Dissolving broken tap

[Rotate]

I was trying to tap a brass strip using a HSS M1.1 tap when it broke, embedding itself in the work. There is no way to physical remove it and considering the size, there's no way that I can drill it out using carbide drill (don't have that size, so it's academic). As I recall, there was a thread about dissolving broken tap, and nitric acid was the acid of choice.

Where can I buy nitric acid in small quantity (in Canada)? Will muriatic acid work just as well? I can get those at Home Depot. How about sufuric acid?

Alum was also mentioned. Where can I buy that?

Thanks.

Albert

[Thrud]

Albert
Try Fisher Scientific. You may have trouble buying chemicals. You can also try a plating shop. You can ask your pharmacist to order it for you if you explain what it is for - a 1 oz or 8 oz bottle is unlikely to get you in trouble, asking for a gallon...is.

You may need to get permits. Good luck.

[WJHartson]

Muriatic acid is diluted HCL and probably won't do the same as Nitric Acid. If you have a university in your area with a chemistry lab they might be willing to give you a little nitric acid or let you use some there to see how it works on desolving the tap.

[Kevin45]

If you have access to a carbide 2 flute end mill that is slightly smaller than the tap it can be taken out by that manner. Run the end mill high speed, 1800 plus, and use slight pressure.

Kevin

[hms50]

You could do it with plain old alum, avalable in grocery stores. Dissolve in hot water, soak part in glass container on stove,(just under a boil). Take part out once in a while and scratch off black oxides. Slow, but safe and cheap!
Good Luck
hms50

[mikem]

Nitric acid is used in making nitro glycerine and dynamite, I think, and that could make it a little tough to get. Could you use some homemade EDM method?

[crypto]

Will acid from an old battery work? I seem to remember doing that once upon a time.

[Rotate]

Thanks everyone. Alum did the trick. It only took 30 minutes before the tap loosened itself. It made the tap go black as shown in the picture, but the brass was untouched.



The image above was taken using Intel microscope that my kids got for Christmas, or was that really a present for myself

Albert



[This message has been edited by Rotate (edited 02-18-2003).]

[davestea]

will this alum method work in steal - or only on brass? aluminum?

------------------
Dave - Castro Valley CA - Smithy, Select Mill, Atlas 6" and Unimat lathe

[Rotate]

Only works with Aluminum, Brass, and other non-ferrous metal. Alum is a sulphate compound (e.g. aluminum sulphate), which dissolved in water. The sulphate reacts with iron and forms ferrous sulphate (stuff you take for anaemia). Fortunately, ferrous sulphate is water soluable, which means that the process of converting iron to ferrous sulphate continues without requiring a lot of mechanical agitation.

I was impressed by how quickly the tap was dissolved.

Albert

[lynnl]

It would work in steel. ...with one major problem. It'd also erode the workpiece as well as the tap. (I think)

[Rotate]

You'r right Lynnl. It will work on steel work, but that kind of defeats the purpose...although if you can apply the alum solution locally (e.g. with blind hold) it will work and use a Helio coil with a bigger hole.

Albert

[hms50]

Good morning gentlemen,

The first time I saw alum dissolve steel involved a broken one gallon jar of pickles in the trunk of my father's brand new car! I was sure baking soda would take care of the citric acid, but had no idea how powerful alum was. We dumped 4 boxes of soda in the trunk, flushed with water and dried with towels and then a hair dryer. A month later, there were holes through the trunk! Poor old Dad!
hms50

[docsteve66]

HMS50: I had forgotten that pickles are madewith alum. A good source of cheap alum would be in the canning supplies in a (southern?) grocery.

[ShavingMaker]

Do you have to heat the solution? I am thinking this would be a good method to remember if you broke off a bolt in an aluminum engine block, but it would be hard to put it in a glass container on Mom's stove!