Fan rotor for a turbomachine or a test engine

A fan rotor for a turbomachine, the rotor comprising a disk carrying blades having roots that are engaged in substantially axial grooves in the outer periphery of the disk, and a substantially frustoconical annular spinner mounted by jaw-clutching on the disk, upstream from the blades, the spinner having a substantially radial inner annular rim that is scalloped or crenellated and that comprises solid portions alternating with gap portions and that, in the assembled position, is received in an outer annular groove of the disk that is defined upstream by a substantially radial outer annular rim that is scalloped or crenellated, wherein the rim of the spinner is connected at its outer periphery to a substantially cylindrical wall that is designed to deform in the event of a fan blade being broken or lost, and wherein the gap portions in the annular rim of the spinner include substantially radial notches for increasing the flexibility in bending of the solid portions of said rim.