| 摘要 |
<p>The drill bit for use in percussion drilling comprises a solid drill bit having one or more cutting edges at its front end and a centrally provided hole, and a rod having a forwardly tapering conical portion. The central hole in the bit has a matching conical internal surface for supporting the bit on the rod by engagement between the conical surfaces. The central hole is bottomed in the bit and comprises a cylindrical internal surface in front of the conical surface. The cylindrical surface having an internal thread matching an external thread on the foremost part of the od. The external thread on the rod being positioned axially in front of the internal thread and at a distance from the bottom of the bit hole when the bit is in operating position having its conical surface engaged with the conical surface of the rod.</p> |
