----- 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