"Larry Jaques" wrote in
message ...
On Sun, 13 Mar 2011 12:48:39 +0000, David Billington
wrote:

Karl Townsend wrote:
Milady needs me for my shop skills. Don't happen that
often.

She has old canning jars. The type with a glass lid and
a little wire
arrangement to pull the glass lid tight. She wants to
put small lights
inside and needs a hole drilled. I haven't measured up
for sure, but
I'm thinking this stuff is 1/8 NPT size.

OK, how do I drill very old glass? I get several points
off for every
one I break.

Karl

The old way would be to use some copper or brass tube with
an OD the
size of the hole you want. Make a dam round the hole with
plasticene and
add some abrasive like valve grinding paste and a bit of
water or oil,
Hold the tube in a drill press running at a slow speed and
repeatadly
apply pressure and lift. The abrasive imbeds in the softer
tube material
like a lap and grinds through the glass.

The new way would be to use a diamond hole saw but still
have the dam to
retain water to keep the glass cool. You can probably buy
them on eBay
for a few dollars in the size you want.

Carbide bits are available for under ten bucks and they
work extremely
well for tile, glass (not tempered), and ceramics. No
cooling
necessary at all. http://tinyurl.com/48c32js HF
apparently doesn't
carry them any more.

Back up the drilling point so the glass doesn't break out
the back
side. Cold clay works well to provide a solid backing. Use
a light
touch and immediately stop the drill upon exiting.
Quick-stopping
cordless drill motors work best for this.


I haven't drilled that species of old glass but certain of
the antique
compositions like to fragment around the periphery of
hole ends with carbide.

Diamond hole drills would be my option. The tricks are to
put them in a pond of water, feed straight, lightly and
slowly
and back the exit hole up with something for support
against
rim breakouts.

If you have any waterproof ring (e.g. big gasket, O ring)
you
can use that as your coolant reservoir after using grease to
affix it to the glass.

I use a modified, quick-setting plaster as breakout
protection
on because it can conform to the glass. It shears
off after drilling with a tiny bit of cleanup. Something
that
didn't involve cleanup would be an improvement.

Regards,

Edward Hennessey


--
You create your opportunities by asking for them.
-- Patty Hansen