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Removal of a broken drill bit with alum


#1

Dissolve Away BROKEN DRILL BITS with Grocery store supplies

I thought some people may find this tip useful. I used Alum to
dissolve away a broken drill bit in a brass part. The brass was
unharmed. I found all the supplies I needed in the grocery store. I
attached a link to a video I made about the simple process. I hope
some people find it useful.

-Adam


#2
I thought some people may find this tip useful. I used Alum to
dissolve away a broken drill bit in a brass part. 

Alum works, though slowly. Boiling it speeds things up. But ordinary
pickle also does the job, and I think, faster than Alum. Mix up a bit
of fresh pickle, so it doesn’t have dissolved copper in it, to avoid
copper plating your work.

Pickle will take out not just carbon or high speed steel drills, but
also carbide, tungsten steel, or cobalt steel. You can speed it up
greatly by putting the pickle and piece in a small jar that you can
then suspend in your ultrasonic cleaner. The combination of the acid
and the ultrasonic to keep fresh acid at the drill even at the bottom
of the partially drilled hole, makes it work much faster than just
soaking. When you’re done, the bit of pickle you mixed up can go
right into your pickle pot. The tiny bit of iron it dissolved from
the bit doesn’t hurt the pickle at all, since it’s already dissolved
now, and no longer can cause copper plating.


#3

OK, this is interesting - I looked at this a while ago because I
want to grow crystals…

‘Alum’ covers a wide range of compounds (a family in fact) - but in
my world it would normally mean KAl(SO4)2.12H2O an intermediate
compound half way between K2SO4 and Al2(SO4)3 - but I’ve also seen
end members referred to as alum.

so now this has peaked my interest - it would be interesting to see
what is actually happening, chemically…

so I started looking it up…

and quickly got no where…

neither Al or K should be displaced by Fe, so something else must be
going on - probably to do with changing the oxidation state of SO4

I shall consult widely!


#4

OK. I’ve asked around (my dad, ex chemist)

best we can determine the alum (and by alum it could be a variety of
materials - Aluminium Ammonium Sulphate for example) is acting as a
mild buffered acid.

Normally when iron is attacked by acid, it forms insoluble decay
products like rust, and depletes the solution. In a buffered
solution, something else occurs, such that the pH is maintained. e.
g. Acid + Fe => Fe 2- + H2 gas. The Fe in solution forms an
intermediate soluble compound like a sulphate, before either
precipitating as orange Fe(OH)2 powder, or substituting for one of
the alum metals - e. g. Al3+ -> Al(OH)3 ppt, regenerating the acid in
the process…

I may have to try it and see if I get orange or white powder. or
something else…


#5

I have always preferred Alum over pickle for removing drill bits. I
find that if you leave silver and sometimes gold with solder seams in
a strong pickle solution for too long the solder seams just fail.

Have fun and make lots of jewelry.
Jo Haemer
timothywgreen.com


#6

Hi guys,

One thing to watch out for: I tried this with “alum” that I bought
from a canning supply.

Just. Did. Not. Work. At all. Ever.

So there may be two or three things going by ‘alum’ in the
commercial world.

I got so frustrated that I tried a super saturated solution, at
about 150F, on a magnetic stirring unit, for 48 hours. Nada.

(drill bit broken off in an aluminum block)

Fresh pickle had the drill bit out as black sludge in about an hour.

So I swear by pickle for doing this. It works, it’s cheap, and I’ve
already got it on hand. (Sodium Bisulphate, just to be clear.)

Regards,
Brian


#7

and gosh, look what google returned as top hit.


#8

Hi Brian,

Alum is an entire class of compounds: from wikipedia…

A2(SO4).M2(SO4)3.24H2O

where
A is a monovalent cation such as potassium or ammonium
M is a trivalent metal ion such as aluminium or chromium(III).

Sodium bisulphate is not alum, but it is a sulphate. I’m guessing
it’s very mildly acidic in solution, and probably works very
similarly to the alum, in that the acid attacks the iron but is too
weak to attack the non-ferrous metals - either because they are inert
or passivated (form thin stable oxide films)

the “trick” seems to be in getting the Fe2+ or Fe3+ ions away from
the surface, making them soluble, or letting them precipitate (as e.
g. FE(OH)2 ) “somewhere else”.

I am not 100% convinced, but the “story” sounds reasonable. a lot of
technology goes into making this sort of thing not happen - e. g.
stainless steel.

which makes me wonder - does it work on stainless steel? or other
metals like Co or Ni or Cr? or just regular steel/iron/high carbon
steel