Four -stage drill bit

The utility model provides a four -stage drill bit, the stalk portion front end of this drill bit body extends there is the cutting part, and extend the concave spiral helicine chip groove that is equipped with toward the inboard at cutting part outside ora terminalis cutting blade, and the drill tip of cutting part extends the first mild section that the segmentation is formed with dark chip groove towards the stalk portion direction, and extend the first slope section that has convergent form chip groove by first mild section according to the preface toward the opposite side, and more shallow chip groove and internal diameter enlarge and the mild section of second of straight extension along first slope section, and be formed with the second slope section of convergent form chip groove between mild section of second and the stalk portion, the drill bit body pierces when holing on the multilayer circuit board when being high -speed, the darker chip groove of usable first mild section, a first slope section convergent form chip groove and the more shallow chip groove of the mild section of second increase appearance bits space, and utilize second slope section to link mutually with great internal diameter and stalk portion, and then make holistic chip removal nature effect and structural strength more good, and the precision and the qualification rate of promotion drilling.