a different tapping fixture. But that looks to be a very useful tool nonetheless.

I have made one finger wheel type tapping knob for a similar size tap (4-40) & it worked quite well. I ground a flat midway on the shank to seat a setscrew in the knob & that allowed the top of tap to extend up into the chuck for centering. I just lightly clamp the jaws so it was free to rotate & slide up & down. One could get fancier with a matching socket that enveloped the shank. There is so little torque required to tap in aluminum it actually goes quite well & I suppose more importantly you can feel by hand.

On the radial I figured let the tapping head do the work & do 20 holes in one tapping operation. Now with an uneventful 'good one' behind me, my entire problem issue was insufficient over-hole depth to accommodate the tap extending further. The instructions are quite clear regarding this, I just made an error on depth.

Hope I don't have to use an EDM but good to have on the project list.


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## Gene Pizzoli (Jan 1, 2019)

Just some advice from a former tool and die maker and later tool designer for GM. Bite the bullet , hollow mill the darn thing out, insert a helo- coil if available, if not insert a pressed bushing with locktight. On the other hand you may get lucky and smash the tap with a prick punch, picking up the shattered pieces as you go along. Aluminum is a ***** because of the galling tendency. The Alum theory is a new one on me since I find to believe it will dissolve hi-speed steel.  Must try it, Gene


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## petertha (Jan 1, 2019)

Thanks Gene.  Ultimately a new crankcase was made after the alum solution failed to do anything useful on that particular tap. Because of the extended alum bath, it also horribly etched the aluminum. Maybe this alum solution breaks down regular HSS taps as claimed. Who knows, its now history. As mentioned, this was a high quality tap that happened to be coated & maybe that slowed the erosion to a crawl. The tap breakage itself was entirely my fault by insufficient cellar depth, tools & lack of proper technique involved. Core drilling of a sheared off tap is something I want to experiment with on the side with some scrap so I have that trick up my sleeve just in case there ever is an unfortunate 'next time'. 

The crankcase assembly has progressed as below. Once I get my new mill issue sorted out (hopefully soon!) building on the radial will recommence with 5 cylinder assemblies. I've got a lot of pictures to upload & document, but I'll do it in a proper build thread. This has been an overly long journey dragged out by regular life stuff & my machines, but I will persevere. To be continued!


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## Cogsy (Jan 1, 2019)

I tried Alum on a snapped drill in brass/bronze? and had some success. In my case it was extremely slow and I think that was because the drill was only 1.8mm (so a small hole to get the solution into) and the flutes were clogged with chips (probably why it snapped off) so the Alum could only attack the top surface of the bit. I estimate it took 10+ hours of simmering away over 7 days, while occasionally scraping out the crud from the hole before I got it all. On the up side, it didn't cause any ill effect to the part at all. I would use the method again but only on a part with either high dollar value (like a casting or big chunk of bronze) or many hours in it, like 15+, as the Alum method was quite labour intensive as well. I think it may work better with a larger diameter hole but I'm hopeful I never find out.


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## dazz (Jan 2, 2019)

Hi
I have successfully used Nitric Acid for at tap embedded in aluminium after Alum didn't do anything.


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## davesmith729 (Jan 2, 2019)

*I have used Alum twice for broken taps in brass and it did dissolve the taps.  You can tell you are getting a chemical reaction because there is a stream of tiny bubbles coming from the hole.  It just takes time.  You might have to coat aluminium with something to protect it but the alum does not see to affect brass.*


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## John Roberts (Jan 2, 2019)

I have never heard of using Alum to dissolve a broken tap. What amount of Alum is mixed to water for the best results?


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## Rocket Man (Jan 2, 2019)

Put the tap extractor on the broken tap then put 1 drop of Muriatic acid acid down the hole.  Wiggle back and forth a bit and watch it foam.  Put more Muriatic acid in the hole 1 drop each time soon aluminum burs that hold the broken tap will be eaten away then the broken tap will screw out.  Be sure to rinse out all the acid very well.  You may be able to save the old treads or drill hole deeper to make more thread.  I was a tool and die maker for many years I took chemistry in college too.  It works I have done it.


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## Dubi (Jan 3, 2019)

dazz said:


> Hi
> I have successfully used Nitric Acid for at tap embedded in aluminium after Alum didn't do anything.


Hi Dazz, What concentration is the Nitric Acid and how long should it take for a small tap?


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## goldstar31 (Jan 3, 2019)

Dubi said:


> Hi Dazz, What concentration is the Nitric Acid and how long should it take for a small tap?



