Patent ID: 7699125
Filing Date: 2010-04-20
Classification: E21B

Abstract:
1. A drilling or service rig comprising: (a) a rig substructure having a mast base; (b) a mast having at least one open side; (c) an elongate worm drive defining a helical groove, disposed within the mast; (d) at least one collar engaging the worm drive, the collar defining a plurality of keyhole openings and comprising a plurality of internal rollers for engaging the helical groove of the worm drive, wherein rotation of the worm drive causes longitudinal movement of the collar along the worm drive, and wherein each roller comprises a roller head and a roller shaft, and is inserted into the collar through a keyhole opening; (e) a top drive assembly attached to the at least one collar and cantilevered from the collar out the open side of the mast; and (f) means for rotating the worm drive.