Scaff V Doughty Arms

[bjkered]

The other way of thinking about it is Doughty give you a spec for their system.

What is the Spec on a Clamp.!!!

 

NO spec therefore Doughty WIN

 

No Spec?

 

Safe working loads for individual couplers

 

Right angle coupler (Class A)

Slipping force in kN 6.1 (1)

Cruciform stiffness in kNm/rad 10.0 (2)

Cruciform bending in kNm 0.24 (2)

 

Right angle coupler (Class B)

Slipping force in kN 9.1 (1)

Cruciform stiffness in kNm/rad 15.0 (1)

Cruciform bending in kNm 0.28 (1)

 

Notes

(1) These figures are based on table 8 of BS EN74-1 : 2005 and are for use with type 4 steel tubes

(2) Data on crusiform strength and stiffness shall be obtained from the supplier / manufacturer

 

Referance TG20:08

 

 

Fair point which I know is fine I was only looking at it from a simple out of the box argument. If you go the scaff route and get paranoid on H/S who is going to sign of the scaff clamp deign route etc. Wher is the bar from is it new or used etc just getting Picky for no reason.

 

I tried to look at it from another angle

[TomHoward]

The flip side of that is that you can't blindly trust the SWL of a rated assembly, you'd have to take the same factors into account.

[Seano]

90degree coupler can hold - 750kg - http://www.doughty-engineering.co.uk/cgi-b...showprod_T57102

 

"Can hold 750kg" in what mode? I suspect this is a "pull apart" load - where a force is trying to separate two tubes in a direction perpendicular to both of them. Does that mean you can use one of these to make a boom-arm and put 750kg on it? (Clue: not on your nelly!)

 

Aren't these clamps essentially made by bolting two half couplers together to make a swivel clamp, and then the 90 degree and parallel versions immobilised with a rolled pin? A rather poor choice for improvising boom-arms with short bits of scaff, I would think, since the load mainly consists of a torque trying to 'swivel' the clamp.

These would be much better for this job, imo.

 

No Spec?

 

Safe working loads for individual couplers

<some snippage of numbers etc. here, blah blah>

Notes

(1) These figures are based on table 8 of BS EN74-1 : 2005 and are for use with type 4 steel tubes

(2) Data on crusiform strength and stiffness shall be obtained from the supplier / manufacturer

 

Referance TG20:08

 

"Safe working loads" you say? Are you sure about that?

I'm a rigger, not a scaffer - but I'm fairly sure interpreting those 'slippage' figures as a SWL would be bad.

 

The data that Doughty (for example) supply about their boom arms (here) is very clear and easy to understand. Which is certainly not something you can say for the figures you've quoted there.

 

I guess 'cruciform stiffness' is the crucial quality of a 90degree clamp if we're talking about - can you explain how you would use those figures to derive a safe working load at a given distance along a boom arm? It isn't something I've never really had to think about, and would genuinely be very interested to learn more. Presumably the maximum permissible bending moment on the tube itself is also a factor?

 

If my initial impression of your post is wrong (ie: that you've just copied and pasted a bunch of numbers you don't understand at all in a misguided attempt to look clever), I'd be grateful if you could elaborate. If my initial impression was right, it would probably be better if you keep schtum, and hopefully this whole dismal thread can quietly fade away.

[simantec]

I don’t pretend to be able to interpret the information that I provided to settle this debate.

 

I was merely trying to inform the person who stated that there were ‘No specs on a scaff clamp therefore Doughty WIN’ that, scaffolding couplers are in fact manufactured to stringent specifications and thought that the information that I forwarded in good faith might assist.

 

At the risk of being shot down in flames again I believe that one of the tests carried out on scaff clamps is to derermine their 'torsional rigidigity'

[LXbydesign]

I would personally put my faith in 90 deg scaf clamps as a cheaper but by no means unsafe way of rigging. Having seen the size of the 'wall' built of scaf used for this years eurovision and the amount of moving lights and LED panels rigged on it and also it was helping to distribute weight down from the mother grid......!

 

Doughty clamps are very well made / tested / certified but they are by no means the one stop answer to safely rigging boom arms.

[johnhuson]

I would personally put my faith in 90 deg scaf clamps as a cheaper but by no means unsafe way of rigging. Having seen the size of the 'wall' built of scaf used for this years eurovision and the amount of moving lights and LED panels rigged on it and also it was helping to distribute weight down from the mother grid......!

 

[pedant] The scaffold structure for Eurovision was actually constructed from a proprietary scaffold system (Layher in this case I believe) rather than using 'standard' scaff couplers. [/pedant]