Elliptical design for shank adapters

Abstract

A shank adapter to form part of a drilling assembly, the shank adapter comprising: a main body extending axially between a first end and a second end; a male spigot portion provided at the second end having an externally threaded section and a non-threaded shank positioned axially intermediate the main body and the threaded section; a radially projecting shoulder positioned axially between the main body and the male spigot portion; the shank having a transition section positioned adjacent to the shoulder at the second end, the transition section having an outside diameter that increases in a direction from the spigot portion to the shoulder; wherein the cross-sectional shape profile of the outer surface of the transition section in the plane of the longitudinal axis comprises a segment of an ellipse having semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: (formula (I)), characterised in that the ratio of the semi-major to semi-minor axes (a:b) is within the range 2b<a<8b.