| 摘要 |
Provided is a spiral tap wherein tool life has been improved by facilitating chip removal during reversed withdrawal after thread-cutting while ensuring favorable cutting properties during thread-cutting. Because a sub-groove (28), which is formed with a concave shape along the back edge (30) of a spiral flute (18) and makes the rake angle of the back edge (30) to be positive, is provided in the spiral flute (18) at least in the portion corresponding to the chamfer (22) of the spiral tap (10), necessary and sufficient chip room is secured while making it possible to increase the rake angle of the back edge (30) in the spiral flute (18). That is to say, the present invention provides a spiral tap (10) wherein tool life has been improved by facilitating chip removal during reversed withdrawal after thread-cutting while ensuring favorable cutting properties during thread-cutting. |
