Alum as metal remover.

I have nearly finished the body of a small carburetor.I was drilling and tapping a 8BA hole when the tap broke.I can't make a core cutter to cut round the tap as there isn't room.I recall reading of alum to remove broken taps but can't remember how it is used.I have a small tub of alum crystals,could someone enlighten me please as how to proceed.

Frank

I think it depends on the type of tap. I think Alum works with carbon steel taps but I’m not sure if it works with HSS. You may need to get some Nitric Acid instead?

Assuming the carb body is aluminium, dissolve a heaped spoon of alum in a glass of warm water, leave the part in it for a few days, every day poking the remains of the tap with a needle until it falls out.

Neil

The body of the carb is brass ,will this be a problem.

Frank

What material is carb?

Don't use alum if the carb is aluminum, if it's brass (or a bronze) then try it.
You may find it of interest to read this article if the carb is aluminium: "How to dissolve steel without affecting aluminium alloy" :-
**LINK**

8BA is a bit small but I've had success with a diamond bur in a hi-speed mini drill. Ask your dentist for a used narrow, cone type; it will rapidly remove the bulk of the tap even if HSS. The remains can be picked out then with a needle. However with an 8BA tap you'll need a steady hand & good eyesight !

Posted by Fowlers Fury on 18/12/2018 23:03:51:

Don't use alum if the carb is aluminum, if it's brass (or a bronze) then try it.
You may find it of interest to read this article if the carb is aluminium: "How to dissolve steel without affecting aluminium alloy" :-
**LINK**

I've used alum in aluminium alloy bike bits for broken taps in the past with no problem. I can't see where in your link it says don't, in fact alum is recommended by a couple of posters.

Edited By Mick Berrisford on 19/12/2018 00:09:35

Thanks to all for your input.I am proceeding as Ian suggested.

Frank

My first attempt was with some alum that I had in stock,nothing was happening but my son pointed out that it was 20 years out of date.I sourced some of amazon and within a week the tao has gone .I did as Niel suggested and piggled about with a needle and today to my delight and suprise a full depth 8 BA tap is gone.I have recharged the cup to make sure the threads are clear.I thank everyone for their help in this matter.

Frank

Or perhaps caught out by the name 'Alum' being used for at least six different chemicals, only one of which is suitable. You want Potassium Aluminium Sulphate, also called Potash Alum or Potassium Alum.

Of the true Alums, Sodium Alum might work as a substitute tap remover, but maybe not Chrome Alum or Ammonium Alum.

Some chemicals called 'Alum' aren't Alum at all: Aluminium Hydroxide and Aluminium Sulphate. These are useless for removing taps.

The confusing nomenclature is historical. Once a common name has caught on in a trade it's difficult to change it.

Dave

I'm glad you posted that. I bought some "alum" online specifically to try it out and over a period of several weeks, absolutely nothing happened to the metal. Obviously not the alum I wanted.

If anyone knows of a source for the right stuff, I'd be much obliged.

Try eBay I bought some from a chemical company (south Essex I believe ) last year to remove a 10 BA from Dads new copper boiler. It worked well but took a week.

Paul

Just looked at my eBay history, Minerals-water Ltd 800g £12 inc postage.

Hope this helps Paul

Thank you very much Paul.

For anyone interested: https://www.ebay.co.uk/itm/500g-Potassium-aluminium-sulphate-Alum-Potash-Alum-Kalinite/140897858272?hash=item20ce2ab2e0:g:j3cAAOSw6EhUR4rw

You can buy alum rock chrystal from lots of outlets. I have used it on my pits for years now after developing an allergy to deodrants. I expect someone will tell me its the wrong sort of alum though.

Rik

They work well though!

Alum is dirt cheap from Arabian food suppliers.

Neil