Re: [ATM] cutting a big piece of plate glass into mirror or tool blanks

[Dominic-Luc Webb <dlwebb@canit.se>]

On Thu, 12 Jul 2007, Guy Brandenburg wrote:

> How many folks have actually tried and succeeded in cutting reasonably
> sized mirror or tool blanks from a large piece of plate glass about 1
> inch thick? Did you find the metal tabs on a wooden spindle worked well?

I have no idea how many people, but I certainly have done this many
times. I could not find in my area (Stockholm) the sheet metal that
people in the States, like James Lerch have used. I have seen James'
rig when I was in Florida some years back for comparison.

I have some disks (different materials) with a shaft in the middle to
connect to one of a few different motors. I do not like to use my
drill because it gets hot after a short time, so I generally use a
motor from a washing machine that easily handles this job.

The active cutting ring is made from a number of iron "teeth" screwed
to the sides of the cutting disk, and this works great. I use #80
grit, really brutal, and right grit for this job!

The piece to be cut is layed down onto a thin sheet of wetted glass,
and clamped lightly to the table. I am not 100% certain, but suspect
this arrangement prevents chipping at the last stage of cutting. I
get clean cuts in any event. I also score a ring on the opposite
side to (hopefully) favor the final break being restricted to the
scored ring.

Before my back went out on me, I was working on a new cutting table
that uses a spring to pull the cutting disk up away from the glass.
This is basically the arrangement as most any drill press would
have (I actually use a drill press for smaller pieces). I then use
weights to push the cutting disk onto the glass with only very slight
pressure.

The glass has a channel made from two concentric rings of putty or
bee's wax rings, so I can restrict the water and grit to the actual
work surface. Motor speed is kept low.

Towards the end of the cut, the extra advantage of the thin plate
glass underneath becomes apparent. The water and grit do not run
off and make a mess, so it is possible to just siphon away the
used water/grit. You can also try smearing a little wax ring as
an extra measure.

Basically, this is no big deal. Perhaps a bigger problem is that
this thicker glass sometimes has hairline fractures and
spontaneously breaks. About 6 months ago, I heard a loud sound
somewhere in my home, like glass breaking. It was in fact a plate
glass piece that was resting on a table that spontaneously burst
into a number of pieces. I now check my plate glass disks with a
little heat and cooling and also with a polarizer. To this end,
Polaroid manufactures some large sheet polarizers (about 1 m^2). A
couple of these makes a quick job of checking the glass, and this
is what I use.


Dominic-Luc Webb

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