Abstract: A rock cutting assembly consists of a rock cutting roller, a shaft on which it is mounted, and a means for varying the mass of the assembly about the drive axis, to vary the balance of the assembly about that axis. Preferably two rollers are mounted on a common drive axis, the axes of the rollers being diametrally opposed and eccentrically displaced by the same distance from the drive axis. The mass-varying means may be a cavity or cavities in the hub or hubs, with means to introduce fluid into and extract it from the cavity or cavities. Alternatively the means may be a weight mounted to permit adjustment to vary the degree of imbalance.

Abstract: A rock cutting assembly which includes a rock cutting roller with the roller being composed of a central hub portion and an annular cutting element which is rotatably mounted on the hub and carries rock cutting formations, means for driving the hub portion of the roller about an axis which is eccentrically displaced from the hub axis, means engaged with the annular cutting element to limit its direction of rotation relatively to that of its hub to one direction only and means for balancing the roller against its eccentricity as the hub is rotated about its drive axis. Preferably the assembly includes a plurality of rock cutting rollers which are rotatable about a common drive axis with the axes of each roller hub being eccentrically displaced by a common distance and in such a direction from the drive axis so that the rollers balance each other as the rollers are rotated about their drive axis.