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Unread 08/04/2007, 11:01 PM   #26
flyguy7150
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Rocket I got a few questions.... First, I will be building a stand for a 90gallon, 48"L x 18" w x 30"h. For this everything according to this design will be 2x4s. The green pieces should be one inch off the ground and one inch from the top right?? The top frame and the bottom frame, how are they attached to the purple legs?? Is everything just screwed down to the green 2x4s or really long screws from the top and bottom frame to the purple pieces or both?? Everything is bolted down with just wood screws right, no brackets?? Would adding one more leg to the back middle do any harm? What size wood screws do you use?? Sorry for all the questions .


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Unread 08/05/2007, 12:06 AM   #27
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Yep, everything is just screwed into the green strips. 2 1/2" to 3" screws will work. They are, in a sense, brackets. They could be cut to a few inches in length and still hold things in place until you attach plywood to the whole thing. Adding another leg won't do harm, but it's not necessary at all. The only harm would be getting in the way at some point.


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Unread 08/05/2007, 12:36 AM   #28
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ok so no need to put like 5inch screws from the top of the top frame to the legs, thank you


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Unread 08/05/2007, 01:51 AM   #29
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You shouldn't. Unless the laws of physics suddenly change. The weight of the tank will hold in that direction.


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Unread 08/05/2007, 08:42 AM   #30
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RocketEngineer -

Why aren't the green fastening strips the same height as the stand? I understand they aren't load bearing, but having them run the full height of the stand makes assembly easier since you can square them up on a flat surface and against the box frames.


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Unread 08/05/2007, 08:49 AM   #31
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great post rocket engineer.i used this same basic layout for my 150g stand and its very rigid and strong.


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Unread 08/05/2007, 10:14 AM   #32
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slevesque - depends on whether you are looking at it sitting down or standing up. I don't have exact numbers but others on RC may have some suggestions. For a tank that short though, you may be able to reduce the lumber sizes a little. What size tank is it?

flyguy7150 - I think Siffy answered all you questions.

Siffy - Thanks for answering all of flyguy7150's questions.

Charlutz - The reason the screw strips are shorter is that it prevents them from being part of the load bearing structure. Because they sit above the bottom frame you are assured its the frame sitting on the floor, not the screw strips. They are below the top surface to ensure that plywood or the tank frame sits directly on the upper box, rather then on the screw strips.

checkinhawk - Thanks for the support.


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Unread 08/05/2007, 10:26 AM   #33
slevesque
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My new tank is a 33L AGA: 48 x 12.5 x 12H

My 55G stand is 28" high and I find it a bit too low. I might go for 30-31" this time. I sit down for watching the tank, so many stuff to look at


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Unread 08/05/2007, 11:15 AM   #34
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Quote:
Originally posted by RocketEngineer


Charlutz - The reason the screw strips are shorter is that it prevents them from being part of the load bearing structure. Because they sit above the bottom frame you are assured its the frame sitting on the floor, not the screw strips. They are below the top surface to ensure that plywood or the tank frame sits directly on the upper box, rather then on the screw strips.
Ah. I see. So by making them shorter, you ensure the screws aren't load bearing. Otherwise, you run the risk that the actual load bearing posts are too short and aren't actually supporting the weight. I understand the principle. I found it easier to build the stands with the fastening posts the same height. I won't have the need to build another stand until probably February. I'll play with it then.


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Unread 08/05/2007, 04:42 PM   #35
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Yep, you just don't want them (the screw strips/green pieces) touching the floor when the tank weight is on them. A small piece of 3/4" plywood or 1xwhatever will shim/hold them up while screwing into them and fall off once the stand is picked up. I might suggest cutting the screw strips an inch longer if you're only able to shim them 1/2" off the floor instead of a full inch so there is plenty of material to screw the top frame into place.


