GB1218915A - Expansible rotary drill bit with hydraulic lock - Google Patents

Abstract

1,218,915. Earth drills. ROTARY OIL TOOL CO. 1 Aug., 1969 [24 Sept., 1968], No. 38667/69. Heading E1F. A rotary drill bit has cutters 45 (e.g. roller cutters, drag cutters or milling cutters) on pivoted arms 42, which can be expanded by relative downward movement of a central tubular member 49. While the drill string is lowered, the cutters are kept retracted by a hydraulic lock formed by injecting liquid into a space 65 through an opening normally sealed by a plug 65d. The spacer communicates with the bore of the drill string through passages 66 which are closed by a central sleeve 68 retained by fingers 71 with projections 72 which engage recesses 76 in the bore. The sleeve 68 is removed to allow the cutters to be expanded by dropping a ball onto the sleeve and applying fluid pressure so that the sleeve slides downwardly to uncover the passages 66. Drilling fluid is then pumped down the outside of the drill string to pass upwardly through the central bore 85, 67, displacing the ball on the sleeve 68. Differential fluid pressure then depresses the central body relative to the drill bit. The differential pressure is increased initially by a restriction 83 at the lower end of the central bore 85, which is by passed by side passages 83a which are uncovered as the tip of the central member slides through a sleeve 51 on the bit. In modification (Fig. 5 not shown) a temporary restriction is effected by a non-return valve which does not allow upward flow (except through a small bore passage) until the side passages are uncovered by the sleeve.