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merryman
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Quote merryman Replybullet Topic: Chemical stud removal
    Posted: 06 Sep 2013 at 9:53am
Does anyone know of a chemical to dissolve broken steel studs in aluminium? A couple of years ago I found someone selling this stuff whilst doing a web search for something else. Now I need some and canít find the supplier. The problem I have is an M5 screw holding a magneto coil to the crankcase. Someone had broken it and the mag was held on by one screw instead of two. I was tempted to fit the new coil with just one screw as the mountings are doweled, but the earth tag is supposed to be clamped by the broken one, (it was clamped to the other on the old coil.) I canít get a drill in straight without a lot of dismantling, but a rubber tube could be fitted round the boss, ideal for chemical removal. New web searches come up with a rather expensive US supplier, and lots of people saying either ďAlumĒ or nitric acid is the stuff to use. Further research indicates that ďAlumĒ can be several aluminium based chemicals and one source reckoned that what is needed was potassium aluminium sulphate, I tried it and it was useless. So has anyone on the forum actually successfully used a chemical remover?
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Jimmy C
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Quote Jimmy C Replybullet Posted: 06 Sep 2013 at 1:31pm
Try the vehicle restoration company, frost.co.uk
Regards, Jim.
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hitchinsm
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Quote hitchinsm Replybullet Posted: 06 Sep 2013 at 3:57pm
Nitric acid is most common in vinegar and lemon juice. If you put aluminium in it with a steel stud you will eventually have a nice clean stud but no aluminium left.

Removing broken studs is an art in my view, as everyone is different and requires a unique approach. The only advice I would give is do not use the common stud extractor as it is tapered and the more you tighten it the more it expands the stud giving it an even better grip on what you are trying to get it out of.

If I have to remove a broken stud from a cylinder block or something important I set it up on the milling machine and use a tungsten carbide centre drill to start off, then change to a tungsten carbide stub drill. Finally either re-tapping or heli coiling the resulting hole.
Regards Mike
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owen
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Quote owen Replybullet Posted: 06 Sep 2013 at 7:56pm
Been looking up on alum (potassium aluminum sulfate), mix 4tbsp alum to 1 cup water. As much as you need to cover the bolt, heat is essential. Not fast can take up to 12 hours, to speed it up it was sugguested you could probably drill out the center of a bolt to help remove the bulk of the metal and then use the alum to dissolve away the rest. I have never tried it but I might experiment on some scrap.
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Stuart.
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Quote Stuart. Replybullet Posted: 06 Sep 2013 at 9:12pm
Providing the broken screw or stud etc that you are trying to remove is at least "flush" with the surrounding casting i use a MIG welder to build up material on top of it.Once you have a healthy blob of weld on top use some vice grips to uncrew the broken screw / stud etc.Heating the surrounding casting also helps removal too.
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Charlie
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Quote Charlie Replybullet Posted: 07 Sep 2013 at 9:42am
Vinegar and lemon juice are acetic acid, not nitric acid if I remember my chemistry correctly.
Another stud removal process is spark erosion, see spark erosion as an example.
'Don't force it! Get a bigger hammer'
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hitchinsm
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Quote hitchinsm Replybullet Posted: 07 Sep 2013 at 4:16pm
You are right, I did mean acetic acid. Have had good results from cider vinegar as it is not too aggressive as long as you are patient and do not expect instant results. Quite good for cleaning out rusty fuel tanks as well.
Regards Mike
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hitchinsm
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Quote hitchinsm Replybullet Posted: 07 Sep 2013 at 4:26pm
When I was serving my apprenticeship I worked in the tool room where we had two spark eroders being used mainly for eroding holes in tungsten carbide. They now have three dimensional machines that will spark erode a gear from solid. There is a Company in Coventry, Wire Tech who do a lot of automotive and F1 work.

They like doing the odd broken tap or stud for cash as well.
Regards Mike
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merryman
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Quote merryman Replybullet Posted: 21 Oct 2013 at 7:47pm
I tried the weld a nut on idea, and the weld got a good hold on the screw, however it just broke further down, pressure of other work meant the magneto was abandoned for a while. Having a little time to spare I finally got round to buying some Nitric acid, (surprisingly cheap and easily available from fleabay). I put some rubber tube round the boss with a jubilee clip to ensure tightness and poured in 2ccs of water and 2ccs of acid, itís evil stuff, giving off a visible white vapour. This was Friday and on return to work today I siphoned out the acid with a syringe to find about 8mm of the stud had gone whilst the alloy casting is unaffected, the threads down the hole seem perfect. I have refilled the tube with fresh dilute acid, so will see what has developed tomorrow.
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Charlie
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Quote Charlie Replybullet Posted: 22 Oct 2013 at 2:36pm
Keep us informed of progress, this sounds like a solution to the problem.
'Don't force it! Get a bigger hammer'
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merryman
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Quote merryman Replybullet Posted: 26 Oct 2013 at 8:53pm
It took another couple of days before I got tired of waiting and the hole was about 12mm deep so I decided there would be enough depth for a new screw to grip properly, the other screw is very long and I suspect they may have bottomed in the holes causing the screw to seize in the first place. I flushed the hole out with water then blew it out with an air line and put some grease on the new screw to help prevent corrosion.

So in conclusion, Nitric acid works, I donít think changing the acid made much difference, it is slow but removes steel without affecting the aluminium. The acid I got was 69% concentrate and I diluted it with an equal quantity of water. Maybe a higher concentration would have worked faster, I donít know.
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