Splicing a ski lift cable
It will come as no surprise that the seats on a chair lift are attached to a metal cable. But did you know that it takes 3 essential steps to install that cable?
First of all, a 15mm diameter rope is installed by helicopter. The actual cable is then pulled through the departure and arrival stations and each pylon after this rope. Finally, the two ends of the cable have to be spliced together to form a continuous loop.
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How is a ski lift cable constructed?
A ski lift cable is actually composed of several little metallic cables and a plastic centre that acts as a support.
The individual small cables are helical and form what we call strands. These strands are then wound in a spiral around the centre of the cable.
There are several advantages to having a compact plastic centre:
The diameter and length don’t change over time
The strands are perfectly supported because it moulds around them.
What is splicing, why and when is it done?
Now that we know what a cable is made of, stick around to learn about splicing. As a reminder, it means attaching two cords or cables together by joining one end to the other. This process has been used for a long time, notably by sailors on boat rigging. Today, a long splice is still the only method that allows you to form a continuous loop without any discernible difference in the cable diameter.
With ski lifts, you need to carry out a splice when a new cable is being installed or when you need to shorten a cable that has gone slack after several years of being in use.
How is a splice carried out?
Carrying out a splice, or splicing, is a delicate operation and carried out almost entirely by hand.
Splicing is a standardised practice. The length of a splice, for example, has to be equal to or over 1,200 times the regular diameter of the cable. In the case of a chair lift with a 45mm diameter cable, that means that the splice needs to be 54 metres long in total!
You start by unwinding the strands at each end of the cable until you reach the required length.
The strands are then rewound together. This simple winding method provides enough friction so that the strands don’t slide around or move.
To avoid having all the strands come out of the cable in the same place, we create “bonds”. This involves removing the centre of the cable for several metres and replacing it with one of the strands. The strand will have been cut, straightened and covered in plastic beforehand to make it the same size and consistency as the cable centre. Finally, you strike the cable to tighten it up and stop it from loosening when it is straightened out. Once again, it’s a very precise process because the cable diameter at the bond sites mustn’t vary by more than 10%. This step is carried out in several places along the splice, once for every strand there is in the cable.
Once all the bonds have been carried out, the cable is gradually straightened out again, then it’s ready to be used to transport chairs and skiers!