Pumpdrill 

Photo by Anthonio Akkermans

The whole pumpdrill.

Note the string wound around the top of the drill. The ends are attached to the ends of the handle (the long bar at the top of the pumpdrill apparatus).

The hardest part of creating a pumpdrill in a primitive situation would be to pierce the handle with a suitable hole for the drill to go through. Perhaps one can be made with the handle going alongside the drill?

Stones provide the counterweight at the bottom. 

Photo by Anthonio Akkermans

A close-up view of how the stones are attached, as well as the drill bit itself.

Note that this is a removable drill bit. When it gets worn down, another bit can be installed in the tip. Thus, the apparatus itself doesn't need to be rebuilt just because the fire bit has worn down.