Cutter bit

A casing-tube cutter bit comprising:

• a mounting part having first and second members, each of the first and second members being substantially plate-shaped, the first and second members being spaced apart from each other along a first direction;
• an excavation part continuously formed with the mounting part, the excavation part being substantially polygonal-pyramid-shaped and having a base and a ridge outwardly opposite to each other, the base having first and second side areas, the first and second members of the mounting part continuously extending from the first and second side areas of the base, respectively;
• and
• a plurality of ultrahard chips disposed in the excavation part and exposed to an outside of the excavation part, each of the plurality of ultrahard chips extending along the first direction to cross the ridge, the plurality of ultrahard chips being spaced apart from one another along a second direction perpendicular to the first direction,
• wherein the ridge of the excavation part has a plane extending along the first direction and the second direction,
• the excavation part has first and second tilt surfaces, the first tilt surface extends from the ridge toward the first member of the mounting part in a first length at a first tilt angle with respect to the plane, and the second tilt surface extends from the ridge toward the second member of the mounting part in a second length at a second tilt angle with respect to the plane,
• the first tilt angle is equal to the second tilt angle, and the first length is shorter than the second length, and
• at least one of the plurality of ultrahard chips is made of a material different from materials of the other of the plurality of ultrahard chips.