QUICK AND EASY WIRE ROPE TERMINATIONS: Hardware and Tools Not Needed by Delbert L. Hall and Steven Santos

Transcription

1 QUICK AND EASY WIRE ROPE TERMINATIONS: Hardware and Tools Not Needed by Delbert L. Hall and Steven Santos Published in TD&T, Vol. 47 No. (Spring 0) Theatre Design & Technology, the journal for design and production professionals in the performing arts and entertainment industry, is published four times a year by United States Institute for Theatre Technology. For information about joining USITT or to purchase back issues of TD&T, please contact the USITT office: USITT 5 South Crouse Avenue, Suite 00 Syracuse, NY 0 tel: USITT ( ) tel: fax: info@office.usitt.org web:

2 Quick & Easy Wire Rope Terminations Hardware and Tools Not Needed By Delbert L. Hall and Steven Santos iber rope is often preferred over wire rope for tasks that involve any type of line, even though wire rope is usually much stronger and less stretchy than most fiber ropes. Why? Because tying a knot in a piece of rope is free, quick, and easy, and terminating wire rope is usually none of these. Making terminations in wire rope requires the use of special hardware, such as cable clips or swaging sleeves, and tools, such as nut drivers, socket wrenches, an expensive swaging tool, or a torque wrench. This article will demonstrate what many people consider unthinkable: tying knots and making quick splices in wire rope. History William Albert, an official the Harz Mountain silver mines in Germany, devised the first operative wire ropes around 84. They were used in the long vertical mine shafts as hoisting cables until 854. These early wire ropes were made using a process not unlike prehistoric techniques for making hemp rope. Workers took three equal lengths of wrought-iron wire and twisted them around each other by hand to make strands. Three or four of these strands were then twisted together to make a rope. Since the earliest days of wire rope, people have explored and experimented with the use of knots in wire rope. Many of those early experiments, and even most modern studies, have shown that most knots tied in wire rope do not hold well because the wire rope is too stiff and slick. But this is not true for all knots, and this article will show some of the knots that do work that are strong and will not slip. Regulations There are a number of regulations relating to the use of knots and splices in wire rope. Tying knots in wire rope is not an acceptable practice in all fields or for all uses. Indeed, the practice is banned in several areas. For instance: OSHA does not allow knots to be tied in wire rope in marine uses. OSHA all but outlaws wire rope knots in construction. Safety and Health Regulations for Construction (Rigging equipment for material handling), 9 CFR 96.5(b)(5), states, Wire rope shall not be secured by knots, except on haul back lines on scrapers. (Haul back lines are cables used to move other cables and do not hold a live load.) The FAA bans the use of knots in wire rope used on aircraft (4.- b/b). spring 0 69

