| 摘要 |
<p>A boring bit portion (34) has left, right and center boring bits (36, 38, 40), as well as left and right plate-like boring bits (42,44) which are extended between said boring bits. Each boring bit (36, 38, 40) is imparted impact force and rotation. The boring bits (36, 38, 40) each have distal end, intermediate and upper end tubular bodies each of which containing a hole portion therein. A bit edge (365, 385, 405) is fixed to each distal end tubular body. A cam (408) is integrally formed on the intermediate tubular body (402) at upper and lower ends thereof. The plate-like boring bits (42, 44) each have a sleeve (422, 442), a center sleeve (423) and a bit piece (424, 444). The boring bits (36, 38, 40) are rotatably connected to each other by means of connecting members (48). The device is provided with an impact force transmitting portion A for transmitting impact force from the boring bits (36, 38, 40) to the plate-like boring bits (42, 44) and a movement direction converting portion B for converting the rotating force of the boring bit (40) into a reciprocating movement through the engagement of a cam surface (426) with the cam (408) and transmitting the force so converted to the plate-like drilling bits (42, 44). <IMAGE></p> |
