Hanging Movers

[paulears]

I'm still disagreeing here. Nobody is suggesting using fabrications with inherent design issues, but simple materials that have proven strength and competent use. I'm not promoting using something prone to failure then backing it up with bonds, I'm using something I consider over qualified for the purpose, but not having been subject to test by destruction, it seems only sensible to add extra levels of safety that may not be needed. In the example I used if a failure occurred, the weakest point would probably be the threads on the bolts, or perhaps even the manufacturers fixing giving way. I'm trying to think of other examples. How about a vertical boom standoff, to hang a light from? The local blacksmith could easily produce something like this - a long bit of (mild steel?) - maybe 30mm x6mm. One end has a half circle bent section, and then a similar piece bolted with 2 M10 nuts and bolts to fix to the pole. The only other things would be a 90 degree twist at the end to mount the light via a bolt and three holes for the 10mm bolts to pass through. Easy blacksmith stuff. It's not rated by design, but the person making it would have no problems telling you a maximum weight - probably the 'real' weight less a de-rate. Would I use one of these? Yep - no doubts at all if I picked it up and felt the weight to be what commercial ones come in at. If I picked it up and it was light, and bendable, then alarm bells would ring - but I really don't need to only consider one from Doughty's.

 

I have a friend who is a rated welder - he works on offshore systems in the gas, wind, oils and nuclear industries and his welding to code is a prerequisite to be able to do the work - but he admits that not all of his work is as good as the next job. Too many variables. He has made me wall brackets so pole mount loudspeakers can be used, when the manufacturers ones don't quite fit - or don't extend far enough. None of these are tested as they are individually produced - what IS tested is the construction method and materials.

 

I really think that we should not dismiss every kind of home brewed device without reviewing it context. everyone knows the strongest bracket is only as strong as the fixing - and how many times do we really not know the real strength of the structures we fix to? We don't do rawlbolts up with torque wrenches, we just use experience, and if it does up too easily we realise the wall construction is compromised somehow.

 

Have you every tried to straighten a G clamp or double hanger to make it into something? They're really tough beasts. Would I drill a couple of holes and then attach it to something else, using it in a way different to the usual use? Yes - I have done. Aluminium, as tim says is pretty weak, especially if it's been bent. With galvanised steel - the strength element is better. I admit it's tricky - but would I perhaps use an unrated hardware store shackle? For some things, then yes - I would - it just depends.

[greenalien]

The thing is, adequate testing for a casting means sonar or X-ray testing to check for cavities and fault lines.

 

Well, maybe if it was for some critical dynamic load, like a helicopter main hub - but for static loading, if it passes the '10 x working load' test, it just isn't likely to break - after a number of tightening / untightening cycles a failure of the fixing bolts, or stripped threads in the captive nuts, is far more probable.

[kerry davies]

Context is indeed all and this context is that of a student wishing to hang lights over peoples heads with home-made fittings.

None of these are tested as they are individually produced - what IS tested is the construction method and materials.

Quite but what else is "tested" is the skill and competence and knowledge of the maker not a guess at that of a semi-anonymous person of indeterminate age.

 

The point I make is that many BR members do indeed have the skills, knowledge and experience to do all sorts of things far more complex than make a few brackets whereas a student is not even responsible for their own actions. They are expected to learn the proper way to do things and fitting non-standard, home-made parts of dubious quality is not it.

 

Suggestions that one student fit safety critical items produced by other students, none of whom we know anything about, are silliness.

[Ashley R]

im going to take a 50/50 stance here.

 

Yes, custom manufactured steel brackets, produced by qualified people, using the correct procedures, using proper materials. That are probably 100x over engineered. in my eyes are fine. And usually these brackets are large things made from steel etc. etc.

 

But consider the context we are discussing in. We are trying to manufacture a Omega Clamp.... Sure the actual aluminum bracket part, would be simple enough for a skilled metalworks teacher to construct, but its the actual omega bit itself, is where I draw the line at. Just looking at the one I just pulled off one of my Mac's they look like wonderfully horrid things to build, without the proper castings etc. And the entire weight of the fixture is hanging off these two small cast aluminum (or whatever they make these from) pins.....

 

Now that's definitely something that I would NOT want home built. Proper Engineering firm, probably yes. But definitely not a school, or anything I could crop up in the workshop out back.

 

 

To the OP: If you cant afford the proper rigging gear, don't hang them. Its that simple in my eyes. Either Cut something from the hire to enable the purchase of the proper clamp from Robe, or rejig the design so they are either omitted, or sitting on the floor.

