Abstract: A machine tool comprises a support mounted for rotation about a machining axis, a first motor operable to rotate the support about the machining axis, a tool holder mounted on the support for rotation about a tool positioning axis which is parallel to and off-set from the machining axis, a second motor operable to rotate the tool holder about the tool positioning axis, and control means. For a constant diameter machining circle, the support and the tool holder are rotated about their respective axes at equal angular velocities so that they rotate as a unit. To adjust the diameter of the machining circle, one of the motors operates for a period at a different angular velocity to the other motor, thereby altering the position of the tool holder relative to the support about the tool positioning axis.

Abstract: A grinding machine includes a rotating grinding wheel and workpiece moving apparatus operable to move a workpiece towards and away from the wheel. The apparatus is arranged to move a workpiece support arcuately about an axis to move a workpiece towards or away from the wheel. A motor turns the workpiece to present different parts of the workpiece to the wheel, and an orientation detector signals the orientation of the workpiece so that the operations of the workpiece moving apparatus, and the motor can be coordinated to cause a desired profile to be ground on the workpiece. The machine also comprises correcting apparatus operable in response to the operation of the workpiece moving apparatus to cause the output of the orientation detector to be altered to compensate for angular alterations in the point of contact of the workpiece with the grinding wheel caused by the arcuate movement of the workpiece support.