Patent ID: 7341120

Claim:
A cutting portion structure of a core drill including a cylindrical core body; and cutting blades, the cutting portion structure comprising: an opening end portion formed on the cylindrical core body, the opening end portion having a tip end portion rounded in a semispherical shape as viewed from a direction substantially perpendicular to a cross-section in a radial direction of the core body, wherein the cutting blades are formed at the opening end portion of the cylindrical core body and arranged in a circumferential direction of the core body to have gaps between the cutting blades, and the cutting blades include diamond grains bound on the opening end portion from an inner peripheral side of the core body to an outer peripheral side of the core body, wherein the opening end portion is partially expanded in the radial direction to have a thickness larger than a thickness of a base end side portion of the core body which is closer to a base end of the core body than the opening end portion is, and the expanded portion of the opening end portion is entirely rounded as viewed from the direction substantially perpendicular to the cross-section in the radial direction, the cutting portion structure further comprising a step portion formed between the opening end portion and the base end side portion of the core body to form a right angle between the step portion and the base end side portion.