A machine (10) for stranding a bundle of yarns, of the type that comprises a supporting frame (11) for a first rotor (12) and a second rotor (13), which are external and are moved by same motor drive means (14) and support an interposed first bow (15) for the torsion of the bundle of yarns (16), within the space generated by the rotation of the first bow (15) there being a second torsion bow (17) which is arranged to rotate in the opposite direction with respect to the first bow (15) and about the same axis of rotation and is supported between two opposite coaxial rotors, a third rotor (18) and a fourth rotor (19), which are moved by symmetric transmission means of the epicyclic type (20, 21), which are interposed respectively between the adjacent first (12) and third (18) rotors and between the adjacent second (13) and fourth (19) rotors. The transmission means of the epicyclic type (20, 21) are constituted, for each pair of rotors, by
- a first gear (22), which is fixed with respect to the supporting frame (11) and coaxial to the axis of rotation of the bows (15, 17),
- two second and third planet gears (23, 24), which are keyed on a same shaft (25), which in turn is coupled freely on a radial protrusion (26) of the respective first (12) or second (13) external rotor,
- a fourth gear (27), which is jointly connected and coaxial to the corresponding third (18) or fourth (19) inner rotor,
- a first toothed belt (28) for transmitting the relative motion between the first fixed gear (22) and a first one (23) of the planet gears, for the rotation of the planet gears about their own axis,
- a second toothed transmission belt (29) between the second (24) of the two planet gears and the fourth gear (27) of the corresponding inner rotor.