HSS drill bits Advantage:
(1) The diameter of the twist drill is limited by the aperture, the spiral groove makes the drill core thinner, and the stiffness of the bit is low; there are only two edges guides, and the axis of the hole is easy to deflect; the cross edge makes it difficult to center, the axial resistance increases, and the bit is easy to swing. Therefore, the shape error of the drilled hole is large.
(2) The front and rear blade surfaces of twist drills are curved surfaces, with different front and back angles along the main cutting edge points, and the front angle of the horizontal edge reaches -55°. The cutting conditions are very poor; the distribution of cutting speed along the cutting edge is unreasonable, and the cutting speed of the tip with the lowest strength is the largest, so the wear is serious. Therefore, the machining hole accuracy is low.
(3) The full edge of the main cutting edge of the drill bit participates in the cutting, and the cutting speed of each point on the edge is not equal, which is easy to form a spiral chip, which is difficult to remove chips. Therefore, the chips are squeezed against the hole wall, often scratching the hole wall, and the surface roughness after processing is very low.