I taught myself enough chemistry up to Matriculation standard during WW2 and had a rather cooperative local chemist- who obtained things which we as boys shouldn't have had.

Having said that, you might Google something called 'Aqua Regia' .  Interesting topic if you like that sort of thing.

Oh, and aluminium, I always thought that nothing more more than caustic soda held in a dam made from child's modelling clay also 'fun'

My father who was extremely clever but had no money used caustic to seal iron radiator pipes in the family greenhouses.  Of course, caustic is useful to remove oil and grease PRIOR to starting to chemically remove iron.

The saponification of fatty acids things, if I recall distant days.

Just before the start of the Festive Season, I was on my way to family and wasted a bit of time before my train in the chemist's trying to get a styptic pencil.  I got looks of utter horror and disbelief when one didn't know what I was talking about and the manageress came on the scene and recalled that her father had a 'cut throat razor'

It's fun be really old- and still completely with it! I suppose that I'l have to open a few cheap batteries.

Regards

Norm


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## Rocket Man (Jan 3, 2019)

Dubi said:


> Hi Dazz, What concentration is the Nitric Acid and how long should it take for a small tap?




Muriatic acid not nitric acid.  I don't think you will find nitric acid unless you know where to look it is not sold anywhere.  Muriatic acid comes in 29% and 40% either one will work I have used them both.  It has a very toxic gas set up a fan to blow it away do not breath it or get it in you eyes.  Muriatic comes in 1 gallon plastic jugs.  Blow oil out of tap hole. Use gas to clean oil out of hole several times blow gas out with air hose too.  I drop of acid each time.  Do not blow acid with air hose and don't get it on you.  When you need to clean acid out of hole use water.  What size tap is it?


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## Cogsy (Jan 4, 2019)

Rocket Man said:


> It has a very toxic gas set up a fan to blow it away do not breath it or get it in you eyes.


Muriatic acid is just a name for dilute (and not especially pure either) hydrochloric acid. So the gas generated by the reaction is simply Hydrogen. Not especially bad for you (at least in low concentrations) but it is highly flammable. In my galvanising days whenever we had to strip already galvanised parts in the 80 foot hydrochloric tanks they would froth wildly and would overflow quickly if left unchecked, so we stood back and threw a piece of paper towel that we'd light up and flare off the gas. The initial 'poof' was exciting and then the entire tank would burn with a mostly light blue flame for half an hour or more til the reaction calmed down. The only ill effects we detected were if large amounts of stripped paint were floating on the surface and they would slowly burn with the hydrogen.


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## Rustkolector (Jan 4, 2019)

I have always thought aluminum alloys and zinc to be very reactive to strong acids and would think any concentrations of nitric, hydrocloric, and sulfuric acids would attack not only the ferrous tap but also the inside surface of the hole. I have personally used alum with good success but I don't remember whether my 2-56 broken tap was carbon steel or HSS. It might have made a difference. I had a good friend who was a noted gunsmith and he removed many broken screws but used a local water jetting company to remove his worst stuck screws. I have seen 4-40 sized screws removed, but I'm not sure just how small a hole water jetting can handle. I do know it was very cost effective and it cut rapidly.
Jeff


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## Cogsy (Jan 4, 2019)

I have used Alum with a HSS drill bit and it worked just fine.


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## BobNZ (Jan 5, 2019)

A spark eroder is versatile and with a bit of skill applied, can remove a broken tap or cut any hard material as long as it electrically conductive.

You can build your own. Do a search on spark eroder, tap eroder, tap disintegrator, metal disintergrator or EDM.
There are many DIY designs plus commercially produced machines.
eg

http://mikesworkshop.weebly.com/a-spark-erosion-apparatus.html
http://pico-systems.com/edm.html
https://groups.yahoo.com/neo/groups/EDMHomeBuilders/info

Commercial operator


You can go as fancy as your time and budget permits but no doubt your career path is not intended to become expert in breaking taps or drills so economy scale investment makes sense.
Once you have one then you may well be likely to use it for other purposes such as making holes of various shapes in hardened parts.

Alum seems to work OK for me when a tap breaks in Al.
The eroder use is not confined to Al but is handy for studs snapped on in cast iron blocks or similar.


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## metalmudler (Jan 6, 2019)

Hi petertha,

I hate those sort of days..
I did one on the second last hole on my Stothert and Pitt cylinder flange in bronze.. Did not have a slug of bronze big enough laying around to make a new one even if I wanted. I had no other option but to buy "Alum". I bought it cheaply here in Aus from an Indian grocery store if I remember correctly.