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Unread 08/05/2007, 08:41 PM   #36
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Quote:
Originally posted by RocketEngineer
leebo_28, you are correct, the screws taking the load would be a dangerous situation. For a 4X4 posts without notching, I can't think of a good way to attach the frames to the legs.

Again folks, this design is meant to be made by folks with minimal tools. Also, the strength of wood in compression is incredible. Look at any tree and consider how much it weights. A single 2X4 under compression in one of these stands could take something like 18000 pounds unless it buckles sideways. For those wishing to use 4X4s and have the tools, I don't see a problem. But a couple 2X4s in each corner are more then enough for most tanks.

Cheers.
This is overall a good post and good basic concept as homebuilt stands are always way overkill. And while I completely agree that loading the stand directly though the wood is better than putting the screws in shear, doing so won't be a problem at all. As there isn't a standard for a typical #8 screw, from one manufacturer, the ultimate strenght of a screw is 361 lbs in shear. If you have a 4 screw connection then that connection's good for 1444 lbs, more than you are going to put on it with any tank (of corse you'd have to check the wood for the connection strenght too but my point is screwing to the side is more than adequate).

And for those that are concerned about deflection you don't need to worry about a thing as all of the weight from your tank will be sitting at the corners. Think of it this way, in order for that top box to deflect, you would have to be putting load on it in the middle somewhere. And in order for that to happen, the glass (including the sides) from your tank would have to deflect to apply that load to the wood.

The sides of your tank are not going to deflect. Looking at the side piece of a standard 75g tank, 21"x48"x3/8 with a load of 10 lbs/ in (that would be a total load on the tank of 960 lbs which would be a conservative estimate) (and assumeing a Youngs modulus of 72GPa http://www.roymech.co.uk/Useful_Tabl...ter/Glass.html) you would get a deflection of 0.00123" barely over a thousandth of an inch, not enough to load that wooden beam.

You would have have to apply a load of 125 lbs/in (a total tank load of 12000 lbs) to get it to deflect 1/64 of an inch, and this load also corresponds to the point that that side piece would break in flexure (and the bottom would have gone way before that, but I'm trying to make a point). Even at 1/64 of an inch you would bairly begin to load that wood beam.

So, in summary, the wooden beam at the top does verturally nothing; it holds the 4 columns at the corners in place providing a little bit of stability.

And how high can you make your stand... if you are worried about tipping it over try this: It would be very difficult for a single person to push or pull 100 lbs without actually sliding on the carpet or wood or whatever first. With that assumption, use this equation as to how high the mid hight of your tank can be:

W= Weight of tank (use a conservative value of 9 lbs/ gallon which would include the weight of the tank itself and your rock and sand)

b = the width of your stand from front to back

h = hight to the middle of your tank

Equation:
h = (1/100)*W*(b/2)

So using that 75 gallon tank example:
W= 75*9 = 675
h = (1/100)*675*(18"/2)=60.75"

Moral of this story, you can build your stand just about however high you want without worries.


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Unread 08/05/2007, 08:57 PM   #37
slevesque
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Well, your formula got me worried

In my case I got a 33L, so

W= 33*9=297
h= (1/100)*297*(13"/2)=19.3"

Since the tank is 12" high this means I'm allowed to have a 13.3" high stand!!! I hope I got that wrong


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Unread 08/06/2007, 05:26 AM   #38
Charlutz
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Quote:
Originally posted by Mykayel
This is overall a good post and good basic concept as homebuilt stands are always way overkill. And while I completely agree that loading the stand directly though the wood is better than putting the screws in shear, doing so won't be a problem at all. As there isn't a standard for a typical #8 screw, from one manufacturer, the ultimate strenght of a screw is 361 lbs in shear. If you have a 4 screw connection then that connection's good for 1444 lbs, more than you are going to put on it with any tank (of corse you'd have to check the wood for the connection strenght too but my point is screwing to the side is more than adequate).


