Abstract: To permit boring with replaceable cutter elements (10, 10a, 10b), particularly into materials where, upon withdrawal of the boring tool from a bore hole (40), grooves or scratches are to be avoided, two cutter elements are positioned on a fluted cylindrical body (1), the cutter elements being so located that the inner cutter element (10b) is positioned on the body so that an effective cutting edge (19) thereof is radially inwardly of the theoretical circle (33) formed by the outer cutter element (10a) upon rotation of the tool, the cutting corner of each cutter element is formed as a relieved or chamfered corner (15) and forms a chopped corner cutting edge (22).

Abstract: To provide for self-centering of boring tools, particularly of larger diameter boring tools having replaceable rotatable cutter bits, the cutter bit closest to the central axis of the tool holder or tool shank, i.e. the radially innermost bit is formed with auxiliary cutting surfaces adjacent the corners of a square or parallelogram-shaped bit, for example by chamfering the corner, with a relief surface therebehind, and positioning the auxiliary cutting surface to intersect the central axis of the boring tool so that, in operation, a small conical tip will be left which is continuously reduced in size and cut; and wherein the cutter bits are positioned on the tool bodies to present cutting edges at the end face which overlap with respect to workpiece removal, so that each cutter bit will independently cut into the workpiece, at least the inner cutter bit being guided in its cutting circle by the radially outer corner fitting against the surface cut in the workpiece.

Abstract: To provide for positive guidance of a bolt formed with a conical enlarged intermediate portion holding a cutter bit by resilient deflection of the bolt in an enlarged recess portion of the cutter bit, the enlarged recess portion is formed as an elongated portion adjacent a bore in which the bolt is threaded, the elongated opening being additionally formed with conical surfaces concentric with the bore so that, prior to resilient deflection of the bolt, the bolt is positively guided and, thereafter, the elongated opening permits deflection of the bolt, the length axis of the elongated enlarged portion being directed towards an abutment surface on the tool body to securely clamp the bit against the abutment surface and determine the direction of resilient deflection of the bolt.

Abstract: To permit resharpening of cutter blades of a helical milling cutter, the cutter blades or bits of a multi-bit cutter have decreasing thickness, and are placed in grooves having the same helix radius, but the centers of the helical axes offset from the center of rotation of the cylindrical cutter body in the direction towards the associated groove, so that cutter blades of lesser thickness are still seated firmly in the bottom of the respective groove. Upon dulling of the cutters, the thinnest one of the cutter blades is discarded, the thickest one only replaced and the worn blades moved up one step along the circumference of the body into grooves which are progressively more shallow, to compensate for decrease in thickness of the respective cutter bits upon regrinding to resharpen the bits.