| 摘要 |
<p>The invention relates to an under reaming drill bit tool 50 comprising a central drill bit assembly 52 having a central housing 54. The central housing has an outer surface and the central drill bit assembly has a central longitudinal axis A. The drill bit assembly comprises at least one under reamer assembly 2 with a cutting assembly (30 figure 1) and is moveable between retracted and extended positions. The or each under reamer assembly has an under reamer housing (4 figure 1) having an outer surface (12 figure 1), at least a portion of the outer surface of the or each reamer housing extends from the cutting assembly and is contiguous with the outer surface of the central housing in both the retracted and the extended positions. A later embodiment relates to a drill bit tool having means to vary the position of the cutting assembly of the central drill bit assembly.</p> |
