Someone else stated: “Drilling speed should be a minute or two,and
you should use the highest speed you can and still keep lubricant in
the hole. Oil is best, but you can use water.”
I disagree with this This may work for drilling stone,
but drilling glass is different. Glass will crack from thermal shock
if it becomes too hot. For this reason, you don’t want to drill at too
high a speed because the heat will build up. For the same reason, you
always want to use water when drilling glass. Don’t use oil because
oil holds the heat. The water acts not only as a lubricant but a
coolant. You are more likely to crack the glass if you use oil. The
same holds true with cutting glass with a diamond saw.
One of my students is trying to drill holes in sea glass, some of it
over 1/2" thick. She is using diamond hollow-core drills and doing it
in water, with frequent in-and-out and light pressure, she says,
though I was not looking over her shoulder. They split every time. Is
there some additional/different trick to this? I’ve only tried
obsidian nodules (“Apache tears”) and I haven’t done at all well
either.
Hi Noel, I have found that drilling glass/ rock no matter the
thickness can be done best by starting with a little drill bit and
working up to the size hole you need rather than starting with a
bigger bit. It seems to work best and extend the life of your bits.
sarah
The technique is correct. Splitting is caused by stress. Even when
the process is right stress can be a problem. General advise would be
to start with a smaller hole and then go larger; if this is even
possible, depending upon the situation.
The other way to relieve stress before drilling would be to temper/
relieve the glass with heat. You 'll need to goggle that, for the
best process.
The last way is to use diamond grinding wheel to remove some surface
glass in and around the area to be drill on both sides of the piece.
How much, how deep is up to experience.
It may be the thickness & the shape of the seaglass that’s causing
this. I’ve successfully drilled holes in glass cabs under water on
top of a thick sponge. Make sure that the drill bit starts at an
angle before gently tilting it upright.
I don’t know much about sea-tumbled glass, but I would expect it to
be pretty stable. Apache tears, on the other hand, are often highly
stressed. I’ve seen them explode when touched to a grinding wheel.
I use regular diamond drill bits, really fine and keep changing the
bit to a larger one every time I go through the stone till I get the
size I want. I am also using a drill press and doing it under water.
I think you should try drilling a small hole first off with a
diamond plated drill or sintered drill is even better and then go up
to the next size drill and gradually move up to the size you want.
Glass is quite brittle like opal and the thicker the glass the more
chance there is of it breaking just as soon as you are nearly
through, I drill half way through and then look at the hole with a
light behind it and make a mark with a pen and drill from the back.
This stops it from breaking out large chips as it comes through.
Good sintered drills are available through Mountain Mist products,
please note I have no vested interest in this company, I am just a
very satisfied customer.
It may be the thickness & the shape of the seaglass that's causing
this. I've successfully drilled holes in glass cabs under water on
top of a thick sponge. Make sure that the drill bit starts at an
angle before gently tilting it upright.
Did you say that the drill bit was a hollow one? I would think you
would use one of the small solid diamond drills with diamond
sintered on it. Was it the glass that split or the drill?
Noel, I frequently drill holes in tumbled glass, and I haven’t had
any problems. I drill a very small pilot hole first (with the hollow
diamond drill), under water, flushing the hole out frequently. When I
get close to the other side, I turn the piece over and come in from
the other side. This prevents blowing out the other side. (You can
see the drilled hole in the glass, so it’s easy to match up.) Once I
have the pilot hole, I then enlarge (and center) it to its final size
and location. Depending on how large you want the hole to be, you may
have to enlarge it in 2 steps or more.
It would be best if the piece of glass was flat on the bottom to
prevent the drill from breaking out at different places before it is
completely ready to “Pop” through.
If the back surface is curved, it should be embedded in some kind of
clay or sticky putty and extremely light pressure. Plus use a vise
to keep the glass from tipping.
If the drill breaks through unevenly the piece of glass will twist
because of uneven pressure. This twisting may cause the drill case
to immediately wedge in the hole with enough pressure to split the
piece of glass.
