300g Saltwater Custom Stand Build

[Mike Thorn]

I'm in the process of constructing a custom 300g salt FOWLR. It's a small tank by MFK standards but I'm doing a few things differently than most might, so I thought I would give back by sharing a few photos and process thoughts. I got a tremendous amount of guidance from Pharaoh's structural analysis thread, some of which I've recalculated here, so for those who love a good OVERKILL CENTRAL, read on.

I was originally planning to do a custom-sized plywood tank, because I have a particularly useful little nook right inside my front door that would house a ~325g volume quite nicely. Quite by accident, I found an acrylic 300 local to me for $450, so I snapped it up. It has some crazing, but it's 3/4" acrylic and overall in good condition, so I think I probably got off with a few dollars saved.

2-year-old for scale...

Empty tank in its prospective space. Final position marked on wall. Former front-of-tank 1" Polycast piece also visible (and for sale, haha)...

A couple initial aesthetic and practical choices are informing the rest of this build:

- I have access and capability to make use of a fairly robust woodworking shop, so I have some tools that will make the more complex parts of the build a little easier.

- Due to the layout of the house, and the height that I want the tank to be seen at, I will be locating the sump (a combo-75+55gal) in the garage, which is on the other side of the wall from the stairs. The door seen behind the tank leads to my small utility closet, through which I will run the overflow and return lines. They will go through the wall behind the tank, under the stairs, through the firewall to the garage, and connect to the sump. This gives me the ability to have a much larger and spacious sump, which will make maintenance and ongoing tinkering (as we all do, just admit it) much easier.

- The flooring in this area is laminate, over a concrete slab, so weight concerns are much reduced. Locating the extra 135gals of sump in another area further reduces the concern. Estimated total weight of the display tank is around 4000lbs, and I'll get into those numbers later.

- I have a robustly energetic 2yo daughter, who spends her days playing around and in the vicinity of the tank.

Largely on that last point, I've done the math and realized that the cost of building a stand that will support a male African elephant vs. the cost of building a stand that will support a measly 4000lbs +/- 20%, is negligible compared to the cost of the rest of the tank (I mean seriously...the heavier lumber will cost me an extra $80, or basically $.003/lb). Given the stability and overall rigidity gained (not to mention peace of mind) it's a no-brainer expense. Chances of a crossbrace weakening and the stand catastrophically failing? Zero.

I drew up some very basic 2D diagrams so I could make a shopping list and cut list.

Since I did a fair amount of 3D modeling and rendering in a past life, I mocked this up in an hour or two as well, accurate to scale and perspective:

So, all that in mind, on to the actual build itself, and a few more details on the construction of the stand that aren't in the diagram above.

To be continued…
(details on lumber choices, and loadbearing calculations)
(details on construction methods, including dovetails and aesthetic)
(details on cost)

 

[Mike Thorn]

Progress, ever slowly...

I'm going to skip over the loadbearing maths for now (suffice to say that a single douglas fir 4x4 post at the height used has an end-load capacity of nearly 18,000lbs) and get straight to construction (blah blah at the end):

10ft 4x4 Douglas Fir, chosen because they're gorgeous and smell like Narnia

Upper and lower stringers marked, and rabbets sketched (more on that below)

Coasters for DAYS

Srsly, I have a huge pile if anyone wants to do something pretty with them

The smaller rabbets, which I used in places where I just need a slip-proof joint and not a shear-resistant joint, I blasted out with the router, which takes about 1/10 the time of chiseling it by hand (even tho I still have to square up the corners by hand)...

And as of today I'm about halfway there with the structurals.

So yeah, it's massively overbuilt, but I'm going to frame in the center holes with plywood so that there will be four little cubbies under the tank, in a sort of scandinavian aesthetic.

I stewed over the design on this for literally weeks (which ended up being weeks longer than I really needed to). I was dead-set on sticking with traditional japanese joinery techniques (like dovetails or locking rabbets), and using NO screws or nails at all. I could have made this work if I'd adapted it closer to the timberframing construction styles that you see in rural areas; these tend to be simple mortise-and-tenon joints with wooden locking pins and corner braces. I would have done this, if I'd had access to some barn beams or larger posts; in the end, I didn't want to spend the time chiseling out 20 mortises and I felt that my joinery skills were probably not up to the finesse level necessary to eliminate shear and flex in these smaller 4x4s.

I ended up just sketching out some simple rabbet joints, which will preserve most of the structural loadbearing strength of the timbers and, since I have a nice straight radial-arm saw, gives me virtually perfectly square joints. You can see the cutouts in the stringers and verticals in the photo above. So far, I've needed a sledge to send the vertical beams home in the joints, which is exactly what I was hoping for.

