Importance

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Abstract

A raise bit is disclosed for enlarging a pilot hole into a large diameter hole by disintegrating the earth formations surrounding the pilot hole. The raise bit includes a removable drive stem for enabling the raise bit to be transported through small drifts. The drive stem is attached to a thrust bearing plate which, in turn, is interconnected to a main bit body. The bit body extends around the drive stem and includes a plurality of rolling cutters for contacting and disintegrating the earth formations surrounding the pilot hole. The interconnection between the thrust bearing plate and the bit body is accomplished by means of an annular shock absorbing ring made of polyurethane. Means are also provided to transport fluid from the interior of the drive stem to contact the rolling cutters on the bit body. These means comprise a fluid passage way extending through the interior of the drive stem. An additional passageway is provided in the drive stem to discharge the fluid radially out of the bottom end of the drive stem. Conduits are provided for communicating with the radial passageway of the drive stem. The conduits further extend through the annular ring, the bit body and through the cutter mountings to direct the fluid against the surfaces of the cutters.

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First Claim