Abstract: A reciprocating tool, such as a sander, which may be driven by a rotary pneumatic motor via an eccentric connection with a gear train. In order to balance the dynamic forces generated by the reciprocating tool element, a weight may be properly positioned within the tool housing and driven by a similar eccentric connection to a gear train. Proper coordination of the gear train will result in the movement of the tool element and the weight in opposite directions at any given instant, thereby increasing the operator's ability to maintain the tool in a desired path of movement.