Step twist drills are suitable for use on machine tools such as radial drilling machines, vertical drilling machines, CNC drilling machines, and machining centers. It is used to process the holes and counterbores of solid workpieces such as carbon steel, alloy steel and non-ferrous metals before tapping. The selection is based on the thread diameter listed in the type and size table, and the coarse or fine thread used. The diameter of the drill bit corresponding to the diameter of the hole before tapping (referring to the diameter of the small end of the drill bit). The step twist drill consists of a handle and a working part. The handle is divided into two types: straight handle and tapered part. It is mainly used to transmit torque after clamping. The working part is stepped and consists of a small diameter d: and a large diameter d2. . When formulating the heat treatment process, the heating time cannot be calculated according to the major diameter or the minor diameter. It is generally calculated based on the arithmetic mean of the major diameter and the minor diameter. For example, the minor diameter is 12mm and the major diameter is 16mm. The calculated size is (12+16 )/2=14mm.
Straight shank step twist drills are required to be quenched within 4/5 of the blade length, with a hardness ≥ 63HRC. The hardness at 25.4mm from the shank end to the blade is not less than 25HRC, and the quenching heating temperature should be the middle or lower limit. If it is made of M2 steel, it can be heated at 1215-1220℃, the grain size is 10.5, and isothermal at 260-280℃x2h after neutral salt classification at 60℃. After isothermal cleaning and straightening, the upper fixture is subjected to shape-limiting tempering.
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GS-ZP-1200
