(A)(b)(c) attached drawing makes the same score bottom outlet to get flat bottom to divide aperture of blind of bottom of peace of via of flat bottom a flight of stairs again, like attached drawing (B) , (C) place is shown. At this moment, but twist drill wear two blade are flat and very symmetrical cutting blade, and before horn repairs wear 8 ° of 3 ° ～ , horn is 2 ° ～ after 3 ° . Especially hind horn cannot big, big cause not only later " plunge into a knife " , and hole bottom face shows waviness, can cause broach to break off again accident. If get the Kong Shi that cut blind, answer if a wear that get a heart pursues (the convex that C) place shows gets a heart, so that broach centering, make get cut smooth. CNC MillingCNC Machining