I thought I'd experiment with cordage the other day, especially thinner and easier to break cordage. I successfully created embers with Jute, waxed leatherworking thread and household string (easily breaks!) The trick with using thinner threads is to twist the thread lots of times around the drill - I usually use cord twice the length of the bow and have at least 8 loops. You can also have the cord slightly slack when using this method - this puts less pressure on the cord. I had to double twist the string as it broke too easily . I also found that I needed to put more downward pressure on the bearing block.