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Torquing Wire Rope Grips


Bryson

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I just had a rigging inspection done. One of the primary findings was that the wire rope grips throughout the system were not torqued to the correct value. There's about 500 or so of the things in various positions (some easier to reach than others...) Not relishing the idea of clambering around the theatre with a manual torque wrench for the rest of my natural life, how would you go about fixing that?

 

Is a pneumatic torque wrench a good or bad idea for wire rope grips? Seems like it might be labour saving, but potentially hard on the gear?

 

Ideas please...

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Is a pneumatic torque wrench a good or bad idea for wire rope grips? Seems like it might be labour saving, but potentially hard on the gear?

 

I don't think it would be particularly labour saving tbh.

 

Unless the grips are falling off, each nut only needs nipping up by half a turn or so. Most of the effort lies in the clambering around and actually getting a socket onto the nut - that's only going to be made more laborious by using a bulkier, heavier tool. (Especially one with a hose hanging off it!)

 

I'd probably want to go the other way - smallest, lightest tool that gives you the leverage to nip it up tight enough. 1/4" drive is plenty, maybe a torque screwdriver rather than a more conventional ratchet.

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What kind of torque are we torquing (sorry) about?

 

Probably about 3.5 Nm (about 2.5 foot pounds in old money). Easily doable with a screwdriver style torque-wrench.

 

If they're a wee bit slack, I wonder if the problem is that they were done up 'properly' with a torque wrench in the first place.

 

The proper procedure is to torque them up, apply the load - and of course when you do that the rope stretches a bit, when it stretches longer it also gets thinner, so the grips become less tight - and then you torque them up again.

 

I can't imagine anyone installing flying gubbins in a theatrical setting loading a bar up to 100% to then re-torque the rope grips.

(But then it's equally rare, I suspect, for people to bother with a torque-wrench anyway and without them we all tend to overtighten things a bit... )

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What kind of torque are we torquing (sorry) about?

 

Probably about 3.5 Nm (about 2.5 foot pounds in old money). Easily doable with a screwdriver style torque-wrench.

 

I don't think that you would be able to get a torque wrench small enough - you will only be able to get torque screwdrivers for that kind of size. I bought one at work, and below about 10Nm, it's all screwdrivers.

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My thoughts;

 

What torque will your inspector sign off? How will he check? Check calibration to national standards?

 

If it's bench work then a power driver might help, but if it's access via the flies then a light weight tool will save on load while climbing. Is there a logging torque driver, does one even exist?

 

How will you log that all the threads have been torqued, to the satisfaction of the inspector.

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They're Crosbys. (What else?) ;) 1990s vintage.

 

The torque value is 15 ftlb as per the table I posted earlier. That's a bit high for screwdriver type application. Needs a socket wrench or similar to apply.

 

Looking at the tables, it seems that the UK requirements are a little different to North American. We do two grips, torqued much higher, rather than three.

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How would you determine 'The right value' for an unbranded, undatable grip that could be a year old or 50 years old?

 

Tighten it until it breaks, then throw it away. ;)

 

Probably about 3.5 Nm (about 2.5 foot pounds in old money).
15 foot pounds..

 

Well there's a thing - we're talking about two different types there, but pretty much the same size. I had no idea that EN 13411-5 Type B clips (aka US. Federal Spec. FFC-450-D) were so different to EN 13411-5 Type A clips (aka DIN 1142). 15 ft.lbs for the 1/4" type B -vs- 2.6 ft.lbs for the 6.5mm type A.

 

Can anyone shed some light on that? Is there a metallurgist in the house?

 

For reference, here's another data sheet with both types: Van Beest (Green Pin) clicky. (Ignore the DIN 741 clips - they're ok to string a wire fence together, but no good for lifting.)

 

E2A: I don't have access to a copy of the standard, but I think that determines the torque so it'll be the same for any compliant grip of that type regardless whatever brand it is.

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I don’t know if it’s practical for you, but one venue here had painted red lines in all the fixed venue rigging (threaded rod etc to suspend fixed lighting bars) across the dual nut assembly.

 

Maybe something like that kind of marking would be a way for you to know if it’s been moved, or even a way to say “done”?

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When we are building theme park rides, its quite common to use "Torque Striping" as David Mentioned using a type of acrylic paint which is designed for this purpose and will crack when opened. Pens are useless as they can be washed off and replaced.

 

The way we do it and which is accepted by TUV and other inspection agencies is to do it in steps:

 

1) Torque to 50% of require torque - Colour 1

2) Torque to 100% of required torque - Colour 2

3) If its independently checked then after they have applied their torque value, colour 2 should not have moved.

 

Sometimes it will move between 50 - 100 but normally the clamp force has already been applied, so it doesn't move.

 

That being said, we learnt the hard way the difference between torque strength and clamping force which is very difference when using nuts / bolts on structures and fittings.

 

For the torque wrench / screwdriver, normally the installer will have their own certified one, and then a separate certified one will be used by the inspector for the final inspection.

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