8020 for tank stand, how large?

[sfsuphysics]

I've seen quite a few old posts involving 8020, unfortunately they are all like this one asking if it's possible (I know it's possible), I'm just curious which dimensions need to be used. I've seen a few BRS videos showing off Vertex stands, of course no details, best I could gauge is that they used 25mm or maybe 30mm stuff, but this is just from eyeballing. I've seen a youtube video of a "Primo Reef" guy who sells the stuff, and I think he said 45mm (1.75") square tube which seems a little like overkill to me, but then again I don't know which is why this post is up.

Tank is a 200g tank that would fit on 4'x3' of top. I was thinking of building it similar to a wood stand, where the top would have pieces that were thicker in the direction of weight and thinner in the opposite direction. Just for kicks I designed it (not CAD) out of 25x50mm pieces (essentially 1x2).

Anyways, I realize it's not cheap, $300 just for the aluminum not even counting attachment pieces or additional labor to tap any holes. But seems it would be so much nicer than bulky wood (will be "in wall" so making it out of plywood is out). And wondered if anyone had thoughts to thickness of the stuff, am I being way under strength? am I going overkill?

I have enough 2" steel square tubing that I could do a stand that way, but I don't weld, and have a "tiny" suspicion it's not exactly something I can pick up in a weekend and make a structurally strong stand.

[mcgyvr]

25 or 30mm extrusion can certainly be used..
I use it at work for machine frames,etc.. holding hundreds of pounds quite often..

Its very strong stuff.. Of course one can build a stand out of balsa wood if done properly so its more about the design than anything..

I get all my material from misumi..
I prefer the 30mm..

[sfsuphysics]

well the tank is 200 gallons, so we're looking at thousands of pounds.

Part of my confusion I think is their deflection calculator (at the 8020 site), seems that if your beam is between the uprights (i.e. not how you build a tank stand) the deflection is significantly less than if the upright "posts" are what support the beam. Also when determining the load, if the tank is 2000 pounds with everything (nice round number) is that the value I use? Knowing full well there is another 3 sides that will be supporting the tank, because that 2000 pounds won't be on one beam alone which I have a feel the calculator takes into account.

[mcgyvr]

Originally Posted by sfsuphysics

well the tank is 200 gallons, so we're looking at thousands of pounds.

Part of my confusion I think is their deflection calculator (at the 8020 site), seems that if your beam is between the uprights (i.e. not how you build a tank stand) the deflection is significantly less than if the upright "posts" are what support the beam. Also when determining the load, if the tank is 2000 pounds with everything (nice round number) is that the value I use? Knowing full well there is another 3 sides that will be supporting the tank, because that 2000 pounds won't be on one beam alone which I have a feel the calculator takes into account.

In FEA... Garbage in = garbage out..
The load is equally distributed over the entire stand (or you sure hope it is).. Not just one side..
Hence 2000 is not correct but the calculator is basically useless for what you want to know..

What number do you think its a suitable vs not result for deflection anyways?

If I tell you that you can expect .020" of deflection in your longest member.. What are you going to do with that data? What deflection are you assuming to be acceptable and whats not? see where I'm going here..

Racking via failure of the fastening methods will be the biggest potential failure point.. That calculator does not tell you that at all..

I will say that if you could balance your 2000lbs on just a single piece of 30 standing vertical.. It would sit there all day not breaking a sweat..

[gljjr]

This is IMHO. I'm not an engineer...

I think if you were to use a plywood panel to tightly fit in the T-Slot of the 8020 you can limit the issue of racking significantly. I would probably rabbet the edges of 3/4" plywood to fit in the T-Slot. I would think a 2040-S will hold significant weight when supported from underneath.

[sfsuphysics]

Originally Posted by mcgyvr

In FEA... Garbage in = garbage out..
The load is equally distributed over the entire stand (or you sure hope it is).. Not just one side..
Hence 2000 is not correct but the calculator is basically useless for what you want to know..

What number do you think its a suitable vs not result for deflection anyways?

