Rotary table (drilling rig)

The rotary table is a heavy-duty mechanical device on a drilling rig used to provide rotational power to the drill string. It is a large circular table positioned at the rig floor, typically driven by an electric motor or, in older rigs, by a diesel engine and transmission.

The primary function of the rotary table is to transmit torque to the drill string, which consists of drill pipe and a drill bit at the bottom. This rotational force allows the drill bit to grind and cut through subsurface formations, creating a borehole.

The rotary table features a large opening in its center called the master bushing. The master bushing holds slips or inserts that grip the drill string, ensuring the rotational force of the table is transferred effectively. Different sizes and types of master bushings are used to accommodate various drill string diameters.

During drilling operations, the rotary table rotates at a controlled speed, measured in revolutions per minute (RPM). The driller adjusts the RPM based on factors such as the type of formation being drilled, the weight on bit, and the desired rate of penetration.

In modern drilling rigs, the function of the rotary table is often replaced by a top drive system. The top drive is a motor suspended from the derrick that directly rotates the drill string from above. However, rotary tables remain in use, particularly on older rigs and in certain specialized drilling operations, such as coring.

Even when a top drive system is the primary driver, a rotary table may still be present on the rig floor, serving as a backup system or to aid in tripping (running pipe in and out of the hole).