To: atm{at}shore.net
From: "Douglas S Angle" 
Reply-To: "Douglas S Angle" 


>> thinwall metallic pipe that has an id of 5 inches and is, lets say, 12
inches long... once one figures >> out a way of attaching the pipe to
a centered holder on a drill press or similar, one should be able to
>> trepan as usual... the hard part is getting the work at the proper
angle and keeping it there... it's >> possible that one might coat
the glass with vaseline or some such and then "embed" it in
plaster or >>hydrostone or similar so that one has a huge block to
put on the drilling/trepanning platform...

We mounted the "thin wall tube" (actually stove pipe) to a wooden
cylinder. The wood was then mounted against casters, with the drive belt
holding it in place.  The advantage here is that it is self centering, and
is feeds just from the weight of the tube and cylinder.  As it cuts through
the plaster and glass, the belt just wanders up the cylinder.  See photos
at http://astrosurf.com/jwisn/diagonal.htm

The glass was sandwiched between window glass with wax, then cast in
plaster.  The wax wasn't strong enough to hold the window glass securely,
and started coming loose.  The water and grit then worked between the
diagonal and the cover glass.  It looked horrible when we took it apart,
but after cleaning off the wax, no scratches on the diagonal.  Your mileage
may vary.

The secondary is a 4.5" minor axis, cut from 7" x 3/4"
borosilicate.  It took 24 hours to cut through.

-Doug



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