David R Posted April 10, 2008 Author Report Share Posted April 10, 2008 Two days with about 150kgs over the four middle legs that are off the ground and it hasn't sagged a bit. How bad would the unevenness have to be before you said the stand wasn't up to standard and was unsafe to use and asked for a refund? So, I'm going to do the liquid nails thing under the ply to take out any unevenness, how big a gap can I rely on it to fill in?? Anyone????? Quote Link to comment Share on other sites More sharing options...
Warren Posted April 10, 2008 Report Share Posted April 10, 2008 It's not going to sag ever without being forcibly modified. 4mm is a lot to take up. What's happened is when the two middle legs were welded to the underside of the top full-length member, the welds have shrunk as they cooled making the bottom side of the top runner shorter than the top side. This causes it to bow upwards. It would be possible to bend it down but it will tend to bend unevenly. The easiest way is to run a hacksaw most of the way through the top runner at the top of each middle leg so the stand can sit flat again at these points. You can then tig weld up the side of the cut to strengthen it. Do not tig weld the top or it will bow in the opposite direction and be hollow instead. Then you can use the no-more-nails option to take up any small errors that are left. Quote Link to comment Share on other sites More sharing options...
David R Posted April 10, 2008 Author Report Share Posted April 10, 2008 Probably a bit much for me to do, considering I've never welded before! So, really I should be taking it back to the guy that made it and telling him to sort it out or give me my money back? Quote Link to comment Share on other sites More sharing options...
livingart Posted April 10, 2008 Report Share Posted April 10, 2008 Probably a bit much for me to do, considering I've never welded before! So, really I should be taking it back to the guy that made it and telling him to sort it out or give me my money back? correct david the stand does not suit the purpose it was made for Quote Link to comment Share on other sites More sharing options...
David R Posted April 10, 2008 Author Report Share Posted April 10, 2008 :evil: That means borrowing the work truck, taking more time off during the day and going out to manukau. I really don't even care if he can fix it or try to repair it, I'm completely over it and would much rather build a wooden stand that I know will be level. Or maybe get toughtanks to make a steel stand, you'd think they would know what they're doing... Quote Link to comment Share on other sites More sharing options...
David R Posted April 10, 2008 Author Report Share Posted April 10, 2008 Those are the front corners, glass is 12mm to give you an idea of how big the gap is. I used a piece of paper to test where the weight is actually resting on the stand, and there wasn't actually many points where I couldn't slide the paper between the stand and the tank. Quote Link to comment Share on other sites More sharing options...
suphew Posted April 10, 2008 Report Share Posted April 10, 2008 Put it on and fill it up, it will be fine. My tank is longer and my stand was at least as bowed, I can move the poly up and down in the middle of my tank, if it wasn't one sheet I would be able to slide it out. It's been like this for two years. I also have five holes drilled (~40mm) in the bottom of my tank making it even weaker than yours. Most people grossly underestimate how strong glass is when make into a cube like a tank, for the bottom of the tank to twist and break either the silicon would have to come undone or you would have to bend the side glass down its axis, neither is likely to happen. The reason tanks break is because of single high pressure points, the poly takes care of this. Quote Link to comment Share on other sites More sharing options...
Warren Posted April 10, 2008 Report Share Posted April 10, 2008 Please show your calculations that justify your statement... Quote Link to comment Share on other sites More sharing options...
suphew Posted April 11, 2008 Report Share Posted April 11, 2008 ok 1570mm - 1500mm = 70mm, or how much longer my tank is. :roll: Silliness aside there are three points really 1) my tank, non-flat stand (proven by poly moving in middle of tank when full), two years, no problems. "Never the real world get in the way of a good calculation" 2) Logic, for the tank to break from twisting, it has to twist. This can only happen if a) the silicone comes loose at the joints so the bottom can twist separately from the sides. Or b) the side glass bends along its axis. If a) happens, its because of a very badly made tank, and would likely have come apart anyway, if b) happens I'll eat my hat. 3) whats the worst that can happen?? It's in a garage, the bottom glass breaks, some water spills, its costs $100 for a new piece of glass and I have to eat my hat. Quote Link to comment Share on other sites More sharing options...
Warren Posted April 11, 2008 Report Share Posted April 11, 2008 Well, you can try if you want but a quick type on the calculator shows you'll likely get in excess of 2000N/mm² or 200kg per square mm of force on the section of the tank at the high points and nothing anywhere else. This assumes a fairly even spread-out of the load due to poly placed under the high points but much more than the glass is good for. If you really want to risk breakage now or any time in the future, go for it. Worst case, if the poly does very little to help with the high points, you'll get over 9000N/mm² or 900kg per square mm - death to the glass and some. I really think advice and an approach like this should be taken only if you don't care if your tank breaks and only if you don't want to sleep well at night... Quote Link to comment Share on other sites More sharing options...