3 Tying a knot in wire rope is an acceptable practice in some industries. For instance, it is a common practice in the theatrical world, and some authorities specifically allow the use of knots and splices in wire rope. The U.S. Army specifically allows the use of knots in wire rope when wire rope fittings are not available and it is necessary to fasten wire rope by some other manner. In the early twentieth century it was commonplace for stage battens to be tied to steel cables using clove hitches and secured with friction tape. In the performer flying industry, guy wires made from /8 diameter galvanized aircraft cable are commonly terminated with a variation of the clove hitch. The Workers Compensation Board of British Columbia allows some uses for logging. As with fiber ropes, the three basic types of wire rope terminations are loops, hitches, and bends. Loops are used when creating a loop or eye in the end of a cable; hitches are used when attaching the cable to a beam or pole; and bends are ways of attaching two cables together to make a longer one. the Knots Although we promised no hardware or tools were needed in our title, tying most of these knots and splices in wire rope does require some electrical tape and a pair of cable cutters. It is also important to remember that the more wires in the wire rope, the more flexible it will be, and the more flexible the wire rope is, the easier it is to tie a knot in it. For the examples illustrated in this article, /8 dia. 7x9 galvanized aircraft cable is used, and the approximate efficiency of the tied knot is noted. There are many more wire rope knots than can fit in this article, so we will concentrate on the ones that we consider the most useful. Knot Name: Flemish Eye Knot Type: Loop Efficiency: Up to 90% Common Uses: Anywhere an eye is needed in a wire rope. Notes: The Flemish Eye (a.k.a. Farmer s Eye, Molly Hogan Eye, or a Canadian Eye) is the most common knot/splice for making an eye. Unlike traditional splices, this splice involves re-twisting the strands of the cable instead of tucking them. There are several slight variations of this splice, but we will cover the variation that our tests have proven to be the strongest (up to 90% efficiency rating in some tests, making it even stronger than using cable clips). Step : Untwist the strands dividing them into two groups: one with three outer strands and the other with three outer strands plus the core strand. Give yourself plenty of leads to work with. Step : Cross the two sets of strands and begin twisting them back together to form the eye. Each set of strands should twist around the other at least three times. Step : Keep twisting until the eye is completely formed. Step 4: Twist the two parts of the tail together to make a single tail strand. 70 spring 0 Step 5: Finish the termination by using electrical tape to secure the tail to the leading part of the cable. This will prevent it from getting caught on things when in use. Some manuals show a cable clip being used to clamp the tail to the leading part of the cable, but since we re not using hardware, tape is fine. Knot Name: Circus Hitch Knot Type: Hitch Efficiency: 60% Common Uses: Terminating a cable to beam or pipe. Flemish Eye Notes: The Circus Hitch (a.k.a. a Carney Knot) is probably the best-known cable knot. This hitch is great for guying cables because it can be tied with tension on the line. It is an extremely secure hitch that will not loosen, even when there is slack in the line. Step : Tie a typical clove hitch around the pipe with your cable. The clove hitch can be used as a means to put significant tension on the leading part of the cable, if desired. Leave yourself plenty of tail with which to create the stopper portion of the hitch. Step : Tightly wrap the tail, at least four wraps, down the leading part of the line. Step : Bend the cable 80 degrees and tightly wrap back down the lead line (over the top of your previous wraps) toward the 4 5

4 pipe. Then feed the end of the cable tail into the small opening between the lead part and the tail directly at the clove hitch, and pull tight. cross hitch general purpose knot Knot Name: General Purpose Knot Knot Type: Hitch Efficiency: 60% Common Uses: Terminating a cable to beam or pipe. Notes: The General Purpose Knot (not a very original name) is another knot that works very well for tying a cable to a beam or pipe. Although it is not as strong or as secure as the Circus Hitch, the General Purpose Knot is extremely fast and easy to tie. It should also be noted that like a Sheet Bend, which will be covered later, this knot is loose and springy until tension is placed on the cable. It is also a knot that must have tension on it to remain secure, so this knot should be not be used in situations were the standing part of the line can become slack. Step : Tie an overhand knot in the cable (we will call this twist of the cable the first wrap ). Step : Pass the working end around whatever it is being attached to and then bring it back through the loop that was created when the overhand knot was made. Be sure that it is threaded through the loop in the proper direction. Step : Thread the end through the loop a second time (opposite the first twist). Step 4: Thread the end through the loop a third time, making another wrap next to the first wrap. Step 5: When a load is placed on the line, the knot will tighten. Knot Name: Simple End Splice Knot Type: Bend / Splice Efficiency: Not rated Common Uses: Temporarily attaching two cables together. Notes: A Simple End Splice (the name we have given this splice because we have never heard it called a specific name) is similar in some ways to a Flemish Eye splice the strands are untwisted and then re-twisted to form the splice. This is not an especially strong splice, but it is quick and easy and keeps the cable the same diameter so that the splice can pass easily over a sheave. This is a great splice to use when replacing a cable, because it allows the use of the old cable to pull the new one through the sheaves. 4 5 spring 0 7

