top shelf of wire rack - uneven surface

[Zane0]

Hey guys - I'm trying to set a rimless ~10 gallon bow front tank on the top shelf of a wire rack. The rack has very high weight tolerance (https://www.amazon.com/dp/B075TJ7955?) so that isn't going to be a problem. The problem is that the tank extends beyond the shelf, onto the posts, as shown in the pics below, which makes for a very uneven surface. I'm pretty sure a rimless can't just rest on the corners. And I don't think placing a foam pad underneath in attempt to even the surface will be adequate. My best idea right now is to just put a 3/4" piece of plywood on top of the four corners and expect it hold up to possible bowing in the middle - not a very good idea. Thoughts?

 

[Myrtle]

If you put wood on the top, just cut a smaller piece to fit underneath to brace the middle?

 

[Hufsa]

In an abundance of caution (because even a few liters of water is a lot of water once its on the floor), I would personally go for two wood plates in this situation. The lower wood plate would have the corners cut out where the top of the "vertical supports*" are, and be thick enough to go above the point where the verticals end. Then I would place a second plate on top of that, and have it support the entire tank bottom. This would allow me to sleep well at night.
But its possible that the second plate is not strictly needed, as long as the tank glass corners do not touch those vertical supports.
Quite a few modern tank stands have portions of the glass bottom "floating" in the air, this is safe as long as the bottom is not subjected to any point pressure.
(*I dont think vertical supports is the right word, but im not a native speaker nor a shelf-o-logist 😁 I hope its still understandable)

 

[tam]

I agree, I think you'd be fine with a board that spanned the top of the legs. If you want something chunkier look for an offcut of kitchen worktop. You could also either measure the difference in height and infill it either exactly or to raise it above the corners as @Hufsa suggested.

 

[The grumpy one]

I would get a piece of 18mm ply about 25cm bigger than the shelf on all sides. Then I would drill a hole, just over the diameter of the upright, halfway through the ply on all corners. The added advantages to this is: Ply will not slip around on the shelf. It will give you some more triangles of strength to the whole structure.

 

[Zane0]

Thank you for all the feedback everyone! I was toying vaguely around w/ similar kinds of notions but the technical breakdown is very helpful & reassuring.

 

[swyftfeet]

this is pretty easy fix on a piece of ply. just get a piece of ply that is at least double thicker than the rise of the posts off the surface of the rest of shelf, and hog out that distance on the corners from the bottom.
if you do it in a controlled manner you should be able to have it rest on both the rest of the shelf and the tops of the posts evenly. but if you had to err in anyone direction I would err on hoggin out more material on the corners so you dont cause ply seperation or an uneven surface if the shelf settles a bit with weight of the tank added.

you need either a drill press (or a strong hand with a handheld) with a forstner bit or a router with any sort of straight, mortising or rabbeting bit.

https://www.homedepot.com/p/DIABLO-7-8-in-High-Speed-Steel-Forstner-Bit-FB-006/100164336

Router Bits - Freud Tools

Learn how Freud's mortising router bits are precisely the best in quality and performance.

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[Tim Harrison]

I'm sure it's very strong in compression. However, I suspect the tolerance to lateral movement isn't great. If you place a tank on top it could parallelogramm and sheer catastrophically.

 

[Malarky]

I think I would also be cautious about that stand, I have used something very similar as a plant stand. It has plastic clips as shelf height adjusters and all the weight is ultimately focussed on plastic feet (at least for mine). Seems like there are potential points of failure, when investment in something with better weight distrubution might provide more security.