Abstract: Motor driven milling and boring machine used primarily for forming screw threads of any selected pitch, external to cylindrical or conic projection or within similar-shaped bore of workpiece, particularly workpieces such as are too large or irregular-shaped to be themselves rotated. A tubular housing, upstanding or tiltably disposable, journals a longitudinally displaceable and rotatable hanger which in turn axially journals a power-driven spindle having a selectively offset-positionable stub portion, terminally carrying a thus radially extensible drive segment which distally positions a rotary milling cutter. A second or planetary tracking motor jointly operates a pair of selectively coupled ring gears of the housing, which in conjunction with a master nut fixed along the housing axis, move the hanger respectively annularly and axially so that the distal cutter may follow a helical path, the pitch of which path is determined by the chosen velocity ratio give the two ring gears.