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I am planning to hang a projector which weighs 8lbs (~3.5kg), on a wall arm.

The arm weighs 4lbs (~1.8kg) and has a load capacity of 44lbs (~19.9kg), and I'll be hanging the projector at the arm's minimum extension (~12").

The fact that the arm is extended away from the wall adds leverage and therefore increases the effective force applied by the weight of the projector so as far as the wall is concerned, it's not just the 8lbs. I'm not savvy enough to calculate this though- perhaps someone can point me in the right direction?

I have (to be confirmed) found a 2" stud with a stud detector in what appears to be 1/2" or 5/8" drywall/plasterboard. I have some molly bolts, various size screws with rawl plugs available.

I am wondering

  1. If I put 2 screws into the stud and 2 molly bolts in the plasterboard would it likely hold?
  2. If it's not a stud, and I use 4 molly bolts, would it likely hold?

Commonly people suggest placing a board behind the arm it seems, but I'm hastened to do this as effectively the questions above still apply.

There's equal leverage, but it increases probability that I would hit 1 or more studs, or enable me to spread the molly bolts around a greater area.

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The answer to "how do I mount an articulating arm to drywall" is "you don't". Find a stud. It's not worth taking the chance considering the cost of the projector.

Your best bet is to get this hung off of the stud. To do this effectively, you should firmly attach a piece of plywood or hardwood to the stud, and then attach the arm to the wood. I suggest pre-drilled lag bolts for attaching the plywood to the stud, and T-nuts with bolts and lock washers to attached the arm to the wood.

If you can't find a stud where you need one, then find them on either side, cut a piece of wood to span them, and bolt the arm to that piece of wood.

  • Do you think two screws into the stud and two molly bolts in the drywall would suffice? – Ben Swinburne May 8 '18 at 19:17
  • I suggest attaching the plywood to the stud with 2 lag bolts, and connecting the arm to the plywood with T-nuts and bolts with lock washers. Molly bolts will not be needed. – longneck May 8 '18 at 19:19
  • I appreciate that, but I'm asking about alternate options- especially as I'm not 100% sure i've found a stud yet or what it's made of. I need to drill and work out what's behind the wall. Exploring all my options :) Thanks! – Ben Swinburne May 8 '18 at 20:14
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    Don't hang it on the drywall. It's not worth the risk. If you don't have a stud right where you need one, then cut your wood to span 2 studs. – longneck May 8 '18 at 20:40
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Your plan is sound. The two screws in the stud, assuming adequate size (at least #14 x 2", properly piloted, for example), will carry the vertical load just fine. The two in the drywall merely add horizontal stability to keep the bracket from flexing against the drywall.

Use expanding togglers of some sort (as you had planned), not plugs.

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