| 摘要 |
A retractable well drilling bit comprises a hollow body which forms the lowermost end of the drilling string; a pair of colinear cylindrical hollow members slidable within the bore of said hollow body; a pair of knives; a vertical rod attached to the lower one of said cylindrical members and slidable within the upper one of said cylindrical members between a knife-retracted and a knife-extended position, said knives being pivotally engaged to the lower end of said rod; and a pair of crossed links pivotally attached to said upper body at the upper ends thereof and to each knife at the lower ends thereof respectively, such that by spacing said upper member from said lower member, said links will pull said knives rotating same in a knife-retracting direction, whereas when said members are approached to each other, said knives will be pushed by said links in a knife-extending position.
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