Abstract: Method for repairing the teeth of a ring gear and a machining device unit including a frame and a moving part bearing a cutting member movable along multiple axes with respect to the frame, the method including: attaching the machining device to the ring gear by tightening parts rigidly attached to the frame of the machining device, engaging with the flanks of the ring gear, defining the position of the machining device with respect to the tooth to be machined by abutting on the flank of a reference tooth, the flank being situated, with respect to the summit of the reference tooth, in the direction opposite the flank of the tooth to be machined, the reference tooth being the tooth to be machined or an immediately preceding tooth, performing the machining of the flank of the tooth to be machined by control of the cutting member per predetermined machining operations.