Plywood stand joint questions

[EvMiBo]

I've build two stands for aquariums, one made from plywood and the other from 2x4's and then skinned. Anyways, on the plywood build I basically connected two pieces of plywood at a 90degree angle, screwed and glued corners with and then added an inside corner vertical support (glued in). That was for a 50g build. But, this one is for a 150g build... I want it to be as strong as possible but I also want to keep the construction somewhat basic. I've thought about mortise and tenon joints some but with 3/4" or 1" ply it might be kind of difficult with limited space. What 90 degree joints are recommended for ply builds? I was thinking something along these lines (attached), does anyone see any issues with this? It's like a mortise and tenon but one side of the mortise is left open, meanwhile it is still glued and screwed but this adds extra support. Would you recommend something else?

Also, fwiw, I've seen people using pocket joints and it's my understanding that these are primarilly used for light load joints, such at cabinet doors, etc... I'm looking for something a bit stronger.

 

[Eud]

I used number 20 biscuits, 3/4" plywood, and no internal corner lumber on mine for a 75.

As long as you're carrying the weight of the tank and water straight to the floor through pieces of plywood in compression you don't really need to worry about if your joints are strong or not. The joint just holds the box together. It doesn't even need to prevent it from racking because you have plywood on all of the sides that prevent the stand from falling over in that direction if you use continuous pieces of plywood and not strips held together with screws.

 

[BengalReefer]

What you're proposing is basically a series of alternating lap joints. This could be done, as long as you made the joints at least 3" wide. Honestly though, using pocket holes will be plenty strong enough. Pocket holes are actually quite strong, placed about every six inches, even stronger than standard glue and screw as they have a better hold on the material.

Also, you should realize that the strength of the joint only needs to prevent racking (twisting or tilting of the cabinet) and does not actually hold the weight of the aquarium. The weight is all pushing down and being supported straight down by the plywood itself. The corners jut need to be strong enough to not let the stand twist if you bump it from the side.

In order to prevent racking and make that joint strong, all you really need to do is to either screw in some triangular gussets in the corners or run 4" bracing along the top (like a euro braced tank).

Also, on a 150, I would strongly consider at least a vertical brace in the center to held distribute weight.

 

[BengalReefer]

Oh, just FYI, I worked in a high end custom cabinet shop for several years, hence my recommendations.

Also, to help reduce the amount of moisture the plywood is exposed to, I would strongly recommend sealing all the edges inside the stand with silicone.

 

[EvMiBo]

I used number 20 biscuits, 3/4" plywood, and no internal corner lumber on mine for a 75.

As long as you're carrying the weight of the tank and water straight to the floor through pieces of plywood in compression you don't really need to worry about if your joints are strong or not. The joint just holds the box together. It doesn't even need to prevent it from racking because you have plywood on all of the sides that prevent the stand from falling over in that direction if you use continuous pieces of plywood and not strips held together with screws.

Unfortunately I don't have a biscuit joiner, though as I'm getting into furniture making it seems like something I'll have to get eventually. That being said it will have to wait for now, thanks for the advice.

What you're proposing is basically a series of alternating lap joints. This could be done, as long as you made the joints at least 3" wide. Honestly though, using pocket holes will be plenty strong enough. Pocket holes are actually quite strong, placed about every six inches, even stronger than standard glue and screw as they have a better hold on the material.

Also, you should realize that the strength of the joint only needs to prevent racking (twisting or tilting of the cabinet) and does not actually hold the weight of the aquarium. The weight is all pushing down and being supported straight down by the plywood itself. The corners jut need to be strong enough to not let the stand twist if you bump it from the side.

In order to prevent racking and make that joint strong, all you really need to do is to either screw in some triangular gussets in the corners or run 4" bracing along the top (like a euro braced tank).

Also, on a 150, I would strongly consider at least a vertical brace in the center to held distribute weight.

Thanks for the helpful post Bengal. I've attached an image asking you a question about a minimum of 3" in the lap joints. I assume you meant "a", but just want to make sure. I like to paint a picture in my head and on paper and/or computer so I know exactly what needs to be accomplished!

