| 摘要 |
PROBLEM TO BE SOLVED: To provide a drill bit for diameter expansion which deals with a lower hole having a narrow diameter with a simple structure.SOLUTION: A drill bit 11 for diameter expansion is used inserted into a lower hole H made in a building frame A to grind a part of the lower hole H and expand its diameter. The drill bit 11 includes: cutting blade parts 21 which grind the part of the lower hole H; a cutting blade holding part 22 which holds the cutting blade parts 21 in a manner such that the cutting blade parts 21 may slide in a radial direction to parallely move; and a shank part 23 supporting the cutting blade holding part 22. The cutting blade parts 21 are moved by a centrifugal force generated by rotation of the drill bit 11 so as to spread to a radial outer side relative to the cutting blade holding part 22.SELECTED DRAWING: Figure 5 |
