For a Flemish bow string you really don't need a jig. I never use one.
What I do is measure out the strands I need depending on the bow weight stagger them by one inch and begin the twisting from there. I usually go twenty inches longer than the bow length. It all depends on how vigorous you are with the twisting for how long the strings need to be. That has been my experience.
I also twist the strands all the way down the string and put a timber hitch on the bottom. Allows for adjustment in the long run.
I know there is a way to put loops on both ends but I like the double or triple color twist all the way down the string.
