weight 326 such that the resultant of the centrifugal forces of the fixed weight and movable weight will be between the two weights and in an amount dependent on the amounts of the two weights as an example if the centrifugal force of the fixed weight 326 equals the centrifugal force of the movable weight and they are operating with the centers of gravity at the same radius from the axis of rotation the resultant will be along a line bisecting the angle between the two and in an amount based thereon the angle between the longtiudinal axis of the movable weight and the resultant is the lead angle which determines the amount of rolling tumbling vibration transmitted to the parts in the bowl to agitate and mill the parts as they advance around the bowl the lead angle and the amount of the vibratory force can be varied by moving the movable weight relative to the axis of rotation by admitting or removing pressure in the cylinder with the movable weight and spring located in the cylinder such that the center of gravity of the movable mass coincides with the axis of rotation the lead angle will be 45 u00b0 coinciding with the base line between the center of gravity 333 of the fixed weight and the center of rotation fig2 illustrates still a different location of the fixed weight 326 on the plate 322 so that the base line from the center of gravity 333 to the axis of rotation 319 forms a 90 u00b0 angle with the longitudinal axis 344 of the cylinder the resultant produced by rotation of the apparatus with the movable weight 352 held in a fixed position relative to the fixed weight is arrived at in the.