A centrifugal grinder has an internal grinding surface shaped as a surface of revolution, and a rotor mounted within the surface for rotation about the axis of the grinding surface. The rotor defines a generally axial inlet passageway for wood chips to be ground, and at least one pocket extending generally outwardly from the axis of the rotor toward the grinding surface. The pocket is provided with a configuration such that its cross section increases at an increasing rate away from the rotor axis. This encourages the wood chips to orient themselves parallel to the grinding surface, such that they take up such parallel orientation by the time they reach the grinding surface.