Scaff couplers for 2" "bar"

[ramdram]

Very recently we contemplated fixing a cross bar to a vertical lighting boom (scaff pole) to have more "space" to hang more lanterns.

 

The length of the cross piece would be around 5ft or so, and, seeing as we appear to be knee deep in scaff clamps then that would be the obvious method of securing the "ledger" to the "standard", using scaffolding parlance because I'm referring to scaff couplers.

 

This way of attaching the bars together with scaff couplers seems to be the ideal solution given the coupler is purpose made for the job and only two nuts to undo (although if I trip over a single coupler then call it one nut.)

 

It then occurred to me that using scaff clamps might be a very cost effective way of flying 2" bars avoiding the cost of the "usual" machined alloy couplers and eyebolts/nuts combo.

 

If you were to consider using a standard right angle double coupler then the coupler could attach to the bar in the usual fashion and you could use a largish thimble for the wire rope to secure it to the other side of the scaff coupler, ie through the hinged clamp piece, with the coupler closed up of course.

 

I had a look at the load bearing qualities of scaff couplers and they express the strength as a force in kN. I did the conversion thing with an online tool and it seems to me, assuming I got the terms correct, "a" standard scaff clamp SWL/WWL (sort of thing, so corrections invited)) exceeds any alloy coupler by quite a few times over...and at a fraction of the cost. Plus they can be of drop forged construction so intrinsically much stronger anyway; granted they are heavier though.

 

This UK site gives the cost (per 25) and even allowing for vat the unit cost is less than £2 brand new. (I gather you can get the couplers in a colour(s) of your choice...and you might have seen trendy looking black and gold units on a "green" pyramid not a million miles away from Chelsea barracks.)

 

http://www.scaffolding-direct.co.uk/forged-scaffolding-fittings/

 

(Quick aside; I noticed on this site that the cost of rated/certificated "spansets", or endless round slings, as they are known in other circles (groan), are quite inexpensive, even cheaper than I pay at my local tractor shop and that is cheap.)

 

(Harking back to a much earlier thread on using "U" bolts as extemporized fixings it might be "better", where possible/practicable of course, to use a scaff clamp instead???)

 

Which brings me to the question: Does anyone use scaff kit as an alternative to the accepted stage supplies or am I re-inventing the wheel sort of thing, or are there considerations I have not covered which renders such clamps a non starter for the "stage"?

[themadhippy]

and you could use a largish thimble for the wire rope to secure it to the other side of the scaff coupler, ie through the hinged clamp piece, with the coupler closed up of course.

unless im seeing this wrong,without a lump of scaff in the coupler the clamp wont clamp together as the bolt thread is to short and will fall open just by looking at it wrong

[IRW]

and you could use a largish thimble for the wire rope to secure it to the other side of the scaff coupler, ie through the hinged clamp piece, with the coupler closed up of course.

unless im seeing this wrong,without a lump of scaff in the coupler the clamp wont clamp together as the bolt thread is to short and will fall open just by looking at it wrong

 

I was just thinking the same thing- Maybe Ramdram has some couplers that are threaded all the way?

 

From that supplier, those clamps work out to £1.50 per fitting. A 1m roundsling is £1.10 from these people. Add in a shackle to do the job properly, and you're not looking at a huge difference.

 

You've also got the added problem of the scaffolding clamp not sitting correctly within the eye of the SWR.

 

Ian

 

(On a different note, that site is going into my favourites for next time I need some round slings/scaff clamps!)

[indyld]

and you could use a largish thimble for the wire rope to secure it to the other side of the scaff coupler, ie through the hinged clamp piece, with the coupler closed up of course.

unless im seeing this wrong,without a lump of scaff in the coupler the clamp wont clamp together as the bolt thread is to short and will fall open just by looking at it wrong

 

Well, thinking about this "new" idea, it surely isn't beyond reason to fit a ring sized piece of steel scaff tube with suitably chamfered inner walls, to attached to Ramdram's oversized thimble. Of course, this needs pre-making onto the thimble.