 Its not an instant thing but it works, so I verify what everyone says about this weird white powder  Apparently also in stick form.. For shaving cuts. 
I imagine it works quicker with a totally fractured tap segment rather than an intact one? More surface area for the Alum to work its chemical magic. Just get on with some other things while it does.. Certainly quicker and cheaper than building EDM


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## metalmudler (Jan 6, 2019)

A curiosity hit me... Can anyone explain the chemisty using Alum as we do?.. It works by removing our sad little  broken ferrous metal tap piece from our non ferrous part, not the other way around as far as I gather. Some sort of oxidization? Can anyone explain it in simple terms?


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## goldstar31 (Jan 6, 2019)

It's a long chain of chemical action but the action changes the offending bit of steel into iron or ferrous sulphate.

For gardeners, ferrous sulphate is the stuff which kills and blackens moss in lawns---- and eats its way into galvanised watering cans.  Alum  also stops bleeding if you use a wet razor

Any clearer?


N


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## metalmudler (Jan 6, 2019)

goldstar31 said:


> It's a long chain of chemical action but the action changes the offending bit of steel into iron or ferrous sulphate.



Thanks N,
I was asking how the reaction works, not how to shave or mow a lawn whilst breeding haggis sir 
Anyone else pls make it clearer without using google or giving the questioner curry? I was under the impression this was a friendly site where we can ask questions about things..


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## goldstar31 (Jan 6, 2019)

Apologies but it is extremely difficult to know just how much a poster knows already.

One may talk down to a poster or beyond them.  Basically it is hydrolysis where the chemical formula changes from aluminium sulphate( alum) to iron sulphate - and the creation of sulphuric acid to do eat into the offending bit of tap ( iron). 

The chemical formula for the reaction is in Google and really worse than my answer.
If I have offended you it was not intentional and I apologise wholeheartedly.

Norman


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## metalmudler (Jan 6, 2019)

Thank you Norman,

Apology accepted and thanks for taking the time to explain it in simple terms.  Apart from heat, could electricity be applied in an electrolytic way or something to maybe speed up the process?

Flat out installing A/C for fotb immigrants here in Sydney atm, so no time to shave  Beard and mow all the way, Muslim style..  Helps me blend in with the new livestock.

Paul


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## goldstar31 (Jan 6, 2019)

Paul
           Oddly, if one puts iron and aluminium together, the reaction  can act as a battery of sorts and certainly generates small amounts of electricity.  However, forgive me, if you put rusted iron and aluminium fillings together- and ignite them , you get a bloody big explosion and this, believe me, is how some iron rails are joined and hopefully, will never happen in OZ, you have incendiary bombs. Don't try it because an ordinary hose will cause further explosions and needs to have a sprinkler system to cool the reaction. 
How do I know all this?  I was a kid in WW2 in the UK.

I was a bit baffled in the second para. I suspect that you were having a 'tongue in cheek' remark.  I think that I understand the 'double entendre' LOL

Cheers

N


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## Chris Murphy (Jan 6, 2019)

Rustkolector said:


> I have always thought aluminum alloys and zinc to be very reactive to strong acids and would think any concentrations of nitric, hydrocloric, and sulfuric acids would attack not only the ferrous tap but also the inside surface of the hole. I have personally used alum with good success but I don't remember whether my 2-56 broken tap was carbon steel or HSS. It might have made a difference. I had a good friend who was a noted gunsmith and he removed many broken screws but used a local water jetting company to remove his worst stuck screws. I have seen 4-40 sized screws removed, but I'm not sure just how small a hole water jetting can handle. I do know it was very cost effective and it cut rapidly.
> Jeff[/QUOTE
> 
> Almost correct-except that aluminium is passivated against nitric acid-but not the other two mineral acids-using nitric acid to remove broken taps in aluminium castings works well-the other two not so well (-or to be accurate-the other two work-but at the expense of also corroding the casting-which is not usually a preferred outcome!)  I've used 30% nitric for the job in the past-so slightly stronger than 'battery acid' to give some equivalency (and yes I know battery acid is sulphuric acid!)    Commercial concentrated nitric acid (which is the way you would generally purchase it-is 67%-so you would dilute this a little over two fold for a working stock.
> The only point of concern is that the process can generate some discolouration of the casting-but that depends largely on the alloy composition.....and hopefully there will be no need to immerse the entire casting in acid-if you're lucky with the location of the broken tap it is usually possible to build a dam using plasticene or modelling clay around the offending hole and broken tap to confine the acid to the vicinity-which reduces any discolouration to a fairly small area. In my cases the alloy was a high tensile casting with a significant Si content-and Si itself does react with nitric acid, and this reaction caused the discolouration. Needless to say-there is no need to entirely dissolve the broken tap, only as much as is needed to remove it-though in the case of very small ones, there is not much difference in the time required! ....and thorough washing after the process is done is required. A bit of baking soda or washing soda in the initial rinses does no harm either to neutralise any residual acid lurking in the threads.


