Core drill

A core drill suitable for a cordless type portable electric drill which comprises cutting chips attached to an opening peripheral edge of a tip end portion of a cylindrical core body such that the cutting chips are apart from one another and protrude radially from inner and outer peripheral surfaces of the core body and is configured to drill an annular groove in a material to form a hole therein,

• wherein the core body is set to have a small wall thickness capable of withstanding a cutting rotational torque, and an outer peripheral surface of the tip end portion of the core body is configured to have a tapered surface such that the outer peripheral surface is closer to the inner peripheral surface in a direction toward a tip end;
• recesses into which the cutting chips are fitted are provided at the opening peripheral edge of the tip end portion of the core body such that the recesses open toward the tip end and extend toward a base end and adjacent to a forward portion of each of the recesses in a rotational direction is a wall portion that is bent radially inward;
• each of the cutting chips is configured to have a stepped portion when viewed from a bottom such that a radially inner portion of a forward end portion of each cutting chip in the rotational direction protrudes forward in the rotational direction and a radially outer portion of the forward end portion recedes rearward in the rotational direction;
• each of the cutting chips is configured to have a stepped portion when viewed from a bottom such that a radially inner portion of a rearward end portion of the cutting chip in the rotational direction is located forward in the rotational direction and a radially outer portion of the rearward end portion recedes rearward in the rotational direction;
• and
• each of the cutting chips is attached to the core body in such a manner that a forward end portion of each of the recesses is in contact with the radially inner portion of the forward end portion of the cutting chip in the rotational direction, and a connecting surface connecting the radially outer portion of the rearward end portion of the cutting chip in the rotational direction to the radially inner portion of the rearward end portion of the cutting chip in the rotational direction is in contact with a portion of the outer peripheral surface of the core body which is adjacent to a rearward portion of the recess in the rotational direction.