broken tap in aluminum cranckase

[petertha]

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.

 

[goldstar31]

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

 

[John S]

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

 

[Walsheng]

Norman:

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

John

 

[Hopper]

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.

 

[goldstar31]

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.

 

[petertha]

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.

 

[ninefinger]

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

 

[petertha]

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.

 

[Cogsy]

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).

 

[petertha]

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....

 

[Cogsy]

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.

 

[petertha]

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?

 

[goldstar31]

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

 

[petertha]

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

 

[goldstar31]

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

 

[petertha]

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

 

[petertha]

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.

 

[mcostello]

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.

 

[keith5700]

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.