Abstract: A boring device adapted to mount boring tools for automatic tool changing, in which an eccentric mounting of relatively rotatable inner spindle 11 and main spindle (2) allows radial adjustment of the tool. Relative rotation of inner and outer spindles is accomplished by axial driving of a threaded bolt (22) by an actuator motor (67), causing rotation of a nut (19) fixed to the inner spindle (11). Continued overtravel of the threaded bolt (22) past an adjustment range (47) and safety range (51) causes releasing operation of a spring biased pull rod (36) which releases a tool clamping mechanism (14) to allow automatic tool changing.