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I have a TV here which weighs around 15 kg. It fits perfectly into the alcove next to my chimney breast, but that's not a convenient viewing angle. So what I want to do is build an arm which attaches to the wall and can swing out and let me use it, and also swing right back in to allow the TV screen to tuck back out of the way.

So I designed this thing here. It's essentially two frames inside eachother. The inner frame is designed to transfer the weight of the TV to the left-hand side, which is attached by hinges to the outermost frame. That's why the bottom-most part of the innermost frame is at that angle. I believe that will transfer the weight in the expected direction.

Then the outer frame is the same, but in reverse. It transfers the weight from the left-hand side to the right-hand side, where it will attach in the same way, by hinges, to a post that's firmly bolted to the wall.

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I put half dovetailed lap joints in all corners except the one with an acute angle. That's because that joint will experience more of a compressive force, so a bridle joint will probably fit okay there. And I think they're easier to cut so that's why I chose it. And the halfdovetaillapjoints are for joints which I think will be more pulled apart at, than pushed together by the weight of the TV. The idea is to glue and clamp these joints. I possibly will not need to use screws.

The whole thing will be made from 1.5"x1.5" pine.

Is this design going to work as I think it will? That is, will the weight be transferred in the manner that I expect?

  • hopefully you understand the diagram. When it comes to CAD and such things, I DON'T KNOW. – Wilson Dec 16 '18 at 20:31
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    This is an interesting design but how are you attaching the TV to the inner frame? The VESA mount on the back of the TV would be the most obvious and safest way I can think of. I would recommend building a prototype and installing a weight that is heavier than your TV to see how the joints hold up with movement and when the entire mechanism is fully-extended. You didn't give dimensions for the TV or your custom mount, but I'm skeptical about 1.5" pine being adequate to hold up to the racking forces. The torque exerted by the TV will multiply the further it extends from the wall. – rob Dec 16 '18 at 21:25
  • @Rob yes I will attach the tv by the vesa mounts. I figure a couple strips of metal will screw into both the inner frame and the tv. Makes sense? – Wilson Dec 16 '18 at 21:36
  • I'd start by making the hinge all thread, and using laminated ply for the beams. April Wilkinson did a YouTube video on a swing out chair recently that has a design you could probably use – Sirex Dec 17 '18 at 6:31
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    The answers so far focus heavily on the wood and joints. Take into consideration the hinges & screws that mount them. You're going to have 15Kg hanging upwards of a meter (just guessing) from the wall. Your diagram shows small hinges with just 2 screws in each leaf holding that weight. I'd want a substantially heavier hinge than what you're showing. I'd consider using door hinges and the screws that come with them. A solid wood door would (probably) weigh somewhere in the 15-30 Kg range and these types of hinges are designed for that weight. – FreeMan Dec 17 '18 at 14:03
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There are several challenges with your design.

  • Since you do not give dimensions for the frame, I will assume it is fairly large. The greater the width the more rotational force will be applied the back frame at the left side where the TV frame mounts to the back frame. This load will have a tendency to cause the back frame to lower at the left. To counter this force you will need to apply cross braces to the back frame to keep the corners square. These cross braces will prevent the TV frame from nesting inside the back frame.
  • As The TV is extended out from the wall, the TV frame will be at an angle to the back frame. This may cause rotational torque which must be resisted by the back frame. The 1.5"deep members will not be deep enough (front to back) to resist this force. The loads you are designing for are not merely the weight of the TV. The weight is magnified by the distance of the back frame width. Think of the mechanical advantage gained from a lever and fulcrum.
  • I am not sure how the half dovetail joints you show will be strong enough to resist the forces. Dovetails work fine for drawer assemblies, but remember there are many dovetails in a box joint. Here you only have one and the tails may not be long enough to avoid wood failure in sheer along the length of the wood in the tail.

I'm sorry to say that there are no simple rules for sizing the members of this frame assembly. My first instinct would be to use a manufactured metal assembly designed to mount a TV rather than experimenting with a makeshift wood project.

  • I agree on using a purchased TV mount. Unless you have a few TVs you're willing to experiment with and are willing to have them fall. – FreeMan Dec 17 '18 at 13:59
  • A brain fart on my part was to not give the dimensions. What I had in mind was an external width of 36" or thereabouts, but that's a point of flexibility. If it's shorter, then I guess the load won't be as bad. Thanks for this answer. I'll study it properly later on. Can you explain what "cross braces" are; are they horizontal and connect the vertical sides? – Wilson Dec 17 '18 at 15:31
  • @Wilson - cross bracing would go diagonally from one corner to another to keep the whole thing from racking/collapsing. I'd consider putting some thin plywood to stiffen the whole thing. Put one sheet on the back of the larger frame (so the smaller frame will still fit between), then put a sheet on the front of the smaller frame (so it doesn't interfere with closing). While TVs are certainly a lot cheaper than they used to be, I'd still tend toward buying a professionally engineered, metal mount for this. – FreeMan Dec 17 '18 at 15:55
  • I took your advice, I have a thing now that's made of metal, not wood. – Wilson Sep 4 at 11:53

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