| 摘要 |
A bit assembly for a drilling apparatus working by impact and rotation or merely by rotation, and comprising a pilot bit (1) drilling the hole centre and in connection with the pilot bit a ring bit (2) is arranged to drill the outer circle of the hole and, further, between pilot bit and ring bit surfaces are arranged to transmit impacts and/or rotary motion from the pilot bit to the ring bit, and the bit assembly also including an arrangement for pulling protectino tube into the hole on drilling. In the bit assembly between ring bit (2) and pilot bit (1) at least an arrangement transmitting rotation is jointly fitted in the ring bit shirt portion (5) by forming the rear edge of the shirt portion seen in the drilling direction to comprise surfaces with different directions, which with one of their portion (4) can transmit rotary motion force to the ring bit (2) and with their adjacent part (3) force to pull said ring bit off the hole.
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