Abstract: A boring tool has a radially adjustable tool bit holder mounted on a head part connectable to an adaptor. A threaded stud for the connection between the head part and the adaptor has a thread arranged in each half, the two threads having different pitches or leads. An adjusting tool for the boring tool has a seat which mates with the threaded stud for rotating the stud relative to the thread arranged on the head part. The tool is marked with a scale in accordance with the formulaS=SG2/SG1 (scale factor)in which SG1 is the lead of one thread G1 on the threaded stud and SG2 is the lead of the other thread G2 on the threaded stud.

Abstract: A boring tool with interchangeable tool bit holders is equipped with weight balancing members pivotable about a common fulcrum located on the rotation axis of the fine boring head. The weight balancing members are in the form of circular segments. They are pivoted from their given position about the common fulcrum by means of pull cords fixed thereto. In principle, each pull cord is fixed to each weight balancing member. Thus, a first pull cord fixed to one side of two weight balancing members is guided about a first guide bolt and a second pull cord fixed to the other side of the two weight balancing members is guided about a second guide bolt.

Abstract: The head of this boring tool carries two bit holders, which can be radially adjusted to different cutting widths by tooth systems provided on sloping faces of the head and/or bit holder. To ensure that there is still reciprocal supporting of the bit holders even in the outermost adjustment range thereof, cams are provided for extending the supporting surfaces. As an alternative to or in addition to this measure, the spacing between the front end face of the head and the surface of the bit holder parallel thereto is made so small that when high cutting forces occur these surfaces are supported on one another before the elastic deformation range of the bit holders is exceeded.