Re: [ATM] trepanning mirror

["Scott Milligan" <starzkey@charter.net>]

Wayne:

An additional method to consider if your central obscuration is larger than
the required hole in the primary mirror: core the hole first, and grind,
polish, and figure the mirror the same way you would work an un-perforated
blank. Any slight edge roll-off that occurs around the hole will be masked
by the secondary shadow, and there is less fuss up front.  Just remember
that the very center of your pitch lap(s) should be relieved before
pressing, else the lap will develop a high spot where the hole overlaps the
lap during the press.

P.S. if you like, bring the mirror down to my place, and we can do the
perforation on my curve generator.

Scott Milligan

Scott Milligan
 
 

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Wayne Hilliard
Sent: Sunday, March 26, 2006 8:44 AM
To: atm@atmlist.net
Subject: [ATM] trepanning mirror

Hi all it's been a while since I posted a question here but I have been 
lurking.

My new project is a gregorian 8 inch f30. On a Springfield style mount.
I want  to pierce the primary. I know that the traditional way seems to be
to 
wax or pitch a piece of glass onto the surface your going to break through
to 
avoid clamshell fractures etc. However I am lacking appropriate pieces of 
glass. I was wondering if casting the mirror into a mass of plaster of Paris

much the same way you cut a diagonal would work? I am only planning on 
casting onto the back of the mirror. Also when to do it. I am planning now
to 
do it before I finish rough grinding ala Ritchie and plaster of Paris the 
slug back into the hole to finish the mirror.. The other way is to partially

go thorough and finish the mirror with the last step being to very gently 
finish trepanning the hole. Right now I'm leaning towards the first way. 

Ideas comments?

Thanks in advance.

Wayne Hilliard


-- 
Wayne Hilliard         "If computers are making the world a global village,
KA1CXD FN32             and I can't figure out how to use one, does that
woodycxd@adelphia.net   make me the global village idiot ?"
                                                     Shoe
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