Abstract: A clutch assembly for a sanding head is disclosed, the assembly giving a sanding head the dual functions of orbital sanding or rotary grinding. The assembly incorporates a clutch plate and actuating means between an eccentric drive head and backup pad secured thereto. The actuator moves the plate axially, depending on the rotational speed of the unit, into engagement with the drive head to effect a rotary grinding action. Release of the clutch plate therefrom due to a drop in speed converts the rotary action to one of an orbital path.