| 摘要 |
PURPOSE:To reduce burden of a blade by a method in which the diameter-expanded blade of a plate of a fun shape is pivotally supported with an acute angular part to the fitting window of a bit body housed with a diameter-expanded piston, and a cutting edge whose long side is contacted with the face of the piston is projected from the bit body. CONSTITUTION:The diameter-expanded blade 12 of an almost triangular or fun- shaped plate is pivotally supported with a pin 13 to the blade fitting window 11 opening in the longitudinal direction of a clindrical pit-expanding bit body 1. The cutting edge 14 is provided downwards and in a freely coming-in and out manner to the inside and outside of the body 1. A diameter-expanded piston 3 is slidably housed in the body 1, and the long side 15 of the blade 12 is contacted with the conical face 31 of the piston 3. The pressure-supporting area A between the body 1 and the blade 12 can thus be increased. |
