A power back-up roll for a rotary veneer lathe comprises a drive roller for applying a rotational force to the outer periphery of a log axially mounted on the veneer lathe, a controllable drive source for driving the roller and a servo-control system for maintaining the static friction between the roller and the log. In a preferred embodiment of the invention, the servocontrol system includes a first DC-generator tachometer for monitoring the peripheral speed of the log, a second DC-generator tachometer for monitoring the peripheral speed of the roller; and a feedback loop, operatively associated with the controllable drive source as well as the first and second tachometers, for matching the peripheral speed of the roller to that of the log.