 

Aside from the whole "intended use" Value Tinned Worms in Brine thing, scaff slips are a bit sharp and poky and could be ugly too I'd imagine.

I've looked at that site recently and they don't 'alf flog off the basic tube and fitting stuff dirt cheap, don't they? Does make one wonder what the difference in build quality etc. vs somewhere like Flints. Of course, Flints aren't known for knocking out cheap scaff fittings, but they do stock the theatre specialist stuff.

[boatman]

Sorry to be picky, but 2" bar is 50.8 mm in diameter (similar to truss) and a lot of standard scaffolding clamps wont open that far. Did you really mean 2" bar in the title or standard scaffold bar at 48.3 mm diameter?

[ramdram]

2" bar as a generic thing as in whatever that equates to in millimetre terms. The test cert for the scaff couplers mentions both 48mm and 50mms, which I presume allows for variations in scaff bar pipe/tune manufacture.

 

The ones we have accommodate any of the bars we own. Plus I found at that the couplers at our venue appear capable of clamping much smaller OD bar as well as; and yes the thread is virtually all down the hinged threaded rod. These clamps have been there for decades, literally, and despite being in the weather for all that time have buffed up a treat with the attention of a wire brush and WD40...

 

As for ugly, it's not really intended to be "nice" looking is it? It's there to do a job and if a machined alloy coupling is more aesthetically pleasing then perhaps we should ask if the punters are in for the show or the kit?

 

Ref the "quality" issue I would say they are of a much, much higher quality that anything from any of the usual suspects in that they are drop forged steel, and, if you did the conversion thing with the load bearing or, in the case of scaff kit terms, the force withstanding "strength", then the alloy stuff is perhaps not quite in their league.

 

If you consider these clamps might be helping to support tonnes of scaff tubes, for months at a times, in all weathers, then even a few tens of kgs of bar and lanterns must be well within their envelope.

 

The torque required on the scaff nut for the strength test is, as as per spec, 54Nm or about 40 ftlbs (almost small petrol engine cylinder head nuts torque). Said clamps are then re-tested at 100Nm (diesel engine torque perhaps?) and are expected to perform as per spec.

 

Hence my post...as in are scaff couplers a viable, and cheaper option, for flying 2" bars?

 

 

Certainly they can support the load of me and another tech ((say 170 kg all up)) without any movement or protest...and all I have to hang is a Disco Darren colour changer (don't even go there), a Quartet zoom profile and a Par 64.)

 

On the topic of thimble size then this may be of interest, oversize thimble, per se, is not exactly an issue in this instance:

 

http://www.fortunerope.com/thimbles.cfm

[Brian]

On the topic of thimble size then this may be of interest, oversize thimble, per se, is not exactly an issue in this instance.

Whilst you can get a thimble big enough to go around a scaff clamp, they're meant for much bigger ropes than we'd normally see in theatre.

[Seano]

As for ugly, it's not really intended to be "nice" looking is it?

It's not a bad rule of thumb with rigging that if it looks crap, it quite probably is crap.

Doesn't apply in every case I suppose, but it definitely does in this case. 48mm, 2inches, whatever - this is a really bad idea.

 

Hence my post...as in are scaff couplers a viable, and cheaper option, for flying 2" bars?

No.

[ramdram]

** laughs out loud **, I have to say that is one take on the topic...that if it looks crap ergo it must be crap...well, I suppose there is a certain truth to that.

 

But, if the coupler works and is a great deal less expensive and altogether a "stronger" piece of kit then it could have an application.

 

There are other types of scaff coupler which might score higher in the "elegance stakes". One is described as a girder clamp coupler in that it has a single coupler with an "L" shaped bit through which is a (possibly) 12mm OD pointed screw for use on metal "I" beams. Available in either drop forged or pressed steel versions.

 

I suppose it would be possible to discard the screw and use an eyenut and bolt for the sake of chic. You could then use a shackle.

 

The attraction as I see it is that we have dozens of these couplers all over the place so they are free, and, if you did consider buying them then the price is very reasonable. Plus they would appear to be better able to withstand abuse than similar offerings designed for the "stage".

