Removing Broken Taps with chemicals

I remember reading a post about removing taps with Aluminum sulfate. I have also googled it and found the information I need with the exception of how and where to get the Aluminum sulfate. Any help in the matter would be appreciated. I have two broken taps in aluminum and the size is 4-40.

Alum (used in pickling) is potassium aluminum sulfate

Old timey baking powder (Calumet) is sodium aluminum sulfate

Amuminum sulfate is a constituent of many fertilizers and is probably available from a garden store. How may 50 lb sacks do you need to etch that tap?

One of these should work.

I am not sure because I haven't tried it but I dont think that alum solution will strip a tap from a ferrous matrix. I have used it to remove steel taps from brass and nickel where it was effective. (but slow 5.40 from 1/4" brass overnight.) I think you need the different materials to cause a charge of electrons to flow and stimulate the reaction.

Charles.

The easiest way to get a small tap out W/O edm,is to buy a carbide spade drill. Run it fast,no lube. It will cut the tap out cleanly,leaving the threads if you carefully center it. I've done this many times. Everytime someone in the museum breaks a tap off I have to be the one who gets it out. a small center cutting end mill tin coated has worked very well,too. Do this drilling only in a mill with the part in a vise.

Last week I used a nitric acid solution to do just that. Search Ebay for "Tap Removal Remover edm Tap and Die aluminum stainless".

max

In the past I have;

find a smaller solid carbide center drill or endmill.

Set up on a Bridgeport at 3k + rpm. (I have tried a canned drill cycle on a VMC and I think i like doing this by hand better if it is a part that you have alot of work into)

I use some cutting fluid and VERY VERY VERY gently start working down on the tap. Air to remove chip/coolant frequently + light so you can see.

If you rush this at all, you will trash the tool and your part. If you are a gorilla and use too much pressure..same thing.If you have any regrinds that small, try one of those first.

I hope that wasn't a form tap.

I had a 3/8" long piece of a Union Butterfield 1/4"x20 tap broke off in 1.3" blind hole close to 1" down in 6061 aluminum.I tried battery acid(sulfuric acid) for a week twice a day filling the hole with acid and heating till it bubbled with a propane torch,letting it sit for 12 hours ,flush with water and pick,managed to get a few bits of tap teeth out, but it wouldn't budge.

Then I tried the alum in boiling water for about 6 hours with no luck.

What worked was putting the part in a small aluminum pot of sulfuric acid on a hotplate set on
the lowest temperature setting outdoors.The battery acid is rather weak,but if you are careful,the concentration(strength) can
be increased by slowly boiling the water out of the acid and water mixture.I drilled a small hole through one side of the part to intersect with the blind hole so that the acid could circulate past the tap.It took about 2 hours and the tap was completely dissolved.

Be extremely careful with acid and the strong
fumes given off.Wear safety goggles,and have some fresh water nearby in case you spill acid on yourself.

Well after a week of soaking the part in baking soda, no affect on the tap. I then purchased a carbide end mill and cut right through the tap. Should have done that from the beginning. Thanks for the halp.

that nearly always works for me...