Rotary drill bit having movable formation-engaging members

摘要

In a rotary drag-type drill bit for drilling subsurface formations, at least one formation-engaging member is movably mounted on the bit body so as to be movable in and out, relative to fixed cutting elements, in response to engagement with the formation being drilled. In one arrangement the formation-engaging member (48) is generally pear-shaped and is bonded within a body of rubber (49) within a tubular sleeve (50) screwed into a threaded socket in the bit body (51). The body of rubber (49), confined within the sleeve (50), offers comparatively solid resistance to impact at right angles to the surface of the bit body. However, when subjected to a force having a sideways component the member (48) tilts against the resilience of the rubber (49), to reduce the extent to which the member projects above the surface of the bit body. The member (48) thus protects an associated cutting element against impact but yields to allow the cutting element to engage the surface of the formation being drilled. <IMAGE>