Acrylic Thickness

[rpgraff]

Glass thickness calculators seem to abound....What about acrylic thickness guidelines?

[ToeCutter]

http://cyro.custhelp.com/cgi-bin/cyro.cfg/php/enduser/std_adp.php?p_faqid=133

There's a link to an excel spreadsheet on there.

Cyro is a bit conservative on those recommendations.

[rpgraff]

Thanks for the reference, but on initial inspection I might be stummped. If I did this right then I probably should be using 3/8" thick acrylic.

the tank would be 24" wide by 30" tall.

B=.212 (Length/Height=.80)

q= 1.083 ( .0361x30)

Hsquared = 900

(.212*1.083*900)/750 = .2755152

[Robbob29]

I know of one on garf.org

http://www.garf.org/Tank/BuildTank.asp

It's glass and acrylic, plus some instuctions

HTH
Robbob

[rpgraff]

thanks, that calculator recommends 1/2". Its probably being safe, and I have to admit, 1/2" probably wouldn't bow much if at all.

[ToeCutter]

Originally posted by rpgraff
Thanks for the reference, but on initial inspection I might be stummped. If I did this right then I probably should be using 3/8" thick acrylic.

the tank would be 24" wide by 30" tall.

B=.212 (Length/Height=.80)

q= 1.083 ( .0361x30)

Hsquared = 900

(.212*1.083*900)/750 = .2755152

You didn't take the square root of the last number you got, which would push the number to .524 or something.

There's a link on that page to an Excel Spreadsheet, where u just plug in the numbers.

The biggest factor in determining thickness is height, that's why such a small tank would need such thick acrylic.

[rpgraff]

uhhhh, DUH!!!! its no fun being a blonde sometimes ..LOL..

Can't believe I forgot to do that

[Zephrant]

I'll second the 1/2" idea, just from experience.

Getting over 24" tall means a thicker sheet than normal. Even with 1/2", there will be a noticeable bow. Make sure you use a center brace on the top, and a strong perimeter brace.

Zeph

[Acrylics]

Originally posted by ToeCutter
http://cyro.custhelp.com/cgi-bin/cyro.cfg/php/enduser/std_adp.php?p_faqid=133


Cyro is a bit conservative on those recommendations.

They're conservative in a number of ways (for good reasons though):

1) The Alpha value of 750 (permissible stress) was an arbitrary number (to give themselves a safety factor). This was to allow for variances in the structure of the material itself. The actual number was closer to 1500. Change the alpha number to 1500 instead of 750 to correct for this.
2) Instead of actually giving the graph (which can be easily made) they give just 6 options for the Beta value. If you fit in between they instruct you to go to the next value rather than using the *correct* value. Simply by plotting their values on a graph - you will end up with a curve which will be more accurate.
3) The formula asks for height of tank and length of tank, these should be *inside* height and length.
4) If you come up with a thickness of say .500", you will have to use 3/4" acrylic because true .500" acrylic does not in fact exist. Their 1/2" acrylic has a noiminal thickness of 12mm which is .472", and given their tolerances actually measures closer to .440-.450". Given this, they will recommend you move to the next thickness as the minimum thickness recommendation is .500". I'm not sure this can be corrected per se, when it comes down to it - the choice of thickness ends up with the consumer.

The reason they are so conservative is two-fold:

A) They know that *most* folks will only get a 90% bond, meaning bubbles 'n such will cover the remaining 10% making the joint weaker.
B) The formula is made so that there will be a minimum amount of deflection. Far less than is standard in the hobby industry.
One *may* also say it's to make more money selling thicker acrylic - this is debateable IMO.

The only part that they are not conservative enough on is the end where they say to use a safety factor of 1.5 if you use an open top. This should be corrected to 2.5 to achieve fairly similar deflection rates.

I'm not down on Cyro at all in regards to this formula, as I think it was done this way for fairly good reasons - but I think it's good to have a better understanding of the formula as well.

James