If the glass is held in some kind of “vise” or clamp that would hold
it so it has no movement during or after drilling, this may keep the
drill case from wedging in the hole and putting pressure on the
glass.
try putting a piece of drafting tape over the mark, put a flashlight
underneath and mark the hole 's point on the tape. drill with a
diamond drill in the appropriate size for the hole.Remember hot dry
glass breaks easily so lubricate the glass (over the tape) with a
bit of wintergreen oil or water glass (more viscous than the
essential oil) stabilize the glass well, and proceed with the drill’s
rotation doing the work- not pressure.
I don't know much about sea-tumbled glass, but I would expect it
to be pretty stable. Apache tears, on the other hand, are often
highly stressed. I've seen them explode when touched to a grinding
wheel.
OK, so the consensus is to start with the smallest hole, and of
course she may be pushing too hard. I will watch next time.
As for the Apache tears, I really want to figure out a way to design
pieces for them, because they have the coolest story! They were
unearthed by a she-wolf digging her den. My daughter (the field
biologist) collected them from the mouth of the den when they were
removing the pups to try to save their lives, because a rancher had
(illegally) killed the mother and rolled a rock over the den
entrance. Sadly, the pups were beyond help. Talk about Apache tears!
There are several things you can do to improve the odds in your
favour. Firstly mount the glass on a sturdy backing plate with dop
wax or similar. This will stop the glass from moving and prevent
burst out when you go through the glass. It can be made of metal or
glass. Very flat work pieces can be mounted with double sided tape.
secondly, make a hole on the wall of the drill bit near the point
where the bit enters the chuck. This will relieve any intrnal
pressure build up. Thirdly, use the fastest speed possible. This
helps disperse any fragments of glass from the hole and reduces the
temptation to lean too hard on the drill to make progress. lastly,
try and mark a groove on the kerf of the drill bit to allow fluid to
remain in contact with the glass/diamond interface and lessen local
heating. Large core bits have slots throughout the circumference to
enable coolant to pass through the bit, you are trying to copy the
effect.
Thirdly, use the fastest speed possible. This helps disperse any
fragments of glass from the hole and reduces the temptation to lean
too hard on the drill to make progress. lastly, try and mark a
groove on the kerf of the drill bit to allow fluid to remain in
contact with the glass/diamond interface and lessen local heating.
Here is the old method for drilling obsidian. Take a brass rod of
required diameter. Put the end of the rod against old file and give
it a sharp blow with a hammer. Rod end now have sharp indentations.
Dip end of the rod in oil and sprinkle some diamond abrasive on it.
Abrasive should adhere temporarily. Bring this end against some flat
chunk of iron and give it another blow with a hammer. The
indentations will close up entrapping some diamond abrasive. You
have just created a drill, which is more superior to commercial ones.
Abrasive is distributed very sparsely and such drill will not
generate a lot of heat. Also brass is much better heat conductor
than steel.
Mount your work on the bottom of some container. Mounting it with dop
wax is a great advice. Use drill press. Fill container with water. I
recommend the slowest speed possible. Bring drill in contact with the
surface and arrange for constant pressure. The simplest way is to
hang some weight from the handle bars used to advance drill head. It
is better to use smaller weight, then larger one. 5# is good starting
point.
Once setup, no attention is required. You can go an do something
else, while it is going.
Thanks for all the responses. My student is convinced (though I’m
less sure) that she is already drilling slow enough, and wants to try
annealing the glass. I figure it can’t hurt, as we have a brick kiln
that cools really really slowly if you don’t open the door.
** I must say I like this plan. I will definitely try it. Is there a
particular grit that is better or worse? How often do you need to
re-do the end of the rod?
My only problem is that the drill press I have access to has only
one speed… unless I can change it inside the housing. I actually
never checked. Oh boy, sounds like fun!
Thanks for all the responses. My student is convinced (though I'm
less sure) that she is already drilling slow enough, and wants to
try annealing the glass. I figure it can't hurt, as we have a brick
kiln that cools really really slowly if you don't open the door.
What kind of glass? there are annealing schedules for each different
type of glass. The idea is you need to heat the glass to just above
its strain point, hold it long enough to relive all the stress in
the glass then cool slowly through the stain point. A basic
description is available at http://www.arrowsprings.com/html/annealing.html
But I seriously doubt this will help. Any commercial glass product
that would have formed sea glass would have been properly annealed
during manufacturing. Insufficiently annealed glass will
spontaneously crack very rapidly after manufacturing it.
