I use Astroflight for making tillering strings since it doesn’t stretch nearly as much as dacron. Alas, the stuff is slippery and the knots I use for adjusting the string length (a bowyer's knot and, my favorite, a slip type bowline) very frequently slip. To eliminate that, I add a few strands of dacron to the end of string that will be knotted, braid it using a simple 3 bundle braid and whip the end with a wrapping of dacron to keep it together.
Attached are pics of a tillering string for 35# and under bows made of 7 strands of Astroflight (a screw-up!) and 5 of B55 dacron. The braiding is 24" long so it can be used on really long and short bows. When making one, allow for extra lenght since the braiding shortens the lenght of the final string.
The second pic shows a slip type bowline knot and a tied-on nock. I've grown to really like tied-on nocks when making bows since there is no need to cut nocks and they can easily be moved to change the effective bow length. The slip type bowline knot is easy to untie- just jerk on the tail/free end of the string. It also doesn't slide off-center in the nock like a bowyer's knot tends to as it tightens and also provides a larger eye for easier nocking and un-nocking when tillering. The last pic shows how to tie one.
c.d.
