Abstract: A rotary actuator with improved damping and stiffness is disclosed. The rotary actuator includes one or more bearing plates that form sliding-surface bearings to provide the desired preload to the rotary actuator. One embodiment of the invention includes a multi-piece bearing plate that makes repair or replacement of the bearing material in the sliding-surface bearings easy to perform. Another embodiment for applications where heat dissipation is critical includes thermal barriers on either side of the sliding-element bearings, with resilient members between the thermal barrier and a bearing ring used to supply the appropriate preload to the output shaft. The invention is particularly suited to precision applications, such as the drive unit for the swivel mechanism on the spindle head of certain types of five-axis milling machines.