Kessil

PSA cheap 2020 Aluminum extrusion on CL

Yes/no. In general yes this is absolutely could be used for an aquarium stand if you engineer it correctly, the real cost starts to add up when you start figuring out how many fasteners you need. That said it's 20x20 mm which is less than 1" in thickness, so unless it's a relatively small aquarium, I wouldn't use it as a stand, you could engineer it to work if you do more than the traditional "4 legs" but might be more trouble than it's worth.
 
@sfsuphysics you think it'll work to build a stand for a Aquarium Masters rimless reef ready tank 48x24x16 (80g)? Or would i need a different size? I have no experience with aluminum stands but love the low profile it offers and want to get a stand for my future fragtank.
 
Here's the thing, legs made out of this stuff absolutely can hold the weight, but that's where they're strongest is compression, however the deflection of horizontal pieces is something to be worried about.

If it were me and I felt compelled to do it, I would do a 6 leg design, with a top platform that attaches to all the legs. and then a bottom platform to prevent the legs from splaying outward, and probably some bars along the back and sides at the midlevel just to tighten everything up. Would also attach a sheet of ply to the top and back to prevent any twisting or racking.

As for fasteners and where to attach, yeah I dunno know, it's a lot of planning to do that I don't have the time to run through (because it's not mine :D) Could you do it, yeah. But with caution, you basically have aluminum that's about 3/4" wide.

Honestly if you were really intrigued about doing something, I would make something a bit less structural first, like a light rack or something just to get a feel for the material and the fasteners and how they work.
 
I've given this some thought in the past, although on a larger scale. It's always come down to:
Increased geometry helps with stiffness faster than material changes.
It works better with a sheet on the top AND bottom (think sandwich composite, aircraft wing, or even I-beam) but few people are going to buy aluminum plate instead of plywood. Once you have a couple sheets of plywood involved it's easier and cheaper to make the rest out of dimensional lumber.
I have access to welders, and when things get big steel is a lot cheaper than aluminum, and of course has stiffness benefits.

As suggested in the OP this would be great for someone looking to frame up a canopy, light brackets, etc. I use a lot of this stuff at work, but there's a reason you don't see many aquarium stands made from it.

I have considered incorporating this into a tank stand in the future, but it would probably be the 3" x 1" variety, and done so specifically because I want slots I can bolt in to on the front and have a geometry in mind that is not conducive with wood.
 
JCC never thought about the sandwich technique, you basically make a torsion box with aluminum instead of a wood grid inlay.

I did think about making my stand with this, had it "engineered" where every attachment point was taken into account, the loads/stresses, and then I looked at the price... and figured I could do it for less than 1/10th the cost from wood plus if I need wiggle room I could do that by cutting the wood in some way. Probably the real reason you don't see many stands made out of this stuff. Plus I have to imagine steel tubing is cheaper as well you just need to be skilled with welding.
 
Torsion box is more or less the explanation. The stand I made for my 8' 300 gallon was that way. 2x4 along the length with 2 layers of 3/4" plywood top and bottom. Slightly overkill perhaps, but it let me put legs in just the 4 corners with a large unsupported span in between. I could have done this with 2x8s or 2x10s on the Rocket Engineer design, but I needed opening height more than internal height. I was also able to pre-stress the ends down (support in the center) when I glued on the top/bottom so that the stand was closer to flat when it was fully loaded.

The last stand for my larger reef was similar, but 1/8" steel plate top and bottom, and a silly amount of welding. I had some very specific requirements. I wanted the base at the same height as my existing tank next to it, needed clearance under to roll the sump in and out, and only wanted 4 legs. I wasn't willing to give up the extra 1" of space, so the legs ended up spaced as close to the Bessel points as other constraints allowed instead of at ends of the 126" span.
 
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