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I wanted to mount my shiny new TV with a swing arm directly into my drywall. I just like the flexibility a swingarm would give me, but there are some issues that make it difficult to mount the swingarm directly into the studs in my wall. So the question became: is this even feasible with drywall anchors alone?
So I started watching this video where he tested out some different drywall anchors (summation of the results are roughly 16 min into the video):
Which Drywall Anchor is Best? Let's find out! - YouTube[^]
I was trying out some physics calculations here and wanted a second opinion to see if I was completely off.
The TV itself weighs about 25 Kg and the swingarm is about 5 Kg alone. When fully extended, the TV extends about 60 cm from the wall. The mount itself (that I had lying around) is secured to the wall with three screws. One 15 cm above the arm, one 5 cm above the arm, and one 5 cm below the arm.
So I'm thinking: I have three forces working on the drywall: F_y , F_x and momentum M_0.
F_y has to withstand at least 30 Kg, which looks good, as one of the three screws, with a proper anchor, should be able to handle this weight alone.
The momentum the TV and mount generate, a little simplified: 30 Kg * 9,81 m/s^2 * 0.6 m = 177 N * m
The outward force at each of the wall screws (I chose it equally, which is a bit simplified, I guess) is (0,15m + 0,05m + 0,05m) * 3 * F_x = 177 Nm => 708 N/3 = 72 Kg/3 => F_x = 25 Kg each?
Yes, I know that I can put up a new drywall that can handle more loads, or I can place a stud or something equivalent to reinforce the TV mount. I just wanted to check if this makes sense from a theoretical viewpoint. There are, of course, some safety margins to consider (30% or so?), but I'll have to deal with that later I guess.
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Do not mount the unit into Drywall using any kind of anchor.
The best way to do it is to cut out a portion of the drywall where you will be mounting the unit and installing board(s) between existing studs, then reinstalling the drywall and mudding it up.
If you cut the drywall carefully you can put the same piece back and just tape and mud around it.
"Ten men in the country could buy the world and ten million can’t buy enough to eat." Will Rogers
PartsBin an Electronics Part Organizer - Release Version 1.3.0 JaxCoder.com
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That is probably what I'll end up doing anyway, but I'm still curious if it will hold. 
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It may hold while against the wall but as soon as you extend it, it will end up on the floor!
"Ten men in the country could buy the world and ten million can’t buy enough to eat." Will Rogers
PartsBin an Electronics Part Organizer - Release Version 1.3.0 JaxCoder.com
Latest Article: SimpleWizardUpdate
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Ditto on last 2 comments from Mike. The weight (torque will be magnified by the length of the arm (moment arm) so dry wall just does not cut it.
"A little time, a little trouble, your better day"
Badfinger
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Mike's right: the stress when it's extended isn't applied linearly on all the screws: the top pair will have more weight on them as the TV tries to pivot around the whole plate, pushing the lower screws inward, towards the wall.
And that's before any kids / grandkids / drunks lean or swing on the TV!
Use a solid foundation, and you'll be fine.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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Will it hold? Sure, but the question is for how long.
Over time, the drywall will crack internally and lose strength as the TV is moved around, eventually getting closer and closer to just the backing paper holding the TV up.
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"installing board(s) between existing studs"
An excellent suggestion.
Swing arm suggests someone wants to move it and even if drywall might hold a fixed mount I can't see it staying up over time when moving it.
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please do.
CI/CD = Continuous Impediment/Continuous Despair
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You mean moment, not momentum, I believe.
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I wouldn't do it. Over time those stupid drywall anchors work their way out, unless you use the butterfly type.
What I would do is install a couple of cross braces between the studs and mount the TV to that using lag bolts.
Check out my IoT graphics library here:
https://honeythecodewitch.com/gfx
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I've even had butterfly anchors come out, along with a chunk of the drywall.
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Yeah, tbh i don't really trust them either. Drywall isn't meant to bear any kind of load.
Check out my IoT graphics library here:
https://honeythecodewitch.com/gfx
And my IoT UI/User Experience library here:
https://honeythecodewitch.com/uix
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You could do all sorts of theoretical calculations but none of them would take into account the complex loads applied by kids (or grandkids) swinging on the end of the arm or by the cleaner doing whatever cleaners do (not currently understood by humans).
Phil
The opinions expressed in this post are not necessarily those of the author, especially if you find them impolite, inaccurate or inflammatory.
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kids (or grandkids) swinging on the end of the arm
You'd hope if said kids are tall enough to reach the arm, they'd be smart enough not to do that.
But, never underestimate what children's stupidity lack of fear will make them do.
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Even 1-year olds are tall enough when they have climbed on the dog and a chair!
Phil
The opinions expressed in this post are not necessarily those of the author, especially if you find them impolite, inaccurate or inflammatory.
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Don't do drywall. It's glorified cardboard.
GCS/GE d--(d) s-/+ a C+++ U+++ P-- L+@ E-- W+++ N+ o+ K- w+++ O? M-- V? PS+ PE Y+ PGP t+ 5? X R+++ tv-- b+(+++) DI+++ D++ G e++ h--- r+++ y+++* Weapons extension: ma- k++ F+2 X
The shortest horror story: On Error Resume Next
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I was thinking more on the lines of chalk with a paper cover.
I’ve given up trying to be calm. However, I am open to feeling slightly less agitated.
I’m begging you for the benefit of everyone, don’t be STUPID.
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Depending on your skills, get a nice piece of wood screwed into nearby studs through the drywall.. Then paint it the same color as the wall. Mount the TV swing arm to that wood. Anybody that judges you for this isn't a friend 
Hogan
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or when judgmental company visits, push the TV back against the wall to cover the hacked up drywall!
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Would a longer arm let you reach a stud? It might be easier than messing with the wall.
I think one of the benefits of using an arm mount is you have more flexibility in where you attach it to the wall vs where you want the tv to rest.
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Don't cut the drywall. Just mount a 1 X 4 to two studs. Then mount the swing arm to the 1 X 4. Paint the 1 X 4 to match the drywall. Don't make it difficult.
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I ran into this problem over a decade ago at a previous home. I wanted to mount the TV over the fireplace but found that the studs were a few inches beyound the width of the mounting bracket. I bought a really nice piece of oak (3/4 x 6 x 30 I think), sanded it, put a nice stain on it, mounted it to the studs, then centered the TV bracket on that with lag bolts.
The difference is that my bracket didtn't extend or swivel, so the mounting board was pretty much hidden by the TV itself. Also, this was around 2009 and the original 42 inch flat screen I was hanging weighed 3x what they are today. (probably 35-40 lbs)
The really fun part was adding a receptacle and hdmi plug behind the TV and running those wires behind the wall/fireplace. 
"Go forth into the source" - Neal Morse
"Hope is contagious"
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