Abstract: A machine and method for separating chip-like particles according to thickness which provides low blinding and high efficiency at high throughput in sustained operation. The machine has a sloping deck mounting a series of spaced flexible louvers or slats which extend parallel to the direction of chip flow down the deck. The slats are canted transversely to the direction of flow, and present unobstructed full length slot-like chip openings between them. The deck is driven with a horizontal gyratory motion such that during the upstream half of each cycle of movement, each slot moves toward chips on the adjacent slat which slopes toward it, and moves away from such chips during the downstream half of the cycle. The path of screening movement is uniform over the entire deck, that is, the motion of the lower or discharge end of the deck matches that of the upper or feed end.