Drilling mud is used to control subsurface pressures, lubricate the drill bit, stabilize the well bore, and carry the cuttings to the surface, among other functions. Mud is pumped from the surface through the hollow drill string, exits through nozzles in the drill bit, and returns to the surface through the annular space between the drill string and the walls of the hole. As the drill bit grinds rocks into drill cuttings , these cuttings become entrained in the mud flow and are carried to the surface. In order to return the mud to the recirculating mud system and to make the solids easier to handle, the solids must be separated from the mud. The first step in separating the cuttings from the mud involves circulating the mixture of mud and cuttings over vibrating screens called shale shakers. The liquid mud passes through the screens and is recirculated back to the mud tanks from which mud is withdrawn for pumping downhole. The drill cuttings remain on top of the shale sha