Broken drill bit

 I would be extremely cautious about using aqua regia.  It is full
reagent nitric and sulfuric acid.  It is one of the 2 acids that
dissolve 24K gold.  It eats up silver violently.  Try some of the
alternative suggestions first.   

Correction: Aqua Regia is a compound of Nitric and Hydrocloric acids

  • A violent reagent - it will dissolve gold, silver, and will even
    attack platinum - Hydrocloric acid alone should dissolve your drill
    bit, or sparex, or alum - a bit of patience will preserve your
    project.

Dear All of you, Thanks ever so much for all your kind suggestions. I
tried quite a few. I did not manage to get any of the chemicals to
work for me, the drill was probably not ordinary carbon steel. I
could not get to the back of the piece or attack it perpendicularly,
so I ended up drilling around the broken bit and soldering a piece of
2,5 mm wire in place there. Now I consider changing all my drills to
ordinary steel ones, so that I can etch them out next time :slight_smile:

But thanks for your concern and your good pieces of advice.

Kind regards
Niels L�vschal, Jyllinge, Denmark
@L_F8vschal
phone (+45) 46 78 89 94

Neil, Stress crack corrosion is a problem where the the area in
between the crystals of the metal or alloy is attacked by a
corrosive agent. This inter-granular area is where the impurities of
an alloy will be concentrated. They are often more susceptible to
the corrosive agent. The residual stress in the metal also plays a
role in the cracking. This type of crack will tend to form in a high
stress area like where a prong has been bent over a stone. The
chlorine or ammonia can actually corrode the grain boundary and
cause a crack that propagates along the grain boundaries and doesn’t
really attack the crystals themselves. The likelihood of this kind
of cracking is intensified by putting the metal in the ultrasonic
cleaner with a chlorine or ammonia based cleaning solution.

Jim

@jbin
James Binnion Metal Arts
4701 San Leandro St #18
Oakland, CA 94601
510-533-5108

I haven’t attempted to use it but I was told by a usually reliable
source that Hydrofloric acid also attacks 24K gold. Norman

I think that depends on how you define ‘short duration’ when I was
working in a jewelry shop here in spokane, there was a woman who was
using bleach or amonia to clean one of her rings. She left it in the
bleach or amonia over night and the next day it had aquired a number
of pits in the metal.

Michael / QuestFox

Now I consider changing all my drills to ordinary steel ones, so
that I can etch them out next time :-) 

You might consider taking one of these drills, similar to what you
had the problem with, and testing it with those various acids and
chemicals, just to see whether or not it reacts at all, free from the
silver masking the reactions. Do that AFTER you’ve checked to see if
the drill is in fact, carbide (see if it will scratch quartz. Carbide
will, steels won’t). I’m aware of no common tool steels, including
the cobalt steels, and the high speed steels of which quality drills
are most commonly made, which would not be attacked by suitible acid
agents. If, however, your drills are carbide, that would explain your
difficulty, and these are not only hard to remove, but are also much
more brittle than steel drills, and therefor easier to break off in
the first place.

Peter Rowe

Jim, Thank you for the well informed response. With 26 years as a
jeweler I learned something new today, this shows the beginners that
there is always something to be learned on a daily basis and more
importantly never take for granted that your way is always the
best.Thanks Again. Best Regards.
Neil George

   I haven't attempted to use it but I was told by a usually
reliable source that Hydrofloric acid also attacks 24K gold.       

It doesn’t. Eats through glass, investment, quartz, the oxides on
titanium and niobium, but not 24K gold.

Peter Rowe

I thought your problem might be carbide but that is just a very
reasonable guess based on high speed performance. These also may be a
high speed steel with enough stainless properties to stand up to
dilute sulfuric acid which would be normaly the most distructive.
Peter maybe right (I think he may always be) That all these would be
atacked enough to fall out… A lot of the suggestions were way out
there. Jesse

G’day; There have been some references to carbide drills recently.
I don’t know very much, but have never heard of a drill being made
entirely of tungsten carbide. They are usually made of steel with a
carbide tip as tungsten carbide is far too brittle - and would be too
expensive - to be used for a complete drill bit. High speed steel
drills will last for ages if properly used and correctly sharpened. I
find that when used with sterling (I don’t drill gold often!) really
fine drills; that is of a diameter of 1mm and below, work best at a
relatively slow speed, not too much downward pressure, lubricated with
saliva (use WD40 or CRC556 if you’re fastidious). Have only 3 0r 4
millimetres protruding from the chuck. If you don’t know how to
properly sharpen and back off such drills, then throw them away as
soon as they don’t cut well. 2.0mm to 0.4mm drills only cost about a
dollar or less.

 have never heard of a drill being made entirely of tungsten
carbide.  They are usually made of steel with a carbide tip as
tungsten carbide is far too brittle - and would be too expensive -
to be used for a complete drill bit. 

Sorry, John . Solid carbide drill bits are widely used to drill
precision holes in materials where steel wears too quickly. I’ve
never seen a big one, but 1/8 inch and smaller are used a lot in
applications like drilling printed circuit boards. You can get
several thousand holes, where high-speed steel would start melting the
epoxy after 3 or 4.

They are brittle, as you say, and expensive as compared to regular
steel (a few dollars per bit.)

Al
mailto:@Alan_Balmer

    work best at a relatively slow speed, not too much downward
pressure, lubricated with saliva 

Interesting, John! Maybe I can give up my Devcon SafeTap.

    If you don't know how to properly sharpen and back off such
drills, 

I learned to sharpen drills, you know how you do, sharpening the big
sizes, and then found that when I need to sharpen those little ones
under 1mm if I just carefully hold them a certain way up to a fine
grind stone whirring away, touch lightly, then turn it round and touch
the other side, doing the ever so slight twist round and down to the
left, then about 60% of the time the drill is magically sharpened! I
amaze myself sometimes!

Bri

B r i a n A d a m J e w e l l e r y E y e w e a r
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz/ photos from Australia!!
http://www.adam.co.nz/jam.htm Jewellery Events on now