For a more efficient bow drill...

[Bear Stone]

For a more efficient bow drill make sure that the business end of the drill is as close to round as you can get it before you burn in the harth board. This promotes maximum contact with the board, a greater friction area and a quick coal.

Bear

 

[RAPPLEBY2000]

This is pretty sound advice!

 

[Polecatsteve]

And on the flip side ....make it as small an area as possible coming into contact with your bearing block to DECREASE friction at that end and maximise speed. Nothing worse than the coal forming in the bearing block!