On Thu, 30 Apr 2015 18:16:06 -0700, wrote:

On Thu, 30 Apr 2015 15:57:05 -0700 (PDT), Gerry
wrote:

On Thursday, April 30, 2015 at 5:25:46 PM UTC-5, wrote:
Not exactly metalworking. I needed to make a replacement glass piece
for a camera because I removed the IR/UV filter and the space needed
filling for proper focusing. I used a 1mm glass slide, the type made
for microscopes. The piece needed to be 8 x 9 mm. I mamaged to get one
and then discovered I had scratched it. So I tried again and was
rewarded with a scratch free piece. I was surprised how hard it was to
cut this glass, for it to break where I wanted it to, and finally
figured out how to score it properly. I hope I never need to do this
again.
Eric

Years ago I did lapidary work. While most everything was done with stone I used to play with glass sometimes. I was able to cut glass with a diamond saw, grind to shape using grinding and sanding wheels with water drip to keep things cool. The glass was mounted to dop sticks using what was called dop wax which was almost like old style sealing wax used with stamps for letters and such. Maybe you can find someone close by that is into lapidary work for help? A designing jeweler may point you in the right direction. I'd bet that your local glass shop has wet belt sanders with different grit belts for finishing glass edges. Maybe they would let you use their belt sanders for your project?
Greetings Gerry,
I have done lapidary work and even have the stuff still to do it. My
stone saw is just not set up to cut stuff so small and the glass is
more brittle than the stones I have cut in the past. I did finish off
the piece by using one of my diamond wheels on my slow speed carbide
grinding/lapping machine. I was actually surprised at how fragile the
glass was. I have cut glass tiles in the past year with one of my
diamond cutting discs cooled and lubricated with water and had no
trouble. But the little pieces I just did were much more prone to
chipping and cracking than the tiles and the diamond cutting disc
caused too much edge chipping, even when run quite slow.
Thanks,
Eric

Microscope slides are soda lime glass. If you had some Corning slides,
they used to be tempered -- probably, they still are.

Although tempered glass is strong, it gets its strength from being
pre-stressed in a way that increases bending strength but also can
make it prone to chipping as the stresses are relieved. Generally, the
chips are quite large; you've probably seen how tempered car windows
shatter into pellets, rather than into sharp little shards.

All of that may be of no help in understanding what you're running
into, but be aware that there are different grades and they may break
in different ways.

--
Ed Huntress