Flying with wire rope - how thin can I go?

[Fletch]

Hi,

 

I would like some help to work out a suitable wire rope to use.....

 

I'm involved in an amateur production of City of Angels and we'd like to make use of the counter weight flying system withn the host theatre to fly some flats. The flying system already terminates to bars so I just need to attach the wire ropes to the bars, using hanging clamps or something similar. We've done this before using 5mm wire rope to BS302 and grips spec'd to DIN1142, as advised by the supplier.

 

However it all seemed slightly over kill as the spec of the cable and grips is something over 1000KG and the flats probably only weight 15KG each, plus the rope looked unsightly as it was fat! I've read some of the lifting regulations, and talked to people at a few suppliers, and I get the impression I have to use 5mm rope as the load is dynamic, although no one will quite give me a definitive answer. Is this really the case or could I use 3mm or even 2mm rope, assuming the load capacity of the rope was up to the job? and if that's possible which grips do I use?

 

Any into greatly appreciated. I'm on to the ABTT to get a copy of their guide to flying and wire ropes.

 

Cheers

Fletch

[gareth]

It all comes down to the load that you're flying (and you're right to consider the dynamic nature of a load being flown in or out). I'll leave it to someone with greater knowledge than me to talk about things like selecting the right size and type of wire rope, terminations, etc. - but as a very rough guide, I seem to recall 2mm having a SWL of something like a quarter of a ton (reduce by the appropriate safety factor when working out how much you can actually hang on it).

 

If seeing the wires is a problem, look at using black wire (either PVC-covered, or the rather nice stuff that's actually coloured black), which is readily available from places like Flints or Rope Assemblies.

[paulears]

I'd like to think I'm quite good with numbers, but would own up to always oversizing. I was hanging some kit in a venue once, and despite checking the specs, over and over again - couldn't really believe what they were telling me - so I used 6mm! Mainly because there was no doubt at all that it would still be fine if somebody in the future used up the remaining free space and hung bigger, or simply more kit. Many venues have stock drifts made up for hanging things like yours - the big snag I've always found is weighing them - or more usually, being unable to weigh them - so hanging things on larger wire seems a sensible precaution unless you actually know how much your flats weigh?

[Ellis]

Fletch,

 

The ABTT guidelines specify a safety factor of 8. In other words, the minimum breaking strain of any part of the system should be at least 8 times the load to be applied. AFAIK this takes into account the dynamic nature of the load. While the steel wire will have a specified safe working load, the process of making it off to the bar and the item being flown will weaken the line and reduce its SWL.

 

DIN bulldogs, while easy to fit are actually difficult to fit correctly. The nuts need to be tightened to a specified torque to balance grip with the weakening effect on the wire. Once made of they should be proof tested.

 

Your simplest solution would be to discuss your requirements with someone like Rope Assemblies. They can make you tested drift wires to meet your requirements and supply them with test certificates stating their swl.

 

Remember that you should have at least three lines on every item, with any two being able to take the entire load within their SWL.

 

As for the SWL of a 5mm steel wire rope Rope assemblies state the following SWLs at 8:1

 

7x7 Wire Core Construction : 188 kg

6x19 Fibre Core Construction : 174 kg

 

That is a hell of a lot lower than your figure of 1000kg (the breaking strain if the 7x7 Wire Core is given as 1500kg). these figures will then be reduced by the process of makign them off.

 

Like many areas of technical theare, flying has the potential to cause serious injury if not done correctly. Talk to the technicians at your host theatre, talk to a expert supplier who specialise in theatre work and keep records for all equipment used.

 

Above all, if the director does not like the look of the wires, don't use the wires - in other words, don't fly anything with under-rated lifting equipment.

[Fletch]

Hi,

 

Thanks for all your advice.

 

Ellis - You are correct I stated the breaking strain of the rope. I do have a torque wrench but you are correct, proofing the cables is more complex.

 

Here is a bit more detailed stance on my question - I didn't put it very eloquently before so I'll add some more....

 

The maths bit.......

If you include the 8 by safety factor then you get a figure of (and including 85% efficiency for using dog clips - not sure if I need to do that but it's safer) 146KG, for the 5mm rope we had from Flints for our last show. I estimate the flats to weigh no more than 40KG - I can lift them easily as they are wood frames with canvas covers - so probably less than that. As you can see that is over 3 times the required load and I haven't even considered the fact that this will be spread over 2 wires (using 3 to fly with the 3rd in affect being a safety).

