Question about DIY acrylic

[CichlidDan]

I am planning out a custom acrylic aquarium and I can get 8'x6' cellcast (the right kind????) acrylic. The tank I have planned fits perfectly on it an leaves room for me to double up the edge on the bottom with strips except that I don't have enough room for the top brace piece. It is going to be 72"x30"x20" so it is out of 1/2" acrylic and I don't want to have to buy another large sheet of 1/2". I was wondering if I can make the top brace piece out of 1/4" acrylic or if that would be dangerous. Because if I can then it will save me a ton of money. Thankyou for any help.

 

[CHOMPERS]

My intuition says yes it can be done, however, something is telling me there is a problem involved. So I looked up the properties of acrylic:
http://www.3d-cam.com/materials/acrylic.asp

The tensile strength says that you are clear to go ahead, but that "something" that caused me to look into the properties is the Charpy Impact tests. The notched and unnotched results highlight the brittle properties while under load. The notched result is to show the strength with a stress concentrator. Since the result for the notched and unnotched is so far apart, it will be a very bad idea to skimp on the top bracing. The corners of the openings are stress concentrators (where stresses concentrate) and is the weak link in the system. You can reinforce these areas by gluing another piece of 1/4" over or under them. I also have concerns of buckling in the top but having two cross braces instead of one will solve that problem.

 

[basslover34]

double up the 1/4 and you'll be good for sure and you'll save a few bucks

 

[spiff]

double up the 1/4 and you'll be good for sure and you'll save a few bucks

I don't think this is a good idea. Two .25's is NOT as strong as one .50 piece. Not to mention how crappy it will look once a bunch of crud wicks into that space between the pieces.

 

[basslover34]

I don't think this is a good idea. Two .25's is NOT as strong as one .50 piece. Not to mention how crappy it will look once a bunch of crud wicks into that space between the pieces.

Neither of us have claimed it to be a strong as a 1/2" piece... it will however be strong enough to do the job propperly and save a couple of bucks... as for how it will look... depends on how the job is done... if it's mounted with a space between them then you'll see a buld up but if they are welded together then there is no reason to have any build up what so ever...

 

[CHOMPERS]

If two pieces of 1/4 are glued together, they will be equally strong as one 1/2 inch piece.

It wasn't my recommendation for two full sheets either. My suggestion was a way to use one piece. Sure it will be ugly, but that is what hoods are for.

 

[johnptc]

If two pieces of 1/4 are glued together, they will be equally strong as one 1/2 inch piece.

i agree



or make a metal ( SS? ) top brace and dont worry about it at all.

my monster concrete tank use 3/4 diameter ss rods as cross braces....there are many options.


cyro plastic calculator says 0.6 thick fyi *


Note: Areas you need to fill out are in red H Enter Height of Tank [in] 20
L Enter Length of Tank [in] 72

Is the top closed ? (yes or no) yes
q Maximum Water Pressure [psi] 0.722
L/H L/H 3.6
a Maximum Allowable Stress for Acrylite GP in Aquarium [psi] 750
b b 0.922688
Tc Thickness of Sheet required with top [in] 0.596067

 

[spiff]

I never said that you said it was as strong, but I am now. Even two glued together pieces isn't as strong as a solid piece. But its close enough.

 

[basslover34]

Two .25's is NOT as strong as one .50 piece.

This is the comment which I have targeted on....not about welding 2 together however if welded together you actually have a stronger piece since the weld itself is stronger than the acrylic that it's holding... I haven't run the math but I beleive that you would be looking at the weld making up any difference that the 2 pieces would have lost vs 1 and then some... I'll leave our resident nerd (Chompers ) to run the numbers

 

[johnptc]

is a 0.25 piece half the strength of a 0.5 piece ???