Abstract: An expandable drill bit for cleaning solidified cement from a well casing used in oil drilling operations. The bit has an initial diameter which allows it to be passed through a permanent restriction in a well casing and thereafter expanded to clean out the casing below the restriction. The bit has three uniformly spaced cutting elements which may be fully retracted within the diameter of the cylindrical outline of the body of the bit and are located at the forwardmost end in a strengthened portion of the body. The cutting elements have projections which are engaged by the forward end of a piston sliding along the axis of the drill body within a cylinder bore and are actuated thereby to their cutting positions, with their cutting edges generally radially extending but slightly forwardly divergent, by the hydraulic pressure on the piston of a fluid forced down through the drilling string which carries the bit.