Pencil size hole in a hard rock

no one has answered, I realize we are a busy populace, but am in
need of info. on how to frill a toth brush or pencil size hole
into a hard rock of granite comp. or something similiar. and
glass, so that it does not keep breaking…I have been using a
dremel. for the lass to only be disappointed, any
sugestions…@perfectp please.

What do you mean by fill. Do you want to set a stone into it?
Do you want to inlay another stone into it? or inlay metal? or
hide the hole entirely? I wouldn’t be able to begin to assist you
with “filling” this hole, untill I knew what it was you were
trying to accomplish.

The best solution here is to use a diamond core drill. This is
a piece of tubing with diamond abrasive on the working edge. If
you are using a hand held dremel then you will have to be
patient. Use plenty of water or oil as coolant, use a pulsing
type action to flush the sludge. It will go more quickly if you
have a drill press setup or can otherwise maintain consistent
position. Hope this helps. Norman

Years ago we needed to drill out a hole in a piece of glass, and
we used wet sand. Practically anything hard enough to survive the
process will do, perhaps an old drill that is long past
sharpening. Place a dam around the area where the hole is to be
drilled, and start drilling, using water liberally to keep the
sand wet and flowing through the work area. Don’t expect it to be
a speedy process.

You can use abrasive grit instead of sand, actually - my father
was fanatical about doing things the hard way. :wink:


You can use a flexible shaft Dremel, or a Foredom, etc. to drill
such holes. The key element is to do it under water, with
diamond drill bits. Hence, the flex shaft to keep the electricity
away from the water. For a pencil diameter hole (assuming #2 lead
pencil size) you might even want to use a small (.25") core
drill. The alternative is to drill a smaller hole, like 1.5mm,
and then use a diamond bur to ream it out. This has the
advantage of automatically cleaning up the “breakout” or chipped
area, which results from drilling straight through from one side.
Hope that this helps you out. Jim Small, SMALL WONDERS

Hi, You didn’t say how thick the piece was. If it is less than 1
inch thick, I’d use a core drill. Core drills are basically
tubes that have diamond grit imbeded in the cutting edges.
They’re available in different diameters. Generally using a core
drill requires the use of a drill press. The stone being drilled
needs to be held stationary & the bit fed against the stone.
Build a dam (about 1 inch high) around the area the hole is being
drilled in & keep it almost filled with water. When drilling,
remove the bit from the hole frequently to flush the grindings
from the hole. Play dough or putty works well for a dam. Dave

How to drill to avoid breakage - ?? Very slowly !! If you’re
drilling a lot of these holes, check with a lapidary tool Co.
for an ultrasonic drill setup or something similar. If you’re
doing one or two, chuck a straight piece of 1/4" copper tubing
into a drill press, add 100 grit carborundum and a water drip,
set the speed control at about 100 rpm and add a little weight
to provide downward pressure on the drill, and go away. Check it
every six or eight hours for a week or so, depending on how
thick your granite is. The same setup with a clay dam at the
drill site to help retain the grit and lubricant should drill
your glass a bit more quikly than it does the granite. The key
here is time and paticience.

Hi Perfectp, Probably every Dremel user will give me heck, but,
thats not what a Dremel is used for! Get a large electric hand
drill, 3/8 " preferably and also get a diamond core drill of the
size that you want. The core drill you should probably get from
the manufacturer (to make sure that you get the size that you
want!) Diamond Pacific is the only one that I’m aware of although
there are probably a lot more out there!!! Clock makers
regularly drill holes in all kinds of Agate and other stone
slabs. Most that I know of use an electric drill with a core
type drill, diamond, under water for lubrication. An inquiry will
also get directions from the same people. A Drill Press will make
things easier, Stones, even with diamond, do not cut through like
butter, but take time to cut. Good Luck JB

First I don’t think the Dremel is powerful enoough to drill a
hole of this size in granite. I drill holes in granite sculpture
bases 1/4" up to 3/4" using carbide tipped cement drills (I
resharpen them usually 2 times to drill a 2-2.5" deep hole. I
use a lot of water to cool and clean. I do thin with a 1.5 hp
radial are drill press and it takes a bit of pressure to get the
drills to drill. I also use diamond coated hole drills, to make
room for washers, nuts, bolt ends etc. I go up to 1.5" diam.
with these. These diamond hole drills “cut” a circle in the stone
that you break out the center to make a hole. They need lots of
water for cooling and flushing the cuttings, but they take very
little pressure to cut the hole. I would still recommend using a
drill press rather than the Dremel, just more control.

