Dual precision under reamer

Abstract

A under reamer that has two arms and is piston activated. The under reamer arms are supported on both side walls by a pin assembly. The under reamer arms are extended outward by a piston assembly which is spring biased to retract the arms. A surface of the under reamer arms adjacent the pivot point is protected via a holder assembly with a surface that matches the surface of the arms adjacent the pivot assembly.

What is claimed is: 
     
         1 . An under reamer device comprising:
 a central shaft with a central opening having wall openings that are spaced 180 degrees apart about the circumference of the shaft;   a pair of arms pivotally mounted to the central shaft so as to pivot into and out of the wall openings in the shaft;   a pair of digging implements that are mounted on the ends of the pair of pivoting arms.   
     
     
         2 . The device of  claim 1 , wherein the pair of arms consist of two arms. 
     
     
         3 . The device of  claim 1 , wherein the arms each include a pivot opening formed adjacent a first end of the arms and wherein a pivot pin extends through the pivot opening and wherein the end of the arms adjacent the pivot pin are rounded. 
     
     
         4 . The device of  claim 3 , further comprising a holder assembly that is mounted to a portion of the shaft so as to be flush with the outer wall of the shaft and wherein the holder assembly includes a rounded surface that mates with the rounded surface of the arms so as to permit rotational movement of the arms with respect to the shaft. 
     
     
         5 . The device of  claim 1 , further comprising a piston assembly that engages with the arms so as to cause the arms to pivot outward and retract inward. 
     
     
         6 . The device of  claim 5 , wherein the piston assembly includes a shaft and a cam and wherein the cam is movable along the central shaft and engages with the arms such that movement of the shaft extends and retracts the arms from the central shaft. 
     
     
         7 . The device of  claim 6 , wherein the arms include opening and the cam includes protrusions that extend into the openings of the arms and wherein the openings in the arms are angled such that movement of the cam as a result of movement of the piston shaft induces the arms to extend outward from the outer surface of the central shaft. 
     
     
         8 . The device of  claim 7 , wherein the shaft of the piston is spring biased such that removal of the force inducing the piston shaft to extend causes the spring to retract the cam and retract the arms. 
     
     
         9 . The device of  claim 1 , wherein the arms have two side surfaces and wherein the side surfaces include an opening that defines an arcuate path. 
     
     
         10 . The device of  claim 9 , further comprising a retaining pin assembly that is coupled to the central shaft wherein each retaining pin assembly a retaining pin that engages with the arcuate path in the side surfaces of the arm such that both sides of the arm are stabilized by the retaining pin.