GB295150A - Improvements in or relating to underreamers for use in well drilling operations - Google Patents

Abstract

295,150. Brown, C. H. Nov. 3, 1927. Borehole apparatus.- An underreamer for use in well-boring operations comprises a body 1 with a bore 2 extending through its lower end, reamer blades 3 being pivotally held in the body by hooking over a flange 10 on a; carrier 4; the carrier is adjustably held in the body by pins 14 with flat faces 19, 20, 21 at different radial distances and adapted to be brought successively into engagement with an upper flange 12 on the carrier to take up wear. The part of the carrier between the pins is diamond shaped, Fig. 4, and the carrier may be turned to provide further against wear; further, sets of carriers with differently spaced flanges are provided to take up additional wear. The cutters are expanded by a conical member 26 welded &c. to enlargements 27, 28 on a mandrel 25 which is pressed upwardly by a spring 29 acting between the carrier 4 and lock nuts 30. Collapse of the cutters is provided for by shoes 35 flanged inwardly and outwardly and sliding in slots 44 in the body, the slots having enlarged lower ends 45, permitting inward movement of the shoes when in this position; the shoes are fixed to arms 36 pivoted at 37 to a member 38 which is pressed against the mandrel 25 by a light spring 41. On withdrawing the tool from the well, the shoes 35 engage, the well casing and check movement of the mandrel &c. until the shoes move into the enlargements 45. When used for straightening a crooked hole, a threaded part 47 of the body 1 is engaged by a string of tubing 48 which co-acts with the well casing to act as a guide.