Stand Top shorter than tank - safe or no?

[swffan]

I have a steel stand and the top is 1/4 to 1/2 inch (closer to 1/4" mark) short on all sides compared to the bottom of the glass tank frame. Is it safe to just put a piece of 3/4" plywood on top and call it a day or no?

[LCDRDATA]

I have a steel stand and the top is 1/4 to 1/2 inch (closer to 1/4" mark) short on all sides compared to the bottom of the glass tank frame. Is it safe to just put a piece of 3/4" plywood on top and call it a day or no?

Assuming the plywood dimensions are equal to or slightly greater than those of your tank, and both are centered on the stand, you should be fine - you're really just trying to ensure the weight gets distributed evenly.

[davelin315]

Depends on the tank's construction a bit, but in general a glass tank is supported only on the edges while acrylic distributes the weight evenly across the bottom. In short that would mean you are taking a risk with your tank since the edges would only be as strong as the sheet of plywood but that's an assumption based on the old rule of thumb. Now that glass tnks are being constructed similarly to acrylic I don't know if the old rules apply (lack of trim has set some of these tanks apart). Does your tank have a base lifting the glass off the surface?

[swffan]

The tanks plastic bottom frame does keep the glass lifted by at least a 1/4". The tank is a new Aqueon tank not a custom made tank. The piece of plywood that its sitting on now is a good inch longer on all sides too. The tank is only 40g so its not a big tank at all, but I'm just paranoid (maybe for no reason).

[John]

Tank is supported by plastic trim...

 

My concern is how the plywood is attached to the steel stand? Don't want the plywood to shift on the steel stand nor the tank to shift on the plywood....

[Origami]

I have a steel stand and the top is 1/4 to 1/2 inch (closer to 1/4" mark) short on all sides compared to the bottom of the glass tank frame. Is it safe to just put a piece of 3/4" plywood on top and call it a day or no?

Chad can probably run the analysis, but a 1/4" cantilever using 3/4" plywood will be fine, I'm sure.

[Coral Hind]

With 3/4" ply you would get no deflection that would cause an issue.

[extreme_tooth_decay]

Chad can probably run the analysis, but a 1/4" cantilever using 3/4" plywood will be fine, I'm sure.

 

+1. Not a problem.

[Chad]

Chad can probably run the analysis, but a 1/4" cantilever using 3/4" plywood will be fine, I'm sure.

 

lol.

 

While yes, I could there isn't any need here, it'll be fine

[Origami]

I think that the limit would more than likely be shear strength than deflection. I wonder how much force it would take to shear regular 3/4" birch plywood? I suspect it would be "a helluva lot of force." Especially when you consider it would be distributed across probably 12 linear feet (in a 120, for example).

[Chad]

If my memory serves (and it might not), I think shear strength in ply would be somewhere around 8,000 psi... (compressive strength in a 2x4 is 12,000 psi) ...so that's a REALLY big number.

[davelin315]

I wouldn't trust it myself... if you've cut the plywood and it gets exposed to water, it'll likely start to warp and come apart at the edges that are supporting it. Figure a 40 gallon tank is around 300-400 lbs and all of the weight is going on the plastic trim. If your ply gets a little bit wet and degrades then it could feasibly collapse down at the corner and then your whole tank could either slide right off the edge or crack from dropping that 1" down to the steel stand. I can't explain it in terms of shear and deflection (tried to look up exactly what shear meant and after seeing the first few Es, Vs, and fractions I lost interest/ability to see what it was... but, that said, I would be worried about the ability of the plywood to hold the tank up given how the weight is distributed across the stand. Of course, my explanation is more of a "well, this doohickey goes here and that doohickey goes there" type as compared to the scientific explanations by those that understand that stuff, but, just sayin'...

[Chad]

^even water degraded, I think ply would be fine. MDF or particle board could be suspect water degraded, but 1/4" of material with a glass tank, which is realistically supported around all the edges, I think it would still be fine. The mode of failure on a compressive load with a little bit of shear would require literally TONS of force per square inch and even then the failure mode just isn't dramatic. I wouldn't sweat it at all.

[countryboy]

I had a tank set up like that for years with 3/4 plywood and never had a issue. Go for it you won't have a problem

[Origami]

Plywood's fine. It's not like MDF or particle board. Exterior grade glues and perpendicular alignment of grain will keep it together. If you're concerned, paint it and seal the edges. Plywood is incredibly strong and dimensionally stable - much more so than natural boards.I have a book around here somewhere about how to make a plywood boat. I even had plans at one point that used plywood as the structural backing for an in-ground vinyl-lined pool. Those are both very challenging environmental settings. It's also used under the roofs of most of our homes as well as behind the siding of a good number of homes built around here. If it were that sensitive to moisture, you can be sure it wouldn't be approved for use in these applications. If you're really, really concerned, use a marine grade plywood. (But that's overkill. You'll be fine with the stuff that's sold at HD or Lowe's.)

[Coral Hind]

3/4" plywood is extremely strong and being its only 1/4" short I don't see why it would be an issue. You could paint it if you think moisture might hurt it.