Drilling device for earth drill

An excavating tool for an earth drill, characterized in that;

• comprising a tubular inner member (3) connected to a kelly bar (1), a tubular second member (5) fitted on the outer side of said inner member (3) so as to be allowed to move up/down freely and an outer member (6) fitted on the outer side of said second member (5) so as to be allowed to move up/down freely:
• a cylindrical bucket (7) and a grab bucket (8) housed in side said cylindrical bucket (7) are mounted at said outer member (6);
• a first hydraulic cylinder (9) is mounted between said inner member (3) and said second member (5), and second hydraulic cylinders (12) which are caused to extend/contract by the pressure oil from said first hydraulic cylinder (9) are mounted between said second member (5) and jaws (8a) of said grab bucket (8);
• a locking mechanism is provided between said inner member (3) and said outer member (6), said locking mechanism is constituted of locking elements (3d, 3j) provided at the outer circumference of said inner member (3) and a locking element bearing plate (6f) provided at the upper portion of said outer member (6), said locking elements (3d, 3j) are allowed to pass through said locking element bearing plate (6f) when said inner member (3) and said outer member (6) achieve a specific relative rotational angle and said locking elements (3d, 3j) become locked at said locking element bearing plate (6f) to disallow relative vertical movement of said inner member (3) and said outer member (6) by rotating said inner member (3) forward when said excavating tool (2) is in a most contracted state;
• and
• projections (3k) provided at the outer circumference of said inner member (3) are fitted at guide rails (5j) extending along the longitudinal direction at the inner circumference of said second member (5) so as to be allowed to move up/down freely, and said inner member (3) is allowed to rotate forward relative to said second member (5) within a predetermined range when said excavating tool (2) is in the most contracted state.