Johnno Posted February 1, 2007 Share Posted February 1, 2007 Our on-stage lighting bars are about thirty feet long and held up at three points. The pipe ends extend about six feet beyond the outermost points of suspension. Hanging two fresnels (Strand #223) near the ends has caused the pipe to flex under their weight dropping the end by about two inches. When focussing, the lanterns bob up-and-down like ducks. I don't think it's unsafe but it is a tad alarming. I'm considering putting a timber batten across the roof beams and fixing some rope or chain around the pipe basically just to stop it bouncing. Is there any advice anywhere concerning rigging near pipe ends? Link to comment Share on other sites More sharing options...
paulears Posted February 1, 2007 Share Posted February 1, 2007 2" down on a 6 foot overhang seems a bit much, unless the centre sections are completely unweighted. A 1K Fresnel isn't that heavy - might be worth checking the wall thickness of the tube - is it 48mm thick wall alloy or thin wall 50mm aerial style tube? Rather than use some kind of out-rigged extra support, I'd go for a length of twin chord lightweight truss. Link to comment Share on other sites More sharing options...
Johnno Posted February 1, 2007 Author Share Posted February 1, 2007 Sorry, I should've said there isn't anything else on the pipe. The centre section is completely obscured by the casing of our drop-down projection screen so can only be used for vertical lighting, and two inches was a guess viewed from ground level. I'll get up with a tape ASAP. Link to comment Share on other sites More sharing options...
Rob Posted February 1, 2007 Share Posted February 1, 2007 It might be worth you creating a bridle at each lifting point instead of just having the flying line / steel cable going straight to the pipe - This would provide support closer to the ends of the pipe. This sort of demonstrates it: If for instance your lifting point was a steel cable coming out of the roof with an eye on the end, you would insert a shackle and then two short steels which would be connected to the pipe, equally spaced apart. This might not be practical if you are short on flying height. All the usual caveats apply - if you aren't competent / don't know how to calculate the load distribution etc etc... Link to comment Share on other sites More sharing options...
AndrewR Posted February 1, 2007 Share Posted February 1, 2007 From the sound of it its just because you are canterlevering the freznels. The weigh of them is pivoting round the outer supports and lifting the center of the bar. Before re-rigging the bar try adding some weight to the middle of it. It should help flatten out the bar and dampen the springness. Usual proviso's blah blah :D :) Link to comment Share on other sites More sharing options...
paulears Posted February 1, 2007 Share Posted February 1, 2007 I'd thought of that one, but came to the conclusion that the weight of the bar, from the outer hanging wire to the centre would be a lot more than the weight of a 223? Maybe with a mover, but I'm not sure about a 1K. Link to comment Share on other sites More sharing options...
AndrewR Posted February 2, 2007 Share Posted February 2, 2007 I'd thought of that one, but came to the conclusion that the weight of the bar, from the outer hanging wire to the centre would be a lot more than the weight of a 223? Maybe with a mover, but I'm not sure about a 1K. Ah! but it only needs to weigh more than 3 foot of bar! (based purely on a quick mental estimate) And I seem to remember 223's are fairly darn heavy! Although even if its a little bit short it will back the bar wobble a fair bit... Link to comment Share on other sites More sharing options...
Don Allen Posted February 2, 2007 Share Posted February 2, 2007 Did not realise it until now but Stand did not put weight in their Patt 223 brochures. Found a site Robin Barton UK http://www.thebartons.org.uk/robin/theatrical/fixtures.php that lists the Patt 223 as 6.8 Kg. Knew they were heavy. Link to comment Share on other sites More sharing options...
Johnno Posted February 3, 2007 Author Share Posted February 3, 2007 In the OP I meant that there are two lanterns at each side. One of them is a #223 and the other is actually a Furse but as they weigh about the same I just said two Strands. This has been my least clear post on the BR. Sorry for the confusion. Thank you for reading it! ;) The pipe is permanently fixed to beam brackets, not hanging on wires. Are there any useful books on rigging? Chris Higgs seems to be well thought of. Link to comment Share on other sites More sharing options...
Chris Higgs Posted February 4, 2007 Share Posted February 4, 2007 Only by people who don't know me. I would have said that the cantilever was a bit long - around a metre is generally recommended in Standards. Link to comment Share on other sites More sharing options...
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