Abstract: The rotor balancing device disclosed herein comprises a cylindrical cup-shaped housing for mounting in a hollow rotor to be balanced having a central pivot on which two bushes are mounted. Two bob weights are connected by tension springs or other restraining devices to the two respective bushes to rotate about a pivot within the housing wall. The inner side of the housing wall and/or the weights have a coating of a contact or thermally activated adhesive. The restraining force of the tension springs is such that when the shaft in which the balancing device is mounted is rotated to a speed between natural frequencies of the vibration of the shaft and is nearer the lower frequency (i.e.

Abstract: A rotor to be balanced has an annular cavity containing two balls free to roll around the cavity. An initially inert thermo-setting adhesive is coated around the cavity. The rotor is rotated to a speed just above its first resonant frequency of vibration and the balls take up balancing positions in the cavity counter balancing the out of balance of the shaft. The adhesive is activated by a temporarily placed external heat source to permanently lock the balls in the balancing position so that the shaft is permanently balanced.