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Re: [APD] RE: Etching (polycarbonate,tank lids)-- or - Airing alternatives to solid sheets

Thanks, Eric.

I thought the original reference was to acrylic sheet
material (the solid sheet stuff) and so I wasn't clear
about "ribs."  

One could put ribs on the solid stuff to increase it's
rigidity and prevent warping. Cementing short vertical
lengths to the sheet will do it -- or one can laminate flat
(horizontal) pieces onto a sheet, although more ribbing
material is needed if it's done that way.

I don't know which method would cost one the most light --
going through ribbed solid sheets or going through the
hollow twin-wall material. I would guess that it's not jsut
a matter of total thickness but all the changes in density
(plastic, air, plastic) that will affect diffusion of the

A big advantage of the twin-wall material is that one
doesn't have to fool with the cement, the fumes from which
are best avoided.

Scott H.
--- Eric Wahlig <ewahlig at earthlink_net> wrote:
> Scott, you asked: "Ribs? Can you elaborate?"
> These are the box channels that are spaced about 7 or 8
> mm apart and run
> the length of the sheet. The sheets come in 45 foot
> lengths by 4 feet wide
> when you buy them in bulk from a manufacturer like GE. My
> guess is because
> that length fits conveniently into a truck trailer.  I
> get the scraps and
> small stuff cut roughly to the size I need  from a local
> greenhouse
> builder. He sells it by the square foot but has a 4
> square foot minimum.
> So, the smallest piece he sells is 1 foot  section sawed
> off of a 45 foot
> long piece and its 4 feet wide. Now a 1' x 4' section can
> be cut in half to
> make 2 tank lids for a 15 or 20H tank but the
> ribs/channels are running
> along the short dimension of 1 foot and this makes for a
> very flexible lid
> as the cat found out when he jumped on it! It didn't
> break but splashed
> water everywhere. Lets say I've got a 120 gal. tank. Then
> I want to get a
> piece that is 4 feet long in the same direction as the
> channels run which
> means I would get a 4 foot piece which would be 4' x 4'
> and cut it in half
> along the channels (rip cut). If I got a 2' piece it
> would also fit the
> tank because it would be 2' x 4' and cost half as much
> but it would be
> structurally weaker as the ribs/channels would run across
> the short
> dimension. I think you posted a link to a picture of this
> stuff a while
> back; probably in the archives somewhere.

S. Hieber

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