Abstract: A portable power tool having an annular ring tool, such as a saw blade or grinding wheel, driven on its periphery by a power unit. A ring tool housing carries the ring tool and is mounted to the power unit, the latter having a drive shaft roller which frictionally engages one surface of the ring tool. Ring tool guide bearings and ring tool support bearings oppose and cooperate with the drive roller to retain the ring tool within the housing during its rotation.The driven shaft axis is canted at an angle extending beyond the center of the ring tool or toward the working side of the ring tool to counteract the torque forces produced by the working operation. Means are also provided to vary the drive roller pressure on the ring tool to balance the torque or, alternatively, to vary the drive shaft axis angle to balance the torque thereby producing dynamic stability during the working operation regardless of work piece resistance.