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Flagg37
09/27/2016, 11:31 PM
I build staircases and at times use 1/2" tempered glass for the rail system. Where the panes meet at a corner I have the glass mitered. I've often wondered why I never see this in custom tank construction. I would think the joint would be stronger since it is longer. Is it simply a cost factor?

OllieNZ
09/28/2016, 12:22 AM
I build staircases and at times use 1/2" tempered glass for the rail system. Where the panes meet at a corner I have the glass mitered. I've often wondered why I never see this in custom tank construction. I would think the joint would be stronger since it is longer. Is it simply a cost factor?
I think so, the Japanese company ADA do make a single piece tank.
http://glassbox-design.com/2011/ada-cube-garden-superior/

Ron Reefman
09/28/2016, 04:26 AM
I have built 5 tanks over the last few years for me and for friends who want custom. I use glass I buy from a local glass shop and they always miter the edges. I never thought about the small increase in surface area. But then I've never had a tank failure in my home made tanks... wish I could say that about tanks made by big companies!

OllieNZ
09/28/2016, 04:31 AM
I have built 5 tanks over the last few years for me and for friends who want custom. I use glass I buy from a local glass shop and they always miter the edges. I never thought about the small increase in surface area. But then I've never had a tank failure in my home made tanks... wish I could say that about tanks made by big companies!
It would be unusual for them to miter the edges unless you specified it.....
A polisher will however put a small bevel on the edges of the glass

fishgate
09/28/2016, 07:23 AM
It really isn't necessary. The joint is very strong using just the 90 degree ends. It is also more work to miter a piece of glass than a piece of wood. You can't cut glass at a miter so it has to be polished/ground to that angle. For custom stuff it is worth it since the price adjust accordingly, but for mass produced stuff it would effect cost too much.

Flagg37
09/28/2016, 11:44 AM
I was thinking more about the custom builds where you're already paying thousands of dollars. I know from experience that the manufacturing cost is minimal compared to the glass itself.

fishgate
09/28/2016, 01:03 PM
I was thinking more about the custom builds where you're already paying thousands of dollars. I know from experience that the manufacturing cost is minimal compared to the glass itself.

I think this would be more for visual reasons anyway since most of the joint strength is the silicone put on the inside of the tank where it doesn't matter how the edges meet. It would be interesting to see a stress to failure test just to see how much more strength miters add. I am sure they add something.

OllieNZ
09/28/2016, 02:13 PM
I think this would be more for visual reasons anyway since most of the joint strength is the silicone put on the inside of the tank where it doesn't matter how the edges meet. It would be interesting to see a stress to failure test just to see how much more strength miters add. I am sure they add something.
All of the strength of the bond is in the peel strength of the silicone between the two panes. The fillet on the inside is not necessary and adds little to no strength, it just offers some protection to the structural seams.
In theory anything that increases the bond area would be beneficial but the decreasing material thickness as the miter progresses may reduce the benefit gained from the increase in bond area.

uncleof6
09/28/2016, 08:33 PM
A miter, would decrease the glass thicknes from inside out, and that would be almost a no no. Thin gets brittle, and the edges would chip out, and you would end up with a mess. Miter plus diamond cut, maybe. It would not add much, if anything, to the appearance of the tank. Face it, panels of glass held together with silicone looks hideous. Myself, I would walk away from it; but someone might call Miracles and get their take on it...

Just a word on "custom" building: A repsonsible custom builder can't be or shouldn't be expected to do something just because a customer wants it... catastrophic liability insurance is too expensive without any claims... ;)

Note: As OllieNZ noted, the strength, or what holds a tank together, is between the glass panels, not with the inner seal. In some cases, it can help; but it is considered sacrificial.

OllieNZ
09/29/2016, 05:37 AM
A miter, would decrease the glass thicknes from inside out, and that would be almost a no no. Thin gets brittle, and the edges would chip out, and you would end up with a mess. Miter plus diamond cut, maybe. It would not add much, if anything, to the appearance of the tank. Face it, panels of glass held together with silicone looks hideous. Myself, I would walk away from it; but someone might call Miracles and get their take on it...

Just a word on "custom" building: A repsonsible custom builder can't be or shouldn't be expected to do something just because a customer wants it... catastrophic liability insurance is too expensive without any claims... ;)

Note: As OllieNZ noted, the strength, or what holds a tank together, is between the glass panels, not with the inner seal. In some cases, it can help; but it is considered sacrificial.
Just out of interest Uncle, can you give a rough peel strength figure for a glass to glass silicone bond?

Flagg37
09/29/2016, 09:58 AM
Just to add to the discussion, a .5000" piece of glass yields .7071" of surface are if it is mitered at 45 degrees. That's almost a 50% increase.

If I was to do this for my tank it would be primarily for aesthetics. Correct me if I'm wrong but it seems as though the weakest point on the tank is not the seams but the glass itself. Meaning that increasing the surface area of the silicone, although nice, is not needed since the joint is sufficient the way it is.

