| 摘要 |
PURPOSE:To form a straight horizontal hole by forming a built-up section equivalent to the diameter of a horizontal hole on the outer peripheral surface of a sleeve pipe on the lower part side and forcing the built-up section to shield forward in slicing contact with the bottom of an inner wall. CONSTITUTION:A plate 17 is wound up and welded with a virtually semi- peripheral part of a sleeve pipe 12 in the lower part which builds up a primary inner wall, being pushed into a horizontal hole C excavated and formed with a bit 13, thereby constituting a built-up section 16 with the plate 17. This sleeve pipe 12 is fitted into a rotary shaft 11 and concentrically supported on the rotary shaft 11 rotatively at a bearing 15. When a cylinder-shaped body 24 is expanded and the rotary shaft 11 is rotated, the horizontal hole C is excavated with the bit 13, which is slightly larger-sized than the sleeve pipe 12. The built-up section opposed to the horizontal hole C is formed on the outer peripheral surface of the sleeve pipe 12 in the lower part. This built-up section 16 moves forward in sliding contact with the horizontal hole C, thereby drilling a hole straightly in orderly manner. |
