An attachment for an oscillatory sanding or abrading device has a pair of flexible support members for supporting the sanding or abrading material. The initial radius of curvature of the flexible support member may be adjusted by a spring loaded adjustment mechanism. An opposing pair of circular recesses formed in opposing faces of the flexible sheets allows for replacement of the springs. The recesses can be formed at both ends of the flexible sheets. Adjustment of the initial radius of curvature is accomplished by inserting springs of varying sizes into one or both pairs of recesses. The radius of curvature of the flexible support member during the sanding process is then a function of the spring constant of the spring used and the applied pressure. The device thus uses a series of discrete adjustments each of which covers a range of contoured shapes.