OllieNZ
09/29/2016, 10:39 AM
Just to add to the discussion, a .5000" piece of glass yields .7071" of surface are if it is mitered at 45 degrees. That's almost a 50% increase.

If I was to do this for my tank it would be primarily for aesthetics. Correct me if I'm wrong but it seems as though the weakest point on the tank is not the seams but the glass itself. Meaning that increasing the surface area of the silicone, although nice, is not needed since the joint is sufficient the way it is.

If you are interested in aesthetics, check out the 'standard' ADA cube garden range for ideas. I'm not sure how the mitre would impact the strength of the joint, it would be something I'd hesitate to do with glass but acrylic on the other hand....

uncleof6
09/30/2016, 01:39 AM
Just out of interest Uncle, can you give a rough peel strength figure for a glass to glass silicone bond?

Momentive RTV108 ~ 40lb/in. (From product data sheet) Momentive/GE Silicone I and II, not published, as the peel strength is irrelevant: they are sealants, with little adhesive properties.

I would have to look around for the exact number but SCS1200 is ~45lb/in.

OllieNZ
09/30/2016, 01:46 AM
Momentive RTV108 ~ 40lb/in. (From product data sheet) Momentive/GE Silicone I and II, not published, as the peel strength is irrelevant: they are sealants, with little adhesive properties.

I would have to look around for the exact number but SCS1200 is ~45lb/in.
Thanks,
That's not a lot of strength. Is there any reason other than cost a structual adhesive is not used for building aquaria?

uncleof6
09/30/2016, 02:57 AM
Just to add to the discussion, a .5000" piece of glass yields .7071" of surface are if it is mitered at 45 degrees. That's almost a 50% increase.

If I was to do this for my tank it would be primarily for aesthetics. Correct me if I'm wrong but it seems as though the weakest point on the tank is not the seams but the glass itself. Meaning that increasing the surface area of the silicone, although nice, is not needed since the joint is sufficient the way it is.

A tank will pop the seams before the glass will break, in most cases. Glass is tensile strength, (resistance to tearing itself apart) and bending stress, (modulus of elasticity or how far will it bend before it breaks) while silicone is peel strength. Peel strength loses, as it is less than the tensile, and shear strength, of the silicone. On the other hand, the information on RTV100 series says that once fully cured the "adhesive strength of the bond will exceed the cohesive strength of the silicone rubber itself." Joint configuration is a factor here, and a butt joint is the strongest, but there are a couple other factors. However, even butt jointed, too much deflection, and the seam(s) will pop; and yes, it is safe to assume that if the seam does not pop, the glass will break.

HighestOlive
10/04/2016, 07:37 AM
Interestingly enough I was reading this thread a couple days ago and now this popped up:

http://ultumnaturesystems.com/

I can't link to the article this was written up in.

uncleof6
10/04/2016, 09:38 PM
Thanks,
That's not a lot of strength. Is there any reason other than cost a structual adhesive is not used for building aquaria?

Other than cost? Can't think of a good enough reason not to use the very best you can get your hands on. Cheap is as cheap does... Most common reason for using low grade consumer silicone is: can't find the good stuff at Home Depot (or fill in the blank for your favorite Big Box store.) In the grand scheme of things, the cost difference is negligible and irrelevant.

OllieNZ
10/04/2016, 11:27 PM
Other than cost? Can't think of a good enough reason not to use the very best you can get your hands on. Cheap is as cheap does... Most common reason for using low grade consumer silicone is: can't find the good stuff at Home Depot (or fill in the blank for your favorite Big Box store.) In the grand scheme of things, the cost difference is negligible and irrelevant.
I've got a tin of hysol in the shed.....
It just seems a bit weird that silicone is the go to adhesive given its relatively low strength,

uncleof6
10/05/2016, 03:38 AM
Well first you need to understand what peel strength actually is. Peel strength is an adhesive property and it is measured by applying an adhesive to a substrate, and then peeling it back at a 180° angle, (think of pulling tape off a piece of glass.) the lower the angle, the harder it will be to "peel" the adhesive off the substrate. At a 90° angle, it is possible to break the glass, before the silicone will let go. This is why we strive to keep the "bending stress" on the glass as low as possible, by using glass of a suitable thickness.

Silicone and glass are similar materials. Glass is basically silicon and oxygen, and silicone is a silicon and oxygen backbone, with organic (carbon and hydrogen) side groups.

Silicone has: Low toxicity, thermal stability, e.g. maintains its physical properties over a wide range of temperatures. These properties include, flexiblity, high elongation, and adhesive strength. It is chemically inert, and naturally mildew resistant (the exact phrase is: Does not support microbiological growth), Resists oxygen, UV radiation, and ozone. Does not adhere to many substrates, but adheres very well to some e.g. glass.

It is about the only, if not the only, adhesive that meets the requirements for building aquariums. That's it in a nutshell.