M&T Ok to use for 120 gallon aquarium stand?

[Jim Lischio]

I am planning to build a stand for a 120 gallon reef tank (similar to this one (http://reefcentral.com/forums/showthread.php?s=&threadid=688951&perpage=25&pagenumber=1)). I asked for suggestions on construction techniques over at Woodnet and one that sounded logical was to use M&T. I have not used this joint before, so I was doing some reading, and found a post here that said M&T was not appropriate for supporting a large load that would create a shearing force on the joint. Should I choose a difference joint or just leave more wood at the top of the mortises (I was going to build a homemade slot mortiser and do loose tenons)? I guess this is why the guys over at ReefCentral just use 2X lumber like they are framing a header. ANY help or advice would be GREATLY appreciated.

Jim

[Chris Friesen]

A M&T joint in a strong hardwood can take a lot of force.

If you're worried about it though, you could always run the rails (horizontal pieces) full-length, and put the tenons on the styles (vertical pieces). That way there is no shear force on the tenon.

The M&T joint does a good job resisting racking, which you want in a carcase like the one you linked to. I would also put a full back panel in there to add more racking resistance and because I don't like the look of the 2x4s that are visible with the doors open.

Also, it seems likely that the side panels of that tank are plywood with additional pieces glued on top to make it look like frame-and-panel construction. You can see that the canopy at least was done this way.

[Jim Lischio]

I thought the same thing about the sides (ply with molding applied), but I was hoping to do M&T with some doors on the sides to access equipment/electrical switches. Also, the top will be 3/4" ply, so that might help resist the top of the mortise breaking out?

Jim

Edit: Great suggestion on running the rails full length.

[Bob Aquino]

You can use m&t joints, but they are not necessary. A plywood box structure is adequate to support the tank. Just make sure it cant rack and it will work. 2X material is way overkill as well. The boys at reefcentral generally arent carpenters or cabinetmakers...

[Anchor Sarslow]

Jim,

I have made a lot of tank stands. My suggestion would be to use simple 2 x 4 stud lumber carcase. and lap the cross pieces onto the risers. and face the cabinet with the desired wood and put heavy layers of poly on it.. You plan on making it a reef tank? will you have the tank drilled and use an overflow system for filtration?

the filter system needs to be worked around. You dont often find real nice cabinetry under a tank.. especially a reef tank the will rot the wood fairly quickly with salt creep and spillage. Lap joinery is good enough. You dont need full M n T.

Any tank larger than 120 and I would tell you to double up some parts .. but you dont need to at this point.. I tend to double up on legs personally but I also make tank racks for stores.. sooo... that is just a habit for me.

[Jim Lischio]

I was avoiding using construction grade lumber because I thought there might be a lot of movement as the wood dries...OK, I'll say it, I was afraid of shrinkage! I bought some 8/4 soft maple instead and was thinking it would suitable for strength and it could be left visible (stained to match the rest of the stand).
Yes, it will be a reef tank. It is 1/2" glass eurobraced with an overflow and bottom already drilled. I got the tank used for $100 because the glass has several deep scratches which I am working on polishing out (the things we do for a bargain!).

BTW, the full back will be 1/2 ply to resist racking and hopefully resist bowing under the weight of the tank.

[Chris Foley]

The only comment that I have is that the weight of the water alone is roughly 1000 lbs. Add the rock, sand and other items and you can easily see how this needs to handle up to 2000 lbs. This is one piece of furniture where overkill is a good thing! If the base fails, you don't have any quick way of removing the tank as they are not designed to be lifted full (even if you could @ that weight)

Just my $0.02

[Keith Devore]

I'm just a new guy, so take this for what it is worth. I just completed an aquarium stand for a 90 gallon FW tank. I used 2x4's and then 'skinned' the outside with hardwood. Turned out OK ... considering the tools I had available at the time. I have had no shrinkage or movement on the stand.

[RickT Harding]

I've always been surprised at the "flimsy" nature of tank stands. I have a 70gal and the weight this little cheap box supports is crazy when you stop and think about it. I don't have a physics degree so I don't know how, but it works.

[Mike Goetzke]

I have built two tank stands. The most recent a cabinet for my sons 55 gal. aquarium. The pics below show some of the construction. I depend on the four vertical walls of plywood for strength. The verticals actually go all the way to the floor. I used mostly pocket hole construction. My face frame is mostly to hold the doors on - not meant to add structural strength to the cabinet. I would suggest you look at the tank and see where the support is needed. It will help you determine how to construct the cabinet. In my case the tank was designed to be supported around the bottom perimeter. Also, make sure the top support is flat. I put the tank on empty and used a piece of paper to verify flatness. Then we filled it slowly and re-checked the flatness. Oh, make sure the surface you are mounting it to is flat too.

