DIY stand 72" long without center support

[Aquaskape]

Hi all, I know there are many threads similar but didn't find one similar to what I wanted to do. I want to create a stand for a rimless 72"x24"x24" tank that is 19mm thick. I wanted to have a clean open look and not have a brace in the center of the stand. I was thinking of using 4x4 posts (four on the left and right) and then sitting four 4x4 posts running horizontally on them and then having 3/4" plywood on top. Sort of a bench furniture style. Is that enough to support the weight of the tank that is roughly 165gallons? Or should four 2x6s be used instead of the 4x4s for the horizontal beams?

 

[RocketEngineer]

Don’t use 4X4s. Anywhere. Their thickness causes the centers to dry unevenly which causes them to twist and/or split over time.
1) A pair of 2X4s is a much better option for legs. Placed in an “L” shape, they are also much stiffer.
2) You can get away with no center brace but you need a top beam that is tall enough not to deflect significantly under the weight of the tank. I’ve been recommending a 2X8 for that width span for many years and never had anyone report on issues. In theory, a 2X6 might do the job but that is a lot more dependent on wood quality which can be harder to quantify.

 

[Aquaskape]

Thanks, so are you saying that the I should do 2x4 for the legs and sandwich them with 2x8 beams that run across the length? If so, would it be three 2x4 legs on each side, with 6 beams, or six 2x4 legs on each side and 3 beams?

 

[Valhalla Reefer]

Thanks, so are you saying that the I should do 2x4 for the legs and sandwich them with 2x8 beams that run across the length? If so, would it be three 2x4 legs on each side, with 6 beams, or six 2x4 legs on each side and 3 beams?

I built a stand for that exact same tank size...and built as RocketEngineer described using 2x8 D. Fir beams for the spans. Here’s a few pics that I could find, if this helps you for the legs.
(Painted with Appliance Epoxy)
Cheers

 

[RocketEngineer]

The pictures Val Halla posted show it quite well. Each corner gets two legs positioned in an L as the picture shows. The beams sit on top of the legs. Only two beams are needed, one in front, one in back. The ends are normally the same size as the larger beams to make it easier to construct but in theory, the end beams could be smaller as long as the end legs were made longer to compensate.

 

[redfishbluefish]

@RocketEngineer is being way too modest (or he doesn't wish to divulge his age :oops:), because years ago he came up with a DIY design that has since been used by thousands of DIY'ers.....me included. Here is his original design using dimensional lumber....no center brace needed:

And here is my five foot stand (before skinning with plywood):

So please, with confidence, believe @RocketEngineer .....he knows what he's talking about! :cool:

 

[Aquaskape]

Thanks guys, exactly what I needed to know!

 

[RocketEngineer]

To be clear, I didn’t come up with the design. I simply posted a colored diagram and the calculations for the cut list. Sure, I did some math in there but nothing THAT hard. And I’m not too old. :p:)

 

[Aquaskape]

Seems like you're a legend here when it comes to stands @RocketEngineer , almost every thread mentions your name. I did have one last question, if I had additional beams, would I be able to get away with reducing them to 2x6s?

 

[don_chuwish]

I built a stand for that exact same tank size...and built as RocketEngineer described using 2x8 D. Fir beams for the spans. Here’s a few pics that I could find, if this helps you for the legs.
(Painted with Appliance Epoxy)
Cheers

That thing is perfect!

 

[don_chuwish]

Thanks guys, exactly what I needed to know!

Be sure to get kiln dried lumber and be very choosy to get the straightest ones possible - no bowing, cupping or crown. Minimal knots - small and tight if any. You might have to go through the whole pile to find the gems.

 

[RocketEngineer]

Seems like you're a legend here when it comes to stands @RocketEngineer , almost every thread mentions your name. I did have one last question, if I had additional beams, would I be able to get away with reducing them to 2x6s?

In theory. You do need to make sure there is a leg supporting the central beam, screws alone won’t gain you much.

 

[don_chuwish]

Beam depth is much more important than beam thickness. I've always liked this reference (sorry, don't remember the source!):
+++
What you need to do to answer your question is to look at the term, I, which is the "Moment of Inertia" of the beam, and is dependent on the SHAPE of the beam.

For a solid rectangular beam, I = (b*h*h*h)/12 or, the width of the beam times the cube of it's height over 12.

So, all things being equal, the deflection of a 2X4 and a 2X6 under a given uniformly distributed load will be proportional to the calclulated values for I for the 2X4 and the 2X6. And, since the width of the beams is going to be the same (1 1/2 inches) in both cases, the ratio of the beam deflections will be the same as the ratio of the cube of their heights:

or (5 1/2)*(5 1/2)*(5 1/2) / (3 1/2)*(3 1/2)*(3 1/2) = 166.4/42.9 = 3.88

So, the 2X6 will be about 4 times as rigid as the 2X4, or, the 2X4 will deflect about 4 times as much as the 2X6.
+++

 

[LBReefer]

I feel way smarter for having read this thread. And I never new where the rocketengineer design came from.

I'm also feeling more confident in my stand build, sans center brace.

 

[Gtinnel]

I built my stand for my 6ft 125 using RocketEngineers model and I do not have a center brace on my stand. I did add legs on either side of the front beam to 1 ft in on both sides (basically solid wood for the first and last foot) so I have a 4 ft opening in the center and my stand is rock solid. I would be willing to put several times the weight of my 125 on it. I did build it out of 2x6s.

 

[zoytoy]

Just wanted to say thanks to you guys, I'm going to be building a stand in the next month or so and that graphic is exactly what I needed.

Thanks!

 

[a4edwin]

@RocketEngineer is being way too modest (or he doesn't wish to divulge his age :oops:), because years ago he came up with a DIY design that has since been used by thousands of DIY'ers.....me included. Here is his original design using dimensional lumber....no center brace needed:

And here is my five foot stand (before skinning with plywood):

So please, with confidence, believe @RocketEngineer .....he knows what he's talking about! :cool:

I think 95% of the diy stands use @rocketengineers I know I did. he made it so easy. You can geek out now too it’s like a celebrity posted on your thread! Lol

 

[Aquaskape]

Thanks everyone, thread was very informative!

 

[Trever]

Are wood stands the way to go though?

 

[Ratherbeflyen]

I'm not sure where the belief comes from that a center brace is needed at all.