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Gem stone drilling done right


Hi All

Heres another question for you, i need to drill some gem stones and
cabs with at least a 3mm hole part way through so it will only be 3
or 4mm deep, now all the diamond drill bits i have seen have only
gone up to 2mm but i found hollow core bits at 3mm so if its hollow
will the piece of gem stone that goes up through the bit break off to
leave a hole or is there a way to remove it, also the stone will be
quite clear how do i get the inside of the hole to look nice and
clean after all i dont want to spoil a nice clear stone with a rough
hole part way through so how do i get the inside smooth or polished,
i have never done this before so if anyone can give me some hints on
this like if there is certain things i need to be able to get it
done right and i have lots of respect for all you guys n gals at the
orchid forum for giving me good advise before.

many thanks


Hi Jason,

If you can obtain access to an ultrasonic drill, Imahashi or
somesuch, this device offers an easy and highly accurate method of
drilling to a prescribed depth. Most of these machines will accept
either of a solid drift, ie all material is removed, or a cored
drift. Wall finish can be controlled by the particulate size used in
the cutting slurry although the finer the slurry the slower the

If you employ a cored drift the residual stub can usually be readily
snapped off by inserting a taper ie needle, and gently levering.
Depending upon the cleavage plane orientation this will either snap
off flush, if you are lucky, or will leave a small angled stub at the
base of the hole. I simply take an old drill bit of the correct
diameter or marginally smaller, grind it to a flat face, insert a
small dab of diamond grit with a drop of extender and grind the base
of the hole flat. This all sounds terribly more complicated and
fiddley than it is in fact.

Your local rockhound club will most likely be able to point you to
an ultrasonic if you are having difficulty in locating one.

Kind regards
Don iorns


hi jason!

if you’re not going all the way through the stone, I’d avoid the
core drills. They will leave a plug and you MAY be able to break it
off… but doing so may just fracture the rest of the stone. It
really depends on what type of stone you’re drilling, what its
cleavage is, etc.

Your best bet is to use diamond cylinder bits and/or ball burs. They
do go quite a bit larger than 2mm (I have them up to 8mm, but I know
they go larger). Lasco Diamond products is my supplier of choice for

Start with the smallest one that you have, go in at an angle to get
started, then flatten it out. Work up a size at a time after you have
the hole drilled to the depth you want. That way, you end up with the
least breakage possibilities. Always work wet (I usually have the
piece I’m drilling submerged in a shallow dish. This keeps the
diamonds lubricated and makes them last longer, and also traps the
dust being created so you don’t breathe it (many stones have toxic
properties), as well as washing out the hole being drilled (makes the
drilling go faster and keeps the bur from clogging).

As for finishing the inside of the hole, it depends on what type of
stone you’re using. You can get wonderful diamond finishing papers
from dental suppliers in a variety of grits. They are flexible
strips, impregnated with diamond. The strips are about 1/4" in width
and you thread them into the hole and “thrum” them back and forth to
polish. They’re designed for shaping and finishing crowns, I believe.
That should beautifully finish any stone that you can drill with

Hope this helps!
Karen Goeller

No Limitations Designs
Hand-made, one-of-a-kind jewelry

i have never done this before so if anyone can give me some hints
on this like if there is certain things i need to be able to get it
done right 

Well, Jason, to some degree you’ve got your work cut out for you, all
for a blind hole. Yes, a core drill or tubing is your best bet, and
yes, the core will more or less snap off, given a bit of persuasion.
But to get a perfect cylindrical section that is clean and polished
is going to take more than that. You’ll probably need to grind the
bottom flat - the core will certainly leave something behind when you
break it. Then you’re going to have to sand and polish it in the
usual lapidary ways - there are many lapidaries here who I’m sure
will post. For a 3mm hole, I suggest a skewer like for shrimp or
kebobs cut and chucked in a flex shaft, with diamond paste. You don’t
want 3mm for sanding, you want more like 2mm so it won’t jam. It’s
gonna take a little while to do…


Hi Jason, I haven’t read ahead, so I don’t know if someone has
suggested this already, but here goes…

First, I have no experience with core drills, so I can’t go there.

…You can cut a 3mm diameter hole with a 2mm bit by using the
drill as a grinder. You need a number of bits anyway. And after an
amount of drilling, a bit will no longer be able to cut a hole but
will be great for enlarging holes. There is always plenty of Diamond
left on a dead drill bit for carving. See?

Now, one way to polish a hole is to take string or yarn and coat it
in glue. Elmer’s will even work, but not as well as others. Dip the
string or yarn into an abrasive when the glue is wet and hang to dry.
I use tumbling grit. You want a progression of grits as you would any
polishing job. Say 180 to 300, to 600, to 1200. You get the picture.
Thread the string/yarn in the hole. It’s actually good to hang the
string on a nail so you can secure one end with your free hand and
move the object up and down with the hand holding the object.

This is also a technique used for enlarging bead holes.

If you use a water soluble glue such as Elmer’s I would not suggest
lubricating with water. If you use epoxy, it’s not very flexible but
you could lube with water. I wonder about hide glues or rubber glues.
I would think they would be best. Isn’t sandpaper made with that
class of glue?

If you find the best let us know.

You might try the same principle with wood dowels or round
toothpicks in a flexshaft.

Happy Holing!

TL Goodwin


I somehow missed the bit about you not wanting to drill all the way

Forget the string part, but maybe it might help someone else. But
the dowel or toothpick in the flexshaft for polishing agents? You
might try it. You wouldn’t need glue, just a slurry and a slow speed.

T L Goodwin
The Pacifik Image.

But the dowel or toothpick in the flexshaft for polishing agents?
You might try it. 

Just about all of that old Chinese jade carving was done with bamboo
sticks and emery sand…Hardwood tools in a flexshaft (or whatever
motor suits) with diamond paste works extremely well, and the tools
last an amazingly long time. I’ve always used diamond, but loose
carborundum is the other choice (much cheaper, but slower, too).
Toothpicks work surprisingly well, too. I’ve used dowels, made
little wheels for the flexshaft - most of them last for many hours.
It’s the best way to polish stone carving, in most people’s opinion.
Sandpaper is fine for where it fits, but in most carving it doesn’t
fit in much of the work.