broken tap in aluminum cranckase

[Gene Pizzoli]

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

 

[petertha]

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!

 

[Cogsy]

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.

 

[dazz]

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

 

[davesmith729]

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.

 

[John Roberts]

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

 

[Rocket Man]

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.

 

[Dubi]

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?

 

[goldstar31]

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

 

[Rocket Man]

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?

 

[Cogsy]

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.

 

[Rustkolector]

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

 

[Cogsy]

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

 

[BobNZ]

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.

 

[metalmudler]

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

 

[metalmudler]

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?

 

[goldstar31]

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

 

[metalmudler]

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..

 

[goldstar31]

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

 

[metalmudler]

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