Larry Jaques wrote:
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.

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

Cooling may not be required but it does help prevent the glass cracking
due to thermally induced stress.