I have found that it doesn't matter which way the notch is facing when using the bow drill. I make some of my hearths from fairly narrow pieces of wood, and for the sake of strength and keeping the successive notches not too far apart (so as not to waste hearth board) I make one notch one side, then the next notch the other side. As I always hold the hearth in place with my left foot, the notches face alternate directions as I work along the hearth, with no apparent effect on the results whatsoever. Wind direction can be a factor, but suely this is best dealt with by facing yourself the right way to start with, not altering the bow drill set-up?