1

enter image description here

enter image description here

The L brackets are rated for 60kg each. Do I need to add more support or is this strong enought?

CesarX
  • 11
  • 1
  • Hard to say since we don't know what load you are going to put on it. If this were my project I'd add more supports and also make them reach closer to the edge. As a user of this desk you don't want it to break when you lean on it. – jwh20 Jan 20 '22 at 21:14
  • Would not want to sit on the front edge. – crip659 Jan 20 '22 at 22:02
  • Plywood spans is rated as follows: 1) 3/4” = 4’ and support 60 lbs. per square foot (psf), 2) 5/8” = 24” and support 55 psf, 3) 1/2” = 16” and support 50 psf. Adjust your brackets accordingly. – Lee Sam Jan 20 '22 at 22:04
  • @jwh20, load information is right in the diagram. – isherwood Jan 20 '22 at 22:22
  • The desk and support system looks sturdy, but will it stands in place is another story. It depends on the strength of the attachment of the brackets to the wall, whether they are attached by strong enough screws to the studs with an adequate embedment length. If there are studs behind each bracket, I would stand a little distance away from the edge and gradually put my upper body weight on it. Wear steel-toed boots while doing this :) The better way is to get the allowable pullout strength of the screw in wood and do some calculations, which is not quite straightforward. – r13 Jan 20 '22 at 22:25
  • It appears that the right-hand edge of the desk abuts the wall. I would recommend a wooden cleat (2"x4" in US terms, something similar in your local lumber yard) be placed along the right hand wall just underneath the desk surface. The desk doesn't have to be screwed down to this cleat (that will help), gravity will ensure that the cleat is supporting the surface. Also, it doesn't have to run all the way to the front edge (unless it's necessary to get to a stud for support), it can stop short and have a tapered front end to finish it nicely and prevent bumping knees on it. – FreeMan Jan 21 '22 at 14:12
  • This cleat could even replace the right-hand most metal bracket, allowing that bracket to be slid to the left to even out the spans somewhat. It could be the 4th bracket described in isherwood's answer. – FreeMan Jan 21 '22 at 14:13

1 Answers1

3

I think you're close, but I like to have my brackets extend at least 2/3 the depth of the desk. This is as much a matter of supporting the top as it is keeping the stresses on the wall attachment reasonable--the shorter the bracket is with respect to the desktop's depth, the exponentially greater the pullout force on the top fastener and the pressure on the bottom of the bracket.

In cases like this where they don't quite meet that standard (and a larger size isn't available), I extend the bracket with a length of lumber secured along the top bar of the bracket which is a bit longer than the bracket--maybe 65cm on your 80cm desk. It's critical that this be secured well at the back end. It's also critical that the brackets are robustly secured to the wall as they'll have strong pullout forces applied near the top. Good brackets have two screw holes there.

Then, I'd probably go with four brackets. This type of bracket is unlikely to be a knee space issue, so you can add more. I don't normally go more than two U.S. stud spaces, or 32" (about 80cm). You're over 100cm. If that's not an option due to your wall framing, put two closer together in the central area and one toward each end.

3cm plywood of good quality will be nice and stiff. That's the rough equivalent of 1-1/8" in English units. You shouldn't see sag front-to-back along the front edge since there won't be a lot of load there, especially if you extend the brackets.

isherwood
  • 137,324
  • 8
  • 170
  • 404
  • Great answer, minor nitpick: force applied to the cantilever is linearly multiplied by the distance from the pivot. Your point about it significantly increasing the pullout force is valid and important but "exponentially" has quantifiable meaning in engineering and this doesn't apply :) – Matthew Jan 21 '22 at 05:02
  • I understand the term, but I'm not sure I agree. I'd expect that the torque and related forces increase at more than a linear rate as the height of the bracket approaches zero. – isherwood Jan 21 '22 at 13:43
  • 1
    Thinking about this more, we're both wrong but you're more correct than me. I'm not going to work it out but the pullout force should be proportional to the torque times the sine of the angle, which increases faster-than-linearly as it increases from zero. Sorry to cast doubt on you! – Matthew Jan 21 '22 at 15:25