First of all, the cutting edge of the bit must be symmetrical from the Angle, or the hole drilled will be larger than the diameter of the bit. In addition, the geometric parameters and Angle of the bit grinding. In fact, these can be ignored, because no one can accurately grasp the data, but the Angle of the bit grinding must be properly mastered. Apex Angle is the most important of the chisel edge grinding because the two main blades of the bit can as vertex Angle in change, we can see from the photos of the two main blade Angle is 118 ° with the change of the vertex Angle, the Angle of the two main blades or greater than 118 ° or less than 118 °, thus we can make a conclusion, grinding bit first hand to steady, cannot appear jitter on the grinding wheel, the second to grasp good grinding Angle so that we can make mechanical workers grinding out the high precision drill.
1. The diameter of the twist drill is limited by the aperture. The spiral groove makes the drill core finer and the bit stiffness low. There are only two edges and the axis of the hole is inclined to skew. The transverse edge makes centering difficult, axial resistance increases, and the bit is easy to swing. Therefore, the shape and position error of the drilling hole is large.
2. The front and rear cutting surfaces of twist drill are curved surfaces. The front and rear angles of each point along the main cutting edge are different. The front Angle of the horizontal edge reaches -55°. Poor cutting conditions. Cutting speed along the cutting edge distribution is not reasonable, the lowest strength of the cutting edge cutting speed is the largest, so serious wear. As a result, the machining hole accuracy is low.
3. All the main cutting edges of the drill bit are involved in cutting, and the cutting speed of each point on the edge is not equal, which is easy to form a spiral chip, making it difficult to remove chips. Therefore, the chip and hole wall extrusion friction, often scratch the hole wall, the surface roughness after processing is very low.