Hole-opener for enlarging pilot hole

Abstract

The hole-opener is designed so that it can be disassembled in the field to replace worn cones or to enlarge the effective diameter of the tool. It comprises: a tubular drive sub, which connects at its front end with a rotating drill string which is being pulled along a pilot hole; a sleeve which slides over the rear portion of the drive sub; and a retainer sub which is connected with the rear end of the drive sub. The drive sub has external protruding bars which engage slots formed in the forward end of the sleeve, for limiting forward movement of the sleeve and locking the drive sub and sleeve together so that they rotate as a unit. The retainer sub has a radial shoulder which abuts the rear end of the sleeve to lock it in place. The retainer sub also transmits axial pull from the drive sub to the sleeve. The sleeve carries rotary cutting elements which are pulled and rotated to cut formation and enlarge the pilot hole.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . A hole-opener for enlarging the diameter of a pilot hole, the hole-opener having front and rear ends and comprising: 
 a tubular drive sub having an external surface, a longitudinal bore and threaded connections at its front and rear ends;    a tubular sleeve for sliding axially over the rear end of the drive sub;    means for locking the sleeve and drive sub together for rotation as a unit;    means, carried by the drive sub, for engaging the front end of the sleeve to stop its axial movement along the drive sub at a pre-determined position;    a retainer sub for threadably engaging the rear end connection of the drive sub and bearing against the rear end of the sleeve to lock the sleeve in the pre-determined position;    the sleeve carrying at least one rotary cutting element assembly at its front end;    the drive sub forming ports for jetting drilling fluid contiguous to the cutting elements when the sleeve is locked in the pre-determined position.    
     
     
         2 . The hole-opener as set forth in  claim 1  wherein the drive sub has outwardly protruding, circumferentially spaced apart bars affixed to its external surface and extending longitudinally thereof and the front end of the sleeve is slotted to engage the bars to stop forward axial movement of the sleeve and to lock the sleeve and drive sub together for rotation as a unit.  
     
     
         3 . A hole-opener for enlarging the diameter of a pilot hole, the hole-opener having front and rear ends and comprising: 
 a tubular drive sub having an external surface, a longitudinal bore and threaded connections at its front and rear ends;    a tubular sleeve mounted on the rear end of the drive sub;    means for locking the sleeve and drive sub together for rotation as a unit;    means, carried by the drive sub and engaging the front end of the sleeve, for stopping the sleeve at a pre-determined position;    a retainer sub threadably engaging the rear end connection of the drive sub and having a shoulder bearing against the rear end of the sleeve to lock the sleeve in the pre-determined position;    the sleeve carrying a plurality of rotary cutting element assemblies at its front end;    the drive sub forming ports for jetting drilling fluid contiguous to the cutting elements.    
     
     
         4 . The hole-opener as set forth in  claim 3  wherein the drive sub has outwardly protruding, circumferentially spaced apart bars affixed to its external surface and extending longitudinally thereof and the front end of the sleeve forms slots engaging the bars so that the bars cooperate with the retainer sub to lock the sleeve axially in the pre-determined position, the bars and sleeve interlock so that the drive sub and sleeve will rotate as a unit and the drive sub will impart pulling force to the sleeve through the retainer sub.