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Discussion Starter · #1 ·
I built this last year to support a removable table top and it failed. The longest overhang has dropped by a 1/2"

I’m limited by space below and cannot use a leg or a support bracket and I don’t want to hang something from the ceiling because the top has to be removable.

I didn’t notch the long 2x4 diagonal piece because I did not want to weaken it so I used a 1x6 over the top to tie it together and it drooped anyway.

Today I pulled it off the wall and out of the room and unless I can figure out how to keep the thing straight and flat, it’s not going back.
So my question is what can I make that can hang off of only two walls without legs that will not bend?

 

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Off-the-cuff thoughts.

a) Can the diagonal be deeper? Strength of a beam is proportional to the square of the depth. So if you use a 2x6 the relative stiffness is
5.5^2 / 3.5 ^2 = 2.47, so almost 2 1/2 times stronger.

b) Can you make the longer overhang an I beam by glueing another 1x6 along the underside?

Is the diagonal drooping or the longest elevation? Does the longest elevation need a stronger joint at the back brace? Perhaps a bolt and barrel nut, also called cross dowel?

http://www.leevalley.com/US/hardware/page.aspx?p=44238&cat=3,41306,45375
 

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Discussion Starter · #3 · (Edited)
Off-the-cuff thoughts.

a) Can the diagonal be deeper? Strength of a beam is proportional to the square of the depth. So if you use a 2x6 the relative stiffness is
5.5^2 / 3.5 ^2 = 2.47, so almost 2 1/2 times stronger.

b) Can you make the longer overhang an I beam by glueing another 1x6 along the underside?

Is the diagonal drooping or the longest elevation? Does the longest elevation need a stronger joint at the back brace? Perhaps a bolt and barrel nut, also called cross dowel?

http://www.leevalley.com/US/hardware/page.aspx?p=44238&cat=3,41306,45375
It can't be any thicker because I have a chest of drawers with wheels underneight and I really can't go any higher because its already to high as it is.. I have jamed a wedge on top of the drawers to level it, but its a pain when when I need to pull out the chest for access behind it where I long items stored.

I have it screwed down pretty good and used gorilla glue. The first short piece which is not a problem got out of whack when the gorilla glue swelled up even with the screws, but it remanded level so I left it alone.

I may try using steel across the top under the pine to help keep it level, but I kind of think the 2x4 diagonal piece is dropping from the span length and I have to change wood to something that will not droop as easily.
 

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The part circled in the first picture- move it laterally until it falls over a wall stud - then drill holes through the back piece and the front diagonal to take a piece of 3/8" or 1/2" pipe, drill a corresponding hole in the stud about 2" deep, insert pipe through shelf members into hole. Pipe will not sag, and shelf can be shimmed on pipe if needed.
 

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make a torsion box

Just take another piece of plywood and secure to the bottom side of what you have. If you want to double the front diagonal and add some more internal braces, that will help and it won't "rack" like what you have now.
A torsion box puts the top in tension and the bottom in compression when you load it. The bottom resists the tendency to bend or compress because the extra layer of plywood can't....

Securing it to the wall would be easy enough if you backed the rear plate with a 1" X 6" which hangs down for screw access. If it doesn't matter, it could also protrude up like a back splash, or both. By having a loose top or removable, you dimish your structure considerably. If you can hang the whole top as a torsion box, on some French Cleats that will work also.

http://www.newwoodworker.com/frenchcleat.html

http://www.thewoodwhisperer.com/videos/french-cleat-storage-system/
 

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Discussion Starter · #7 · (Edited)
The part circled in the first picture- move it laterally until it falls over a wall stud - then drill holes through the back piece and the front diagonal to take a piece of 3/8" or 1/2" pipe, drill a corresponding hole in the stud about 2" deep, insert pipe through shelf members into hole. Pipe will not sag, and shelf can be shimmed on pipe if needed.
I really don’t want to drill that size hole into the studs because they are pretty stressed out supporting two tile roofs and I’m a even a little nervous driving screw in for fear of splitting them. Unfortunately my track house was built by south of the border unskilled day laborers. I worry every time we have an earthquake because the house makes some horrible noises.

What if you bore a hole in the 2X6 and installed a steel bar in it?
This may actually work for the overhang and I just might do that except that it has to be no bigger than a 2x4 in the middle and front.


Just take another piece of plywood and secure to the bottom side of what you have. If you want to double the front diagonal and add some more internal braces, that will help and it won't "rack" like what you have now.
A torsion box puts the top in tension and the bottom in compression when you load it. The bottom resists the tendency to bend or compress because the extra layer of plywood can't....
I wonder if instead of a solid Dug Fir 2x4, maybe I should laminate 3 or 4 1x4s together and run the grains opposite each other.
I don't really need the french cleats because I can just fasten the two sides to the wall with screws
 

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I am wondering if it is really the "timbers" of the shelf that is sagging? Or is it that the whole assembly is just slightly pulling away from the wall? It would not take much movement at the wall to translate into 1/2" at the front.

Have you used just regular screws to holt this assembly to the studs? Or have you torqued down lag bolts. I am guessing you used screws. If you drill pilot holes into the studs and use lag bolts you will not weaken the studs. Do you know that this is a load bearing wall to which you are mounting the shelf?

Why is the framework angled the way it is? You could use a support bracket ABOVE the shelf if the bracket was more rectangular. Ther are several more things that you could do.

George
 

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Discussion Starter · #9 ·
I am wondering if it is really the "timbers" of the shelf that is sagging? Or is it that the whole assembly is just slightly pulling away from the wall? It would not take much movement at the wall to translate into 1/2" at the front.

Have you used just regular screws to holt this assembly to the studs? Or have you torqued down lag bolts. I am guessing you used screws. If you drill pilot holes into the studs and use lag bolts you will not weaken the studs. Do you know that this is a load bearing wall to which you are mounting the shelf?

Why is the framework angled the way it is? You could use a support bracket ABOVE the shelf if the bracket was more rectangular. Ther are several more things that you could do.

George
Yes the wall is definitely a load bearing wall and from what I can see using a stud finder the studs are at random intervals and not 16”OC. Plus there are a couple of places where they are closer to 24”OC. The wall not only supports a large tile roof above but also supports the garage tile roof at mid point. There is not a square wall in the house and by the looks of the framing in the attic the wood is very low quality and twisted with huge cracks. I have added more support where I could without removing the gypsum board. There used to be a large banging every night when the house changed temperatures between day and night.

I worked in and around construction my whole life and I have never seen anything like this. I don’t know how it even passed inspection and it’s not just the framing, but the electrical and plumbing too. There were some class action law suits toward the builder, but nothing ever came of it.

Anyway you make a good point that I didn’t think about. I used screws to fasten it to the wall and I guess they could have been drawn into the wood a little. Actually there were a couple of screws pretty deep and I wasn’t sure there was even a screw there. Maybe I should use fender washers to prevent that from happening. And also a 2x6 for the back as was mention by some of the others to keep it from twisting on the wall.

The frame is angled because I wanted both ends supported to a fixed height and cantilevered the front support. Only I had to use two pieces for the cantilever because I did not want the 2x4 to be compromised with a notch and tied the top with the ¾” pine to keep it light. I could not do that using a rectangle frame. The only flex would have to come from the 2x4 itself or as you say maybe the back came lose.
 

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Discussion Starter · #11 ·
"The frame is angled because I wanted both ends supported to a fixed height and cantilevered the front support"

?????

G
Shelf Span corner to corner for rigidness because no place to support a corner. A rectangle corner can twist without support.
 
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