To: Jan Bentz 
From: Stan Truitt 
Cc: atmlist 
Reply-To: Stan Truitt 


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Optical contact (the phenomenon),  also known as "contacting"
(the verb), has been  used for precision assembly since the Second World
War and perhaps longer.  It is not "wringing" which is a
temporary arrangement, but can last for many decades.  A 25 cm open face
trihedral mirror assembly of 18 cm clear aperture was fabricated in
California and placed on the moon in the early 1970s.  It was providing
return retro-reflections to Haleakala well into the 1990s, and probably
still is.

E. A. Moelwyn-Hughes in the last chapter of his "States of
Matter"(Oliver and Boyd, Edinburgh and London, 1961) describes the
physics of this intermolecular attraction.  Properly done, the optical,
thermal, and acoustic characteristics of the contacted interface disappear.
 When done with exquisite cleanliness, and vacuum baked (240 C.), small
fused silica contacted assemblies behaved as if one piece and were not
separable without breaking. When broken, many of the fractures propagated
irrespective of the original interfaces.

The advent of HEPA filtered laminar flow clean benches removed the
"black art" aspects of the process, and the use of Selvyt
polishing cloths (just before contacting) eliminated the "infinite
patience" consideration.  Jan Bentz's description of the contacting
and separation processes is splendidly accurate. When the components were
all made of the same glass, clean, well aged (or vacuum baked) assemblies
were not observed to separate using "hair dryer" techniques.

Surface deformations of thin contacted components were interferometrically
measured to be on the same order as the match (concave to convex, in
curvature) of the surfaces contacted.

I have photos of some contacted assemblies, test setups, and of interfacial
flaws that I would be happy to digitize and share with interested ATMs.


Cordially,

Stan Truitt
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Re: ATM Sticking
Together
Optical contact (the
phenomenon), 
also known as =B3contacting=B2 (the verb), has been  used for
precision assembly since the Second World War and perhaps longer. 
It is not =B3wringing=B2 which is a temporary arrangement, but can last for
many decades.  A 25 cm open face trihedral mirror assembly of 18
cm clear aperture was fabricated in California and placed on the moon in
the early 1970s.  It was providing return retro-reflections to
Haleakala well into the 1990s, and probably still is.

E. A. Moelwyn-Hughes in the last chapter of his =B3States of
Matter=B2(Oliver and Boyd, Edinburgh and London, 1961) describes the
physics of this intermolecular attraction.  Properly done, the
optical, thermal, and acoustic characteristics of the contacted interface
disappear.  When done with exquisite cleanliness, and vacuum baked
(240 C.), small fused silica contacted assemblies behaved as if one piece
and were not separable without breaking. When broken, many of the fractures
propagated irrespective of the original interfaces.

The advent of HEPA filtered laminar flow clean benches removed the
=B3black art=B2 aspects of the process, and the use of Selvyt polishing
cloths (just before contacting) eliminated the =B3infinite patience=B2
consideration.  Jan Bentz=B9s description of the contacting and
separation processes is splendidly accurate. When the components were all
made of the same glass, clean, well aged (or vacuum baked) assemblies were
not observed to separate using =B3hair dryer=B2 techniques.

Surface deformations of thin contacted components were interferometrically
measured to be on the same order as the match (concave to convex, in
curvature) of the surfaces contacted.

I have photos of some contacted assemblies, test setups, and of interfacial
flaws that I would be happy to digitize and share with interested
ATMs.


Cordially,

Stan
Truitt


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