The spindle, carved to reduce friction at one end and maximize it at the other, is held at one end by the bearing block, and at the other by the hearth. The string of the bow is wrapped once around it, so that it is taut enough not to slip during operation. A variation on this called the Egyptian Bow Drill attaches the string by wrapping it around multiple times.
The usual position that a person assumes whilst operating the bow drill is as follows: the right knee is placed on the ground (assuming a right-handed operator) and the arch of the left foot is on the board, pinning it in place. The left wrist, holding the handhold, is hooked around the left shin so it can generate enough downward pressure and speed; achieved by pushing down with the handhold and spinning the drill. The heat of the friction between the hearth and the spindle both creates charred, fuzzy dust and causes it to ignite - forming a coal or ember. The handhold is lubricated and the spindle is carved to about thumb thickness, usually six to eight inches long.
An indentation and a "v" notch into the center of the dent is made into the fireboard and the spindle is placed on it. The notch allows a place for the dust collect while it is being abraded off the spindle and the hearth. Eventually, the friction generates heat to ignite the dust, which can be used to light tinder.
Whilst a "v" is most common, other methods to create a cavity to contain the dust whilst it is being ignited can be used. For example: drilling part-way into a hearth made by lashing two sticks together from one side, and then drilling from the other side to meet this hole; or using the area where two branches separate. This is to keep the coal off wet or snow covered ground.
The hearth and spindle can both be soft woods; yucca, aspen, cedar, basswood, and most willows all work very well. Combinations such as hazel and poplar also work well. The bow should be stiff but slightly limber and around 30 inches long. The bearing block can be made of anything but bone, antler, and stone work the best as they can be easily greased, do not create as much friction, and do not burn.
This is by far the easiest method of producing a coal by primitive means and anyone can do it by using good materials and maintaining a calm mentality, concentrating only on working everything slowly and smoothly.
To use one hand is placed on the hole board while the other turns the shaft to wind the cord around its length thus raising the hole board to near the top where the cord becomes taut. Placing the tip against the material to be drilled and held upright, a smooth downward pressure is exerted on the board causing the drill to rapidly spin. Once the bottom is reached, the weight is relieved and the drill allowed to rebound re-winding the cord around the shaft and the process is repeated. It is a skill simple in concept but takes some practice to master and greatly speeds up the process of making small holes.