Broken drill bit soaked in Alum : it is not working

I broke a 1.5mm drill bit while drilling aluminium ; it was almost through but not quite as there is a ''pimple'' on the other side. I have soaked the work piece in a saturated Alum solution for the past week but nothing is happening.

I then bought an old aluminium sauce pan to heat things up and get it moving but still nothing is happening.

I have previously used Alum to dissolve a broken M2 tap that was stuck in brass. It took a month at room temperature but it eventually dissolved the tap. I did not have to heat it up. That was a through hole so perhaps the Alum could react on the broken tap from both ends.

Do not have much chemical knowledge so cannot tell why it is not working, but since you know where it is on the otherside, place a 1 mm punch on it and hit that with a hammer, should work very quick. Niko.

Edited By speelwerk on 07/06/2016 13:03:27

Have you not tried using the other end ( shank ) of the broken drill to tap through the dimple at the other end ?

George.

Looks like Niko beat me to it.

Edited By mechman48 on 07/06/2016 13:04:06

I might give that a go tomorrow. I did not want to muck up the hole as it is to be tapped for an M2 screw.

Interesting.....are you sure you have real alum?.........not a substitute or "equivalent". So much stuff is changed and does not work like it did....I've posted before that my last(failed) attempt to buy alum met with a "too dangerous" from the first chemists I tried and "how do you spell it" from the pharmacist at Boots...!?!

Yes, that's what I was thinking. If it's "supermarket" alum it could be some kind of substitute.

The days of being able to buy many types of useful chemicals over the counter at a chemists has sadly long gone.

The 'proper Alum' question popped in to my mind too - I bought mine direct from a chemical company in Manchester, and as soon as you put a bit of steel into a hot saturated solution it fizzes and dissolves very quickly.

I fear you may have a 'nanny state' substitute.

Andy

Will the fact that alum is aluminium potassium sulphate have any thing to do with it as the parent metal that he is trying to dissolve out of is aluminium ( Don't know just an idea )

Roy

'Alum' is a generic term for a small group of similar chemicals, so yes there may be some differences. However it is a long time since I had to access the subject in the grey matter and now the details are elusive. Google 'alum wiki' for some information.

Francis

1.5 mm is a bit small for M2, minimum for me is 1.6 and others will even go to 1.7, anyway you have enough material to clean up the bore before tapping M2. Niko.

Even more confusing than Francis suggests. In addition to the Alum family and various Alum substitutes, two rather different chemicals are commonly called "Alum".

Aluminium Sulphate is used for treating water, and I think it's the wrong one.

I've never tried it, but I think the Alum needed for dissolving a tap is Aluminium Potassium Sulphate as used in styptic pencils for shaving accidents.

The internet is your friend if you want to buy some.

Cheers,

Dave

Brian,

as others have said, you need "potassium aluminium sulfate" - KAl(SO₄)₂ 12H₂O - and it will dissolve steel but not aluminium.

Thor
 

Edited By Thor on 07/06/2016 17:35:20

I have the correct Alum. Remember, it worked on the broken tap in the brass work piece.

I have found another source of Alum so I will give that a try soon.

I was also met with blank looks when I tried to buy it locally so I ended up buying it from India and China. I recently discovered that the local Indian grocery store has it on the shelf. They have two types : shaving Alum in a block form and eating Alum in crystal form. I have not tried either yet. What I am using at the moment was purchased on ebay from India (potassium aluminium sulphate).

Edited By Brian John on 07/06/2016 17:50:01

I have dissolved steel from a cast aluminium crankcase using nitric acid. The process is dangerous and smelly, and the fumes are corrosive (as is the acid) - but it worked.

I am not recommending this to anyone.

Tim

Brian,

was the broken drill coated? (with TiN or something similar)

Thor

Concentrated Nitric acid will not dissolve Aluminium, or Iron, for that matter, since it is an extremely active oxidising agent. It will produce a protective oxide film on Aluminium, or on iron. Steel being an Iron alloy may be partially dissolved by the acid removing the alloying metals. If so, you may be left with a black residue of Iron Oxide and carbon.

Proper Alum, as already mentioned will not dissolve Aluminium, because with the "parent" Aluminum and that in the Potassium Aluminium Sulphate, the solubility product for Aluminium will already have been reached.

Even if the drill had been TiN coated, the Alum should have got to work on the exposed iron at the fracture.

Silly questions:

1) If the solution had functioned before, is it exhausted perhaps?

2) Have you tried a freshly made up solution?

3) Maybe the Aluminium container is an inhibiting factor on the chemical reaction?

4) Have you tried using a glass or plastic container?

Just a few thoughts

Howard

That will be the eating variety then!

I had a similar problem when I broke a 12BA tap on my 5"g terrier Stepney side tanks in April.

I ordered a bag of Alum off ebay for about £3.

Soaked in some of the stuff and no result. So added all the bag and shoved it in the oven while cooking sunday roast.

Kept taking it out to have a poke around with no discernable difference.

Then a bit longer and 'hey presto' the broken tap deteriorated into nothing.

There is a very good write up on the Newcastle and Tyneside MES club website of the use of Alum.

Cheers,

Julian

Howard : this is a freshly made batch from the same packet of alum.

It is soaking in a small glass jar. The glass jar was placed in the aluminium saucepan in a water bath to raise the temperature.

As you know where it is coming out from the dimple I would try a 1.5 mm carbide cutter. Keep bringing it down on to the stop a few thou at a time, you should be able to drift the drill out then. How long did the item take to make ? It may be less frustrating to start again !