A really handy thing to have in your pocket for the occasional Bow-Drill Fire Start is a metal top to a soda bottle. (You remember those real glass bottles with the pop tops.) Easier to find might be the metal tops to a beer bottle. This little item can be used as the top pivot for the drill if you back it with a block of wood. The rim of the bottle cap will bite into the block of wood you are pressing on and the drill will quickly dimple the cap enough to stay centered. Provides a nice "friction-free" bearing for the top of the drill that keeps the drill nicely centered.

About the best set of directions for using a bow drill I have ever found!