Wood chip bar screen deck arrangement

A screening apparatus for separating a particular material by material thickness comprising in combination:

• a screen deck defining a screening area with screening openings and extending from a receiving end to a discharge end, with delivery means for distributing material onto the screening deck at the receiving end to move toward the discharge end so that large material moves longitudinally the length of the deck from the receiving end to the discharge end, and smaller thickness material passes through the screening deck;
• said deck having a plurality of individual screening bars extending from the receiving end to the discharge end and arranged in spaced relationship to define openings therebetween for passing therebetween the material of smaller thickness;
• said bars extending parallel to each other, with bars being fixedly mounted with respect to each other into at least two independent grids, and with the bars of at least one of said grids including a first group of bars having top surfaces thereof which are coplanar and a second group of bars having top surfaces noncoplanar with said top surfaces of said first group of bars.
• said independent grids being connected to drive means for moving the grids in an orbital motion throughout the bar length, for causing material spanning adjacent bars on the deck to be tipped to present a thickness, dimension for size discrimination.