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