Drill bit of high draw ratio

The utility model provides a drill bit of high draw ratio, includes drilling rod, drillstock, flange and macaroni, is equipped with cutting fluid circulation structure on the drill bit, the diameter of macaroni is 0.45 to 0.55 times of the drilling rod diameter, the periphery of being connected the terminal surface of drilling rod and macaroni has set firmly the reaming blade, and the ream drill diameter of reaming blade is greater than the diameter of drilling rod, the front end periphery of macaroni has set firmly the centering blade, and the centering blade is used for drilling out the centering taper hole on waiting to bore hole component, and the main aspects diameter of centering taper hole is greater than the diameter of macaroni. The beneficial effects are that: can not appear when boring the deep hole beating partially, beating greatly and the easily disconnected condition of drill bit, consequently can effectively solve with lower cost and bore the problem of getting the macropore deep hole with sin