| 摘要 |
A power boring bit is fabricated from a shaft member and a disc which has a channel extending from the circumference thereof to a coaxial aperture through which the shaft extends. The shaft has a pointed tip portion at one end which provides cutting surfaces extending from the point of the tip portion and circumscribing a circle of rotation of maximum radius. A generally axially extending planar shoulder portion is provided on the tip portion with the radial distance to the shoulder portion being less than the maximum radius. One edge portion of the disc bounding the channel is bent to extend from the plane of the body of the disc towards the point and thereby define a cutting lip portion which has a free end providing a cutting edge extending from the periphery of the disc to closely adjacent the axial shoulder portion intermediate the width thereof and inwardly of the circle of rotation of maximum radius. |
