Noob question about a TV mount

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I'm fairly new to welding and have only done some lawn-art stuff for fun and some carts for tools.  This will be my first structural project.We recently moved into a new home and there is a built-in TV cabinet that has an opening 5 feet high and 4 feet wide with closing doors for the TV.  Problem is that it is made for the old tube TVs and doesn't fit a flat-screen.  I don't want to modify the cabinet because it has a twin on the other side of the fireplace and I want to keep them symmetrical.I found a articulating TV mount that would allow me to turn the TV 90 degrees and push it back into the cabinet when I wanted to put it out of view, but it isn't long enough such that I can mount it to the back wall, so I need to build some type of support wall that is 10 inches forward of the back wall.  Rather than building a large vertical wood brace, I'm thinking that metal would look better as it would match the articulating mount.I was thinking of a vertical beam with two top and two bottom plates.  One plate would go on either side of the shelf above and the shelf below, so they would effective clamp on either side of the shelf, using 4 bolts.  Then I would design a plate that fit the screw holes of the articulating mount and weld that to the center of the beam.  The TV is a 55' flat screen that weighs about 40 pounds.  The mount extends up to 3 feet, so that would be 120 ft-pounds of pressure on the structure when the TV is extended, which will be 99.9% of the time.  So, my questions are:1.  Is this a good design or am I missing something?2.  What size beam do I need?  Will something like 3 inch suffice?3.  What size plates do I need on the top and bottom, and for the TV mount?  I was thinking about 1/4 inch, but I have no idea how to determine what is actually necessary.4.  Anything else I am missing?I'd appreciate any help I can get.  I'd hate to see the TV come smashing to the ground.
Reply:

Originally Posted by Canoecruiser

I can't quite visualize the finished product from the description (maybe after a cup of joe).  By "beam" do you mean square tube?  With 1/4" plates and 3" tube what you tie it to would be the weak link.  You could probably hang on that mount depending on your doughnut consumption habits, but a 55 foot TV is a biiig screen!

Just don't do this.....
Reply:The commercially available TV mounts have a neat trick that may be hard to duplicate.They come in 2 parts. One half is fastened to the wall and the other half bolts to the TV. Then you only have to lift the TV to settle it into the bracket on the wall and let it latch into place.We love to design and implement our own solutions, but sometimes paying for somebody else's engineering is worth it.Be wary of The Numbers: Figures don't lie,. but liars can figure.Welders:2008 Lincoln 140 GMAW&FCAW2012 HF 165 'toy' GTAW&SMAW1970's Cobbled together O/A
Reply:Take a look at Mono Price dot com. They have many many mounts. Good prices too.www.tjsperformance.comDynasty 300 DXHTP 240HTP Microcut 380Hyperthem 85JD2 Hyd Bender and HF Hyd Ring Roller all in one =(Frankenbender)Bpt. Mill/DRO4' x 8' CNC Plasma TableInstagram: tjsperformanceYT: TJS Welding and Fabrication
Reply:

Originally Posted by mike837go

The commercially available TV mounts have a neat trick that may be hard to duplicate.They come in 2 parts. One half is fastened to the wall and the other half bolts to the TV. Then you only have to lift the TV to settle it into the bracket on the wall and let it latch into place.We love to design and implement our own solutions, but sometimes paying for somebody else's engineering is worth it.
Reply:

Originally Posted by TJS

Take a look at Mono Price dot com. They have many many mounts. Good prices too.
Reply:

Originally Posted by guitarjim

Actually, I don't love to design and implement my own solution.  The trouble is that the cabinet is too deep for the commercial mounts, so I need to build something out from the wall for the TV mount to connect to.  My plan is to use a commercial mount, I'm not trying to reinvent that.  But, it's better for me to use a metal pole-type structure to attach it to, rather than building a wooden brace that would take up more physical space to achieve the same strength.
Reply:1/4" is overkill for the plates.Basically you are making steel studs for the commercial mount to attach to. I  I   Top and bottom plates can be 1/8"  4 holes per plate for the bolts.   Stud: 2x2 x1/8"attach the mount. Like this style?

Ed Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:You could bend up something in 22 gauge sheetmetal if you have a break/brake.

Sincerely,William McCormickIf I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.
Reply:If the cabinet is strong enough you could make up a square tubing frame, bolt that to the cabinet and then attach the tv mount to that. Just don't underestimate how strong the mount has to be as kids have been killed by toppling tvs that werent properly attached.