[Brian]

What derating factor have they included in their SWL figure? Is it the same as we use?

[ramdram]

Strictly speaking I believe the derating factor you mentioned applies depending on the load angle on an eye bolt/nut or bow shackle (corrections welcomed of course).

 

No mention, in any of the literature I have seen, is made of derating factors owing to applied angles of load. Slippage is mentioned but that is not applicable to anything other than along a pole. Ref my original idea of using a thimble though one side the coupler then the load angle could "swivel" within the clamp.

 

(However the distortion load on a coupler is some 17kN which equates to over 1700kgmf so the chances of actually breaking one is quite slim unless the load is enormous. I had envisaged the hangs being vertical, or very nearly, for our particular usage. Even at an angle of 45 degrees the load bearing is still pretty impressive give the size of the coupler.)

 

From this link there are several other types of coupler which shows the SWL of 6.5kN (say 600kgmf):

 

http://www.orchardhireandsales.ltd.uk/scaffolding-fittings.htm

 

It may be that using the half coupler, with the hole, would allow for an eyenut and suitable sized bolt, or eyebolt and nut.

 

I would say the derating factor has to be the same regardless of the application, after all the math pertaining to the angle of load is the same for an eye whether on a scaff coupler or an alloy unit.

 

This might help for those not familiar with said math on derating factors:

 

 

http://www.thecrosbygroup.com/html/default.htm

 

or

 

http://www.nobles.com.au/products.aspx?doc_id=2430

 

 

 

(Slightly OT: Whilst doing the google thing on scaffolding I chanced on this:

 

Code of Practice for Metal Scaffolding Safety

 

from this site:

 

www.labour.gov.hk/eng/public/os/B/mss.pdf

 

On P76 there are diagrams of ground anchors...which might have been usefully employed instead of the concrete (above)ground anchors used in the recent truss collapse incidents.)

[Giles Favell]

Whilst drop forged fittings (and pressed steel) are fine for general use around the stage - as soon as they become part of a flying system, the situation becomes trickey. All parts of the flying system must be suitably rated, tracable etc.etc. and must conform to LOLER. It would be impossible to justify a bodged up fitting from an empty closed up scaff clamp and an over-sized thimble used incorrectly. I'm afraid the first insurance inspection would have it all down straight away.

Thinbles should be used with the appropriate sized cable or rope, and are generally used in conjunction with a shackle pin or similar, which is not going to distort or damage the thimble.

It is always dangerous to use hardware 'differently' than intended - for all I know, you may find that the centre bar of these couplers has been engineered down, and replies on pressure from both sides for full integrity.... one hopes not - but you don't know. http://www.blue-room.org.uk/public/style_emoticons/default/rolleyes.gif

in practical terms, barrel clamps are much prefered for flying stage bars because they have much less of a tendancy to snag borders and adjacent LX bars etc. (plus a much lower risk of coming undone)

[ramdram]

All very fair points GF, thanks. We don't have any flown overstage bars at all so the notion of snagging other kit was not a possibility for us.

 

The "mission creep" sort of thing might well fall foul of the insurance inspection. Plus as you rightly say the LOLER "regs" must be considered too.

 

I suppose the most likely scaff coupler design to "require" LOLER might be the girder clamps with coupler, although I did not see any mention of LOLER regs in any of the sites I visited.

 

The only regs, so to speak, were EN74 and BS 1139.

 

Anyway thanks for all the replies, the topic is probably done to death by now...and my question has been more than answered.

[Brian]

... although I did not see any mention of LOLER regs in any of the sites I visited...

That's because LOLER doesn't apply to scaff when used in its normal setting. Or indeed when used in a static setting even in theatre.

 

For LOLER to apply there must be some element of lifting or lowering of a load ie movement of a load.

 

Doesn't mean PUWER doesn't apply though.

[ramdram]

Regulation 4

 

Suitability of work equipment

 

...is the most relevant bit from PUWER.

 

Again, much obliged for the heads up from all who responded.

 

As a result the notion of flying a bar has been suspended...in favour of an easier to get at fixed solution where we can use standard half couplers as per spec.