US Patent 7617887 Method for casing drilling, drilling unit and adapter device

A method for casing drilling, a drilling unit and an adapter device. The adapter device to be used in extension drill equipment drilling comprises an inner piece which can be rotated by the rotation device of the rock drilling machine. Around the inner piece, there is an outer piece which can be moved in the axial direction with respect to the inner piece. By changing the axial position of the outer piece, it can be selected whether the rotation force is directed from the rotation device to the inner rod or to the outer tube used in casing drilling during threading.