[paulears]

Absolutely Ashley - bending a bit of steel is within my limits, but the twisting part - no way. Let's be honest - if you needed an omega bracket - but one twice as deep, maybe to clear some projecting obstruction - you could quite safely fabricate the drop - but you'd have to cannibalise a real bracket for the special parts - and probably, I guess, would even a local engineering company - because they're critical components and some designs are quite tricky to make I suspect - How would you actually cut a spiral into what I think is a rather special alloy. This is where I personally have my own limit - but maybe there are people out there with the capability to produce such a part - but I bet the machinery is pretty special too. Probably has a posh name too!

[greenalien]

A component that you make yourself doesn't have to look like the commercial item - it just has to have the same function. An omega bracket is just a way of fitting a hanging clamp to a 2-hole fixing on the base of a moving head. The weak points are the fixing bolts and their threaded holes in the fixture, not the bracket. You could make something equally strong from a length of 1/2" x 1 1/2" flat steel with 3 holes drilled in it, attached to the mover with enough penny washers to space it out far enough, using appropriately-sized high-tension bolts. No need to bend anything, and the bar won't break.

Let's stop pretending that we're dealing with aerospace engineering here, it's simple stuff that doesn't need a mountain of Health and Safety paperwork.

[Ynot]

The weak points are the fixing bolts and their threaded holes in the fixture, not the bracket. You could make something equally strong from a length of 1/2" x 1 1/2" flat steel with 3 holes drilled in it, attached to the mover with enough penny washers to space it out far enough, using appropriately-sized high-tension bolts.

Er, possibly not.

The majority of posters are referring to the twist-lock mechanism of the type of Omega Clamp that many larger brand moving heads utilise, NOT those which just have a couple of threaded holes to bolt into.

[jono9691]

I'm going to go with dont make them on this one mainly because it looks far too likely that threaded bolts might get jammed into a twistlock chassis.

 

Use the specified components in its manual, if that isnt possible with the budget then there IS plenty they can do with those fixtures on the ground.

 

I don't think knocked up rigging components is a can of worms to open lightly under any circumstance.

[greenalien]

The majority of posters are referring to the twist-lock mechanism of the type of Omega Clamp that many larger brand moving heads utilise, NOT those which just have a couple of threaded holes to bolt into.

 

I'm certainly not suggesting that anyone should use threaded bolts where twistlock items are required - using the correct fasteners is vital. Unlike bolts, twistlock connectors tend to be manufacturer-specific so if these are needed then this is definitely a case for using the manufacturers component.

[gyro_gearloose]

Unlike bolts, twistlock connectors tend to be manufacturer-specific

Really? So it won't be a fixed wing head version of one of these then?* They have a maximum tensile strength of 10,000 Newtons, or just over 1,000Kg. If we apply a fairly conservative safety factor of 10 to 1 ( and feel free to shoot me down in flames if this is too low :) ), then each bolt would have a SWL of 100Kg and the OPs Robe uses four of them. Thats more than enough for a unit which weighs around 10Kg, wouldn't you say?

 

*Actually, it might not be. I just spent a few minutes Googling and found that the Camloc fasteners look very similar to those used on many moving heads. However, the point is that Robe, Martin, or any other moving light manufacturer will buy their nuts and bolts from a small handful of suppliers and not go to the expense of making them in-house.

 

Edit : Had a another quick Google and I've found that the Robe 150XT uses Dzus fasteners.

[Seano]

However, the point is that Robe, Martin, or any other moving light manufacturer will buy their nuts and bolts from a small handful of suppliers and not go to the expense of making them in-house.

 

Regardless of the source, they are still a bit er.. 'specialist' and are therefore likely to be relatively tricky/expensive to obtain in small quantities. Something which may tend to make the 'home-made hardware' option look even less attractive.

[Brian]

...likely to be relatively tricky/expensive to obtain in small quantities.

Not really.

[Seano]

Not really.

 

You might be right. I did try sticking 'Dzus' into fleabay before I posted funnily enough, but it looked to me like its almost all panel fasteners for motorcycle fairings and wotnot.

 

I just looked again, and see three lots that look like contenders: one vendor of AJW 4-50 fasteners, AJW 6-40 fasteners and a single batch of AJW 5-50 fasteners. Any idea which of those (if any) would be the right size gyro-gearloose?

[gyro_gearloose]

Here's a link to the official Robe part that the OPs Robe uses. Without one of them, or any of the others you've linked to, in front of me that I can measure I can't really say if the ones on ebay will fit, however they look very similar. You could always look up the Dzus catalogues and check for yourself, if you wanted to.

[Seano]

You could always look up the Dzus catalogues and check for yourself, if you wanted to.

Nah. Merely curious, but not *that* curious. :)

Thanks for the link.