Sport Aviation / Experimenter magazine “Technically Speaking” August 2015 Article
Our monthly column in Sport Aviation/Experimenter Magazine for the month of August was an article on Twist Welding cables.
This is technique that we developed over the years and have refined and now use on a regular basis. When working on aircraft with cables of any type.
Twist Weld (Cable End Treatment)
What is Twist Welding? “Twist Welding” is a process for treating the end of a cable to prevent it from unraveling. The idea was originally shared with us by one of our students. He had been in the
cable industry for nearly 30 years and had a more basic version of our technique, but didn’t have a name for it. We coined the term “Twist Welding” while developing and refining the technique.(Figure: 1)
We have been using the twist welding method on everything from aircraft control cables to bicycle shifters. One universal problem with any cable is what to do with the that’s been cut off. Many times the cable is in an environment where it is either being manipulated or removed and reinstalled on a regular basis for maintenance purposes. This generally results in the individual wires, within the end of the cable, becoming untwisted and frayed.
This frayed cable end presents a problem. If you pull the cable through the hole, it may not be possible to gather up all individual wires tight enough to actually reinsert them once again (Figure: 3). One method for handling this is to “Twist Weld” the end of the cable to prevent it from becoming frayed in the first place. This twist weld
method is extremely effective and we have yet to see cable treated in this manner become untwisted.
This process is very simple and can be done with hand tools normally found in most toolboxes. All that is required is a slow turning variable speed cordless drill, a propane torch and a vice or a pair
of pliers (Figure: 4).
Insert the damaged end of the cable into the cordless drill chuck and tighten the chuck on to the cable. Hold the other end of the cable 2 to 4 inches away from the drill chuck using either a vice or a pair of pliers. With a propane torch, on low heat, apply the flame to the cable. Once the cable begins to turn to an orange color, it is time to start spinning the cable at a very low speed.
Continue to twist the cable while simultaneously heating. As the cable is twisted, it will fuse the cable wires together forming a solid single wire. Continue twisting until there’s enough stress built up in the cable to separate the cable in the 2 pieces (Figure: 5).
Refining the Process
A couple of points that will really improve the outcome of this process. 1. Use a cordless drill that turns at a very low speed. Say, somewhere in the neighborhood of 20 to 100 RPM. 2. Apply few pounds of tension on to the cable by pulling the cordless drill during this turning process (Figure: 6). This will do two things. First, it will help maintain a nice straight end after the cable separates. Secondly, it helps to narrow the diameter of the cable during the twisting process. This narrowing will make it much simpler to insert into a hole such as the throttle arm on a Bing carburetor (Figure: 7). If we take the cable end, where we have applied the twist weld method, we can sand down the
cross-section and reveal the fused nature of each individual wire. The cable wire strands are literally welded together (Figure: 8).
Points of Interest
Keep in mind that this process is affecting the structural integrity of the cable, but only in the area where we have applied that heat to the cable. This simply means that you should leave enough additional cable beyond the twist weld area for the actual attachment. Another factor to take into consideration, beyond the structural integrity, is the increased susceptibility to corrosion. An example of this is where we have burned off the galvanizing on a steel cable.
A narrowed cable end is much easier to insert. Figure: 8 Fused nature of the wires in the cable after twist welding are susceptible to corrosion.
One way to deal with the potential corrosion problem is to simply dip the twist welded end of the
cable into a container of paint or primer. An etching primer from a spray can is thin enough that it will soak into the cable strands when the cable is dipped into the primer. Spray a small amount of primer into a paper cup, insert the cable, and let it soak for a for a while (Figure: 9).
Allow the cable can absorb as much of the paint is possible. Remove the cable from the primer and hang it vertically, allowing the excess primer to drip off the end of the cable. This will keep the thickness of the paint on the cable end thin enough that it won’t increase the cable diameter and interfere with the ability to insert the cable into a small diameter hole (Figure: 10). Once you have used the twist weld method you will become a convert. This method works so well, looks so good, and is so quick and easy to accomplish, you will find yourself looking for opportunities to use it on your own aircraft. And it is one trick you’ll enjoy sharing with your friends. Watch How to Video on EAA Hints for Homebuilder http://www.eaavideo.org/video.aspx?v=3742597802001