Blackboard eraser

A blackboard eraser comprising:

• a cube having two symmetrically arranged semi-cylindrical grooves defined in a longitudinal direction therein, two rectangular grooves are arranged adjacent to each end of the semi-cylindrical grooves, and an elevated surface having a central brush affixed thereon is formed between the two semi-cylindrical grooves;
• a longitudinal groove is further defined, underneath each of the semi-cylindrical grooves;
• a lid is disposed on top of the cube, and when closed forms a closed chamber below the lid and above the two semi-cylindrical grooves side brushes are affixed to an inner surface of the lid so as to be respectively positioned along each of the longitudinal grooves;
• two soft-surfaced rollers respectively disposed, in the semi-cylindrical grooves;
• a shaft-washer, which has a shaft for inserting into a central hole of a positioning-washer, affixed to each end of the rollers by inserting symmetric rods;
• the positioning-washer, which has the central hole, placed in the rectangular groove adjacent to each end of the semi-cylindrical grooves;
• whereby the shaft-washers and the positioning-washers are respectively disposed in the grooves at each end of the semi-cylindrical grooves, thereby enabling the rollers to rotate freely in the semi-cylindrical grooves;
• when the blackboard eraser is rolling on a blackboard, chalk dust sticks to the rollers and is carried to the side brushes, the side brushes then wipe the dust, which falls into closed chamber.