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## metalmudler (Jan 6, 2019)

Norman,

After making my own BP and fuse for fireworks, it was obviously the next step.. 
"Don't try it"... To late!

Had my fun   .     Grandfather worked on train lines, heard the stories.
Sadly not allowed fireworks of any kind  here in OZ anymore  I guess its the old story of the irresponsible people ruining it for the responsible people.
 I can use the remainder of the bag to color cement, but what am I to do with left over tub of aluminium powder.  
LOL Yes Norm, you got the second para mate 

Paul


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## Cogsy (Jan 6, 2019)

goldstar31 said:


> However, forgive me, if you put rusted iron and aluminium fillings together- and ignite them , you get a bloody big explosion and this, believe me, is how some iron rails are joined and hopefully, will never happen in OZ, you have incendiary bombs. Don't try it because an ordinary hose will cause further explosions and needs to have a sprinkler system to cool the reaction.


In the right concentrations and particle sizes what you describe here is called thermite. It isn't inherently explosive, although steam explosions are certainly possible when it is ignited due to it's extremely high reaction temperature. And while you're correct that a hose won't put it out, neither will a sprinkler. For open days at uni we set up a pot of thermite above a large clear tank of water and the molten iron generated by the reaction drops into the tank with such energy that some water is split into it's components, which ignites at the surface of the water - so effectively we burn water. It's a very impressive demonstration.
Thermite is still used for welding railway tracks together in some parts of the world (including some parts of the USA I believe).


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## Dubi (Jan 7, 2019)

goldstar31 said:


> I taught myself enough chemistry up to Matriculation standard during WW2 and had a rather cooperative local chemist- who obtained things which we as boys shouldn't have had.
> 
> Having said that, you might Google something called 'Aqua Regia' .  Interesting topic if you like that sort of thing.
> 
> ...


Hello Norm,
A very Happy New Year to you and your family. Thank you for a very informative reply. I will certainly investigate Aqua Regia. 

Your comment about Septic Pencil reminds me that my Mother always had one in the Medical cabinet in the bathroom but this was in the 1950's.

regards,
Dubi.

ps: As a kid I had great fun with Sodium Metal!!!


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## Dubi (Jan 7, 2019)

Rocket Man said:


> Muriatic acid not nitric acid.  I don't think you will find nitric acid unless you know where to look it is not sold anywhere.  Muriatic acid comes in 29% and 40% either one will work I have used them both.  It has a very toxic gas set up a fan to blow it away do not breath it or get it in you eyes.  Muriatic comes in 1 gallon plastic jugs.  Blow oil out of tap hole. Use gas to clean oil out of hole several times blow gas out with air hose too.  I drop of acid each time.  Do not blow acid with air hose and don't get it on you.  When you need to clean acid out of hole use water.  What size tap is it?


Hi Dazz,
Happy New Year to you and your family. So far lately we have not broken a tap in the workshop. Let us see what happens this New Year, thank you for the information.

warm regards,

Dubi.


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## davesmith729 (Jan 7, 2019)

alum works and it is safe


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## mcostello (Jan 7, 2019)

I tried it on a broken tap for a week simmering on a wood stove and it did not work at all. I wonder if there is something to add to the mix to get it to start on a different type of metal tap, such as more included chrome?


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## goldstar31 (Jan 7, 2019)

mcostello said:


> I tried it on a broken tap for a week simmering on a wood stove and it did not work at all. I wonder if there is something to add to the mix to get it to start on a different type of metal tap, such as more included chrome?



Not wishing to be controversial but have you and others checked to see what your chemical was?
Again, large quantities of 'non iron' alloys might also affect reactions.
I have lathe tools that contain no iron whatsoever. On the other hand, I have rusting HSS lathe tools.

Intriguing, to say the least

Norman

Later, I was unable to find that Nitric Acid  on my E-Bay list-- but sheafs of warning labels.


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## John Roberts (Jan 8, 2019)

Still waiting for anyone who has successfully used Alum to tell us the ratio of alum to water? Thanks in advance.


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## Gene Pizzoli (Jan 8, 2019)

goldstar31 said:


> Not wishing to be controversial but have you and others checked to see what your chemical was?
> Again, large quantities of 'non iron' alloys might also affect reactions.
> I have lathe tools that contain no iron whatsoever. On the other hand, I have rusting HSS lathe tools.
> 
> ...


