| 摘要 |
PROBLEM TO BE SOLVED: To obtain a helical drill wherein even a much used helical drill is little worn and scarcely comes to a halt owing to generation of biting with a helical rail. SOLUTION: In a helical drill for drilling rock wherein a helical rail 7 extending helically on a shaft 5 positioned between an insertion end part 2 and a tool head 3, a width x of a crest part 8 of the helical rail 7 is the more increased the nearer toward the tool head 3. Suitably a diameter 6 of a core of the shaft 5 is the more increased the nearer toward an insertion end part 2, and a transection of a helical groove 11 decreased owing to change of the width of the crest part 8 of the helical rail 7 is compensated for by the core diameter 6 to be the more decreased the nearer toward the tool head 3. Suitably the transection of the helical groove 11 is the more increased the nearer toward the insertion end part 2. Further, an inclined angle x of the helical rail 7 is changed along the shaft 5, and suitably the inclined angleαis the more decreased the nearer toward the insertion end part 2. |
