(1) The rake angle at each point on the main cutting edge of a standard twist drill has a large difference between inside and outside. The rake angle of the main cutting edge at the outer edge of the drill bit is approximately +30°; near the core, the rake angle is approximately -30°, and the rake angle at the near core is too small, resulting in large chip deformation and large cutting resistance; near the outer edge When the front corner is too large, the strength of the cutting edge is often insufficient when machining hard materials.
(2) Longitudinal edge is too long, and the rake angle of the horizontal edge is very negative, reaching -54° to -60°, which will generate a large axial force.
(3) Compared with other types of cutting tools, the main cutting edge of a standard twist drill is very long, which is not conducive to chipping and chip breaking.
(4) The secondary backlash angle of the secondary cutting edge at the land is zero, resulting in increased friction between the secondary flank and the hole wall, increased cutting temperature, large wear at the outer edge of the drill, and deterioration of the machined surface roughness. .

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