A pumpdrill is basically a bowdrill operated in a different
manner. It uses a drill and fireboard just like a bowdrill. The main
difference is in how the drill is rotated.
A pumpdrill works by pumping a cross-piece of wood up and down.
This is tied to the drill in such a way that the pumping action causes the
drill to rotate first one way and then the other quickly (similar to the
drill in the bowdrill). Note the twist in the cordage which is attached to
the top of the drill and to both ends of the crosspiece.
A counterweight (at the bottom of the drill) is necessary to
provide momentum to the drill. Without it, the drill would lose its momentum
instantly because of the friction with the fireboard.
View the move (below) to see how the pumpdrill works.