If I tell you that you can expect .020" of deflection in your longest member.. What are you going to do with that data? What deflection are you assuming to be acceptable and whats not? see where I'm going here..

Never really thought of it, although 0.02" is half a mm and I don't think I would bat an eye at that number.

I will say that if you could balance your 2000lbs on just a single piece of 30 standing vertical.. It would sit there all day not breaking a sweat..

Ok, I can get behind that. Assuming there's flex to the side that makes me worry less about it

[sfsuphysics]

Originally Posted by gljjr

This is IMHO. I'm not an engineer...

I think if you were to use a plywood panel to tightly fit in the T-Slot of the 8020 you can limit the issue of racking significantly. I would probably rabbet the edges of 3/4" plywood to fit in the T-Slot. I would think a 2040-S will hold significant weight when supported from underneath.

Yeah but the allure of using it is to have an open design, have a lot of access from behind/side plus access from front via doors/sliding panels. The top would definitely be "bolted" to a 3/4" piece of ply so racking in that direction is not an issue, but then that's not the direction things would fall

Those flat plates they sell seem like a good alternative to stiffen up the vertical structures quite a bit.

Here's an interesting question, given the nature of the beast (salt water, humidity, electricity brimming...) is there any issues with galvanic corrosion given than many of their fasteners are zinc which is in contact with aluminum?

[mcgyvr]

minor surface rust on the fasteners is possible overtime but galvanic corrosion is not an issue..

The stuff is plenty strong.. Hard to screw it up here..
Go 30 or larger and you should be just fine..
This is a good solid reference design..
http://4.bp.blogspot.com/-MTPGWe50vE...0/DSC_0053.JPG

and another.. plenty strong..
had to upload this because it came from another reef site that is somehow banned here..

[sfsuphysics]

Yeah I've seen the long one before, but no information on what it's built out of. Does look like they used the rectangular pieces at the corners, for added strength? Useless? and best as I can figure out with my super awesome paint copy/paste skills that tank is 18 widths of the top tubing tall, which if it's an 18" tall tank makes it 1" material, if it's a 24" tank makes it 1.33" material which doesn't make sense because they don't sell 34mm material (or 35mm)

And both of those kind of go away from my thinking which is to use the rectangular profile from the top bars, to get added thickness but make it thinner in the horizontal direction, similar to how you would build it out of wood. No one would use a 6x6 beam for the top of a tank stand, even the most overkilly of overkill builds.

[mcgyvr]

Originally Posted by sfsuphysics

Yeah I've seen the long one before, but no information on what it's built out of. Does look like they used the rectangular pieces at the corners, for added strength? Useless? and best as I can figure out with my super awesome paint copy/paste skills that tank is 18 widths of the top tubing tall, which if it's an 18" tall tank makes it 1" material, if it's a 24" tank makes it 1.33" material which doesn't make sense because they don't sell 34mm material (or 35mm)

And both of those kind of go away from my thinking which is to use the rectangular profile from the top bars, to get added thickness but make it thinner in the horizontal direction, similar to how you would build it out of wood. No one would use a 6x6 beam for the top of a tank stand, even the most overkilly of overkill builds.

First one uses the cam fasterners..
Second (attached photo) uses the inside corner brackets..
Both look like 30x30 material (one uses the double 30x60 for the verticals)

And you can just use 30x60 for your horizontals at top..(just like wood)

[karimwassef]

Looks slick. Any low cost, high volume sources?

[mcgyvr]

Originally Posted by karimwassef

Looks slick. Any low cost, high volume sources?

I get mine from misumi
That stuff is really never "low cost"..
But its fun has heck to build stuff with.. Its like adult Legos for me
https://us.misumi-ec.com/vona2/mech/...0/M1501000000/

[sfsuphysics]

Originally Posted by karimwassef

Looks slick. Any low cost, high volume sources?

Doubt your project, yeah even your project, would be high enough volume to warrant any discounts. As mentioned it ain't cheap when you compare it to something like wood, or even square steel tubing. But compared to the price of a stand someone else is building then yeah it is reasonable.