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I have a boom lamp from CB2 that's about two years old in my living room. The angle between the arm and the stand is adjustable. Unfortunately, the mechanism that holds the lamp up (I'm afraid I don't know the correct term for it, but you can see it below) seems to have stopped working and now within a day or two of my adjusting it, it succumbs to gravity and the lamp head falls to the lowest possible setting. Is there anything I can do to keep the head of the lamp up short of epoxying it in place?

View of the faulty mechanism in the lamp's handle

EDIT: at the risk of outing myself as a complete noob I have attached an image below with the component I plan to fit the washer to circled in red. The washer will go inside of the joint mechanism so that it's not visible when the lamp is fully assembled.

Lamp, taken apart

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It looks like there are teeth that should prevent it from moving -- does the knob loosen and allow it to fall? How easy is it to move the arm by pulling on it (while it's tightened)? I notice you've tagged with "epoxy" -- is that an acceptable fix, that will not allow this to move anymore? –  gregmac Nov 11 '13 at 1:45
    
I'm unable to get the teeth tight enough that I can't change the angle manually. I suppose this means that the knob does not lead to loosen more than a little in order for the lamp to fall, but I will check on the state of the knob next time the lamp does fall. I would prefer to avoid epoxying the lamp in place and am hoping to find alternatives but would certainly prefer epoxying to throwing the lamp away. –  kuzzooroo Nov 11 '13 at 1:56
    
If you are unable to get the teeth tight enough that you can't change the angle manually, it sounds like the screw is not properly engaging the threads, i.e, it's stripped. I assume you've tried pliers. You may be able to use a tap and die to re-thread both the screw and the nut. Or, you may be able to find replacement parts online. –  getterdun Nov 11 '13 at 5:55
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4 Answers

up vote 1 down vote accepted

It sounds as if the knurled knob loosens over time. There are a number of solutions.

The knurled knob seems to be either the head of a bolt or a specialized nut. In either case, a washer between the knurled head and the body of the lamp arm may help. A flat washer may be enough.

flat washer

If not a lock washer should help.

lock washer

Another approach is a locking fluid spread on the threads of the bolt that prevents loosening, such as this stuff.

locktite

There are different versions, depending on whether you want it to be removeable or permanent.

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Another solution may be to use a rubber washer, even an o-ring. That will absorb the small vibrations that typically allow screws to loosen as well as provide better friction. Rubber, silicon, or felt should work. –  Jason Nov 11 '13 at 17:03
    
@Jason Good point! (Although some felt is fairly slippery). –  bib Nov 11 '13 at 17:40
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There is no way that the teeth of this mechanism is faulty, you can see they are quite sharp still.

So the failure is coming from one of the following:

  1. You are not tightening the nut hard enough
  2. The thread of the nut has stripped and comes loose automatically
  3. The movement/weight of the load is loosening the bolt

possible solutions to the listed scenarios are as follows

  1. rock the arm back and forward while tighten the nut with your other hand.
  2. Go to the local hardware and buy a Wingnut to replace the current nut (to match the current bolt. wingnut
  3. In this case, the proposed washer should work perfectly

I would recommend the use of the wingnut and washer.

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Do not put the washer on the inside, that will either do nothing or make the situation worse. The washer idea would need to be of the outside so that the teeth still engage, the washer would just work to fill the gap between the screw/threaded rod and the nut allowing a more snug fit.

I have another idea though. Without seeing the rest of the inside it is impossible to tell but it looks like the threaded section is a threaded rod:

enter image description here

Why that is important is because it doesn't have a defined end on either side and can come loose. If my guess is right, there is a nut on the inside holding it in and most likely is a knurled furniture nut molded into the plastic (not important to fully understand). So, if I'm right with the outer nut removed (your knob) you should be able to turn the threaded section (this may be fairly difficult still). If you can, turn it in the same direction you would to tighten the knob on and keep turning in until you can't; then try the putting on the knob a securing it tight. You should notice a difference immediately, if you weren't able to turn the threaded rod then I probably just guessed wrong, sorry it happens.

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I suspect the toothed mechanism is not well made, having met several examples of similar mechanisms that were cranked out by the lowest third-world bidder to vaguely look like the right thing, but with no hope of working. If I'm wrong, one of the other answers will work.

If I'm right, physics is your friend. There appears to be a counterweight on the lamp arm (opposite the head of the lamp.) If it is adjustable (might have a clamping screw or something like that), move it further out the arm. If it is not adjustable, add some weight to it. Get the lamp closer to (or exactly) balanced, so that the pivot mechanism is not fighting the lamp wanting to slump one direction.

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