| 摘要 |
<p>A percussion drill bit has an anvil portion and a removable head portion incorporating cutting inserts arranged in circumferentially-spaced groups separated by fluid flow passageways, at least some of the inserts // being arranged at axial and radial positions with respect to the drill axis so that during working operation these inserts penetrate the formation being drilled by generally equal amounts and are thus subject to generally the same loading. The removable head portion is retained on the anvil portion of the bit by a splined and threaded lock nut arranged so that the threads are not subjected to cyclical fatigue loading due to operation of the percussion force generating tool.</p> |
