Hole forming device for all casing pipes with same upper diameter and lower diameter

The utility model relates to the technical field of all-casing drilling, and discloses an all-casing hole-forming device with the same upper and lower diameters, which comprises a driving mechanism, a transmission chain, a connector, a movable drill bit, a connecting rotating shaft and a transmission sleeve, the connector is mounted at the bottom of a drilling bucket, the driving mechanism is arranged at the upper end of the connector, a cavity is formed in the connector, and the transmission sleeve is arranged in the cavity. A connecting through groove is formed in the outer wall of one side of the connector, the transmission chain is arranged in the connecting through groove, the upper end of the transmission chain is connected with the driving mechanism, the transmission sleeve is arranged in the middle of the bottom end in the connector, and the middle of the front end and the middle of the rear end of the transmission sleeve are correspondingly and rotationally connected with the inner wall of the connec