| 摘要 |
Provided is a core drill which is capable of drilling a hole and consumes small electric power consumption when the core drill is applied to a codeless type electric drill. A core body 2 is formed to have a small thickness. An outer peripheral surface of a tip end portion of the core body has a tapered surface which is thinner toward the tip end and is edged at the tip end. Recesses 2B are formed at an opening peripheral edge of the tip end portion to attach cutting chips. A portion of the core body which is adjacent to a forward portion of each of the recesses in the rotational direction is bent radially inward. Each of the cutting chips 3 is configured to have a stepped portion when viewed from the bottom such that a radially inner portion 3a of a forward end portion 3 protrudes forward in the rotational direction and a radially outer portion of the forward end portion 3 recedes rearward in the rotational direction. Each of the cutting chips 3 is configured to have a stepped portion when viewed from the bottom such that a radially inner portion of a rearward end portion is located forward in the rotational direction and a radially outer portion of the rearward end portion is located rearward in the rotational direction. The cutting chips 3 are attached to the core body 2 in such a manner that a forward end portion of each of the recesses is located at the radially inner portion 3a of the forward end portion of the cutting chip in the rotational direction, and the connecting surface connecting a radially outer portion to a radially inner portion of a rearward end portion in the rotational is in contact with a portion of the outer peripheral surface adjacent to a rearward portion of the recess in the rotational direction.
|
