Patent ID: 11959337
Assignee: MINCON NORDIC OY
Field: Civil engineering (Other fields)
Classification: CPC E | IPC E

Claim 8:
9. A drilling unit according to claim 7, wherein
the first locking means comprise circumferential grooves and the second locking means comprise a locking cavity on the surface of the ring bit segment, wherein the circumferential grooves are arranged to receive the ring bit segments and the locking cavities for locking the ring bit assembly and the pilot bit together when reaming the center hole for the casing; and
the first locking means further comprise longitudinal grooves and retrieve shoulders, and the second locking means further comprise a retrieve cavity on the surface of the ring bit segment, wherein the longitudinal grooves and the retrieve shoulders are arranged to receive the ring bit segments and the retrieve cavities for removing the ring bit assembly from the hole.