not quite true rimless = thinner thickness = more tank?!

[guserto4]

In dreaming about a tank bigger than my 100g I started to ponder acrylic thickness and cost on rimless v. closed top and came up with this question-

First, the setup:
Let's pretend we have a 48" acrylic cube design. The spreadsheet I have says to go rimless would require 2" thick acrylic. 2" is super pricey! But if we didn't go rimless we could step it back to 1.5".

SO, the question is...
If the cube was built rimless with 1.5" AND THEN another 1.5" thick 48"x48" piece of acrylic was used as a rim, with the center (46.5"x46.5") cut out so that the "closed top" was even with the inside & outside edges of the walls of the cube, would it suffice?! How much of a difference in tensile strength is there between a welded acrylic joint and a lite or sheet itself? When does central bracing become required?! What if the tank wasn't a cube??

Any thoughts are much appreciated. Thanks!

 

[geaux xman]

how tall is the tank? a true cube at 48x48x48"(tall) ?

 

[BigOldReef]

My tank is 96x33x28 - My tank has a stainless steel 2x2 frame and entirely open top. The tank is all 3/4" and has no bowing.

If you're going to have a top, consider steel and powdercoating.

 

[TheFishTeen]

IMO, steel doesn't look very stylish with aquariums unless they're going in wall.

But back on the main subject, I find it hard to believe 2" acrylic would need to be used on even the 48"x48"x48" dimensions.

 

[evsalty]

IMO, steel doesn't look very stylish with aquariums unless they're going in wall.

But back on the main subject, I find it hard to believe 2" acrylic would need to be used on even the 48"x48"x48" dimensions.

I have a 16x16x10 rimless acrylic tank that is 3/8" on the bottom, sides and rear. The front if 1/2". The front is the only panel that does not bow. The 3/8" holds together but if you do not want to see any bowing then thicker acrylic is neccessary like the 1/2" front panel.

For that 48" cube I can see 2" being needed to not have any bowing.

 

[geaux xman]

I'm no expert but if 24" tall tanks still needs bracing with 1" acrylic, I can easily see 48" tall still needing bracing with 2" acrylic.

My LFS has a 75"x?x14"(tall) with 1" acrylic and his tank a good amount of bow.

I believe Ching Chai's old tank is a rimless acrylic tank, around 3-400g. He gave it to someone and I think theres a build thread too. I think it is something like 60x42x30 or around there..

 

[geaux xman]

Ching Chai's old rimless 66x36x30" 1.5" acrylic.

http://reefkeeping.com/issues/2008-05/totm/index.php

with a 48" tall tank, i really dont see the need for it to be rimless. easier for light penetration, but thats about it.

 

[guserto4]

I got the acrylic thickness calculator from SD Plastic's website here in San Diego.

http://www.sdplastics.com/aquaria1.html

Once I stumbled across it I started dreaming, and dreaming big. I haven't seen or heard of this framed but still rimless method before, but I imagine it's partly bc you end up with a bit of leftover acrylic which means extra $$ (I just imagine I would use the extra for a sump).

As far as thickness- it's not the length or width (well...) of the tank but the height that increases the required thickness. If you look at a tank in section, draw a 45-45-90 triangle (triangle is perpendicular to tank wall) the influence of water increases along the hypotenuse. That is to say with a 24" tall tank, at the bottom there is 24" of lateral force acting on the wall, 48" tall tank, 48" of lateral influence. Water outside of the triangle does not put any force on the tank wall. The only way length and width play a factor is by cutting off the triangle. A tall but not-so-deep tank needs less thickness than the same height tank that is wider/longer.

This "rimless" frame idea comes down to how well it counteracts the tendency for the water to push the walls out. Tensile strength of welded joints vs. tensile strength of a sheet of acrylic. (I think) part of the need for thicker acrylic on rimless (besides bowing) is to provide more surface area to bond the sheets together.