| 摘要 |
PROBLEM TO BE SOLVED: To provide a new type of drilling instrument which is inserted into a drill pipe, and rotated without using rotational force of the drill pipe. SOLUTION: The drilling instrument is formed of an outer body capable of passing in the drill rod, an inner body movably installed in the outer body, four or more side cutters attached to the inner body, and a position control device which can move the inner body to either a first location or a second location with respect to the outer body according to water pressure. When the inner body is drawn into the outer body, a free end of each side cutter is pinched by the outer body and the inner body, whereby the side cutters are extended. When the inner body is free with respect to the outer body, the side cutters assume a housed position by means of a spring.
|
