Patent ID: 8006782

Claim:
A drill head assembly, comprising: a shaft having a shaft axis and a plurality of external threads; an oscillator assembly operatively associated with the shaft, the oscillator assembly having at least one eccentrically weighted rotor configured to rotate about a pivot point to generate an oscillating vibratory force, wherein an oscillation centerline is defined transverse to the shaft axis and including the pivot point; a lower bearing coupled to the shaft on a first side of the oscillation centerline; an upper bearing coupled to the shaft on a second side of the oscillation centerline, the second side being opposite the first side; an internally threaded base nut adapted to be selectively secured in position on the shaft by engaging the plurality of external threads; a bearing spacer moveably secured on the shaft between the upper bearing and the base nut; and a plurality of bolts biased against the based nut, wherein advancement of the plurality of bolts relative to the base nut forces the bearing spacer away from the base nut thereby applying a preload to the lower bearing and the upper bearing.