Patent ID: 7124843

Claim:
A bit assembly for a hammering and rotating drill, comprising: a main drill body which drills essentially a middle portion of a hole in a drilling direction at a main drilling surface; and at least one outer drilling bit mounted bit mounted in the main drill body which drills an outer circle of the hole located about the middle portion and having an outer diameter, the at least one outer drilling bits drilling at an outer drilling surface which is located relative to the drilling direction behind the main drilling surface; wherein the main drill body includes a respective at least one counter cavity in which the respective at least one outer drilling bit is mounted, the at least one counter cavity having an axial directions which either has a same direction as the drilling direction or has a deviation outwards from the drilling direction; and wherein the at least one outer drilling bit can be moved at least a part of the way out of the at least one counter cavity in a direction which deviates from the axial direction of the at least one counter cavity in order to make the outer diameter smaller.