| 摘要 |
<p>A rock drill bit has diamonds in its sidewall which are set blunt in a purely radial direction but which each have a bottom edge tangential to a helical line passing through a cutting tip of the respective diamond. The helix angle is normally from 0 degree to 30 degrees, and the diamonds in question can lie on a nominally conical surface of included angle between 10 and 20 degrees. The bit preferably has an upper set of diamonds facilitating retrieval and precluding oversize drilling. Mud channels pass adjacent each diamond.</p> |
