Drill bit shaft structure for excavation apparatus

Abstract

The drill bit shaft structure for an excavation apparatus has a thin-walled shaft portion formed on a hollow drill bit shaft. The thin-walled shaft portion has a thinner wall than that of shaft portions of the hollow drill bit shaft adjacent to both ends of the thin-walled shaft portion. A cylindrical body provided with an adjustable joining structure is disposed so as to envelop the thin-walled shaft portion. Both ends of the cylindrical body are connected to the shaft portions of the hollow drill bit shaft adjacent to the both ends of the thin-walled shaft portion. The direction of excavation is controlled by bending the thin-walled shaft portion and the cylindrical body.

1 . A drill bit shaft structure for an excavation apparatus, comprising:
 a hollow drill bit shaft;   a thin-walled shaft portion formed on the hollow drill bit shaft, which has a predetermined length along an axial direction of the hollow drill bit shaft, and which has a thinner wall than that of shaft portions of the hollow drill bit shaft adjacent to both ends of the thin-walled shaft portion; and   a cylindrical body provided with an adjustable joining structure and disposed so as to envelop the thin-walled shaft portion; wherein   the cylindrical body has two end parts connected to the shaft portions of the hollow drill bit shaft adjacent to the both ends of the thin-walled shaft portion; and   the direction of excavation is controlled by bending the thin-walled shaft portion and the cylindrical body.   
   
   
       2 . The drill bit shaft structure for an excavation apparatus according to  claim 1 , wherein the adjustable joining structure of the cylindrical body is an Oldham coupler. 
   
   
       3 . The drill bit shaft structure for an excavation apparatus according to  claim 1 , wherein the adjustable joining structure of the cylindrical body is formed by wrapping metal wire of a predetermined thickness in multiple layers in a coil shape. 
   
   
       4 . The drill bit shaft structure for an excavation apparatus according to  claim 1 , wherein:
 an inside diameter of the thin-walled shaft portion is equal to that of the remaining shaft portion of the hollow drill bit shaft, and   an outside diameter of the thin-walled shaft portion is less than that of the remaining shaft portion of the hollow drill bit shaft.   
   
   
       5 . The drill bit shaft structure for an excavation apparatus according to  claim 4 , wherein a shock absorber comprising heat-resistant rubber or other resin material is disposed between the thin-walled shaft portion and the cylindrical body.