Sizing plywood top for DIY stand

[wickette]

I fit tested my 75g DIY Stand today. Used the standard 2x4 frame design. The top panel is 1/2" plywood. The top came out a little smaller than I planned, the plywood top is on 1/4" longer than the tank (so edge of the plywood is 1/8" from the tank).

Is this a problem?

 

[Katrina71]

Pics?

 

[lapin]

If as you say the plywood is bigger than the tank by 1/4" you are fine.

 

[Peace River]

As @Katrina71 mentioned pics usually help and as @lapin said you should be fine based on what you have described. I am curious if you have a rimless tank or a tank with a frame - either way you should be okay but if would be helpful to know where is the contact between the tank and the stand.

 

[Quietman]

If by standard 2x4 frame you mean full 2x4 frame - 4 piece top and bottom with at least 4 legs and the plywood top fully covers/overlap the top frame then there's no issue.

But I would always do a weight test. I even filled a brute can on top of my Red Sea Reefer stand. Never know about internal flaws in wood or hard to see cracks. Any water is too much water to clean off my wood floors...with my wife watching.

 

[wickette]

As @Katrina71 mentioned pics usually help and as @lapin said you should be fine based on what you have described. I am curious if you have a rimless tank or a tank with a frame - either way you should be okay but if would be helpful to know where is the contact between the tank and the stand.

Im not at all worried about the plywood not being supported, What I dont know is, will plywood properties of plywood. (will isplinter/crush if load is placed on the edge.


Anyway, all the questions answered:

It's a braced (not rimless tank), my 2x4 frame a better supported version of the design constantly referenced on reef2reef.

I dont feel 100% confident about my planing abilities so Im using the plywood to ensure the entire surface is flat.


The problem I have is that 4' plywood is too big to use a fence. I wanted a 49.5" wide board, this was my best attempt (one side 49-1/2" the other 49-5/16"


Photos attached, Ive already moved the tank back inside. Plywood needs sanding/painting. Popsickle stick thrown in there for scale

 

[Quietman]

Oh... plywood is very strong...stronger than dimensional lumber actually. And you're not using the 1/4" span to bear weight. And even if you were, 1/4" of half 1/2" plywood could take it. Now the edge should be sealed of course against water damage causing swelling and weakening.

 

[wickette]

Oh... plywood is very strong...stronger than dimensional lumber actually. And you're not using the 1/4" span to bear weight. And even if you were, 1/4" of half 1/2" plywood could take it. Now the edge should be sealed of course against water damage causing swelling and weakening.

Thanks, thats what I thought, needed reassurance.

 

[BZOFIQ]

You're good - don't overthink it.

 

[wickette]

You're good - don't overthink it.

Speaking of over thinking things, (this is a stupid question that doesn't warrant its own post, why don't I want to cut a (rounded) hole in the support plywood so that its only a 4" wide frame/doughnut?

With a full sheet I have to make sure the panel is totally secured to the frame since nothing is supporting the middle. (and Im pretty sure it will still sag eventually with nails/wood glue

 

[TheHarold]

You should be good. Though I personally always make my tops 3/4", and then side panels 1/2". Overkill is good

 

[Quietman]

For framed aquarium, the skin on the sides and top are just for appearance and perhaps to prevent any twisting if the stand gets bumped. A framed aquarium really only needs supported on two ends (yeah, I'd never do that either). So make sure the aquarium is level and you can skip the top skin or go as thin as you want. Do make sure the stand has cross brace or back panel/side panels screwed into prevent twisting. Never mind...i just looked at your stand frame pic - you don't have any twist worries.

 

[wickette]

You should be good. Though I personally always make my tops 3/4", and then side panels 1/2". Overkill is good

Any specific type of wood?

I used fir not pine lumber and plywood. So its almost as strong as 1'' ordinary pine. (but cheaper, lighter, water resistant). Its still way too heavy. And I havent added the cabinet door yet.

Im way too cheap and incompetent to buy hardwoods for anything Im making myself (not that I can tell any of them apart)

 

[foxt]

Speaking of over thinking things, (this is a stupid question that doesn't warrant its own post, why don't I want to cut a (rounded) hole in the support plywood so that its only a 4" wide frame/doughnut?

