Really strange 'almost' accident

[paulears]

Rigging an empty bar with a load of Cantata F's, all with the big barndoors. Flew bar right out to just add an extra weight, then in again to its dead. Ian up ladder focussing. Gets to second from far end and shouts "who forgot the barn door on this one?". Reply comes back "Nope, they ALL have one". The next upstage bar has a set of tabs on a track, and they are very tall - can't fly completely out (but never do). Sticking out of the track, 15 feet above his head, point down was the missing barndoor! He came down the ladder very carefully, looking up.

 

What had happened was that when the bar was flown back in, the barndoor flap had gone betwen the two rails of the track, then bent at right angles, making a hook that wrenched the doors off the frame.

 

I've never seen this happen before.

[gareth]

It sounds like this shouldn't really have happened .... Cantata barndoors are fitted with the little retaining screw in a captive nut at the bottom of the unit, which 'hooks' itself underneath the bottom of the colour runners when done up - surely if this screw had been tightened down properly the barndoors should never have come out of the unit? (Well, not without the flyman really having to give the hauling line a damned good heave, anyway ...)

[PDD]

We had much a similar problem with some CCT Minuette fresnels. The barndoors kept getting knocked by an adjacent tab track which was being paged upstage to allow for a piece of scenery, to the extent that eventually one fell out. Needless to say I then fitted all the units with additional safety bonds onto the barndoors. Minuettes don't have a retaining screw or any sort of clip. The additional safety is now a permanent feature, even though it really gets in the way of focusing.

[gareth]

The additional safety is now a permanent feature, even though it really gets in the way of focusing.

That's an essential feature for any type of barndoor which doesn't have some other means of 'locking' it into the lantern. Minuettes and the old variety of ADB fresnels (without the 'lid' on the open side of the colour runners) seem to be among the worst offenders for allowing barndoors to fall out.

 

Having had a chat with Paul on MSN, it turns out that the problem he experienced wasn't actually the barndoors coming out of the runners - it appears that the leaves of the barndoor unit, and the ring to which they were attached, physically separated from the backplate. So maybe there's a case for safety bonds on barndoors even if they do have a means of physically locking them into the lantern ....?

[david.elsbury]

Having had a chat with Paul on MSN, it turns out that the problem he experienced wasn't actually the barndoors coming out of the runners - it appears that the leaves of the barndoor unit, and the ring to which they were attached, physically separated from the backplate. So maybe there's a case for safety bonds on barndoors even if they do have a means of physically locking them into the lantern ....?

<{POST_SNAPBACK}>

What, one bond for each leaf of the barndoor, or just for the top one? It goes on and on...

[Chris Higgs]

The lanterns I recall using had a number of nuts and bolts holding the rotating frame to the backplate. If these loosened, the rotating plate fell off the backplate. A safety bond wouldn't have helped.

The leaves themselves could fall off if two screws came loose (Patt 123 and 223, I think). Certainly not something a safety bond would prevent, either.

 

Isn't this an example of the importance of not relying on the kit to do all the work?You need to maintain them as well as keeping your eyes peeled during use, especially when moving bars or trusses.

You could still have a set of barndoors swinging on a safety bond and disintegrating from the main assembly. (Residual risk)

[paulears]

We are about to have our old triple drum winches replaced with single drum versions and a clew plate to run the 3 drops. The suppliers rate the chance of failure as less than the dangers of uneven drum winding on 3 drum winches. I am informed that a single suspension cable is perfectly acceptable under LOLER. My request for safeties is not considered necessary. This surprises me a little. I had always used the secondary suspension 'requirement' as good practice. Has anyone else got winch systems like this?

[Chris Higgs]

Using a single winch line of say 8mm diameter 6x19 1770 grade rope will provide a SWL of around 500 kgs factor of safety of 8 (as recommended).

If the new ones replace old 3 compartment 5 cwt/250kg Handy Hoists (Youngs No. 1??) then you may have a factor of safety in the order of 16:1 on that single rope and its terminations.

The other components, winch, blocks and fixings won't necessarily have the same factor, though.

 

LOLER says, in essence, that when working under suspended loads is necessary, the employer must take extra precautions, and lists some options including increasing safety factors.

 

If the factor typically used in such cases is between 5:1 and 8:1; 16 may be considered sufficient, given that it is in a fixed installation and subject to inspection and maintenance, of course.

I understand your concerns, though; should something fail, there is nothing (except the clew hitting the head block!) to prevent the barrel coming in.

 

HTH

[Stu]

As Chris mentioned above, the barndoors seem to be a description of the 743 (and others I expect) old stylee doors.