Mike

http://img.photobucket.com/albums/v212/mbg/Eric%20Aquarium%20Stand/th_IMG_1405.jpg (http://img.photobucket.com/albums/v212/mbg/Eric%20Aquarium%20Stand/IMG_1405.jpg)
http://img.photobucket.com/albums/v212/mbg/Eric%20Aquarium%20Stand/th_IMG_1398_1_1.jpg (http://img.photobucket.com/albums/v212/mbg/Eric%20Aquarium%20Stand/IMG_1398_1_1.jpg)

[Cliff Rohrabacher]

I disagree with the notion of weight on the M&Ts not because that as a factor would be problematic ( it might indeed) but because The top of the stand is setting on the uprights and not the M&Ts.

The top may bend a tad to placing some loading on the rail beneath but that won't be primarily at the M&T but rather in the middle. The loading that transfers to the M&Ts won't be substantial. And you can always make the front rail very thick and even laminated.

[Lee Schierer]

The only comment that I have is that the weight of the water alone is roughly 1000 lbs. Add the rock, sand and other items and you can easily see how this needs to handle up to 2000 lbs. This is one piece of furniture where overkill is a good thing! If the base fails, you don't have any quick way of removing the tank as they are not designed to be lifted full (even if you could @ that weight)

Just my $0.02

The volume of the rock & sand will displace a certain amount of the water so the total weight doesn't go up that much by adding the rocks and sand. Wet sand weighs roughly 120 pounds per cubic foot water weighs 62 pounds per cubic foot. So for every cubic foot of sand added you only gain about 60 pounds...You'll probably need about 1-1/2 cubic feet of sand or about 180 pounds more than the water it displaces. Total aquarium weight (water, sand & 200# of rock) not counting the tank will probably be about 1250 pounds.

[Chris Friesen]

The only comment that I have is that the weight of the water alone is roughly 1000 lbs. Add the rock, sand and other items and you can easily see how this needs to handle up to 2000 lbs.

A single short chunk of 2x4 can handle something like 30000 lbs of compression along the grain. Your wimpy aquarium is as nothing! :)

[Jim Lischio]

Thanks for everyone's responses so far. I agree with Lee's weight estimate, which puts the weight on each corner at about 315 pounds (not that much), so I guess I shouldn't be overly concerned with the M&T joint strength. I was going to use a 1/2" thick tenon (this is just under 1/3 of the stock thickness), will this be OK?

I chose 8/4 maple (surfaced dimensions are 1.75" x 5") based on this template (http://www.reefcentral.org/forums/showthread.php?threadid=1169964) over at ReefCentral. It says that a 2x4 will support up to 90 gallons and to use 2X6 for 125g to 150g and most people think that is overkill. I am a little concerning about sagging in the middle of the front since there will be no center support and inset doors, but I can always laminate an extra piece behind the front rail.

Jim

[Michael Merrill]

I've built many stands for my salt aquariums, and up to about 55g size I agree that a plywood framed cabinet is OK, but beyond that I always go with 2x4 frame with a "facade" approach. My current tank is 90g with this 2x4 construction and I sleep fine every night due to that. It's just good insurance, a 50-100g salt water clean up isn't worth the little extra work.

I also paint the entire inside of the stand/frame to seal it with Int/Ext paint.

[Paul Johnstone]

If this makes you breathe easier, I bought a used 180 gallon with a stand already. It had been in service for 4 years, so I trusted it.

The guy used 3/4 plywood for the sides, and basically frace frames for the back and front.. The back face frame had no supports over the 6' span, although it is fairly wide. I screwed in some supports, just to make me feel better.

I've been told by a pro builder that all the wieght of the aquarium is on the corners, so a little bit of bowing on the long horizontal pieces is ok.

Also, you might consider pocket screws on the inside to pull the MT tight.
A little extra overkill.

I've seen stands for big tanks in pet stores made out of 1/2 particle board.. now that's crazy, especially since I question if it would maintain structural integrity when wet.

One final tip .. build a rectangular base at the bottom.. this helps spread out the weight on your floor.

But 8/4 maple would make an awesome stand..

[Chris Foley]

Ah, but the 2x4 is not the issue.....

The real issue is the deflection of the cross pieces. if the deflection is two much across a the span the stresses shift and can damage the aquaruim as it tries to handle the shearing stresses and bending moments created by the imbalance.

Also, my 2000# estimate is how I would design it. Lee's numbers on 200# of rock is about right for 120 gallon unit (1.5#/gallon is typical). Once you think about kids running into things and all other types of mishaps, you need to add safety factors into such an item. I personally think the 2x6 cross member on a 2x4 frame with a facade is the 100% way to do it in a workshop. Now, if I play the engineer (that I do IRL) I would model the system, apply all types of loads and then test it. But, I would need to sell about 200,000 units to pay for all the engineering. :D

[Chris Foley]

I've been told by a pro builder that all the wieght of the aquarium is on the corners, so a little bit of bowing on the long horizontal pieces is ok.

