The rotor has an oscillating arm having an external part carrying work tools. A connecting device (32) has a threaded element (33) that passes through the each hole (28,29,31) of the engaging and engaged portions of the internal part and external part of the arm. The device also has an insert (38) with a tapping (39) arranged in the interior of the engaging portion (24), with the threaded element screwed in the tapping, and a shoulder (36) resting on the engaged portion (25) to tighten the engaged portion against the engaging portion along the geometric axis (35).