David R Posted April 11, 2008 Author Report Share Posted April 11, 2008 3) whats the worst that can happen?? It's in a garage, the bottom glass breaks, some water spills, its costs $100 for a new piece of glass and I have to eat my hat. Um, and I come home to find my impossible-to-replace 14" ornate bichir, my 4 year old 10" dat, my big school of clown loaches (probably over $500 worth if you bought them from a shop, or 5 years + if you grew them out) plus numerous other fish dead or dieing in an empty tank. :evil: Quote Link to comment Share on other sites More sharing options...
David R Posted April 11, 2008 Author Report Share Posted April 11, 2008 Thanks Warren, I think even with the liquid-nails trick it is too uneven. I'm not happy with the stand, and I have your expert opinion to say it is a big risk to take, so I guess the guy doesn't have much of a choice other than to give me my money back. :evil: I guess I should start drawing some plans for a wooden stand, or perhaps phone toughtanks? Quote Link to comment Share on other sites More sharing options...
tHEcONCH Posted April 11, 2008 Report Share Posted April 11, 2008 If you are good with wood, have you considered making a wooden 'tray' to sit on top of the metal? You could make one to your satisfaction (ie flat), then glue it with 'No More Nails or similar to the top of the metal stand, using the No More Nails and/or packers to take up any unevenness and transfer the load to the stand. I'd recommend still using a layer of Polystyrene too, which you could probably hide in the tray with a bit of trim to keep it neat. Quote Link to comment Share on other sites More sharing options...
Warren Posted April 11, 2008 Report Share Posted April 11, 2008 This is actually a very good option. If you have a decent saw you could make long thin wedges as packers and then use the no more nails to take up the last very small gaps... Alternatively you could try planing the wood to create hollows where the high-points are. Quote Link to comment Share on other sites More sharing options...
suphew Posted April 11, 2008 Report Share Posted April 11, 2008 Well, you can try if you want but a quick type on the calculator shows you'll likely get in excess of 2000N/mm² or 200kg per square mm of force on the section of the tank at the high points and nothing anywhere else. This assumes a fairly even spread-out of the load due to poly placed under the high points but much more than the glass is good for. If you really want to risk breakage now or any time in the future, go for it. Worst case, if the poly does very little to help with the high points, you'll get over 9000N/mm² or 900kg per square mm - death to the glass and some. To have made this calculation you would have needed to know what the area of the high points was, which you dont know, so this is a pure guess. Secondly, (correct me if I'm wrong, I'm not a mathematician) but to get 900kg psmm wouldn't you need 900kg?? The tank holds round 600l of water if completely full to the brim so 600kg of water plus glass plus gravel etc, I think you would be lucky to get to 900kg total. So to have 900kg psmm would put the whole weight on 1 square millimeter. Um, and I come home to find my impossible-to-replace 14" ornate bichir, my 4 year old 10" dat, my big school of clown loaches (probably over $500 worth if you bought them from a shop, or 5 years + if you grew them out) plus numerous other fish dead or dieing in an empty tank. If it was going to break why would it wait till you had added your fish, The most stress the glass is going to have is when the weight is changing, i.e. when you are filling the tank. I guess I should start drawing some plans for a wooden stand Wood is never going to be flatter than steel. Plus the joints can move, wood can bow and twist over time, I would think it would be more of a risk than the steel one. (BTW my stand is made from wood). There are likely hundreds of tanks in New Zealand as large if not larger, most of the owners wont have even checked to see how twisted their stand were. I have personally helped moved 3 tanks larger (not including my own), one 4 times the volume of yours and I know for a fact the owners only properly checked the stands after they were filled for testing. And this was for level not twist. But when it comes down to it, it's your peace of mind. I just think your panicking for no reason and will end up spending money you didn't need to. Quote Link to comment Share on other sites More sharing options...
livingart Posted April 11, 2008 Report Share Posted April 11, 2008 yes good idea, forgot that gannets 2.4m x 60cm x 60cm tank came with a badly made wooden stand, we got a 30mm sheet of marine ply base size, laid that on stand and packed it to take out all of deflection then 10 mm of poly on top, tank has 100+kg of rock in it and still going strong Quote Link to comment Share on other sites More sharing options...
suphew Posted April 11, 2008 Report Share Posted April 11, 2008 BTW if you actually are that worried about this, buy a kitchen bench top, which will be dead flat and very unlikely to bend. A secondhand one will do, paint the bottom with oil based paint to seal it, and to make double sure screw some box section to the bottom of it. Sit this on your stand and pack out between the stand and the bench top. But first make sure your stand legs are all firmly attached (bolted) down to the concrete or the stand might bend once the weight goes on. Quote Link to comment Share on other sites More sharing options...
