Abstract: Disclosed is a robotic device having a sub-assembly constructed and arranged for zero error Z-axis compliance. The sub-assembly includes a vertically positioned bearing assembly having a shaft received in a ball bushing. The ball bushing may be received in a race. Spherical-shaped bearings are positioned in the bushing and project outwardly from the outer and inner surfaces of the bushing to form a smooth linear traveling surface. A plurality of lines of bearings may be positioned in the bushing. Each line of bearings may be skewed from the longitudinal axis of the bushing so that the lines of bearings form a blanket bearing surface covering substantially the outer surface of the shaft and inner surface of a race. In such a construction each bearing engages a different portion of the shaft and race as the bushing and shaft move in a vertical direction along the Z-axis. This reduces the wear on all contact surfaces and prolongs the life of the sub-assembly.