I don't think it's the shear of the screw that is the main problem. It's the shear strength of the wood which is low. All of the pressure of the tank will be concentrated on the screw. My concern is that it would be enough to rip the wood.

Quote:
Originally posted by Mykayel
And for those that are concerned about deflection you don't need to worry about a thing as all of the weight from your tank will be sitting at the corners. Think of it this way, in order for that top box to deflect, you would have to be putting load on it in the middle somewhere. And in order for that to happen, the glass (including the sides) from your tank would have to deflect to apply that load to the wood.


Doesn't this depend somewhat on the height of the stand? If the stand is taller, the posts will lean in under weight.

Quote:
Originally posted by Mykayel

And how high can you make your stand... if you are worried about tipping it over try this: It would be very difficult for a single person to push or pull 100 lbs without actually sliding on the carpet or wood or whatever first. With that assumption, use this equation as to how high the mid hight of your tank can be:


Taller stands will rock more easily due to leverage. It's the same as using a prybar. It's much easier to move a tank on a tall stand. Add in the fact that it will be top heavy, making it that much easier. Not saying the tank needs to lie on the ground, but you do need to consider height in the build.


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Unread 08/06/2007, 01:31 PM   #39
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Mykayel, Thanks for you comments.

But I don't agree on some points.

1) Screws in wood are likely to tear out sideways due to the shear forces on them. As the screws are in single shear, the wood is likely to fail before the screw itself. I for one would never trust a screw to take shear loading and transfer it from one piece of wood to another but this is just me.

2) You made the assumption that the tank was glass and with some simple additions such as a plywood top, this design could be used for an acrylic tank. In this case deflection IS an issue and needs to be accounted for.

3) I would like to know what that formula pertains to and what all the variables that make up that 1/100 factor come from. I have never seen it before so would like more info on it.

Thanks for the comments everyone.


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Unread 08/06/2007, 01:48 PM   #40
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Quote:
Originally posted by RocketEngineer
2) You made the assumption that the tank was glass and with some simple additions such as a plywood top, this design could be used for an acrylic tank. In this case deflection IS an issue and needs to be accounted for.
It's also making the assumption the glass is tempered, isn't it?
Quote:
Originally posted by RocketEngineer
3) I would like to know what that formula pertains to and what all the variables that make up that 1/100 factor come from. I have never seen it before so would like more info on it.
I think the 100 comes from this statement.
Quote:
Originally posted by Mykayel
It would be very difficult for a single person to push or pull 100 lbs without actually sliding on the carpet or wood or whatever first.
I believe he's just comparing simplified moments. f1 * d1 = f2 * d2 where f1 is the weight of the tank, d1 is the width of the tank, f2 is amount of force one can push before sliding on carpet, and solve for d2 which is where that force can be applied (ie, middle of tank height). It's not exact, but gives a ballpark.


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Unread 08/06/2007, 06:36 PM   #41
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Subscribing to the thread so I can have it for future reference. Great info.


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Unread 08/06/2007, 06:42 PM   #42
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Quote:
Originally posted by RocketEngineer
Mykayel, Thanks for you comments.

But I don't agree on some points.

1) Screws in wood are likely to tear out sideways due to the shear forces on them. As the screws are in single shear, the wood is likely to fail before the screw itself. I for one would never trust a screw to take shear loading and transfer it from one piece of wood to another but this is just me.
Not necessarily. I’ll say it again, homemade tank stands are usually way over built because they built by a gut feeling, not by facts. Structural wood connections use single shear screws all the time. Here is a connection from my old 55 gallon tank , and as I stated before, that connection is good for about 1400 lbs, for that 55 gallon tank that weighed a total of about 500 lbs, that one corner, and hence that one connection would be loaded to 125 lbs. That’s a safety factor of better than 10. Double that load for a 120g tank and you’d be at a safety factor of 5. You are telling me you aren’t comfortable with that?? What kind of factors of safety do you use in your line of work??

