Glass thickness question

[Drstrangelove]

This is great info!

I'm looking to build a 10x4x4 plywood tank, and have been stuck on what's the best viewing window configuration.

If I were to put 3 windows that are 36"L x 24"T, with 6" of support on each side of the tank and 2 braces in the front for strength...and in the middle of the front plywood panel, 36" of water pressure...I could use 12mm(1/2") glass? Or would that be stretching the Safety Factor a bit much?

Some calculators will show 12mm as the correct thickness for 2 foot high glass, but the one I use shows it to be 10.8mm. I'd probably opt for 12mm since the cost is probably very similar.


http://www.fnzas.org.nz/?page_id=1635

Here's a nice one to use.

 

[Drstrangelove]

Thanks,
I see your tank (Nice !) is in 15 mm glass
The price I was quoted was 4 times that of 12 mm and only marginally cheaper than 19 mm
is this a local pricing issue or inline with prices in the southern hemisphere?

I don't make glass, but I work in a production process and understand it's costing issues.

At 'standard' thickness (which is to say common glass thickness), the actual cost should be the setup cost, plus the cost of materials and conversion plus markup. At similar, common sizes, 15mm glass is 25% more material than 12mm glass, so it should be similar to cost of 12mm plus 25% unless other factors prevail.

Non standard lengths and widths are hard to estimate because we don't know what dies or special process the manufacturer has to use or what his setup costs are. If for example, he only makes 12mm, then setting up for one person to make 15mm or 19mm may be very expensive. If he doesn't have the equipment or skilled employees to make thicker glass, he may need to have a third party make it. If his process is less efficient for thicker glass, he may need to charge more for waste.

I'd shop around for another supplier as in the states, I examined one tank maker and found that prices are stable (roughly flat) from 8mm to 24mm glass. [This does not mean that it's the same price, but that the cost per pound of finished glass is almost the same. Glass which is twice as thick will cost twice as much. Glass which is three times as long will cost three times as much. You can determine this from the volume of the glass produced, L x W x H x thickness.] Despite not being a glass maker, this means that the process for 8-24mm glass is such that actual cost varies only by the amount of material with the 'standard' lengths and heights.

In short, for that particular tank maker, he was able to produce glass within those widths (8mm to 24mm) and at standard lengths with price increasing directly proportional to the quantity of materials used. 50% more material = 50% more cost, 200% more material = 200% more cost, etc.

 

[TheSinisterSOB]

Some calculators will show 12mm as the correct thickness for 2 foot high glass, but the one I use shows it to be 10.8mm. I'd probably opt for 12mm since the cost is probably very similar.


http://www.fnzas.org.nz/?page_id=1635

Here's a nice one to use.

Awesome, thanks for that calculator.

Looks like I've got my viewing window calculations, and seems I dont need super thick glass depending on where I put it in the front panel of the tank and how its braced.

Panel Height 762mm = 30inch
Panel Length 1219.2mm = 48inch
Safety Factor 3

Glass Thickness = 13.4069238922mm = 0.5275591inch
Deflection = 0.636585338167mm = .023622inch

 

[David R]

Here's another calculator based on Warrens calculations but in an easier to use format; http://www.theaquatools.com/building-your-aquarium

Thanks,
I see your tank (Nice !) is in 15 mm glass
The price I was quoted was 4 times that of 12 mm and only marginally cheaper than 19 mm
is this a local pricing issue or inline with prices in the southern hemisphere?

Was that directed at me? If so, the big difference with going from 12mm to 15mm is the cutting and edge working. 15mm is pretty borderline to cut using traditional methods and is usually cut oversized in the factory then has the edges machined down to the correct size, thus the price difference between 12mm and 15mm being far greater than 15mm and 19mm. I was lucky with my tank that the tank maker was able to source 15mm offcuts rather than paying the rate for new glass per sheet. Mine was cut the "normal" way and the edges are simply rough arrised with a sander rather than being perfectly machined. This saved me ~70% on the cost of "new" glass with machined edges.

 

[kevinp]

It turns out that my gut feeling that I would need to use all of the tank dimensions (L*W*H) to calculate the volume and weight of the water to calculate the glass thickness was wrong.


While walking along the beach it occured to me that if I was standing neck deep in the sea the weight of the billions of gallons of water at 24 inches should if my understaning was correct do something like push my lungs through my eye sockets.


I went for a paddle and can confirm my toes are still are the end of my feet and not competing with my knee caps for space.


It also turns out contrary to what I was taught at school pressure in a liquid is not even. It is higher at the bottom.




Thanks to all of the replies I have been able to conclude the following:-


1. I will be able to use 12mm glass in 2 windows.
2. My Physics teacher was a liar (high velocity chalk and blackboard rubbers also indicate sadistic tendencies).
3. Jacob Zuma's house probably has a lot of 15 mil glass.
The millions of Tax payers money spent obviously went to pay the market rate for glass and that there is absoultley no corruption going on there at all