| 摘要 |
Drill bit for drilling bore holes in earth formations, the bit's cutting face provided with cutter preforms composed of polycrystalline diamonds on a tungsten carbide substrate mounted in sets from the center of the bit's face to its periphery. The first set consists of one center cutter preform. Each succeeding set has at least two preforms, all of which in a set are disposed at an equal radius from the bit's axis of rotation and, insofar as practical, are displaced from adjacent preforms in the same set by equal arcs around the axis, the cutting path of a set overlapping with that of the next set, the distance along the path between preforms for each set being not greater than about five inches. The outermost preform set is disposed in or above the junk slots. Gage protectors are optionally placed on the drill bit's sides to hold it away from the casing, such gage protectors composed of aluminum which wears to the diameter of the drill bit during use or a resilient material which compresses to the overall diameter of the drill bit during drilling operations and prevents damage to or from the casing when the bit is lowered or withdrawn. The drill bit is conveniently manufactured in three parts, a pin shank, a body spacer and a cap, with the body spacer welded to both the cap and the pin shank, the latter being threadably received through the body spacer by the cap, thus placing the body spacer in a state of compression.
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