Spiral tap

Abstract

As shown in FIG. 1, a helical flute has a constant lead part and a gradually increased lead part. The constant lead part has an axial length ranging from 0.3xLA to 1.2xLA and includes at least entirety of a leading part, so that the cutting performance of a cutting edge at the leading part and shape of chips (curled shape, etc.) are stable. In the constant lead part, because a lead is the smallest and a helix angle is large, a rake angle of the cutting edge is large, so that an excellent cutting quality is obtained and the chips become curled well. Meanwhile, in the gradually increased lead part, because of the lead gradually increased toward a shank, the chips are rapidly discharged toward the shank. Thus, the excellent cutting performance and the chip discharge performance rendered by the gradually increased lead are highly stabilized by the presence of the constant lead part. In this way, the durability is further improved.

Dependencies are inferred from the claim text.