These diamond hole drills usually only drill 1/4" to 1" at a
time, the center must be removed and then more drilling til
bottom is hit, and the center has to be taken out again. Not too
big a deal but it makes it a bit slower.

Hope this is of help.
John Dach
MidLife Crisis Enterprises
C.T. Designs
Cynthias sculptures are at:

Hello, The safest (but longest time wise) way to drill a hole in
a rock is with a hollow rod and silicon carbide. The rod should
be a hollow tube. For the size you mention a car antennae would
work well. You will need a drill press. I mount the rock onto a
copper sheet. There is enough copper so that you can clamp this
sheet to the drill table. Next thing to do is to build a well
around where you want the hole. I use a larger diameter short
piece of tube or pipe. I seal it with window putty or some
other temporary caulk. Place water in the well and silicon
carbide grains. You are going to have to hand feed this
operation. Get comfortable because it will take about an hour
for each half inch. Add fresh grit and water as needed. Let the
rod touch the stone for ten seconds and then come off for a
while. Repeat and repeat and repeat. You have to raise the rod
to let it cool and not crack the rock due to heating. It also
allows the grit to re-enter the cut. There should be almost no
pressure on the rod. Too much pressure builds heat fast.There is
a special drill designed for this type of drilling. It raises
and lowers the bit by a rotating cam. These have been around for
40 or more years. You can try a diamond core drill. They have a
tendency to over heat and diamonds fall off (which leaves you
with the hollow core as above). Another way is to look in the
Lapidary Journal and find someone that does this commercially.
The price will be far lower than the hours it is going to take.
Steve Ramsdell

perfectp: check out the reply i posted last month about drilling
through rock - the only update i would add is to start the hole
the same way, but work it larger ONLY after you have the first
hole all the way through; do not try to drill it big first!!
good luck - ive rock worker/stone finisher

Actually if you are going to use sand or grit and water, a softer
thing than a steel drill will work better. Try a wood (try both
hard wood and soft wood) dowell which will “pick up” the
sand/grit (it should imbed into the wood and be held in place)
and “hold it in place”. It will take a long while to drill but
it will drill. Diamond is a LOT faster. John Dach

A safety issue that was touched on but needs to be emphasized:
NOT A GOOD IDEA to use a Dremel with the motor in the handpiece,
as you will be drilling with the stone under water. Use a flex
shaft tool.

If you’re interested in doing this kind of thing on a regular
basis, want to set stones in rocks, etc., consider a workshop
tentatively being offered next summer at the Mendocino Art
Center on the coast of Northern California. It’s being taught by
Dana Driver, who creates precious gem and precious metal
masterpieces with stones she finds on the beaches. She carves,
drills, rivets, sets stones in them, you name it. Some of her
pieces accept 5/16" tubing for rivets - about “pencil size”.
She’s figured it out - the right bits and burs to use, where to
get them, how to set your drill up efficiently. People look at
these things and say “huh? how’d she DO that?!” (Not one drop of
glue.) I don’t think the summer schedule has been officially
released yet, so can’t give you details, but if you’re
interested call the Mendocino Art Center at (707)937-5818, 9-5
pacific time. Rene Roberts

For what it’s worth, I use a Dremel with a flexible shaft when I
carve fire agate. It works fine and is way cheaper than a
foredom. Some carvers I have seen buy several cordless Dremels
and use a dedicated grit with each so they dont have to
change bits. Lee Einer