Who has had a DIY stand fail??

  • We are currently upgrading MFK. thanks! -neo
guppy said:
...I had no diagonal bracing but did …a 5/8" marine grade plywood top, and 1/2" plywood sheathing…
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Actually you did have cross bracing in all of your plywood. If you cut all of your plywood into big X's you would have your cross bracing. Leaving it in one piece doesn't make it weaker, it is stronger. In one piece, it gives bracing in infinite directions in the plane of the plywood.

2x6's when glued do provide bracing but it is minimal in many of the applications of aquariums. For longevity, it is not something to bank on.

Here is a mind exercise: if you build a cube with twelve tooth picks, it won’t be very strong. If you skin it with paper, it will be much stronger. If you skin it with cardboard, the strength is further increased. If you did the same experiment with 2x4’s, you wouldn’t want to stand on the top of the bare cube. If it were skinned with plywood, it would be pretty darn strong.
 
lol thats a tad harsh. i only asked cause i've been worried about your collapsing stands thing, and was thinking about doing one myself. im not new to fishkeeping, but i sure am new to building stands, and as its a cheaper alternative it seems sensible. but at the same time i dont want hundreds of gallons on my floor. ultimatejays post was good for me cause i understood what he did and how he did it, so if i was to do one myself i would try and copy that. i then asked you if that stand was sound for these reasons, so if i choose to go ahead with it, everything would be ok. i asked 'cause i wanted the piece of mind from someone who seems to know exactly what hes talking about in this area. and when im unsure, i will sure as hell ask again. sorry you took it the wrong way, just wanna do it right!...

edit* o and the question was based at will the stand there be ok long term with that sort of cross brasing, because like you said in previous posts, its important for the other forces to be accounted for, and you said many people miss this important factor
 
CHOMPERS said:
Actually you did have cross bracing in all of your plywood. If you cut all of your plywood into big X's you would have your cross bracing. Leaving it in one piece doesn't make it weaker, it is stronger. In one piece, it gives bracing in infinite directions in the plane of the plywood.

2x6's when glued do provide bracing but it is minimal in many of the applications of aquariums. For longevity, it is not something to bank on.

Here is a mind exercise: if you build a cube with twelve tooth picks, it won’t be very strong. If you skin it with paper, it will be much stronger. If you skin it with cardboard, the strength is further increased. If you did the same experiment with 2x4’s, you wouldn’t want to stand on the top of the bare cube. If it were skinned with plywood, it would be pretty darn strong.
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I hadn't thought of it in that way, only as the bracing as seperat mitre cut peices, I'm just too linear I guess, lol.
 
Davo, the answer is no. Before you build, get a refresher on that original post and pay attention to the forces involved. The calculations are there and you can plug your numbers in. When you build big, you can't get away with 'dumb luck'. If you need the equations again when you do build, just ask. Know what weight your tank is going to be before copying something someone else did. When in the design phase, imagine your tank built of the weakest possible materials: I like the tooth picks and tissue paper example. If you built your stand scaled down and made of tooth picks and covered with tissue paper, and then held it between your hands under pressure, where would it start to buckle, tear, rip, twist, or deform in anyway.

Here is another mind exercise:
Build a rectangle out of Popsicle sticks pinned together. How much lateral force will the top resist in relation to the bottom (side to side). Next, imagine a triangle built the same way. Triangles are the strongest shapes that you can build with. If the above rectangle is made with two triangles, it will be much stronger than without.

Now imagine UltimateJay's original stand design built out of Popsicle sticks pinned together. Holding it in your hands, how much force will it hold before collapsing sideways? Did you notice that his stand has one lag bolt in each joint? It is essentially pinned together. He also glued it together. I have tested many “stronger than the wood itself” glues and have yet to find one that is stronger than any hardwood. (I have not tested Gorilla Glue.) Glues can make the above statement because soft woods will tear at the surface of the glue. Using your fingernail, you can easily dig out the wood fiber between the rings of softwoods (but not from the heart wood at the center of the tree). Try this with a piece of dry aged softwood. Then ask yourself if you would trust a tank (of the weight of what you wish to support) to this material and glue.

Want a rude awakening? Glue two 2x4’s together at each end at a 90 degree angle with your favorite glue. Do not use fasteners. The next day break them apart to see how strong your glue of choice really is or if you get tearing in the wood fibers.

You can measure this force with a large fish scale and then calculate the moment (eng. term, sorry) force of the glue by multiplying the force on the scale by the distance to the glued joint. Then multiply this by the number of legs that are in your design. If your answer is less than your calculated lateral force, you are guaranteed failure before your tank is even filled. And pinning with a single lag bolt in each joint is not going to help.
 
ah i get the rectangle and triangle bit, and can see incorporating that idea would help. also to use as "skinning", is there a better/stronger substitute than plywood, or in this case, will just the thickness of the plywood be the thing to alter(depending on tank size its holding)? i'll draw some designs and post my ideas before i do it before i go ahead when i get around to it
 
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