I thought I'd have a bit of fun at seeing how small a bow drill set I could make. The picture to the left shows the set I managed to welcome an ember with. The drill was about 8cm in height in the end and the length of the cord to traverse was about 16cm. I did try a smaller bow (to the left) but that didn't work. These smaller sets are fiddly and not as efficient as a normal sized set but it worked. In practice. If the materials are available I would say go for a normal sized set. But on the other hand, if all you can find are smaller bits of dry wood then it can work - it just needs a bit more patience. With a small drill it's may not be as easy to apply the downward pressure - this got so small that my hand was resting on my shoe! I also used a thinner cord by wrapping it multiple times around the drill - this way the cord can be slacker so less pressure and less prone to snap.