 

Our rig is still all 743s with these doors, and in the last few months I have made it my little mission to make sure all of these doors have a bond back to the yoke. To do this on ours I threaded the loop through the gap between the door and the rotating plate, passed the karabiner hook through the loop, then up to the yoke, around and clipping back on itself. This way it doesn't get in the way of focussing (that much anyway) and if the rotating plate ever came off the front it'll still be caught.

 

Just a little idea...

 

I'd be interested to know Chris if this form of rigging the safety decreases the SWL of the bonds, or their ability to do the job. They are all SLX or Doughty 5kg SWL bonds.

 

Stu

[paulears]

If the new ones replace old 3 compartment 5 cwt/250kg Handy Hoists (Youngs No. 1??)

<{POST_SNAPBACK}>

 

Spot on Chris! Exactly right!.

 

Thanks for comments - appreciated.

[Kristian]

Rigging an empty bar with a load of Cantata F's, all with the big barndoors. Flew bar right out to just add an extra weight, then in again to its dead. Ian up ladder focussing. Gets to second from far end and shouts "who forgot the barn door on this one?". Reply comes back "Nope, they ALL have one". The next upstage bar has a set of tabs on a track, and they are very tall - can't fly completely out (but never do). Sticking out of the  track, 15 feet above his head, point down was the missing barndoor! He came down the ladder very carefully, looking up.

 

What had happened was that when the bar was flown back in, the barndoor flap had gone betwen the two rails of the track, then bent at right angles, making a hook that wrenched the doors off the frame.

 

I've never seen this happen before.

<{POST_SNAPBACK}>

Barndoor did not have a safety (WIRE, not chain) on it then....?

K. ;-)

 

Looking closer at your comment, the barndoors left the mounting frame that is part of the barndoor unit?? bloody odd! are the doors Strand doors, or are they a different manufacturer? Will look closer next time I have a set in my grubby paws.

 

May all your parcans be the right way up, and thanks for pointing this out!

K.

 

Moderation: Quotes fixed and two posts merged, please use the edit button if your post is still the last in the topic.

[Chris Higgs]

I'd be interested to know Chris if this form of rigging the safety decreases the SWL of the bonds, or their ability to do the job. They are all SLX or Doughty 5kg SWL bonds.

<{POST_SNAPBACK}>

Sorry to have missed the question.

 

A wire rope (or any rope) is weakened by the amount the fibres or wires are bent.

the smaller the diameter, the more it weakens the rope. A small eye in the wire will be technically weaker than a longer loop (standards call for a loop without a thimble to be at least 10 x rope diameter long at 'rest', e.g. a 4mm wire should have a 40mm long eye when not under load).

 

The more tight wraps (not around 48mm tube, that's a good bend) you add, the weaker; that's why a thin edge acts as a 'knife'. Think of pulley sheaves - they are always at least 18 x rope diameter for wire - 5mm wire = 90mm diameter pulley.

[Kristian]

I'd be interested to know Chris if this form of rigging the safety decreases the SWL of the bonds, or their ability to do the job. They are all SLX or Doughty 5kg SWL bonds.

<{POST_SNAPBACK}>

Sorry to have missed the question.

 

A wire rope (or any rope) is weakened by the amount the fibres or wires are bent.

the smaller the diameter, the more it weakens the rope. A small eye in the wire will be technically weaker than a longer loop (standards call for a loop without a thimble to be at least 10 x rope diameter long at 'rest', e.g. a 4mm wire should have a 40mm long eye when not under load).

 

The more tight wraps (not around 48mm tube, that's a good bend) you add, the weaker; that's why a thin edge acts as a 'knife'. Think of pulley sheaves - they are always at least 18 x rope diameter for wire - 5mm wire = 90mm diameter pulley.

<{POST_SNAPBACK}>

Also a good practice is to keep the safteys as taught as possible, without encumbering "focusability".

One for the LD, to make sure that his plot has the lamps in roughly the right orientation.

The further a lamp falls before the saftey catches it, the heavier the load, taking into account gravity and acceleration!

Credit to ourselves, in general, most (UK) lampies understand this, but one to watch, and keep the newer guys up to speed.

Safe rigging to you all.

Kris.

[Stu]

Following on from my original point / question a few weeks back, I am very glad that I introduced a policy of safeting barndoors, as I came in on Monday (after a week off work so not sure of the circumstances) to find a set of 743 doors hanging 7m off the ground by the safety bond - the door had come clean off the runner plate as usual.

 

Anyway, there is a safety for the bin.

 

Credit to ourselves, in general, most (UK) lampies understand this, but one to watch, and keep the newer guys up to speed.

The problem is making this aware to olduns and as well as newuns - some of my colleagues simply don't believe me, or that the (for instance) doubling off the safety, if done right, won't hinder focussing. I must admit I'm not perfect right and am still forcing myself to do this but I think it's an important enough an issue to make aware to my colleagues.

 

Stu