TOOL FOR DRILLING OF STRAIGHT HOLE Russian patent published in 1997 - IPC

FIELD: mining industry. SUBSTANCE: tool consists of drill bit, main link, two centralizers and subsequent links of drill string. Centralizers are of different diameters and installed on main link so that centralizer with large diameter is located closer to drill bit. Distance from drill bit to centralizer of small diameter is maximum possible to ensure longitudinal stability of main link and diameter of large centralizer to provide for minimum possible gap between its supporting surfaces and hole walls. Diameter of small centralizer is determined by the formula given in the invention description. EFFECT: higher efficiency.