Cleat fastener size for shelf

[Thalermade]

Here is the info.
I am building my BIL a basic corner shelf to hold his new 42 inch plasma panel TV. He does not want a full corner shelf, but wants the "floating shelf look". The idea is to build a shelf that will be narrow as possible front to back (the stand the tv sits on is 13 inches front to back).
The shelf will be diagonal of course and may span 48 inches from side to side. I am planning to make the shelf at least 18 inches front to back so there are at least two studs to bolt the cleat into. The tv weighs 85 pounds. The shelf will probably resemble a torsion box by the time there is the top, bottom and front piece connecting the top and bottom which will also hide the wall cleat and provide extra support to the most likely 3/4 inch shelf material (haven't decided between red oak or birch ply).

It will be bolted through 1/2 inch drywall into 2 by 4 wall studs.
I want to be secure, but do not want to go to far overboard, as the bigger the fastener the "taller" the cleat. But do plan on erring on the side of safety.

I am thinking 1 inch thick, 1 1/2 inch high cleats using a 1/2 by 3 inch lag bolts with washers.

Am I headed in the right direction? I found plenty on the strength and span of wood, but nothing comprehendable on size strength and shear of bolts.

Thanks for your input.
Russ

[Black wallnut]

I'm thinking that 1/2" is extereme overkill! If you use four 1/4" lag bolts even at grade "2" which would be ones with no marks on the head your load rating would be several times what you would need. If it makes you feel safer just move up to 5/16".

With 1/2" dia the threads are very deep and will require considerable force needed just to tighten.

IMHO use 5/15" lags in 1/4" drilled holes in wall and 5/16" clearance holes in cleat; use hand soap on each lags threads.

On some farming machinery that I used to service ( while it was being pulled by a tractor) our catwalks were supported by no more than 2 3/8" grade 5 fasteners on each end.

[Thalermade]

Thanks Mark, that is the info I was hoping to get.


Russ

[bigfoot]

I think this is the reference material you are looking for, and I agree that 1/2 seems way overkill.

http://www.fastenal.com/content/docu...renceGuide.pdf

I did skim this quick, and found this :

"When no shear strength is given for common carbon steels with hardness up to 40 HRC, 60 % of their
ultimate tensile strength is often used once given a suitable safety factor. This should only be used as an
estimation."

[jziegler]

You can probably use shelf material thinner than 3/4" for your shefl, 1/2" is most likely fine, since the frame will be supporting most of the weight, especailly if you put in a number of cross pieces. I made some floating display shelves in my kitchen, and used 1/4" ply for those, with 1x2 poplar frames, about every foot or so. The TV is heavier, of course, but's I'd think 3/4 is overkill.

I think that I used 1/4" lags, possibly 5/16" for the kitchen shelves.

Jim

[Black wallnut]

You can probably use shelf material thinner than 3/4" for your shefl, 1/2" is most likely fine, since the frame will be supporting most of the weight, especailly if you put in a number of cross pieces. I made some floating display shelves in my kitchen, and used 1/4" ply for those, with 1x2 poplar frames, about every foot or so. The TV is heavier, of course, but's I'd think 3/4 is overkill.

Jim

I disagree. Widescreen TV's concentrate their weight, at least the ones I've looked at, on four small feet in roughly the middle third of the screen. I'd use 3/4" ply for the top of the shelf for sure. To save weight or to have more off cuts you could use 1/2" or even 1/4" for the bottom.

[jziegler]

I disagree. Widescreen TV's concentrate their weight, at least the ones I've looked at, on four small feet in roughly the middle third of the screen. I'd use 3/4" ply for the top of the shelf for sure. To save weight or to have more off cuts you could use 1/2" or even 1/4" for the bottom.

Well, I stand corrected. I haven't looked at the base of the flat panel tvs in that much detail, I'm still at least a couple years away from buying one. I figured that the weight would be more spread out on the base than 4 feet. Seems 4 feet in the middle third of the screen wouldn't be the most stable arrangement, but hey, I'm not designing the things.

Jim