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Not DIY hifi as such - but DIY woodwork nonetheless

J

jamington2004

pfm Member
Have a couple of ceiling brackets for my speakers - attached the ceiling joists with really chunky coach screws about 10mm thick and 10cm long

They have been supporting 20kg - and about rise to 25kg

Anyway, I need to pack them out at the top a bit to lower the bracket about an inch for my new speakers.

I am a bit worried about removing them completely as I am not sure if the coach screw will be as firm in the wood if I remove and put back in the same place (they need to go back in the same hole)

If the consensus is that they won’t be as strong when they go back in - the other option is to loosen them a bit and slide a shim / spacer in there, working around the coach screws in situ.

Any advice much appreciated :) :)
Kind regards
Jamie
 
10cm coach screws? Jesus, what are you hanging up, a car? In all seriousness, you will know if they are secure when you tighten them up. If they tighten up normally and you still have say 3/4 of the length in the joist then you can hang 25kg on them all day. You could hang me on them all day for that matter.
 
Ah good point thanks Barry. I guess I will know easily enough if I add the spacers in situ

but would rather remove them fully to add a proper spacer with the holes in the right place. What do you think about that will be the old hole still be useable if I get a slightly longer coach screw? Don’t really want to try it if not sure as I can’t move them and make a new hole
 
Thanks Steve reassuring to know I have gone overkill on the screws :)

same question remains to be really sure - removing the screws and reinserting them in the same hole won’t make them less secure?
 
Only less secure if you take them in or out many many times. Or if you pilot too large of a hole and overtighten them and damage the timber round the thread.

The force required to pull a regular screw from a joist is huge. For a coach screw? You’d need to have concrete or granite speakers before you came close to pulling that out as long as you’ve put the right size pilot in
 
Ok great thanks - I won’t be taking them out many many times.

I definitely didn’t drill a big pilot hole - would have just been a little one to get them going

I did however tighten them up with all my strength at the end! Lots of creaking noises and cracks in the plasterboard.

Didn’t want them to work lose over time but I guess now I know better :) :) :)
 
jamington2004 said:
Thanks Steve reassuring to know I have gone overkill on the screws :)

same question remains to be really sure - removing the screws and reinserting them in the same hole won’t make them less secure?
Click to expand...
Less secure? Yeah, probably only good for half a car.

In all seriousness, overkill isn't in it. Now one thing that you have done wrong is to load the screws in the weakest axis. That's why overkill is necessary, because you are pulling them directly out. If you were loading them in shear (ie 90 degrees) the failure force would be massive, but in tension a screw into softwood isn't great. Obviously it's difficult to attach a bracket to a joist and have the fasteners in shear, you can't do it without cutting holes in the ceiling and nobody wants to do that.

If your screws won't bite, then remove them and stick a bit of softwood up the hole. Matches or cocktail sticks are ideal. Then wind it up. You are back on hanging your granny territory once it nips up.

My dad is a retired craft teacher. One of the practicals he used to do with the kids was get them to estimate the failure strength of a 1" wood screw into softwood. He had a test rig with a cable and a hydraulic ram with a pressure gauge. The forces that one screw will take, in shear, are massive. None of the kids ever got close, they all imagined that you had to have 3 or 4 screws to hold the weight of a schoolkid. Not so, he had one screw into a beam with a bracket, and the single screw would hold his weight easily.
 
Awesome :)
Yeah that’s really interesting.
And thanks for the tip about shoving some matchsticks up there if it doesn’t tighten at the end
I knew about that for door hinges but had no idea that would work and keep this kind of thing secure :)

I will give it a go tomorrow and post back if come across any issues thanks everyone

love this place
 
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