The method of drilling holes in solid materials with a twist drill is called drilling. The dimensional accuracy of lathe drilling processing is low, generally reaching tTll-IT12, and the surface roughness value is R. Above 12. Spm, it belongs to the scope of rough machining, and generally requires subsequent processing.
Features and sharpening of twist drills Twist drills are commonly used cutting tools for processing inner holes. The lathe consists of a working part and a shank.
l) The geometry of the working part of the twist drill The working part of the twist drill is generally made of high-speed steel and has high hardness. 1) Spiral groove. The working part of the twist drill has two symmetrical helical grooves, which form two symmetrical front and back cutting edges, and are channels for chip discharge and coolant injection.
The angle between the outermost helix on the helical groove and the axis is the helix angle after it is expanded into a straight line. Since the helix angle lead of the same drill bit is fixed on the lathe, the helix angle at different diameters varies with the diameter. The closer to the center, the smaller the helix angle. The nominal helix angle on the drill bit refers to the helix angle at the diameter d of the outer edge, and the helix angle of standard drill bits is between 180-300.
2) Front. Refers to the helical groove surface near the cutting edge formed by the helical groove, which is the first surface of the drill that the chips come into contact with when they flow out.
3) The main back. Refers to the helical conical surface of the drill top, and the surface of the drill bit opposite to the transition surface of the workpiece.
4) Main cutting edge. It is the two intersection lines formed by the two fronts and the two backs, which are responsible for the main cutting work.
5) vertex angle (2K,). The apex angle is the angle between the two main cutting edges of the drill. Changes in the included angle of the lathe will affect the straightness of the main cutting edge. The apex angle of a standard twist drill is generally 1180. The two main cutting edges of the elbow are straight lines; when the apex angle is greater than 1180, the two main cutting edges are concave curves; when the apex angle is less than 118', the two main cutting edges are convex curves.
It also affects the cutting condition. When the apex angle is large, it will cause the rake angle to increase, making cutting labor-saving. However, because the main cutting edge is short and the centering force is poor, the diameter of the drill hole is easy to expand. Therefore, the cutting diameter is harder. When cutting the material, the apex angle can be appropriately increased; and when the cutting diameter is smaller and the softer material with higher precision is required, the apex angle can be appropriately reduced.
6) Front corner. The front angle is the angle between the front and the base. The biggest influence on the rake angle of the lathe is the helix angle. The larger the helix angle, the larger the rake angle. Since the helix angle changes with the size of the measured diameter, the rake angle of any point on the main cutting edge is the base plane passing through this point. The included angle between the fronts, then, at the diameter of the outer edge, the larger the rake angle, and the negative rake angle at 1/3 of the drill diameter at this g/medium -30' to 3002, and gradually increases, The range of variation is about -30. , 30. The ~ ~.