Drill string rod with guidance shoulder

Abstract

A drill string rod and a drill string assembly includes a drill rod and a drill bit. The rod includes a threaded male end and a female end. An axially extending shoulder is provided at the male end and has an axial length greater than an outside diameter of the shoulder to provide a shoulder driven rod exhibiting enhanced guidance to achieve straighter holes and better collaring.

1 . A drill string rod to form part of a drill string, the rod comprising:
 a hollow elongate main length section extending axially between a male end and a female end, the male end including a spigot having a threaded section projecting axially from a shoulder that axially separates the spigot and the main length section, the shoulder having an outside diameter that is greater than an outside diameter of the main length section,   wherein an axial length of the shoulder over which the greater outside diameter of the shoulder extends is greater than the outside diameter of the shoulder.   
     
     
         2 . The rod as claimed in  claim 1 , wherein the outside diameter the shoulder is a maximum outside diameter of the rod. 
     
     
         3 . The rod as claimed in  claim 2 , wherein the maximum outside diameter of the rod at the shoulder is uniform or approximately uniform over the axial length of the shoulder. 
     
     
         4 . The rod as claimed in  claim 1 , wherein the female end includes a sleeve portion having an internal threaded section to cooperate with the threaded section of the spigot of a further drill rod of the drill string, an outside diameter of the sleeve portion being greater than the outside diameter of the main length section. 
     
     
         5 . The rod as claimed in  claim 4 , wherein the outside diameter of the shoulder is equal to or approximately equal to the outside diameter of the sleeve portion. 
     
     
         6 . The rod as claimed in  claim 1 , wherein the spigot extends axially from an annular end surface of the shoulder, an axial length of the spigot being configured such that the annular end surface of the shoulder is arranged to abut an annular end surface of the female end of a neighbouring rod of the drill string. 
     
     
         7 . The rod as claimed in  claim 1 , wherein an axial length of the spigot is less than or equal to the axial length of the shoulder. 
     
     
         8 . The rod as claimed in  claim 1 , wherein an outside diameter of the spigot is equal to or less than the outside diameter of the main length section along a full axial length of the spigot. 
     
     
         9 . The rod as claimed in  claim 1 , further comprising an internal bore extending axially through the main length section and the spigot, the internal bore being of uniform internal diameter along a full axial length of the main length section and the spigot. 
     
     
         10 . The rod as claimed in  claim 1 , wherein the threaded section includes at least one axially extending helical ridge and trough, wherein the outside diameter along the threaded section at radial positions of the ridge and trough is uniform over a full axial length of the threaded section. 
     
     
         11 . The rod as claimed in  claim 1 , further comprising a transition section positioned axially at a junction of the main length section and the shoulder, wherein an outside diameter at the transition section changes according to at least one radius of curvature. 
     
     
         12 . The rod as claimed in  claim 11 , wherein the outside diameter at the transition section decreases radially according to a first radius of curvature from the main length section to an intermediate section and the outside diameter increases radially according to a second radius of curvature from the intermediate section to the shoulder. 
     
     
         13 . A drill rod assembly to form part of a drill string, the assembly comprising:
 a drill rod including a hollow elongate main length section extending axially between a male end and a female end, the male end including a spigot having a threaded section projecting axially from a shoulder that axially separates the spigot and the main length section, the shoulder having an outside diameter that is greater than an outside diameter of the main length section, wherein an axial length of the shoulder over which the greater outside diameter of the shoulder extends is greater than the outside diameter of the shoulder; and   a drill bit releasably attachable to the male end of the drill rod; the drill bit having an axially forward cutting head and an axially rearward mounting sleeve to attach to the male end of the drill rod, wherein an outside diameter of the mounting sleeve is equal to or approximately equal to the outside diameter of the shoulder.   
     
     
         14 . The assembly as claimed in  claim 13 , wherein the outside diameter of the mounting sleeve is uniform or approximately uniform over an axial length of the mounting sleeve being defined between a rearwardmost end of the drill bit and an axially forwardmost end of the mounting sleeve at which region the outside diameter of the mounting sleeve increases to form a junction with the cutting head. 
     
     
         15 . The assembly as claimed in  claim 14  wherein the axial length of the shoulder is approximately equal to or less than an axial length of the mounting sleeve.