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Hey Matt!
Several years ago in Panama I got a 1/4" diamond core drill with the intention
of drilling a hole in a vent window. The drill drills glass OK but it has
to be done wet. Before starting on the vent window I decided I would try it
out on a scrap 122 2-door front window I had lying around. I started drilling
in a puddle of water with a fairly low-speed hand-held electric drill. Pretty
soon I started getting some milkiness in the water, indicating that the
cuttings were circulating in the water. I could see that I had gotten about
0.020" (that's half a mm for those who don't deal in real measurements) into
the glass. Suddenly there was a bang and the entire window was in pieces less
than 3/8" (1 cm) across. They bounced around corners, under doors, etc and
when I moved out two years later I was still finding pieces. I am sure it
relates to the tempering of the tempered glass. The deal is that the tempering
imparts a residual compressive stress into the surface. It can't just grow
because it is attached to the core, which is, in fact the same glass. So the
core is under an equivalent tensile stress, so when a flaw gets to a critical
size, the core breaks. The flaw is the drill, having removed the compressively
stressed outer surface.
A few years later I toured the Ford glass factory in Broken Arrow. It is over
a mile long, starting with molten glass being poured into a sheet about 10 feet
wide at one end and going the whole length of the plant in cooling and treating.
It is cut, finished, formed and drilled before tempering. I asked some of
the engineers about drilling a hole in tempered glass. They set me straight
forthwith. You can't do it.
I've tried a wide variety of adhesives on my 164 over the 31+ years I have
owned it and most of them won't make it much over 6 months. One of my best
successes was the foam plastic adhesive tape you use for sticking stuff to
walls. I've had that last on the upper vent window pivot for about 5 years
before it finally gave out. Most of the others lasted from 2 months to 2 years.
If anybody finds something that really works, I surely would like to know about
it!
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma
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