Flexible Drill Shaft

Abstract

A flexible drill shaft for drilling lateral boreholes comprising: a helical outer wire coil spring; and at least one inner helical wire coil spring residing concentrically within the outer coil spring, with the coils of adjacent springs having an opposite pitch; wherein the wire forming each helical spring has a cross section such that when the drill shaft is in a straight alignment there is planar contact between adjacent coils of the spring.

1 . A flexible drill shaft for drilling lateral boreholes comprising:
 a helical outer wire coil spring; and   at least one inner helical wire coil spring residing concentrically within the outer coil spring, with the coils of adjacent springs having an opposite pitch;   wherein the wire forming each helical spring has a cross section such that when the drill shaft is in a straight alignment there is planar contact between adjacent coils of the spring.   
   
   
       2 . A flexible drill shaft according to  claim 1  wherein the cross section of the wire is square, rectangular or lozenge. 
   
   
       3 . A flexible drill shaft according  claim 1  wherein there are ridges on the contact surface of the coils. 
   
   
       4 . A flexible drill shaft according to  claim 1  wherein there are grooves on the contact surface of the coils. 
   
   
       5 . A flexible drill shaft according to  claim 1  wherein the coil springs are formed from at least two wires coiled in parallel. 
   
   
       6 . A flexible drill shaft according to  claim 1  wherein the coil springs have a preload. 
   
   
       7 . A flexible drill shaft according to  claim 1  comprising a torque spike filter. 
   
   
       8 . A drilling apparatus comprising the drill shaft according to  claim 1  and a drill bit attached to the lower end of the shaft. 
   
   
       9 . A method of making a flexible drill shaft according to  claim 1  comprising:
 winding wire to form a helical coil spring;   applying a mechanical deformation to the wire as it is being wound; and   using the helical coil spring to form a flexible drill shaft;   wherein the mechanical deformation applied results in the wire after being wound having a cross section such that when an axial load is applied to the drill shaft there is planar contact between adjacent coils of the spring.   
   
   
       10 . A method of making a flexible drill shaft according to  claim 9  comprising:
 applying a preload as the wire is being wound.   
   
   
       11 . A method according to  claim 9  comprising using dimensional or thermal expansion to tightly assemble two or more coil springs.