....

One final tip .. build a rectangular base at the bottom.. this helps spread out the weight on your floor.

But 8/4 maple would make an awesome stand..


The engineering side would not support such a statement. It does have greater strength in the corners. The weight is greater in the corners but if you build a stand with only 4 corners, the aquarium will break.

The idea about the square base is dead on though.

Also, remember this thing will be VERY top heavy.

[Jim Kountz]

Go to a pet store and look at the ones they sell for these tanks. They are mostly all particle board and only support the rim of the tank. I have one of these cheaper stands holding a 45 gallon bowfront and the bottom is not even touching the stand, only the rim. Been like that for about 10 years now. It wont break.

[Chris Foley]

Go to a pet store and look at the ones they sell for these tanks. They are mostly all particle board and only support the rim of the tank. I have one of these cheaper stands holding a 45 gallon bowfront and the bottom is not even touching the stand, only the rim. Been like that for about 10 years now. It wont break.

Exactly...it supports the rim all the way around not just on the corners.

[Paul Johnstone]

The engineering side would not support such a statement. It does have greater strength in the corners. The weight is greater in the corners but if you build a stand with only 4 corners, the aquarium will break.

The idea about the square base is dead on though.

Also, remember this thing will be VERY top heavy.

The thing is this.. I asked him about it because I bought a canceled order from him. The cross support pieces were slightly dipped. He insisted the most important thing was corner support. The stand held 3 45 gallon tanks
vertically. It was well designed not to rack. Amazingly, the whole thing was made out of 3/4 plywood.

I wouldn't advocate setting up the tank with just cinder blocks under the corner, but I've seen people do it.

Actually, my recommendation is to build a top for the stand and then put a sheet of styrofoam (1/2" or 3/4" is fine) between the tank and stand top. This allows for any unevenness in the top.. The sytrofoam will compress if the bulk of wieght is on one corner. That's what I did with my 180.. although I admit it doesn't look as pretty that way.

I'm not advocating doing the bare minimum. He should be find with 8/4 maple. I just don't want him to worry too much.

[Chris Foley]

I don't think that I have seen that approach with the styrofoam but it makes sense. I would make sure that is is mildew resistant though. In tanks this size, I don't know if they reccomend support on the bottom glass itself. Maybe just a strip of 1/4" rubber around the rim of the bottom would work. Does your 180 have a midspan support or is it just one solid piece across the bottom?

I fully agree with the 8/4 maple and can't wait to see the pics! :)

[Jim Lischio]

Don't hold your breath waiting for the pics...we have a 4 month old, but a very understanding wife (I'm blessed to have both, but not blessed with time).

[Paul Johnstone]

I don't think that I have seen that approach with the styrofoam but it makes sense. I would make sure that is is mildew resistant though. In tanks this size, I don't know if they reccomend support on the bottom glass itself. Maybe just a strip of 1/4" rubber around the rim of the bottom would work. Does your 180 have a midspan support or is it just one solid piece across the bottom?

I fully agree with the 8/4 maple and can't wait to see the pics! :)

There's a bottom trim piece that protrudes on my tank (and most tanks)
The tank really doesn't "sink" that far into the styrofoam (I had to move the tank after it sat full of water for a year). Therefore, the bottom glass
does not make contact with the styrofoam.

Mildew hasn't been a problem.

The tank I have has a 2' by 6' footprint. I would've put a center brace on the stand if I built it, but the stand I got with the tank didn't have it.
Actually, I would've probably way overdid it if I built it..

If you were asking if the tank itself has a middle support, I don't think it does. It has one across the top, but not on the bottom.

[Anchor Sarslow]

Jim,

Having built stands to hold over 1000 gallons worth of water (and more), your 8x4 is very suitable. I have built stands for 55's out of simple kiln dried 2 x 2 strips.

Comments. Yes, you only need to support the corners. Dont foget the rigidity of the glass itself.

For long term purposes, I would only use the ply for facing. the reason is that it rots far faster than stud or solid hardwood. and you can replace it if it gets water damage.

The stands in stores are made to maximize profit not tank stand longitivity. The average fishtank keeper is not in the keeping for tha long haul. I would estimate 7 years or less.

Ply and particleboard can do wonders but is not made for the long haul.. or for frequent accidents.. that the average person make a lot of with water..

Your plan will work just fine for a 120. I would still double up on you corners. a 1 x 4 will be fine for cross pieces (length and depth.) 2 x 4 corner risers or larger. It has plenty of collumn strength that way.