 

Looking at 2mm wire (and assuming I use acceptable grips or pre-made wire) then the SWL is stated as 33KG with an 8 x safety factor (from rope assemblies www.ropeassemblies.co.uk/catalogue.php?id2=45&id=81). So in my mind it seems that this will be adequate (with 3 of them) to fly a flat weighing no more than 66KG, so I'm still 20KG in hand.

 

My real question..........

With this in mind, I was wondering what the considerations are on using rope thinner than 5mm (apart from SWL question which I think we have covered), and indeed if it was an acceptable practice for flying scenery in terms of regs and BS / EN standards? I'm just a bit thrown by some of the regs etc and was wondering whether there is a blanket rule on only using wire rope greater than 5mm or if this isn't the case, as the maths suggest 2mm rope will be adequate.

 

If in doubt I'll use over spec'd rope like last time and I agree pre-made wire would be best - I'll get some more advice from Flints and Rope Assemblies.

 

Gareth - Black wire is a good suggestion - unfortunately it's a bit prohibitively expensive, more than twice the price!

 

Thanks all,

 

Fletch

[robloxley]

Ref black wire: your director won't see if the wire is thin or thick, just whether it shines/reflects or is inconspicuous black, IMHO.

Also think about future use when making up drifts, as in the future you may want something a bit stronger and not to have to buy a whole new set of drifts.

Would always go for premade & tested assemblies rather than the hassle of dogs etc.

[Jivemaster]

You can black the ropes with spray paint or a big felt pen!

 

However, as the venue is ultimately responsible to HSE for all the happenings there you must convince them that you have done all required to ensure safety, so they hold the upper hand. You have to prove to them that your design is safe, inc static, and dynamic components and loads and safety factors, Also considering fixing methods.

[trussmonkey]

why black things out with black paint or marker pens when black steel wire rope is pennies more than the galvanised version. Talk to Siobhan at Rope Assemblies they are fantastic. They will almost next day it to you and give you great advise too . I have used them for years

 

TM

[Andrew C]

why black things out with black paint or marker pens when black steel wire rope is pennies more than the galvanised version.

I refer the Honourable Gentleman to the answer given previously

Gareth - Black wire is a good suggestion - unfortunately it's a bit prohibitively expensive, more than twice the price!

[Fletch]

Hi All,

 

Thanks for the info - I spoke to a very helpful chap at Flints who told me almost everything I need to know! Will have a chat with Rope Assemblies too (thanks for the name trussmonkey) and compare the costs.

 

Getting pre-made drifts is best as they are tested which isn't something most people can do, I certainly can't, and as previously suggested painting a standard steel is not a problem - so a can of matt black spray it is - and as we are am dram the cheap option is the winner! Also, for anyone who reads this, it was also suggested to use rated shackles for any connections to flats etc, such as Crosby ones. Common sense really, but not unless you've done it before!

 

Sorted.

 

Thanks

Fletch

[gareth]

Glad you've found a solution that works for you. You're quite right to use rated shackles - under LOLER, any component of a suspension system has to be rated, with the potential for big trouble if it isn't!

[Ellis]

Glad you've found a solution that works for you. You're quite right to use rated shackles - under LOLER, any component of a suspension system has to be rated, with the potential for big trouble if it isn't!

Not only should EVERY component of your lifting system be SWL or WWL rated (and labelled), everything should have a unique identity marked on it and the certificate isued by the supplier or tester.

 

As for the venue being ultimately responsible, that is not the case. The venue are responsible for ensuing that their equipment is safe. The producers of a show are responsible for all aspects of their production. In the intersts of their own safety, many venue staff will help visiting companies to keep their production safe.

[erroneousblack]

DIN bulldogs, while easy to fit are actually difficult to fit correctly. The nuts need to be tightened to a specified torque to balance grip with the weakening effect on the wire. Once made of they should be proof tested.

 

3.5 Newton Metres to be precise!

 

Remember to take care of your shackles, the only time you should ever unscrew them is when your attatching them!

[Ellis]

 

DIN bulldogs, while easy to fit are actually difficult to fit correctly. The nuts need to be tightened to a specified torque to balance grip with the weakening effect on the wire. Once made of they should be proof tested.

 

3.5 Newton Metres to be precise!

 

 

IIRC, the torque is different for each size of bulldog - covering two different torque wrench ranges.

[erroneousblack]

IIRC, the torque is different for each size of bulldog - covering two different torque wrench ranges.

Quite right Ellis, I failed to add that this is for 6mm wire rope, which is the most common used in mainstream theatre.