So, I finally gave in and bought a box of HeadLok timber screws, which are exterior-grade star-drive badass-looking things that are supposed to replace 3/8" lag bolts with no predrilling. They also have a big wide flat head, which I liked because it won't ever, ever tear out. The screws are more or less not structural; by the time the stand is complete, with all the interior plywood, it will be fully rigid and have zero shear in any direction, but for the extra $40 the screws cost I will sleep better. Once the stand is done, I'll countersink the screws and plug the holes with some leftover Monkey Pod wood I have in the shop, which will add a nice little pop of dark grainy texture in contrast with the light and clear Fir.

Once the frame is boxed in, I'll go pick up some 1/2" or 5/8" birch plywood and clad the back of the stand, the top where the aquarium will sit, and the inner cubes, while leaving the beams exposed wherever possible.

Total cost so far is approximately $160. The 10-ft 4x4's cost approximately $12 each and the box of HeadLoks was $40. The ply will be around $40/sheet and I'll need 2 sheets. Haven't decided how to finish it yet; I'm leaning towards either Waterlox, or a simple varnish+beeswax (because this).

 

[Zex Marquis]

Looking good so far

 

[Thomas18]

Cant wait to see more, my dad wants to do a very simular build in his front enterance but south americans rather then saltwater.

 

[nzafi]

Never built a stand but I will need to, so I am doing lots of research. I thought I read somewhere that 2x4s are better than 4x4s because of how they are made so it is better to use those. Is that complete crap?

 

[Mike Thorn]

N nzafi Yes and no. The argument is that since 4x4's are typically cut from the weaker heartwood center of the log (which you can easily see in half of the pile I posted above), compared to 2x4's which are typically cut outside of that zone, you'll intrinsically get a stronger timber with the 2x4's, and double them where necessary.

I chose not to do that for a couple reasons - the endload capacity of a southern larch fir 4x4 at 30" tall is around 17,000 lbs, optimally (no idea what the reduction is for heartwood, but let's assume it's not more than 50%, haha). Also, it looks vastly prettier than pine 2x4's so I knew I could play with having some of the beams exposed. Also, it's just a nicer piece of lumber to work with. Feels more manly or something. I don't know, lol.

By contrast, the same length of southern pine 2x4 has an endload capacity of around 4300lbs, or when doubled up, around 8300lbs (according to this calculator, which I used for this stand build). So, even with a softer center-core 4x4, you're probably still way ahead in terms of loadbearing capacity.

You're also way behind in terms of cost; like I said, for this tank I've spent around $140 in lumber; you could have done the same size stand, even with doubled 2x4's, for probably half the cost (assuming you use standard 3" coarse-thread screws for mating the 2x4s and not more expensive exterior decking screws).

Had I planned on sheathing the whole thing and never ever seeing it, I probably would have opted for 2x6's or something along those lines and split the difference between cost and load capacity.

On another note, I also seriously considered using 2x6's and building a simple box-joint bench-style stand like this one (in the end it was a cost and aesthetic choice for me). I'm sure that even an 8ft stand, built in the box-joint style with 2x6's, would have a low enough deflection that you could get away without a center brace. That would look incredible (I calculated the deflection of my 4x4-style stand under 4000lbs load and determined it's some ridiculously small number, like 5-thou, even with only two longways supports).

 

[nzafi]

I am planning to a 8x4 plywood tank and wanted to build the stand myself. I was thinking of just doing something like what joey had.

That stand should be easy to do as I am not a handy person and half of what you wrote in your email might as well be chinese to me Utlimately, I want something simple and extremely sturdy that will also allow easy access to a large sump underneath. I am not concerned about looks because I plan on wrapping the stand is something really nice as I am planning for this to be a show tank and in my family room.

 

[Mike Thorn]

Joey's done a couple big tanks, with success, so I'd trust his work. I have a strong tendency to over-engineer my work, which isn't necessarily a bad thing but is not always a good thing either, haha.

If you're planning an 8x4, you're already ahead, because - I'm guessing - you're only going 24" deep or so, and thus the weight of the tank will be spread over a much wider surface area, which means that you don't need such massive loadbearing capability in your upright beams.

In other words, what Joey did up there should serve you just fine!

 

[nzafi]

I am planning to actually do 36in tall tank but probably only 30in of water. The other challenge is I was thinking of doing a stand that is about 42in tall. I want plenty of space for comfort. Let's me have a 24in tall sump with probably 15-16in of room.

 

[tlindsey]

I am planning to actually do 36in tall tank but probably only 30in of water. The other challenge is I was thinking of doing a stand that is about 42in tall. I want plenty of space for comfort. Let's me have a 24in tall sump with probably 15-16in of room.

Purchase a inexpensive Mitre Saw if you are going to cut 2×4 believe me you won't ever regret buying it. Ryobi was the one I purchased for my stand build. Remember general rule measure twice and cut once. I also like to add that I personally was hesitant at first on building a srand for my 180 gallon. I am so proud of myself everytime I look at the aquarium on the stand.