| 摘要 |
A cutting head comprising a hollow cylindrical core with a helical flight;
€¢ a threading tooth presenting an extended and a retracted position;
€¢ displacement means for displacing said threading tooth between said retracted position and said extended position, said displacement means comprising:
€¢ an inner hollow tubular member mounted to move into said hollow cylindrical core in translation along said longitudinal axis and disposed at least at the bottom end of said hollow cylindrical core;
€¢ a rack fixed to the inner hollow tubular member,
€¢ at least a gear cooperating with the rack, said gear being mounted on the bottom end of the hollow cylindrical core,
€¢ a lever connected to the gear;
€¢ a connecting rod pivotally connected to the lever and to the threading tooth, whereby the translation of the rack causes the displacement of the threading tooth. |
