Only the highest quality materials and components should be used in any entertainment rigging application.
All reputable manufacturers of rigging components employ scientists, metallurgists, and engineers to ensure that their products are designed properly, manufactured uniformly, and will reliably meet their stated load ratings. They use standardized test procedures, proven over decades, to ensure quality and reliability.
Conversely “copy cat” manufacturers often do nothing to ensure safety. In these modern times of international trade, thousands of suppliers exist that sell cheap parts that may closely resemble the originals they’re based upon, but these suppliers sometimes have little to no regard for meeting any stated rating – if they state it at all.
Such products, which are found many places, including local hardware stores, are unsafe and can fail unexpectedly. Do not purchase them.
If this article can convince you of anything, please let it convince you to purchase only the highest quality parts, materials, and components. The money you’ll save in the local hardware store for a length of wire rope, or a handful of shackles, will not pay for even one hour of legal representation. Are you with me so far?
Reputable companies such as The Crosby Group have been manufacturing high quality components in the U.S. for many decades. They publish meaningful manufacturing data, and they stand behind their work. Numerous other companies, domestic and abroad, also meet high-quality standards. Seek them out.
Establish a commercial account with a suitable supplier, especially if you intend to become a regular customer. If your usage is sporadic, consider using a distributor like McMaster-Carr, Grainger, or another industrial supply house.
Don’t be afraid to speak with the sales department and demand – yes demand – the material data sheets on each product that will let you sleep well at night. If your supplier can’t provide the information that you request, find another one.
At all costs, do not accept off-shore substitutes that may look the same as an engineered product, but might possibly perform at a far lower standard.
If you purchase your parts and materials from a manufacturer who routinely performs proof-testing of batch samples, rates them accurately, and is willing to publish comprehensive test data, then you can’t go wrong.
You’ll pay more for such parts, assuredly, but the life you save might be your own.
Handling Forged Parts
Shackle bodies are typically forged, quenched, and tempered, and supplied with an alloy-steel bolt.
While we’re not going to get into metallurgy, suffice it to say that forged steel is very strong, but also rather brittle. Think of it as the opposite of sheet metal, which is highly ductile.
When you drop a shackle – and that’s a pretty easy thing to do – the brittle steel can become invisibly fractured from the impact of the fall, reducing its strength considerably. If you’ve ever seen a shackle explode under load, you’ll recognize the wisdom in discarding a shackle, or other forged part, that may have been inadvertently damaged.
For this reason, always carry numerous spare parts to your gig. You can’t replace the dropped shackle if there’s no others left in your rigging kit. And as “DeLoria’s Shackle Dropping Law” states: After you’ve dropped one shackle, you’re likely to drop another a few minutes later.
Bridling & Reeving
“Oh Lord, please don’t let me be misunderstood”—Eric Burden and The Animals
Two of the most misunderstood aspects of rigging are reeving and bridling. I’ll go into further detail about both of them next time, but must state this now: Never, ever reeve a Spanset, wire rope, or other suspension device through eyebolts, shackles, or other supporting points (Figure 4).
Unfortunately, and for reasons that elude me, such practice is very often seen. There is never any legitimate reason to reeve suspension points when you’re rigging loudspeakers for public usage. Reeving can be useful on construction sites, when the load needs to be shifted to align with some other fixture, but should never be used in the sound reinforcement industry.
A reeved attachment will always significantly increase the load on the parts that are used in the suspension system.
(click to enlarge)
The additional load incurred from a reeved attachment can far exceed the weight of the suspended object itself. This is a simple function of the vector forces involved, which in turn are a function of the geometry of the reeve, but often may be difficult to understand due to the counter-intuitive nature of vector geometry.
Similarly, bridling, especially at acute angles, will put far more stress on the rigging components than the actual weight of the load itself. This is also counter-intuitive, and perhaps equally difficult to comprehend. Nonetheless it is true.
In the next installment, I’ll show exactly how reeving and tight-angle bridles magnify the load on the various components that are intended to keep your rig from plummeting to the ground. In the meantime, stay safe out there.
Ken DeLoria is the founder and former owner of Apogee Sound, a manufacturer of loudspeakers and many associated rigging accessories. For more than 30 years, he has been a sound engineer, a hands-on rigger, and a safety supervisor at numerous events and permanent installations. See part 1 of this series here.
See our gallery for more examples of rigging component fatigue, and go to next page for sidebar “Fatigue Properties.”