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Issue #34: September 21, 2017
 
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Swaging Wire Rope


I love wire rope, aka galvanized aircraft cable or GAC. Why? Compared to most fiber ropes, it is extremely strong, more resistant to abrasion, and can be terminated with 100% efficiency. It is this last attribute that is the subject of this newsletter.
 
 
Wire rope
Before beginning a discussion on terminating wire rope, it may be helpful to understand a bit more about it. All wire rope is made of wires that form a strand - one of these multi-wire strands forms the core, and the others are laid helically around a core.
 
The core is the foundation of the wire rope and most wire rope used in theatrical or aerial applications has an independent wire rope core (IWRC). What is commonly called "aircraft cable" is actually 7x7 or 7x19 IWRC wire rope. The notation "7x19" means that the wire rope has a total of 7 strands (six strands wrapped around a core strand) and each strand is made up of 19 wires. Therefore, a 7x19 cable has a total of 133 wires, whereas a 7x7 cable has only 49 wires. Generally speaking, the more wires in a wire rope, the more flexible it is. 
 
 
 
Besides diameter and construction, there are other factors in wire rope specifications: direction of lay, grade of rope, lubrication, and coating. Most of these specifications are not factors for most people when selecting wire rope. Although nylon or vinyl-coated wire rope is not commonly used in theatres, it is commonly sold in hardware stores and, therefore, does sometimes find its way into stage or aerial use. The extruded flexible coating can extend the service life of a wire rope, by reducing wear. However, the nylon or vinyl coating MUST be removed at the ends before the cable termination is applied.
 
Cable Thimbles
No matter how a cable/wire rope is terminated, it is often important that the eye be protected from damage and wear. The most common type of cable thimble is called a pattern thimble, of which there are three varieties: thin pattern aircraft thimbles – for light duty application (meets Mil. Spec. AN-100), standard pattern thimbles – for light duty applications (galvanized thimbles must meet Fed. Spec. FF-T-276b Type II), and heavy duty pattern thimbles – for medium to heavy duty applications (galvanized thimbles must meet Fed. Spec. FF-T-276b Type III). Open thimbles are similar in size and construction to standard pattern thimbles, but are "U" shaped, having not been bent closed into the familiar tear-drop shape. Pattern thimbles are available in galvanized steel or in Type 304 stainless steel. Stainless steel hardware is commonly used in saltwater or in corrosive environments. Galvanized thimbles are best for most theatrical applications. An endless thimble, available only in Type 316 stainless steel, has no end to catch on things.
 
 
 
Swage Fittings
Swage fittings or sleeves, as they are commonly called, are available in two different patterns: oval and stop. Oval sleeves are used for making an eye termination, while stop sleeves put an end on a cable which prevents the cable from being pulled through a hole in a piece of steel. For theatrical and aerial work, oval sleeves are more commonly used. The two largest manufacturers of swage fittings in the United States are National Telephone Supply Company of Cleveland, Ohio, which manufactures the “Nicopress” brand, and Loos & Company of Naples, Florida, which manufactures the Locoloc brand. There are also imported swaging sleeves.
 
When applied correctly, a single oval copper sleeve will achieve a 100% cable strength termination when the cable is looped around a thimble. This is not only outlined in both manufacturers' testing data and catalogs but is also outlined in FAA documents and Military Standard MS-51844.  It should be noted that the Wire Rope Users Manual uses a conservative 95% efficiency rating for cables 1” in diameter and smaller.
 
Oval sleeves made of plain copper, tin-plated copper, galvanized copper, stainless steel and aluminum are available. The tin and galvanized plated sleeves are intended for use on either galvanized or bright steel aircraft cable. A plated sleeve would be used in very humid areas where there is a concern of electrolysis between the two dissimilar metals.  Stainless steel sleeves are for use only with stainless cable. Aluminum sleeves, intended for use on either galvanized or bright steel aircraft cable, are a cause of some debate within the theatre community and are not recommended for aerial work.
 
Swaging sleeves are crimped onto a cable by a special tool. The number of crimps needed to secure the sleeve depends on the sleeve and the tool used to crimp it. Typically, oval sleeves for 1/16” cable require only one crimp; whereas, oval sleeves for 1/8” cable require three crimps; and larger sleeves usually require four crimps. After the sleeve is crimped, it should be checked with a “Go/No-Go” gauge to ensure that sufficient pressure was used to form the termination. If a crimp is not sufficient to allow the crimp to slide into the appropriate slot on the “Go/No-Go” gauge, the tool must be adjusted, if the tool is adjustable (some are not), and re-crimped. According to Barry Grothause, vice president of sales with Loos and Company, crimps made with insufficient pressure to pass the “Go/No-Go” gauge test do not need to be replaced; the sleeve can simply be re-crimped after the tool is properly adjusted.
 
To make a thimble eye splice with an oval sleeve it is important to determine the proper swaging tool and sleeve, along with the correct number of presses needed. This information can be gotten from the manufacturer's instructions supplied with the tool or the FAA document: FAA-AC No. 43.13-1B, Section 8, Inspection and Repair of Control Cables and Turnbuckles. See References. The swaging tool must be in good working order and in proper adjustment, or the crimps may not be properly made.
 
The cable end should extend past the compression sleeve slightly as the sleeve will elongate during the compression process. When the compressions have been competedcompressions in this order, it is easy to judge how much cable will be sticking past the sleeve when all of the compressions are done.
 
 
 
To make a compression in a sleeve, have the sleeve well centered in the tool groove.  Have the major axis of the sleeve set into the tool jaws so that when the jaws are closed they are compressing the major axis of the sleeve.  If the sleeve does not appear to be aligned with the tool after the start of the press, stop, re-align the sleeve with the tool and then continue the press.
 

Swaging Tools
Manual swaging tools are available for a wide variety of prices. Inexpensive swaging tools can be purchased at many big box store for around $30, while more professional tools can cost hundreds of dollars. All, if properly adjusted will do the job. However, many of the inexpensive imported tools do not come with Go No-go gauge. You MUST check your every crimp with a Go/No-Go gauge, so this is a problem. Both Nicopress and Locoloc tools come with Go/No-Go gauges. I have swaging tools from both of these companies and like both – for different reasons. ZFX (ZFXflying.com) sells a Go/No-Go gauge for Nicopress swaging tools that I like a great deal.
 
Some swaging tools have only one cavity (groove) and can be used for only a single size of wire rope. Other tools have multiple cavities and can be used for multiple sizes of wire ropes (between 1/16” and 3/16”). While it is possible to hand swage wire rope that is ¼” or less, larger diameters will require a hydraulic tool. Fortunately, for most aerial work, you will probably never need a cable greater than ¼” diameter.

Conclusion
Wire rope extremely strong, more resistant to abrasion than fiber rope, and can be terminated with 100% efficiency. It is also surprisingly affordable. I am a huge fan of using wire rope and swaging terminations. As you grow as an aerial rigger, swaging wire rope is something that you should learn to do. It will certainly help you solve many rigging problems.
 
 


 Safe rigging,

-Delbert
Need to learn rigging math? Check-out my book. You can purchase it from Amazon.com.
 
You might also be interested in the latest book that Brian Sickels and I have written. Available at Amazon.com.
 

Delbert L. Hall, PhD

ETCP Certified Rigger - Theatre
ETCP Recognized Trainer
Member of IATSE Local 699
ACE Safety Consultant
Flying Director - D2 Flying Effects


 
Copyright © 2017 Delbert L. Hall, LLC, All rights reserved.


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