With a full sheet I have to make sure the panel is totally secured to the frame since nothing is supporting the middle. (and Im pretty sure it will still sag eventually with nails/wood glue

I don't follow - what do you mean by "nothing is supporting the middle"? You have cross braces at the top of the frame, or are they not flush with the rails?

If by "donut", you mean can you just cut a section out of the top panel so that it has a 4" wide border all around the top (no plywood in the middle, under the tank), sure, I guess you could do that, but why would you want to? Weight?

The full panel as you have it now acts as another stabilizer for the entire top, and for the panel itself. By weakening it into a 4" wide perimeter, you lose some of that stabilization and resistance to warping. you could be putting as much as 800 - 900 pounds on top of this thing, which makes it top heavy to begin with, and I'd want as much rigidity as I could get.

As the previous poster mentioned, if you were thinking of cutting the top to a 4" strip to save weight, you could first consider using a thinner panel for the top. That would save weight, but still provide some additional structure.

 

[wickette]

For framed aquarium, the skin on the sides and top are just for appearance and perhaps to prevent any twisting if the stand gets bumped. A framed aquarium really only needs supported on two ends (yeah, I'd never do that either). So make sure the aquarium is level and you can skip the top skin or go as thin as you want. Do make sure the stand has cross brace or back panel/side panels screwed into prevent twisting. Never mind...i just looked at your stand frame pic - you don't have any twist worries.

This is what it looks like right now (from behind),
My top is level, but not totally flat. I went over the top with a sanding block, you can all the paint spots on top are where the frame is beveled down... hence the need for a flat top.

