Garage door industry magazine for garage door dealers, garage door manufacturers, garage door distributors, garage door installers, loading docks, garage door operators and openers, gates, and tools for the door industry.
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56 International Door & Operator Industry™ The most common cable diameters used are 3/32", 1/8", 5/32", 3/16" and 1/4". If you have been around doors for a while, you are probably able to look at the cable and tell what diameter it is. If you have diffculty doing this, the cable diameter can be measured with a caliper. (See Figure 1 on how to correctly measure with a caliper). The two common types of cable construction in use are 7x7 fexible cable, and 7x19 which is more fexible. In addition to being more fexible, 7x19 is a little stronger, lasts longer and costs more than 7x7 cable. Since cable on overhead doors wind on to cable drums or run over sheaves (pulleys), 7 x 19 cable is commonly used. The two types of cable used for overhead doors are galvanized and stainless steel, with galvanized cable being the most common. Both types of cable are sometimes referred to as "aircraft cable", but are not actually used on aircraft. The diameter of the drum or pulley in relationship to the diameter of the cable is a critical factor in establishing the cables ability to resist bending fatigue. To picture this, think of a clothes hanger being bent repeatedly back and forth at the same point. It will eventually break. All cable running over pulleys or drums are subjected to bending stresses, and the cable will eventually fatigue. The tighter and faster the bend, the quicker the eventual fatigue. As the number of wires per strand in a cable increases (7 x7 to 7 x 19 construction); the ability to resist fatigue increases as well. To understand this more in the feld, the technician must be able to identify the size of drum and confrm what the proper diameter cable needs to be per the size of the grooves in the drum. An example would be, most 4" diameter standard lift drums that I know of are only designed to accept 1/8" cable. Replacing a set of 1/8" cables to 5/32" because you think they will last longer because of the bigger diameter on a door with this type of drum would be a mistake. After the proper diameter, construction and type have been identifed, it must be understood that deviating from this diameter with the thought that "bigger is better" is not always the case. THE CABLE ASSEMBLY Whether you are replacing cables with a pre-made set of cable assemblies or fabricating a set of cable assemblies in the feld, let me frst suggest you always replace cables in pairs. Think of these cables as being a pair of shoes. You normally just don't buy one shoe if the sole is worn out on your left shoe even if you could fnd an exact mate. I have seen this mistake made time and time again. The errors that occurs when you do this is that you do not get the single new cable to match the exact length of the existing one. I have also seen where a different diameter of cable was used as the replacement cable. The new cable can stretch slightly after it has been installed and in use for a while. The net result of this is that door becomes out of level. Fabricating a cable assembly: The steps involved in fabricating a cable assembly include: 1) Cutting the cable; 2) Forming and swaging the loop end; and 3) Swaging the stop end. Cutting the Cable: With respect to cutting, the important points are 1) cutting to an accurate length; 2) making sure the 2 cables are cut to the same length; and 3) using the proper cable cutting tool to cut the cable to avoid frayed ends on the cut. Whether you are working on a standard lift, high lift or vertical lift door, proper cable length is a critical factor in the proper operation of the door. Specifcally to a high lift or vertical lift door, improper cable length will grossly affect the balance of the door if not done correctly. There is no guarantee, especially if you are working on an older door that has possibly had the cables replaced on it before, that the cables that are on there are of the proper length. If you are not sure about the length being correct, I would recommend you stop and confrm before making a mistake. Understanding and calculating proper cable length is a subject amongst itself. Seek expertise from an experienced technician or contact a manufacture for more detailed information if needed. When fabricating a cable assembly in the feld, use care to make sure the cables are cut to the accurate length, and Continued on page 58 Figure 1 - How to measure cable diameter TECHNICAL (continued from page 54) 1/24/14 10:54 AM