Abstract: Workpieces having three-dimensional surfaces can be efficiently sanded by rotatable sanding members mounted on spindles which are supported for movement in a circle of revolution over the surfaces of the workpieces as the individual spindles are selectively rotated about their longitudinal axes in either of two opposite directions during predetermined portions of each circle of revolution. A sanding apparatus for accomplishing this function includes a cone clutch arrangement for selectively reversing the direction of rotation in accordance with a cam directed control arrangement acting on pivotally supported yokes carrying the individual spindles.