| 摘要 |
A rotating drill bit (10) includes a leg (12) and journal arm (14) on which is mounted a cone-shaped cutter (16). The cutter (14) rotates on the journal arm (14) by means of an anti-friction bearing including rollers (20) and ball bearings (26). Air is pumped through the journal arm (14) through conduits (30, 32 and 34). Air flows through the passages between rollers (20) and is collected in a cavity (52). The cavity (52) is vented to the borehole through a slot (54) in the trailing edge of the journal arm (14). A very narrow clearance in the order of a few thousandths of an inch is provided for rotational movement between the cone mouth shoulder (36) and last machined surface (40). Cone mouth shoulder (36) completely covers the last machined surface (40) around the entire periphery of the journal arm (14) except for the approximately 45 DEG slot (54) in the trailing edge of the journal arm (14). |
