Abstract: A sifting and screening mechanism dynamically balanced in all three planes including a base, a screen assembly with an inclined screened frame having a screening surface with an inlet end and an outlet end, a linear bearing, a resilient mount assembly supporting the outlet end of the screened frame on the linear bearing to permit a generally reciprocating motion of the outlet end of the screen frame, a rotating eccentric drive attached to the screen assembly beneath the center of gravity of the assembly to impart a circular motion in a generally horizontal plane to the screen assembly at the center of gravity which, in combination with the linear motion of the outlet end of the screen, creates generally elliptical motion of the screen, a balancing shaft rotatably mounted on the base and spaced apart from the eccentric drive, a belt drive between the eccentric drive and the balancing shaft for maintaining the rate of rotation of the balancing shaft at the same speed as the eccentric drive, and two balance weig