Quote:
Originally posted by RocketEngineer

2) You made the assumption that the tank was glass and with some simple additions such as a plywood top, this design could be used for an acrylic tank. In this case deflection IS an issue and needs to be accounted for.
Yes I did assume it was glass (I didn't assume tempered, I just used that value from the website, but I seriously doubt the Young's modulus is much different from tempered glass) but a plywood top wouldn’t make a difference. For those concerned about deflections, you need to know two equations illustrated in this little example. I would recommend keeping your deflections to l/600 which as you can see using a single 2x4 won’t work, but a 2x6 would give you a deflection of 0.033” or l/Defleciton of 1444.


Quote:
Originally posted by RocketEngineer

3) I would like to know what that formula pertains to and what all the variables that make up that 1/100 factor come from. I have never seen it before so would like more info on it.
Simple statics using the 100 lb force as I stated, just sum the moments about any point, I chose the corner labeled point A:



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Unread 08/07/2007, 06:50 AM   #43
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Instead of having a full pane of plywood to cover the back of the stand, would it be OK to use triangular shaped plywood in each corner, let's say 1' long?


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Unread 08/07/2007, 10:13 AM   #44
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slevesque,

That should work fine. The corner braces do not carry any of the weight of the tank. They only carry shear loads caused when someone leans up against the tank. Four one foot long triangles properly attached to the frame will be able to handle a lot of shear loads before you start breaking screws or tearing the wood.


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Unread 08/09/2007, 09:49 AM   #45
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First of all, thanks for the thread. I know basically nothing about this stuff and it's been very helpful. I just have a question or two.

I want to build a stand like this for my 55g (48.25"x12.75"). The thing is I want to put a 29g (30.25"x12.50") inside the stand for a sump and in order to do that I would have to build the stand a little deeper than the 55g tank. I was thinking that I could make the inside of the stand 13" deep, leave off the screw strips and put a piece of plywood on top to set the 55g on. If I did this, would the plywood effectively distribute the weight of the 55g onto the 2x4s or would the it break under the weight?


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Unread 08/09/2007, 12:52 PM   #46
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Jen D, First I need a little more information about the 55G. Is it glass or acrylic? If glass, does it have a plastic frame around the bottom?

If the tank is glass and has the plastic frame, you only need to support the perimeter of the tank. This means you could leave off the plywood top and just rest the tank on the 2X4s.

You could use 2X2s screw strips and have the sump rest up against these. This would give you the space needed for the sump.

Hope that helps


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Unread 08/09/2007, 02:30 PM   #47
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It's glass with plastic trim. I was going to use the plywood because the stand would be too deep to support the long sides of the tank if I make it with a 13" opening inside the stand. The tank would only rest on the 2x4s on the short sides.

I like the idea of the 2x2 screw strips. Now that I rethink it I could use the 2x4 screw strips, too. I had it in my head that the sump was going to be up against the short side of the stand, but it doesn't have to be... duh.


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Unread 08/10/2007, 03:16 AM   #48
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thanks rocketengineer!!! I built my first ever stand tonight with the help of your plans...here are some pics!






one question i have is why not make the green boards or screw boards the run entire hieght of the stand? and how should I go about putting a floor and top on it?


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Unread 08/10/2007, 03:25 AM   #49
Siffy
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Quote:
Originally posted by RocketEngineer
The reason the screw strips are shorter is that it prevents them from being part of the load bearing structure. Because they sit above the bottom frame you are assured its the frame sitting on the floor, not the screw strips. They are below the top surface to ensure that plywood or the tank frame sits directly on the upper box, rather then on the screw strips.



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Unread 08/10/2007, 03:30 AM   #50
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As for a top and floor. If your tank has a glass bottom that's tempered a top isn't required. The tank can just sit on the 2x's. For a floor I'd just notch the corners out the size of the screw strips and install it through the opening at an angle it should fit. I'd make it the full width and length of the stand except at the corners.


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