Abstract: An assembly for surface finishing, comprising a pair of heads which are movable on linear slides. Each head comprises a series of cup brushes that finish the surface of the workpiece. The two heads are tied to a single motor/gearbox combination by a crankshaft which allows each head to move with a phase relationship determined by the linkage to counterbalance the motions and acceleration forces against each other. By counterbalancing the heads in this manner, faster oscillation speeds can be achieved without undesirable vibration. The result is a better treatment of the surface of the workpiece.