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Hi Shelley and Rick,
When I was building my sub I pondered how to deal with the Plexi an
lot. What I settled on is just what I thought was the best and easiest for
me. There is no substitute for a properly machined cone and properly
machined housing, machined after all welding is done. That isn't
easy.
If view port lenses was flat and even thickness then a face contact O-ring
would be good but you would have to also machine the flat area of the viewport
housing and groove after welding.
Using an O-ring on the sides of the viewport housing, contacting the OD of
the lens, was an option but again, there is warpege in the housing after
welding. Also you have to take into account the coefficient of expansion
of the Plexiglas. In order to leave enough room for it to not be crushing
itself while the sub is outside on a hot day, you'd have to leave room
for expansion. Then in cold water the gap would open up to much for an
O-ring not to be extruded.
The same if you put a chamfer on the outer edge of the lens
and made a three point seal with an O-ring just under the retaining
ring. When the lens cooled and shrunk, the gap would be too great to
trust.
Kittredge just glued his in with SekoFlex, and after all my pondering,
I decided to machine the lenses with a clearance gap between the lens OD
and housing ID and glue them in also. I spread on the urethane
sealant and pushed the lens in almost all the way to leaving a bit of a
urethane bed for the lens to mate against. I know with the annuals filled,
I don't have expansion room, but it seems to work.
I did the shrinking and later annealed my lenses. My fifteen inch
lens shrunk about an eight of an inch in diameter on the first cycle and didn't
shrink hardly at all in the second annealing cycle.
So far it's working fine.
Dan H.
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