A twisting method is described, for twisting free end portions of bar conductors for the stator or rotor bar winding of an electrical machine. The twisting method allows achieving a non uniform twisting of the bar conductors from the welding side of the stator or rotor core by means of a twisting fixture. The twisting fixture comprises a pocket member including a main structure provided with an arc of adjacent pockets and a secondary structure, provided with at least one further pocket, which can axially translate with respect to the main structure.