| 摘要 |
This invention relates to drilling apparatus having a flexible drill string, a motor supported by the drill string, two-stage planetary gear-reduction means driven by the motor, and a drill bit driven by the gear-reduction means. In the gear-reduction means the second stage sun, planet and ring gears have increased longitudinal dimension for carrying the increased torque loading, and the second stage planet gears are split into sections and supported at each end of each section to prevent excessive outward deflection of their bearing shafts.
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