Building a Cable Assembly
What type of wire rope assembly or lanyard you require will depend on a number of factors. How is the assembly going to be used? Does it need to meet any explisit specifications? What are the possible environmental conditions which could affect the assembly? Numerous aspects need to be considered when properly designing and selecting your assembly
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Step One - Cable Strength
First, determine the strength of the cable you require, that is the weight your assembly will need to bear. Once you have determined the required weight load, you will need to arrive at the the required Safety Factor. If your required weight bearing load is 100 lbs, you would increase the load by some factor to ensure safety. Generally speaking, it is a factor of 4 to 6 times. So you would be looking at a breaking point of 400 to 600 lbs. The more critical the assembly, the higher the Safety Factor. There is variety of application of lanyards and wire rope assemblies uses so be sure to consider all possible factors such as friction and environmental factors.
See Cable Charts for a list of break loads.
Step Two - Commercial or Mill Spec Cable
Choose between Commercial or MIL-DTL-83420 (Military Specification) cable (or simply, dry vs. lubricated cable). Will the cable be going over pulleys, sheaves, or are there other factors resulting in friction? While both types of cable will have the same break strength minimum, the MIL-DTL-83420 is a higher quality product which generally results in better performance and endurance due to the internal lubrication. However, you will pay a premium price for MIL-DTL-83420 cable. So if you’re looking at more of a straight-line application with very little flex then Commercial grade cable should work best.
Step Three - Stainless or Galvanized Cable
Choose the type of steel your cable is to be built around. There are two primary considerations; environment and cost. Where exposure to the elements is not a factor, galvanized cable and zinc-plated fittings are generally you best option (as well as being more economical). Where corrosion is a concern, stainless steel cable and fittings are your first and best choice but you will pay a premium price over galvanized.
Step Four - Cable Flexibility
How flexibly does your cable need to be? 7x7 or 7x19 describes the construction type of cable or wire rope. The 7x7 and 7x19 are the most common used in cable or wire rope assemblies. Cable is constructed by wrapping a wire or strand helically or spirally around a core. In 7x7 cables, there are 7 strands (6 strands wrapped around a core strand) and each strand consists of 7 individual wires (again 6 wrapped around one core). The 7x19 has 7 strands and each strand consist of 19 wires (one core wrapped by 6 which are wrapped by 12). Both of these are considered Aircraft Grade Cable. While both are flexible, the 7x19 is more flexible.
Step Five - Assembly Length
What is the proper length of the assembly? To determine the correct measurement of the assembly, first consider what points of assembly are most important. Is the use of the end-fittings vital for the connection of parts of a larger project? How does the size of the loop impact the final length of the assembly? The ultimate use of the assemblies will be the determinate factor in proper length measurement. NCA's team can help you determine the best measurement criteria for your wire rope assembly or lanyard.
Step Six - Cable Coating
Does the cable or wire rope require coating for the assembly or lanyard. The three most common coating options are; Bare (no coating), Nylon, or PVC(Polyvinyl chloride). Questions to consider are - What are the conditions under which the assembly will be operating? Is there a need to reduce friction? Will the environment be an issue? Does the appearance of the cable matter? If yes to these, than you should a coated cable will be your best choice. PVC coating will be better for general purpose coating. It is more flexible and therefore easier to strip as well as being less expensive. Nylon coating wears better than PVC. However, it is not as flexible and it is more expensive than PVC. Nylon coating is more appropriate for working over pulleys and sheaves.
Step Seven - End Fittings
What is the best end fitting? There are many options. The most common are loops, sleeves, stamped eyes, strap eyes or strap forks, plain ball or ball shank, stop sleeve, thimbles, threaded studs, retaining tabs, or winch hooks. The ultimate use of the lanyard or assembly will dictate the appropriate end-fitting. If you have any questions as to best option or there is a unique end fitting you need to make your assembly, please contact the NCA team.