----- Original Message -----
Sent: Monday, January 23, 2006
19:43
Subject: Re: [PSUBS-MAILIST] acrylic
dimension change
Brian,
No, I didn't machine the faces of the
lenses.
I made my viewport housings deeper then
the thickest lens by about .050 of an inch. Yes, deeper
then the lens is thick. I then ordered some
stuff from West Marine that was a combination of urethane and something
else. (I forgot what) It's recommended for sealing both painted
steel and acrylic, among other things.
Before installing the lens, I buttered the lens housing
with the urethane bonding stuff and pressed the lens in almost all the
way, then bolted on the retaining ring. The ring pushed in on
the lens until the outside was flush and the urethane squished out after
it filled the .050 plus gap. PVHO standards say there should
be a urethane cushion between the lens and housing anyway, so I have a
cushion and it doubles as a seal.
Also, I machined the diameter of the lens so they would
be .100 smaller then the housing opening. I let that gap fill
with urethane also. I did add and O-ring seal to them after the
urethane hardened, but it wasn't necessary. I already had a 45
degree chamfer on the lenses to accept the O-ring from my first design
idea. So I put it in. Remember, your not going to get the lens
out very easy if you put them in like this, but it makes a good
seal.
Another note, If you have any imperfections or
scratches on your lenses, put the scratches on the outside.
They disappear when your sub is in the water.
Dan H.
----- Original Message -----
Sent: Monday, January 23, 2006 8:16
PM
Subject: Re: [PSUBS-MAILIST]
acrylic dimension change
Dan,
That's very interesting about the acrylic faces not being even,
I'm only familiar with the plexiglass that is commonly purchased which
is "sheet" acrylic. The cast acrylic is a new one for me, I
assumed the cast was similar to the sheet but I guess not. So then
you probably had to machine the faces perfectly flat and the sand and
polish them to get them crystal clear. How smooth were you able to
get the acrylic with just a machine tool?
Thanks
Brian
----- Original Message -----
Sent: Monday, January 23, 2006
10:46
Subject: Re: [PSUBS-MAILIST]
acrylic dimension change
Brian,
I first shrunk my viewports with a higher heating
process. This was before final machining. I
probably did have some thickness shrinking then but I didn't have an
exact measurement of the thickness before hand. When you get
your acrylic it won't be exact thickness anyway. My pieces were
all different thicknesses. I don't remember the exact variations
but I'm thinking they varied about .030 thousants of an inch.
They even very from one edge to the other of the same piece.
I was told that thick acrylic sheets is made by
pouring the liquid acrylic between two sheets of glass and there
is always some bulging of the glass form.
If you need exact thickness you should have your
acrylic in hand before you machine your housings.
Dan H.
----- Original Message -----
Sent: Monday, January 23, 2006
11:34 AM
Subject: [PSUBS-MAILIST]
acrylic dimension change
Hey Dan H,
When you annealed your viewports did you have any change in the
thickness ? I'm getting ready to machine my viewport
flanges but I haven't purchased the acrylic yet, I'm just
wondering if that dimension is going to change on me.
Thanks,
Brian