Maybe I could use a combination of the proposed lap joint and pocket joints, maybe over kill though as you mentioned it's basically their to prevent racking.

euro-bracing the top with spare wood sounds good as well.

if you don't mind, could you explain the vertical brace some more? should this also be from top to bottom (the same length vertically as the plywood itself)? I should be able to put a couple of these in..

thanks for the help guys.

 

[BengalReefer]

"A" is correct, they should be at least 3" vertically (so there is enough plywood in each tab to support itself well). Lap joints with pocket screws would work just fine. When it comes to stuff like this, overbuilding is good peace of mind

As for the vertical bracing, I'm assuming it's a standard 150 that is six feet long... For that length, I would recommend at least one vertical support in the middle to both help support the weight and to keep the front and back from bowing out. The easiest way would be to put a full piece of plywood parallel to the sides right in the middle, running top to bottom and front to back. This however cuts your sump area in half.

How are you planning to make the front and back of your stand? Are you making the back a full solid piece, or leaving some of it open? Do you plan on having doors on the front, if so how many and how big? These will dictate how you can add bracing, and also affects the strength of the plywood stand... Part of the reason so many people use 2x4's is because they can hold the weight using limited space, leaving lots of room for large openings.

 

[BengalReefer]

If you can give me a more detailed idea of how you want to build your stand, what you want to have included in it, I will gladly sketch something up on the computer for you...

 

[EvMiBo]

"A" is correct, they should be at least 3" vertically (so there is enough plywood in each tab to support itself well). Lap joints with pocket screws would work just fine. When it comes to stuff like this, overbuilding is good peace of mind

As for the vertical bracing, I'm assuming it's a standard 150 that is six feet long... For that length, I would recommend at least one vertical support in the middle to both help support the weight and to keep the front and back from bowing out. The easiest way would be to put a full piece of plywood parallel to the sides right in the middle, running top to bottom and front to back. This however cuts your sump area in half.

How are you planning to make the front and back of your stand? Are you making the back a full solid piece, or leaving some of it open? Do you plan on having doors on the front, if so how many and how big? These will dictate how you can add bracing, and also affects the strength of the plywood stand... Part of the reason so many people use 2x4's is because they can hold the weight using limited space, leaving lots of room for large openings.

I should have mentioned this earlier, but it's actually a 150g High. 48"L x 24"D x 30"H. The tank will be a "peninsula" style tank so having access to both sides is preferred. I'm thinking about a 30" wide x 28" high openings on each side (where doors will be). Also, the overall height of the stand is probably going to be about 38-40" tall. Would you recommend 1" ply over 3/4" for a build like this? Do you think I need more vertical support for something like this?

Edit: I've started a google sketchup but won't be able to finish it until later tonight or tomorrow. I work nights right now so we'll see. Basically I want the footprint ~24" x 54" (54" for some room for overflow plumbing from glass-holes.com, return plumbing, mp40's etc). About 39" tall and I've already mentioned the openings for doors. Also, one final thing, I'll be cutting out holes in a solid piece of ply for the two larger sides, instead of cutting each strip (hope that makes sense!).

Thanks

 

[BengalReefer]

Here's a brief sketchup... of course you would add all the trim and stuff over it. Should give you an idea though.

http://sketchup.google.com/3dwarehouse/details?mid=ec36004ff5c1c8d22b5960c151ab0bc1

 

[EvMiBo]

Thanks for taking the time to make that Bengal. I believe I will do something just like that, I actually like the idea of shelves within the stand. I'm sure they will add some support too. Do you think I should still be adding some vertical supports in there as well? I kind of already intended to do vertical corner supports, which I could make the same length as the outer ply pieces..

 

[BengalReefer]

Some vertical 2x2's in the corners would certainly be nice, no need for full blown 2x4's though. The shelves I think are handy for storage of filters and other dry goods, as well as the option of mounting your power strips to the under sides of them so they are off the floor away from spills. Plus they add some good support around the door opening.