Are your lathe tools ceramic. What are they made of if not an Iron alloy


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## goldstar31 (Jan 8, 2019)

Gene Pizzoli said:


> Are your lathe tools ceramic. What are they made of if not an Iron alloy



None are ceramic but quite a few are tungsten- which in  its format are from mined.  
Personally, I'm not unduly bothered as my problem( small and insignificant) is removing a broken screw on an three insert milling cutter.

For others, I was reading up George Thomas( Model Engineers Workshop Manual) and in addition to him using nitric acid he made up a trepanning tool in certain applications. What sort or how he made it was never written up.  I understand the principle and have quite a lot of broken tungsten carbide  drills which could be altered to form spade drills as I have quite a few assorted tool and cutter grinders- some with diamond and CBN wheels.

Again, my daughter who is a consultant dentist/orthodontist probably throws away lots of suitable drills- and I have a Dremel type drill as well.

However, I am cognisant of the fact that others have considerably less tooling than me- and I'm merely trying to add to the fund of helping

But Thank you

Norman


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## Cogsy (Jan 8, 2019)

You want it to be a saturated solution so heat the water and continue to stir in Alum until it won't dissolve any more. Then keep the solution simmering away as it does its job. As some of the water evaporates away, the Alum will begin to recrystallise, so you will need to keep the water topped up.


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## John Roberts (Jan 9, 2019)

Many thanks Codsy.


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## Dubi (Jan 9, 2019)

metalmudler said:


> Norman,
> 
> After making my own BP and fuse for fireworks, it was obviously the next step..
> "Don't try it"... To late!
> ...


Be careful the Boys in Blue do not visit you.


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## OldRon (Jan 9, 2019)

Does this discussion pertain to a thread cutting tap broken off in aluminum OR dissimilar metal and electrolysis?

 IF stubbed off thread tap then having worked in several aircraft manufacturing machine shops I have seen plenty of that in expensive parts and the majority of the parts were saved by a tap burner. For those that are not familiar with the process then it is very similar to Electrical Discharge Machining, albeit crude. If the part is transportable then it should not be difficult to find a shop with a tap burner. Those of you that are creative and have a TIG welder could build your own tap burner.

"An Ounce of Prevention is Worth a Pound of Cure".

Switching from removing material to create a threads TO displacing material to form threads significantly reduces the risk of stubbing off thread cutting taps in work pieces and it improved the consistency of the thread classification. If you have CNC machinery that supports G02 and G03 with depth in the axis of rotation then from ¼' and larger thread milling is your best friend. I build my own 2 flute single point thread cutters on my CNC milling machine using the Machinery's Handbook to get the correct profile for each thread series. If the hole to be threaded is blind and it's large enough then I mill the threads. I would much rather chase threads than chase a stubbed off thread cutting tap.

I hope all ended well for the OP.


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## metalmudler (Jan 10, 2019)

Dubi said:


> Be careful the Boys in Blue do not visit you.


Why would they? That was going back some time now, when I was a teen, not a middle aged man. That's why my previous post included acknowledgement of them/it being illegal. Thanks for any concern though.
 I do not recommend anyone make their own or even possess them/it today in OZ. 
Although new years eve, Sydney. There were still illegal fireworks arrests!



John Roberts said:


> Still waiting for anyone who has successfully used Alum to tell us the ratio of alum to water? Thanks in advance.


Hi John, I used a saturated solution as cogsy described to remove a 2mm tap from a bronze cylinder flange (cant remember if it was carbon steel or hss). It was an open hole through the flange. I did it in a warm oven and kept the broken tap hole covered with the undissolved crystals in the solution whilest still submerged. It worked in a few days by loosening the tap pieces enough to pick them out with a pin.


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## sedge (Jan 11, 2019)

There is a watchmakers product called Vissin made by Bergeon that might be worth investigating, should be available from horology suppliers.
Bergeon Vissin liquid was specifically designed to dissolve screws which have broken inside a watch plate, bridge or case. Item is set in a glass alcohol cup or appropriate container, cover with Vissin then heat. Bring to a slow boil, the liquid will eat away the broken screw and when a black substance exudes from the screw hole, you know the screw has been completely removed. Immediately rinse the piece under running water and clean with benzine. Use caution because the liquid can eat through more than just the broken screw you want to remove.


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## mcostello (Jan 11, 2019)

I called the maker of the Alum and they told Me it was Aluminum Ammonium or some such, so I had the wrong thing. Will get the right stuff and keep it on hand. This may explain the many complaints from people who cannot get it to work.


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