A battery powered impact driver is capable of driving a 6" screw into a solid piece of wood, without the need of predrilling, in less than 10 seconds. The impact unit consists of a gear drive, spindle, spring, hammer and anvil, to which a tool is connected to drive the screw or bolt. The periodic torsional impacting action of the hammer is achieved by a windup and release mechanism. T

he dynamic interaction between these parts is simulated using ABAQUS/Explicit. With the model, it is possible to predict the kinematics of the impact mechanism, including torque spike characteristics and driving speed. Key characteristics of the model have been validated by tests. Thus, analysis leads the design towards finding the most efficient combination of cam lead angle, hammer release clearance, inertias, and other design variables. High-speed camera test video clips compare well with simulation animations.