The triangles in the back 1/2" (actually 15/32") plywood as the top, Sides are 11/32" ply, front is 13/32" ply.
All of the plywood is screwed,nailed,and glued on.

~~~from this point on Im just showing off~~~

I did the load calculation on the stand
sheer strength is 17,400 lbs, (was 2k higher before I added those feet)
Tensile strength of each corner is 3,800lbs + whatever the wood glue ,adds (which is somewhere between 100 and 4,000lbs). My house will collapse before the stand does.

I had to add the feet because the tank is going over the main beam of the house, and the floor above the main beam is almost 1/4" higher than the rest of the room. Those middle feet are 1/4" shorter than the sides, so the tank doesnt see-saw

p.s. it looks like crap now because I dont know how to work with plywood, but Ive gotten handy with drywall so I primed stand with killz2, then painted it with matte black paint. Then spackled over the screws and nails like the stand is made of sheet-rock, Then used drywall primer over the spackle (that green is the darkest primer I had on hand)

 

[wickette]

I don't follow - what do you mean by "nothing is supporting the middle"? You have cross braces at the top of the frame, or are they not flush with the rails?

Not flush the 9 middle cross beams are 3" tall, all the edges are standard 3-1/2", I didn't want to risk them pushing up on the trim or down on the floor. I would put insulation foam over them if I keep the top intact.... but extra work.

If by "donut", you mean can you just cut a section out of the top panel so that it has a 4" wide border all around the top (no plywood in the middle, under the tank), sure, I guess you could do that, but why would you want to? Weight?

The stand weighs 120lbs, the sump and tank will add 1200+, the 2lbs saved wont make any difference. I cant move the stand by myself with no panel on op.

Id take out the middle to remove a point of failure. With the sump directly over it, at somepoint in the 1-10 years from now the moisture find a way into that panel, making the plywood swell,droop, fall apart, or more likely mold. If that chunk isnt there, it can't fail, and since the bottom of the tank is elevated, more air can circulate, slowing down moisture buildup.
Also if the silicone in the tanks bottom begins to wear out, it would be a lot easier to detect and diagnose.
....but Im talking out of my butt, these things will probably never come up.

The plywood is unsanded, I just dont want to sand the whole thing =P

The full panel as you have it now acts as another stabilizer for the entire top, and for the panel itself. By weakening it into a 4" wide perimeter, you lose some of that stabilization and resistance to warping. you could be putting as much as 800 - 900 pounds on top of this thing, which makes it top heavy to begin with, and I'd want as much rigidity as I could get.

This is true, if the tank wasn't otherwise skinned keeping the top intact has much more pros than potential cons.

As the previous poster mentioned, if you were thinking of cutting the top to a 4" strip to save weight, you could first consider using a thinner panel for the top. That would save weight, but still provide some additional structure.

I know me, if I took that peice out, in 2 days Id turn it into an extra shelf inside the frame, Ill never save any weight.

 

[touchstone88]

Not flush the 9 middle cross beams are 3" tall, all the edges are standard 3-1/2", I didn't want to risk them pushing up on the trim or down on the floor. I would put insulation foam over them if I keep the top intact.... but extra work.



The stand weighs 120lbs, the sump and tank will add 1200+, the 2lbs saved wont make any difference. I cant move the stand by myself with no panel on op.

Id take out the middle to remove a point of failure. With the sump directly over it, at somepoint in the 1-10 years from now the moisture find a way into that panel, making the plywood swell,droop, fall apart, or more likely mold. If that chunk isnt there, it can't fail, and since the bottom of the tank is elevated, more air can circulate, slowing down moisture buildup.
Also if the silicone in the tanks bottom begins to wear out, it would be a lot easier to detect and diagnose.
....but Im talking out of my ***, these things will probably never come up.

The plywood is unsanded, I just dont want to sand the whole thing =P



This is true, if the tank wasn't otherwise skinned keeping the top intact has much more pros than potential cons.


I know me, if I took that peice out, in 2 days Id turn it into an extra shelf inside the frame, Ill never save any weight.

Thinkin out loud- IMHO you don’t want any type of padding directly under a rimmed tank, that’s begging for unequal weight distribution and uneven force against the rim.

You could always set the tank on top- and the dude is right, mdf board is exponentially stronger than dimensional lumber- fill the tank up and let the stand settle for a week or two. With your corners 1/2” taler than cross braces just means the cross braces are superfluous to supporting the tank (even if they were flush the 2x4stand’s corners bear the brunt). I didn’t even tack my ply top (metal stand) and it’s great.

If I’m tracking alright it sounds fino dayo, you can always sand the edges flush-i’d personally bump up to 1” ply (3/4”) for piece of mind but sounds like you sorted it out, well done!

 

[foxt]

Nice work!

Your concerns about the top are unfounded.

First, the length of your unsupported spans is notthat significant, the panel isn’t going to sag overtime. MDF might, 1/2” plywood won’t. Think about the spans between roof rafters, and the loads involved there. As you point out, there is no load inside the perimeter of the top, just the weight of the panel itself. It won’t sag.

Seal both sides of the panel, and there won’t be any issues related to moisture. If you cut the panel as you suggest, you’ll have the same concern for the cut edges, and will need to seal those as well.

If the tank does spring a leak at the bottom someday, you will know, regardless of whether that top panel is there or not.

A benefit of keeping the top intact that you may not yet realize, it gives you something to attach things to, like lights, power strips, plumbing and wiring, etc.

If it were me, it seems like less work to leaves the panel whole, and more benefit. But, based on the pics of your build, losing that inside chunk of the top won’t cause any structural issues down the road.

 

[touchstone88]

Nice work!

Your concerns about the top are unfounded.

First, the length of your unsupported spans is notthat significant, the panel isn’t going to sag overtime. MDF might, 1/2” plywood won’t. Think about the spans between roof rafters, and the loads involved there. As you point out, there is no load inside the perimeter of the top, just the weight of the panel itself. It won’t sag.

Seal both sides of the panel, and there won’t be any issues related to moisture. If you cut the panel as you suggest, you’ll have the same concern for the cut edges, and will need to seal those as well.

If the tank does spring a leak at the bottom someday, you will know, regardless of whether that top panel is there or not.

A benefit of keeping the top intact that you may not yet realize, it gives you something to attach things to, like lights, power strips, plumbing and wiring, etc.

If it were me, it seems like less work to leaves the panel whole, and more benefit. But, based on the pics of your build, losing that inside chunk of the top won’t cause any structural issues down the road.

a mis-informed post by yours truly who didn’t understand MDF is the garbage beefed up particle board!
:shame:

 

[foxt]

FWIW how would MDF would sag in this application- as it’s denser than ply and equally as effective as the base it rests on-especially if primed.
Though, if you don’t have primer on hand the cost effectivene point diminishes somewhat

Am I mistaken?

Ever see or own one of those shelf units that have MDF shelves and steel supports? Or worse yet, the MDF tank stands? The MDF eventually sags, even if nothing is loading them. Or it swells. I forgot that the OP said he was going to pad those cross braces so that the top panel would be fully supported, perhaps the MDF wouldn't sag then. Still might swell though, no matter how well you try to seal those edges.