[ATM] Cutting Porthole in half

[Don R Surles]

my $.02 worth...if I was going to invest my time and $$$ in making a 
mirror I would start with the best blank possible, say a well-annealed 
pyrex blank that is blanchard ground flat on the back and  beveled on the 
edges.  this may cost a few dollars more but i can tell you from 
experience that having put time and money into a plate glass mirror or one 
of pyrex that has a chip in the back or front certainly reduces the level 
of pride in the finished product.

i would also forgo the pleasures of hogging out a blank as well as the 
pleasures of making plaster of paris tools with tiles.  for our 
Mid-Atlantic Mirror Making weekends we use pre-generated curve pyrex 
blanks and full size plate glass tools with the opposite curve.  we start 
with 220 grit and concentrate on producing a scratch/sleek free 
well-corrected parabolic surface.  if someone wants the pleasures of 
hogging and tool making then do it on the side with a practice mirror.

start your mirror making experience with the materials that offer the most 
probablity of success...there are multitudes of opportunities for less 
than desireable results but quality of materials can be eliminated as a 
factor before you begin. 

don...





Michael Lindner <mikell at optonline.net> 
Sent by: atm-bounces at atmlist.net
12/22/2006 10:26 AM

To
"Thomas A. Moulton" <tom at moulton.us>
cc
atm at atmlist.net
Subject
Re: [ATM] Cutting Porthole in half






Thomas A. Moulton wrote:
> What would be the best way to slice a porthole window in half?
> 
> Would a glass shop with water jet be able to do it?

No. You need a diamond band saw ow wire saw. Frankly, I wouldn't bother. 
The cost of cutting this and blanchard grinding the resulting blanks 
flat again will likely be more than the blanks are worth, and you risk 
breaking the blank. I have a friend who looked into having a 20x4" 
zerodur blank split in half and eventually decided that wasn't worth the 
money and risk. If you're doing this just to get a thinner blank, an 
easier way is to sell the 3" blank and buy a thinner one with the money. 
Just my $0.02.

Clear skies.
-- 
Michael Lindner
http://www.starastronomy.org *** http://home.att.net/~mikel
http://www.atmsite.org *** http://www.atmlist.net
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