The spring cord in a ballista's torsion springs is typically pretensioned using a stretcher and a clip to allow them to produce greater power. However, in order to maintain the pretension of the springs the ends of the cord have to be locked in place somehow. The beginning of a three-ply spring cord is easiest to lock using a three-ply eye-splice described in this article. Similar splices exist for other cordage types.
While there is ample documentation about three-ply eye splices on the Internet, most of it manages to make a very simple technique very difficult to understand. There are exceptions, though:
- Eye splice (video on Youtube)
In the beginning of the video the technique used here is explained in just a few seconds, but that's enough. That said, this article attempts to expand on that explanation in as clear fashion as possible.
The measurements given here apply to the cheiroballistra; please adjust them to the size of your washers. In a ballista context the most important thing is to make the loop long enough to place the thick weave below the washer, so that it does not consume precious space inside the washer.
The process step by step Edit
Tape the end of the cord. Mark a 11cm long section from the end:
Tape the cord from the other side of the mark:
Measure 13cm from the first mark:
Align the two marks you made side by side to form a loop:
Remove the tape from the end of the cord and unwind the plies. The tape at 11cm mark will keep the rest of the cord intact:
Use permanent markers of different colors to mark the ends of the plies:
Tape the ends of the plies to keep them intact:
Tape the cord next to the 13cm mark:
Use a metal pin to wedge an opening between the plies next to the second mark:
Push one of the separated plies (here red) through the opening in the cord:
Draw the ply to tighten it:
Take another ply (here black) and push it through the main cord at the next crown, and tighten it:
Take the last ply (here blue) and do the same:
Repeat the process from the beginning in the same order until the plies are too short to push through the cord.
Finally remove the tapes from the inside of the loop: