Charlutz
Members
In my presentation on standbuilding at February’s meeting, I forgot to cover one thing I had in my notes – span lengths. The stand I built at the meeting was the first small tank stand I’ve done. Usually, I build stands for larger tanks, 4-8 footers, or multi-tank ranks. For those stands, I use 2x4’s instead of the 1x3 that I used to build the 20L/29G stand.
The question is how long can the span be between vertical posts on a stand. Or, when do you need a center post to support the weight so that the top rail supporting the tank does not bend or bow down under the weight of the tank. This bowing is called “deflection.â€
I know from my real world experience that with 2x4’s you can support a 4’ tank like a 75g or 90g without a center post. I also know that one center post on my 7’ tank has worked fine. In my internet travels, I “met†an engineer on the reef forums who also is a stand builder and was able to run deflection calculations. He calculated that when using 2x wood, you could do a 4 foot span with 2x4, a 6 foot span with 2x6 and an 8 foot span with 2x8 and have acceptably minimal levels of deflection for coventional sized tanks. Obviously if you had a very tall or deep (front to back) tank it would be much heavier than a standard sized tank and owuld need more support. But for most conventional sized tanks, a maximum span length is useful if you want to build a stand with no center posts for aesthetics, or if your sump configuration needed the extra space, etc. I call it the “2 by rule.†The 1x3 is nice for the smaller tanks, say under 40g, because it is nice and light. 2x4's are not much more expensive, $1.93 each vs. $1.57 for the 1x3.
Using a 2x8 severely limits your space below the top tank though. Another approach is to build what I think is called a “micro lam†or laminated beam. Instead of using a single 2x8, you can make a sandwich of two 2x4’s with a layer of plywood in between. The three beams glued together are much stronger than a single beam. Remember when we talked about the vertical strength of plywood because of the multiply, cross grain construction? This is where it is useful.
The question is how long can the span be between vertical posts on a stand. Or, when do you need a center post to support the weight so that the top rail supporting the tank does not bend or bow down under the weight of the tank. This bowing is called “deflection.â€
I know from my real world experience that with 2x4’s you can support a 4’ tank like a 75g or 90g without a center post. I also know that one center post on my 7’ tank has worked fine. In my internet travels, I “met†an engineer on the reef forums who also is a stand builder and was able to run deflection calculations. He calculated that when using 2x wood, you could do a 4 foot span with 2x4, a 6 foot span with 2x6 and an 8 foot span with 2x8 and have acceptably minimal levels of deflection for coventional sized tanks. Obviously if you had a very tall or deep (front to back) tank it would be much heavier than a standard sized tank and owuld need more support. But for most conventional sized tanks, a maximum span length is useful if you want to build a stand with no center posts for aesthetics, or if your sump configuration needed the extra space, etc. I call it the “2 by rule.†The 1x3 is nice for the smaller tanks, say under 40g, because it is nice and light. 2x4's are not much more expensive, $1.93 each vs. $1.57 for the 1x3.
Using a 2x8 severely limits your space below the top tank though. Another approach is to build what I think is called a “micro lam†or laminated beam. Instead of using a single 2x8, you can make a sandwich of two 2x4’s with a layer of plywood in between. The three beams glued together are much stronger than a single beam. Remember when we talked about the vertical strength of plywood because of the multiply, cross grain construction? This is where it is useful.