Also, just a thought, I know most people put traditional hinged doors on their stands but personally I would rather keep the amount of metal inside to a minimum. I would consider mounting wooden brackets to the inside of the door and frame so that you have one single door that you place on and slide down into the brackets. This way the entire door can be lifted off and set aside, giving maximum acess.

If you want to go the traditionally hinged route, I suggest you make sure to get hinges that will allow you to open the doors at least 120 degrees. Nothing more irritating than trying to acess a cabinet and having the doors sticking you in the side cause try won't open past 90...

 

[EvMiBo]

Also, just a thought, I know most people put traditional hinged doors on their stands but personally I would rather keep the amount of metal inside to a minimum. I would consider mounting wooden brackets to the inside of the door and frame so that you have one single door that you place on and slide down into the brackets. This way the entire door can be lifted off and set aside, giving maximum acess.

I'm interested but I'm having a bit of trouble understanding what you're suggesting for the wooden bracket piece.

 

[BengalReefer]

I'm at work now, but I will sketch up a quick thing later to show you what I mean.

 

[EvMiBo]

Again, I appreciate all of the help!!

 

[BengalReefer]

No problem! I just downloaded sketchup a week ago, so I've been finding excuses to play with it. Plus I've been learning so much from people on here about this hobby that the least I can do is help others with the parts of it I do know

 

[BengalReefer]

Ok, here, take a look at this:

http://sketchup.google.com/3dwarehouse/details?mid=1c2f1fadc243d8fb2b5960c151ab0bc1

The red blocks are secured to the inside of the stand. The blue and green blocks are secured to the inside of the door. The black part of the door sits flush inside the cutout, while the molding attached to it covers the seam and sits on the outside of the cabinet. The green block matched up with the red block and the blue one sits behind and over the red block, this is what holds the door in.

The key is where the black part of the door is shorter than the opening. This is the same distance (or ideally like an 1/4" more) as how far the blue block hangs over the edge of the red one. So to take the door off, you lift it up until the blue block clears the red one, then pull the door out and the whole thing comes off. To replace it, reverse... place the door in as high as it fits, then slide it down so that the blue blocks slide over the red ones.

 

[EvMiBo]

interesting idea. took me a couple of takes but I see what you're saying now. I can see myself knocking my head on a red piece sooner or later but I still like the idea.

 

[EvMiBo]

A 1/2" piece of ply would rest on the 1x4's on the bottom (all inside of the ply shell). I would include the shelves within the stand but they're not "sketched" yet because I want to be sure my 40g breeder sump would work well with them.

How do you get the 3D view that you've linked?

Also, what do you think about a small door/opening on the left side so I could have easier access to drygoods, etc?? Would this compromise the structures strength?

 

[BengalReefer]

Yeah, the red blocks are a bit of a hazard, but the trade off is you have one single door that completely removes. Positives and negatives to either way you do it.

Since the 40 breeder is 36" long, I might consider sliding it all the way to the left inside. Then you can put a small shelf or just a brace high enough above it so you have easy access to the sump. That way the sump wouldn't stick into the right side at all, and you could make a couple shelves there for all your storage. Plus, you could add a door on the end of the peninsula that opens up directly to all of those shelves.

If you wanted to do a door on the left side, depending on how big it is I would recommend adding another 2x2 support to the right of it, as you would be starting to lose some of the integrity of the plywood with so much of that side being opened

That 3D view shows up because I actually uploaded the drawings to 3dwarehouse. There should also be a link so you can download it and open the drawing in sketchup on your computer.

 

[EvMiBo]

Actually, I really like your suggestion by pushing the 40 breeder all the way to the left, this will allow it to be closer to the bulkheads and ultimately make plumbing less of a headache...

I've added the new opening where the shelving will be for dry goods, etc. I also added a picture explaining that the new vertical piece there is 6" (on the small plywood panel), should be strong enough, no?

Is there anything else you think I need to make it stronger, or will it be strong enough?

Thanks again.