Re: ATM Behavior of glass upon trepanning

[Dave Gault <daveg@tpg.com.au>]

G'day Don,

ToobWiz@aol.com wrote

>I am just about finished figuring the spherical surfaces, and would now

>like to trepan the mirrors to size, 45mm and 60mm dia.
>Can the behavior of the glass be predicted?

I have done a bit of trepanning and I have a couple of web-pages
explaining what I did. You are welcome to visit my website, url under my
sig. and follow the links to diagonal making and reference sphere....

I have measured the diameters of the cutter, disk and hole and they are
as follows.....

3inch tooling
ID = 73.8mm   OD =76.1mm
Disk diameter = 73.4mm   Hole diameter = 76.5mm

4inch tooling
ID = 98.5mm   OD =100.5mm
Disk diameter = 98.0mm   Hole diameter = 101.1mm

All cutting was with 80grit carbo and at 110rpm and it seems you need to
allow about 0.4mm  difference between cutter and cuttee.  I remember the
larger tool had a bit of run-out which would account for the larger
difference in diameters.

The most critical times of the trepanning process is the start of the
cut and break through.   I'd apply something like varnish to the optical
faces which can be soaked off later and I'd also rig up a plywood
cutter guide to stop the cutter waltzing around.   Make a dam of
plastacine or putty in the inside and outside of the cut to keep the
grit in place.

Have fun.

--
Regards
Dave
http://www4.tpgi.com.au/users/daveg/index.html