Abstract: A circular hole cutting device (1) for making a circular hole in an object comprises a bit holder (3) which can be attached to a drive shaft of an electric power tool in such a way that the bit holder (3) with a bit (2) attached to a far end of the bit holder (3) rotates together with the drive shaft on a common axis, a cover (4) which is fitted to the bit holder (3) relatively rotatably about its axis, and a radial rod (5) attached to the cover (4) such that the amount of projection of the radial rod (5) in a direction intersecting the bit (2) can be varied. The physical size of the cover (4) is determined such that the bit (2) projects from a far end of the cover (4). The radial rod (5) has a pivot shaft (52) having a pointed end formed by bending a terminal part of the radial rod (5) approximately at right angles.

Abstract: A drill bit and a manufacturing method thereof that ensures integral mounting of a drill and a drill holder with a simplified construction and in a simplified manner are disclosed. The drill bit has a drill with a bit and a shank, and a drill holder formed with an axial insertion hole for fitting the shank. An engaging part is formed at a base end of the drill. A blind hole that intersects the insertion hole is formed in the drill holder to form a restricting part, or a stopper equivalent to the restricting part is fitted in the bottom of the blind hole. Engagement of a top of the stopper or the restricting part with the engaging part prevents a relative rotation of the drill to the drill holder.

Abstract: A center drill used for machining a hole in a work piece which is adapted to be partially enclosed in a cup shape drill member in a side view thereof, includes a drill portion provided on a leading end of the center drill, and a dust extractor radially outwardly extending from a portion of the center drill which is enclosed in the cup shape drill member.

Abstract: A shank 1 has, at the front end of its drive shaft 2, a drive collar 3 formed substantially integrally with the drive shaft 2. The drive collar 3 is formed, centrally of its front side, with a boss 4 projecting therefrom, and has a bolt receiving through-hole 7 bored therein at a position spaced apart from the boss 4 and in parallel relation to the axis of the shank 1. The base 16 of a hole saw body 15 has a center hole 18 bored in a center portion thereof for engagement with the boss 4, and also has at least one threaded hole 20 bored at a position spaced apart from the center hole 18. A bolt 6 for thread engagement with the threaded hole 20 of the base 16 of the hole saw body 15 is received in the bolt receiving through-hole 7 of the drive collar 3 in order to lock the hole saw body 15 to the drive collar 3 and to transmit drive torque to the hole saw body 15.