A rotary float includes an elongated tubular arm with a drive shaft rotatably mounted therethrough. A drive unit is coupled to a rearward end of the shaft to rotate the shaft. A swivel on the forward end of the drive shaft connects the drive shaft to a collet shaft within an extension tube, and transmits rotational force from the drive shaft to the collet shaft. The extension tube is connected to the arm at a knuckle joint, which permits the extension tube to pivot about the forward end of the arm. A bit is mounted on the forward end of the collet shaft, for grinding a surface adjacent the forward end of the extension tube.