HO has a 50″ plasma TV, probably 100lb, that he wants mounted on a swivel-arm mount such that it can be viewed in a corner at about 30º-45º angle, but also able to stack back against one wall sometimes. The walls are genuine plaster vintage 1970 or so. That means plaster over gypsum lath. All the articulated TV mounts of sufficient size and reach hang from a 7 1/2″ to 10″ high by 18 1/2″ to 25″ wide mounting plate and they specify mounting with lag screws to two studs 16″ or more apart. To get the pivot point far enough from the corner to enable stacking back flat against the wall but not too far from the corner, the mounting plate would have to be placed where it crosses only one stud. With 100 pounds hanging at 26″ maximum extension, what will the force be on that top lag screw? Is the calculation weight x extension / height of back plate top screw? If so, the force could be over 400lb. I’m thinking of making a backboard of 3/4″ plywood screwed with 10 x 4″ screws to the corner stud and the next stud out, extending another 8″ beyond. I would then use 4 1/2″ lag screws through the mounting plate and plywood into the stud and 1″ lag screws at the corners of the mounting plate for additional support from the plywood. Anybody see a problem or have a better idea? Thanks,
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Duct tape.
Clearly you're a Myth Busters
Clearly you're a Myth Busters viewer.
If they can lift an old Cadillac with a crane and 100 strips of duct tape, then how hard could it be to hang a TV with it, right?
More of a Red Green viewer.
I think you have a good idea going there.
I can't give any quantitative numbers and am probably overkilling the support, but.....
I would tend to laminate two layers of 3/4" plywood together for your backer plate - a little box frame trim to hide the plywood edges.
I would be more comfortable with the resulting 1-1/2" thickness.
Increase screw lengths for the new thickness.
I mounted a much smaller (and lighter!) flat screen for a customer just last week with the same scenario - 45* in corner or pivot to flat on one wall - I only needed one stud for support though.
Jim
I would worry less about the weight of the tv and more about the client's teenagers who get to goofing around and pull down on the tv and the mount fails and tv breaks. Client then says you didn't install the mount per instructions and wants your insurance to pick up the cost of the new tv and mount (which some other bozo already installed and said what a jerk you were).
Yep, I'd either use doubled ply that spans two studs, or get a metal plate cut for a more trim looking backing plate, or cut out some plaster and run some heavy duty backing between studs.
3/16" metal plate can be suprisingly inexpensive for a wide one piece backing, or I'd probably go for two pieces of 1/2" x 2" metal strap for top and bottom support of the tv mount. It's definitely overkill, but when the tv is torn off the wall it will be obvious that it's not your fault. Metal strap is easy to work with and cleans up nicely for a professional looking retrofit when spray painted to match the tv mount.
Thanks all, for your responses.
On another forum I found this link to an American Wood Products Connection Calculator for nails, screws, lags and bolts in a huge variety of main member wood species, attaching side members of steel, OSB, plywood and a variety of solid wood species of various thicknesses:
http://www.awc.org/calculators/connections/ccstyle.asp
When I entered withdrawal loading, lag screw, 5/16, 2 1/2" doug fir main member 3 1/2", steel side member it gave me a force of 634lb.
#10 screws, 2 1/2" hold 3/4" plywood to studs with 330lb withdrawal force.
5/16" x 1" lag screws in 3/4" cedar main member (there is no plywood choice, so I took the softest solid wood I found) came out to 158lb.
I think my plywood backboard will work great and to be safe, maybe I'll try to find a piece of 1" or double up with 3/8" and 3/4". I may even have a scrap of 3/4" oak 7-ply lying around.
A. You can always drill more holes through the mounting plate to screw more screws into the stud.
B. Where the other screws penetrate the plaster lath only, use the Type of anchor made by Hilti or Toggler. They work really well. Ratings are per screw.
http://www.toggler.com/products/snaptoggle/overview.php
Yeah, that's a lot of weight on a span between studs but old school plaster lath is pretty darn strong and hard to pull away from the studs.
Hope this helps,
Frankie
Yep. Togglers are the best anchor around for drywall or stucco.
Remember, those numbers are for the normal load, and you will be using at least two of them!
Also, you can put in longer screws than 2.5"!
With 100 pounds hanging at 26" maximum extension, what will the force be on that top lag screw?
If the top lag screw were 26" above the pivot point then the force would be 100lb outward. Hard to tell what the pivot point is for the mounting bracket as you describe it, but it sounds like we could take a height of 7" worst case, or about 3.5x the outward extension, meaning about 350lb outward force. This would be divided between the bolts at the top.
3/4" plywood can easily handle this if the bolts don't pull out. I'd either put tee nuts behind the plywood, or just run carriage bolts through from the back. Someone obsessive would find a piece of scrap steel maybe 3/16 thick and drill/tap it for bolts, then fasten to the back of the plywood.
Carriage bolts from he back...Great idea.
I like through bolting with 1/4" machine bolts and use a Chicago screw or threaded cap screw on the back. With double plywood lagged into the framing, Jenny Craig could have a party dangling off the tv.
"...Jenny Craig could have a party dangling off the tv."
Now there's a visual I didn't need. :)