The present invention relates to improvements in rotary drilling machines. In particular, it relates to the use of novel table bushing assemblies which dampen vibrations generated during drilling operations.
A drilling machine is a motor driven device with a rotating drill steel and an end cutting tool (the drill bit) that creates a hole in solid material. Drilling machines are used in a variety of applications. In earth drilling operations, such as water well drilling, the drill steel is stabilized at or near the ground surface by a concentric series of bushings in the drill table. A small, carefully measured, clearance is required between the drill steel and the innermost table bushing to allow rotation and movement of the drill steel. The contact between the drill steel and table bushing, however, causes wear to the bushing. As a result, the inner diameter of the bushing is enlarged and the clearance between the drill steel and the bushing is increased. The drill steel is thus inadequately stabilized and deflects or bows under high thrust loads. When the drill steel bows while turning, it hits against the bushing and causes vibrations in the drill table.
Under current designs, the vibrations generated by the drill steel are transmitted through the drill table to the main structure of the drilling machine causing physical damage to various components of the drill. In order to decrease or stop vibration, the drill operator must decrease the thrust load, change the speed of the drill steel, or completely stop the drilling operation. All of these adjustments decrease the productivity of the drilling machine.