landy Posted November 7, 2006 Share Posted November 7, 2006 Mornin' all, with google giving me no joy I come asking your opinion. I have come across some wall bracket, you know the standard type Like this but they are rigged horizontally in pairs with an alli barrel in between. The lamps are then rigged off half twist boom arms. Now I can see why it was done this way as the walls inconveniently have lots of windows, but I have a nagging thought that this is bad / not so good practise. Opinions? Moderation:Link Fixed Link to comment Share on other sites More sharing options...
Bryson Posted November 7, 2006 Share Posted November 7, 2006 For some reason (bizarre website coding, I think) the link you provided has no pics and none of the buttons work properly. So here's the pic in question: http://www.flints.co.uk/acatalog/Dout_Pipe_to_Wall.JPG If the pipe is mounted horizontally, why the boom arms? What prevents the lights from just hanging on the pipe? That said, I can't see any reason why these shouldn't be used horizontally, or vertically. But I'd only use a boom arm if the pipe is vertical. Link to comment Share on other sites More sharing options...
Brian Posted November 7, 2006 Share Posted November 7, 2006 As long as they are rated for the job they are fine. Link to comment Share on other sites More sharing options...
landy Posted November 7, 2006 Author Share Posted November 7, 2006 If the pipe is mounted horizontally, why the boom arms? What prevents the lights from just hanging on the pipe? That said, I can't see any reason why these shouldn't be used horizontally, or vertically. But I'd only use a boom arm if the pipe is vertical. Sorry for not being clear, the brackets are horizontal and the barrel is vertical. Odd about the link as I tested it once posted. Link to comment Share on other sites More sharing options...
Bryson Posted November 7, 2006 Share Posted November 7, 2006 Ah. Well that's pretty common practice. I have two right here. Don't worry about it. (Assuming that Brian's post has also been attended to, obviously.) Link to comment Share on other sites More sharing options...
Brian Posted November 7, 2006 Share Posted November 7, 2006 Sorry for not being clear, the brackets are horizontal and the barrel is vertical.This is certainly the weakest orientation for them. All the weight is trying to twist the brackets arms downwards where they meet the wall. I don't have time to work out the force required to do that at the moment but my feeling is that it's not that high. Link to comment Share on other sites More sharing options...
landy Posted November 7, 2006 Author Share Posted November 7, 2006 Many thanks chaps, presently there are 3 650W type lamps rigged but my worry was 'next time' when thing get bigger and better. Link to comment Share on other sites More sharing options...
Bryson Posted November 7, 2006 Share Posted November 7, 2006 It's the actual fixings and the wall I'd be worried about, rather than the brackets. It wants to be fixed into a good sturdy wall with some good solid Rawlbolts or similar. Link to comment Share on other sites More sharing options...
landy Posted November 7, 2006 Author Share Posted November 7, 2006 I am told its M10 rawlbolt, and the chap installing it had trouble drilling into the wall, which hints at a firm wall. Link to comment Share on other sites More sharing options...
jayselway Posted November 8, 2006 Share Posted November 8, 2006 Trouble drilling also can mean that situation you get where it goes: "Drill, Drill, Drill, LURCH" and the chuck is suddenly up against the wall! Had that all day today with cr*p walls in a venue I'm refurbing! Link to comment Share on other sites More sharing options...
Mikey Posted November 8, 2006 Share Posted November 8, 2006 Those brackets are fine for a vertical bar. I've stood on brackets mounted the way you want them (I'm not that slim!). The weakest point is your wall fixings, as long as they're sound you're sorted.I would maybe put a scaff clamp or bolt through the vertical tube to make sure it never slips downwards through the saddles. Cheers, Mike. Link to comment Share on other sites More sharing options...
Seano Posted November 8, 2006 Share Posted November 8, 2006 I would maybe put a scaff clamp or bolt through the vertical tube to make sure it never slips downwards through the saddles. Possibly not a great idea. Mounted vertically (with a horizontal bar) one individual bracket is strong.To take a closer look at the forces acting on the bracket. You've got the weight of the bar pulling down on the left, and the friction of the "feet" against the wall, combined with the sheer strength of the bolts providing a force upwards over on the right. Because these forces aren't in line, there's are also some moments (as in torque, not time) to think about - the weight on the left and the reaction on the right result in a moment trying to turn the bracket anticlockwise. This is counteracted by a moment made up by the horizontal forces at the feet - on the top foot, the bolt under tension pulling the foot into the wall, and on the bottom foot the wall pushing against the foot - together they make an equal and opposite moment trying to turn the bracket clockwise. The distance between the feet is roughly the same as the distance between the bar and the wall - so those horizontal forces have about the same magnitude as the weight of the bar. Mounted horizontally (vertical bar), one individual bracket is not strong.At each foot that resisting moment (kind of) consists of the tension of the bolt pulling the middle of the "foot" in, and the wall pushing against the bottom of the "foot". These are only half the width of the bracket apart, and so the force pulling on the bolt (and crushing the plaster on the wall) is much greater than the weight of the bar. Its like trying to lever out the bolt with a crowbar. Therefore, if you were to mount a vertical bar using just one of these brackets, that would be bad. Fortunately, you don't do that - the bar has two or more brackets. When the saddle is nice and tight, the connection between the bar and the bracket is quite rigid. You can think of the brackets and the bar as a rigid object - the distance between the top and bottom bracket is quite a bit more than the distance between the bar and the wall, so the tension at the top bracket and compression at the bottom bracket are less than the weight of the bar. If the saddles were loose, and the bar was free to cottle about (but prevented from sliding by some kind of flexible connection), the bracket would be effectively on its own again - that 'crowbar' effect. So putting that clamp or bolt in just moves the problem along, from a slipping bar to potential failure of the brackets' fixings. Imo, its a better idea to use good quality locking nuts on the saddles and give them a good inspection for any signs of corrosion (and maybe a quick tweak with a torque wrench) on a regular basis. (Like, for example, each time you derig the lanterns to take them away and PAT test them.) Hope that makes sense. (But suspect it may not)Seanx Link to comment Share on other sites More sharing options...
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