Using a brass tube is a good way if the hole is large enough for what
you need. I plug the end of the brass tube with a wooden plug, and
chuck that end in to the drill chuck or an adapter I made that will
accept brass tube up to 1" in diameter and still fit in a 1/2"
capacity chuck. I then file one shallow notch on the opposite end of
the tube. I put valve grinding compound inside the tube, and go for
it. As it spins on the glass it creates some friction, which makes the
compound flow out as it gets warmed up slighly, and the notch picks it
up and it gets carried under the edge of the bras tube and some of
the grit will get embedded in the brass tubes edge. Makes a beautiful
nice hole in glass and cersamics etc.... I fyour really concerned just
get a pack of the diamond burrs for use in a dremel tool at the big
box builder supply stores and they can cut most any glass, pottery,
clay, ceramics etc, but of course yu have to free hand the hole but
slow and steady you'll get a hole....MAking a dam of putty or play
dough around the area you want the hole and filling it with water
helps keep the bit cool or just trickle water on the area your
cutting......I can't really recomend water and using an electric tool,
as I use primarily air operated tools, but I know of lots of folks
that used a dremel tool with diamond burrs to drill aquarium tanks and
lived to tell about it by using a little common sense its totally
doable.

Clay pots are perhaps the worst things to drill since lots are
imports and poorly made/ fired, and they can bust out the side of the
hole and surounding material very easy if your not carefull and have
the proper speed and bit in use.

On Thu, 15 Dec 2005 09:43:33 -0500, Hal wrote:
On Wed, 14 Dec 2005 22:35:57 GMT, Snooze wrote:

If you drill into a ceramic or clay pot, buy a few cheap ceramic tiles
and pots from a garden/hardware shop to practice on first, because it's
really easy to crack them. First drill a small pilot hole with a thin
drill bit, then work up to a larger bit.

Step drilling works well for hard materials where relieving the
pressure on the drill web (at the point) is advantageous. Step
drilling a brittle material with a twist drill is a bit tricky, since
the most likely time to break or crack out the hole is when the bit
breaks through the back side and the twist of the drill tends to grab
onto the last of the material being removed from the hole. If you
are limited to a twist drill, may I suggest you regrind the cutting
edges of the twist drill to a very long point, like a 60 degree
included angle, instead of the 118 degree recommended for general
drilling and a zero or negative rake on the cutting edge may help.
The longer point helps in making the breakthrough more gradual and the
negative rake makes the bit push/scrape off more than cut off
material. Consistent drill feed is most important, especially at the
point of break through. Even with caution the last bite/breakthrough
tends to be a problem since the drill can grab if too much feed is
allowed and the bigger bite may crack the material.

Best for drilling brittle materials is a spade drill. They are
shaped like a tear drop and designed for cutting glass or brittle
materials. Still one needs a drill press with positive feed to be
sure of repeated success.

Probably cheaper is valve grinding compound (abrasive) and copper or
aluminum tubing. The soft metals will accept a charge of the
abrasive and wear away a hole in the harder material. Constant feed
and caution are necessary, but I've drilled several holes in glass
using this method on a drill press.

Regards,

Hal

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