Patent ID: 7347291
Filing Date: 2008-03-25
Classification: E21B

Abstract:
1. A bit assembly for a drilling apparatus working by impact and rotation or merely by rotation, and comprising a pilot bit which drills a center portion of a hole, a ring bit in connection with the pilot bit which said ring bit is arranged to drill an outer circle portion of the hole, surfaces, between the pilot bit and the ring bit, which are arranged to transmit impacts and/or rotary motion from the pilot bit to the ring bit, a pulling arrangement which pulls a protecting tube into the hole on drilling, a blocking arrangement which blocks rotation and axial motion between the pilot bit and the ring bit, said blocking arrangement being jointly fitted in a rear edge of a shirt portion of the ring bit so that the blocking arrangement is located on a diameter portion greater than a diameter of a groove-free inner surface of the ring bit, a locking nose of the pilot bit which can be fitted to the shirt portion, the shirt portion having a counter-groove shape for fitting the locking nose which reaches through the shirt, which counter-groove shape comprises a first surfaces that can transmit rotary motion force to the ring bit and a second surface that can transmit a force to pull the ring bit off the hole.