Abstract: A drum screen for cleaning and classifying wood chips is mounted for rotation. The screen has apertures of varying size to permit cleaned chips to pass through to be deposited on conveyors located below. An internal annular spiral baffle extends the full length of the drum and a series of chip lifters are located between the flights of the spiral baffle and project radially inwards from the interior surface of the drum. Wood chips are fed into the drum at one end and are carried through the drum while being lifted towards the axis of the drum by the chip lifters to effect loosening of waste material from the chips. Cleaned chips pass through the apertures in the drum and chips too large to pass through are carried forward and discharged from the end of the drum onto a conveyor. A casing surrounds the upper portion of the drum and partially encloses the discharge end of the drum. An air suction device is connected to the discharge end of the drum, drawing off all waste material loosened from the chips.