J.R. Clancy releases iRigging Application

It's always good to have rigging information at your fingertips - it sure beats guessing or digging in your tool box for that chart of numbers. J. R. Clancy has turned its popular rigging slide rule tool into a free iPhone application. Installers and users of theatre stage rigging should find this handy. The new application delivers instant information in English and metric (SI) units.

iRigging provides wire rope data, including: minimum sheave diameter; cable breaking strength; and recommendations for quantity of cable clips, wire turn-back for cable clips, proper torque for cable clip bolts, and Nicopress sleeve crimp quantities. Other data includes: allowable fleet angles, uniform and midpoint batten loading, arbor capacity, weight of counterweights, recommended working loads for equipment, motor current, stage ropes, and weight of stage fabrics.

The tool is free and currently available at Apple App Store.

More information about J. R. Clancy is available at www.jrclancy.com. As of this date there is no information available about the iRigging application on their web site.

Note: The app does not include iCommonSense, so you have to provide that yourself. It does feature standard GIGO* operation, though.

* Garbage-In yields Garbage-Out

Have fun with it, just don’t be an iDiot and drop your iPhone from the iGrid – it might hit someone in the iHead. Has anyone released the iLanyard to keep this from happening?

Cable Bending Radius

Wire rope, like all flexible cables, has a limit as to how sharply you can bend it before it is permanently deformed. This is called the d:D ratio. It is the ratio of the diameter of a sheave to the diameter of the cable. It depends upon the stranding and lay of the rope, and it is usually in the range of 20:1 to 40:1. This ratio is for maximizing the life of the cable as it flexes repeatedly while it transitions from straight to curved and back to straight as the cable passes over the sheave.

For a 1/8" diameter cable, not typically used for stage rigging, but frequently used for operating smoke vent hatches, this would typically use a 4" diameter sheave (32:1 d:D ratio). The picture below is a 1/8" diameter cable that operates a smoke vent. You can see that it is bent under tension over the sharp edge of a steel I-Beam with no pulley or block to smooth-out it's travel around the corner. You can also see where the cable strands have broken due to repeated operation.

So, why is this important? The smoke vents should be configured to allow both manual opening and closing and for the automatic release in coordination with the Fire Alarm and the Fire Curtain systems. It is very typical (but shouldn't be) that the Smoke Vents are rigged by someone other than the Stage Rigging contractor. When that happens, the manual operation system is either non-existent (so you have to climb up on the roof in a rain storm to close the hatches), or is 'user hostile' (isn't convenient for the staff to use on a day-to-day basis).


Dysfunctional mess (left). Neatly marked and operated with a RED handline (right). Sign reads: NOTICE - Smoke Vent Operation Line Inside". Sign is on both sides of hinged protective screen panel. Panel in front of line set is painted red.