5 simple end splice 4 Knot Name: Double Sheet Bend (a.k.a. Double Cat s Paw knot) Knot Type: Bend Efficiency: 60% Common Uses: Attaching two cables together, or attaching a cable to a fiber rope. Notes: For a stronger attachment than the simple end splice, a Double Sheet Bend (a.k.a. Double Cat s Paw knot) is generally a good knot. When first tied, this knot is rather loose, and it can take several hundred pounds of force to tighten it completely, but when tight, it will hold quite well. We should also note that there is a different knot for rope that also goes by the name Double Cat s Paw, so do not be confused if you see this name. This knot can also eliminate the need for an expensive Klein Haven Grip and it works better too. Step : Bend one cable to form a bight. Step : Insert the working end of the second cable up through the bight, wrap around the back of the bight, and then over the top of the bight, making certain that it passes under itself. Note: a Single Sheet Bend, as seen at the end of this step, is a good knot, but not as secure as a Double Sheet Bend. Step : To make this a Double Sheet Bend, (continuing in the same direction) pass the working end around the back of the bight a second time, and again over the top of the bight, making certain that it passes under the standing part again. Then pull tight. (Because of the stiffness of the wire rope, the cable can spring out of the position normally associated with a sheet bend. This does not affect its holding strength.) double sheet bend Step : Untwist the strands of one cable (at least 00 times the diameter of the cable) dividing each into two groups: one with three outer strands and the other with three outer strands plus the core strand. Cut off the bundle with three stands and re-twist the end back in place. Step : Untwist the strands of the second cable, dividing each into two groups: one with three outer strands and the other with three outer strands plus the core strand. Untwist this bundle a couple of inches longer than you did for the first cable. Cut-off the bundle with the four strands and re-twist the strands back into place. (We are using a black colored cable to make the splice more visible.) Step : Twist the two bundles of strands together to make a single cable. Step 4: Cut these tail strands to the proper length and twist into place. Step 5: Use electrical tape at the ends of the splice to prevent the wire from fraying-out and catching. Keep the tape as smooth as possible (on small diameter cable run the tape down the cable rather than wrapping the cable). 7 spring 0 5

6 Conclusion Just like working with knots in rope, making splices and knots in wire rope takes practice and testing. When you learn how to properly tie the knots and understand how they will behave in use, they will come in handy. While it may seem very unorthodox to tie knots in wire rope, this practice has a long history. As with any type of rigging, never put something into practice until you are proficient at it and you are certain that you are using the proper tool/technique for the job. v Delbert L. Hall is a professor at East Tennessee State University, and is president of D Flying Effects, LLC. He has been rigging performer flying effects for over twenty-nine years. Delbert is an ETCP certified rigger and an ETCP recognized trainer who regularly presents workshops on various aspects of rigging. He is very active with USITT s Technical Production commission and has published the results of many of his destructive tests on theatrical hardware on the website LoadLab (delberthall.com/loadlab/). Delbert is also the creator of RigCalc, a calculator app for solving numerous rigging problems ( Steven Santos is the founder, executive director and head rigger for Simply Circus. He has worked on rigging projects for television shows, the circus and theater productions. Steven is passionate about raising the bar in the world of rigging. He regularly teaches aerial rigging classes and has written many articles on rigging topics, including the Aerial Arts FAQ, the Aerial Fabrics FAQ, the Guide to Inspecting Climbing Ropes in School Gyms, the Guide to Inspecting & Maintaining Unsealed Ball-Bearing Swivels and the Hair Hang FAQ. Steven is currently writing a college level textbook on circus and aerial rigging. References Budworth, G. and Dalton, J. 00. The Book of Knots. New York: Barnes and Noble. Certex, USA, Inc. 99. Some Things Every User Should Know About Use and Care of Wire Rope and Wire Rope Slings. Accessed online at Department of the Army Field Manual No Rigging Techniques, Procedures, and Applications. Accessed online at Occupational Health & Safety Administration. Regulation (Standards 9 CFR). Accessed online at owadisp.show_document?p_table=standards&p_id=0686. Sayenga, Donald. Modern History of Wire Rope. Accessed online at Toss, B The Complete Rigger s Apprentice. Camden, Maine: International Marine. Workers Compensation Board of British Columbia A Manual on Splicing. Accessed online at health_and_safety/by_topic/assets/pdf/splicing.pdf. spring 0 7

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