Using keyclamps for a lighting frame

[theatrcymraeglampy]

Hi All,

 

I've been working in a theatre that uses keyclamps to create a ladder that is usually spotlined from the grid on the side of the stage, and then lights are hung off it.

 

(For arguments sake say it has a 1m scaff on top, with two 90 degree key clamps, then 2m of scaff runs to the bottom set of 90 degree key clamps to make a square, and there is another set of key clamps in the middle to create a middle bar).

 

What concerns me is, is that as far as I am aware keyclamps are not load bearing? So the only thing stopping the 2 pieces of scaff falling down to the ground with all the lights, projectors e.t.c on is the bolt that you use an allen key to tighten.

 

What do people think of this? I was very hesitant when using it, as I was rigging it off a bridge FOH and I added a safety back to a fixed RSJ and safety'd all of the lights & projector to that instead.

 

 

Apologies if this has been explaned badly.

 

 

Paul.

[paulears]

Nope, make perfect sense. You see these all over, and most have exactly the problem you have described. I've seen a few mods done that seem to work. One is tightening the allen bolts, then undoing them again and drilling the place where the allen bolt marked, making a recess (not all the way through, into which the bolt can sit, before it bites, preventing the clamp coming off even if the bolt loosens. The other method is a small hole through which a split pin can be inserted, or a hole straight through from one side to the other with a bolt through the entire thing. Either way this gives a primary and secondary method of keeping it together. I've never seen an unmodified key clamp frame fail, but nothing, as they say is impossible.

 

I've found that a right angle 90 degree clamp can slip off fairly easily when making up handrails, but noticed that the other 90 degree clamp - the ones that slide onto a tube, and then have providion for another tube to slide in at 90 degrees tend to bind when trying to get them off, as the angle moves away from 90, the edges act as a brake. In your example, I'm guessing these are the kind you use for the cross bar. loosening their allen bolts doesn't let the tube slide unless you move it very carefully at the right angle. Moving one end before the other jams it up - so maybe using these on all corners is safer?

[Nat_Keiller]

It is quite common to see frames made with key-clamps drilled thru where the allen bolt sits and then fixed with M8 or M10 nut and bolt sets.

 

In no way suggesting this would comply with maufacturers guidelines on it (since you are modifying the product), but it is an accepted way among many of building key-clamp sytle frames and ladders.

 

'Proper' 'LOLER' stlye ladder (welded scaff tested to LOLER regs) might be a better solution, but definately a lot more expensive.