----- 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