Warren Posted April 11, 2008 Report Share Posted April 11, 2008 Oops, did get it out by a factor of 100 (I hate unit conversions!!), so only 9kg/mm² or 90n/mm² :oops: However, this is still too high by a considerable amount when you consider the maximum loading for glass is approx 19.2n/mm². Hope you understand the basic laws of physics and the risk you are taking with your tank. I assumed a certain cross-section and multiplied it by 10 and worked with this. The calculations are based on 625mm² of contact area or a total of 25x25mm which you are very unlikely to actually achieve with this stand. The earlier figure is based on poly partially spreading the load over a larger area. Even so, at 20n/mm² it's still higher than the strength of the glass... Can't understand why you'd want to take this risk. When you compare these loadings with what you'd have if the supporting surface was flat you can see why there is concern. The loadings on a properly supported tank drop from 90n/mm² to 0.05n/mm² or 1680 times less. When you can offer something to back up your claims please comment further. Quote Link to comment Share on other sites More sharing options...
puttputt Posted April 11, 2008 Report Share Posted April 11, 2008 Funny, I would have thought the fact that he found your calculations to be out by a factor of 100 was definitely "something to offer". Quote Link to comment Share on other sites More sharing options...
suphew Posted April 11, 2008 Report Share Posted April 11, 2008 When you can offer something to back up your claims please comment further. Ok, its big, made of glass and has been sitting in my lounge for a few years..... thats about all the back up I feel that I need. Oops, did get it out by a factor of 100 (I hate unit conversions!!), so only 9kg/mm² or 90n/mm² However, this is still too high by a considerable amount when you consider the maximum loading for glass is approx 19.2n/mm². Hope you understand the basic laws of physics and the risk you are taking with your tank. I assumed a certain cross-section and multiplied it by 10 and worked with this. The calculations are based on 625mm² of contact area or a total of 25x25mm which you are very unlikely to actually achieve with this stand. The earlier figure is based on poly partially spreading the load over a larger area. Even so, at 20n/mm² it's still higher than the strength of the glass... Can't understand why you'd want to take this risk. When you compare these loadings with what you'd have if the supporting surface was flat you can see why there is concern. The loadings on a properly supported tank drop from 90n/mm² to 0.05n/mm² or 1680 times less. There are so many guesses, assumptions, and holes in this calculation I'm not even going to start on it. As I said before "But when it comes down to it, it's your peace of mind. I just think your panicking for no reason and will end up spending money you didn't need to.". Go with the the benchtop or 30mm marine ply, a hundred or two is often worth peace of mind. Quote Link to comment Share on other sites More sharing options...
David R Posted April 11, 2008 Author Report Share Posted April 11, 2008 If it was going to break why would it wait till you had added your fish, The most stress the glass is going to have is when the weight is changing, i.e. when you are filling the tank. Not sure, it could just badly stress the tank and all it takes is a rock being moved or a slight sag in the steel over time, small earthquake who knows. Still, not a nice thought when keeping hard-to-replace [impossible] fish. Wood is never going to be flatter than steel. Plus the joints can move, wood can bow and twist over time, I would think it would be more of a risk than the steel one. (BTW my stand is made from wood). I disagree. I made a a stand for my old 5'x2'x2' from 4x2 pine clears. It was put thru a thicknesser to get every piece dead flat and the same size. The legs had notches cut out of the top for the top pieces, and it was a lot more level on top than this steel stand is. Steel will always expand and contract when welded, so it is hard to get it perfect. Warren, would it be possible to compensate for a 1-2mm unevenness with the liquid nails thing?? Quote Link to comment Share on other sites More sharing options...
suphew Posted April 11, 2008 Report Share Posted April 11, 2008 To weld steel flat is easy, you attached it firmly to a solid flat surface before you weld it. Pretty common practice as I understood it. Quote Link to comment Share on other sites More sharing options...
Warren Posted April 11, 2008 Report Share Posted April 11, 2008 To weld steel flat is easy, you attached it firmly to a solid flat surface before you weld it. Pretty common practice as I understood it. I give up, you seem know everything you need to know about welding and stress calculation. As I don't know everything there is to know, I will not comment further. In my 25 years experience of welding, structural design and fabrication I regularly learn new things... Quote Link to comment Share on other sites More sharing options...
David R Posted April 11, 2008 Author Report Share Posted April 11, 2008 As I don't know everything there is to know, I will not comment further. Could you give me your opinion on the liquid nails filling the 1-2mm unevenness? :lol: Quote Link to comment Share on other sites More sharing options...
Warren Posted April 11, 2008 Report Share Posted April 11, 2008 I personally think it will be ok. If you put quite a bit on every metal surface before putting down the ply so it oozes out plenty once fitted you can then place the tank on the ply to it conforms to the same flatness as the tank. You will likely need some small wedges around the edges of the ply in a few places to push low areas upwards. At the corners the ply will tend to droop away from the surface of the glass. If it happens, push a wedge into the glue between the wood and steel until the wood comes up at touches the tank. No-more-nails takes quite a while to go hard so maybe wait a week before removing the tank and adding the poly before filling. I've done this many times on uneven stands and on tanks much bigger than this one. If a little time is taken checking good even contact all the way round you'll end up with and very flat base. Quote Link to comment Share on other sites More sharing options...
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