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What are the shortcomings of twist drill?
- Jan 09, 2018 -

Standard twist drill main cutting edge at each point of the front angle difference between inside and outside the same big difference. The rake angle of the main cutting edge at the outer edge of the drill bit is about + 30 °; while near the center of the drill bit, the rake angle is about -30 °; the rake angle at the near core is too small, resulting in large chip deformation and large cutting resistance; Anterior angle is too large, in the processing of hard materials, the cutting edge strength often inadequate.

Chisel too long, chisel rake angle is a great negative value of -5 4 ° ~ -6 0 °, which will have a great axial force.

Compared with other types of cutting tools, the main cutting edge of the standard twist drill is long, not conducive to the chip and chip breaking.

The minor relief angle of the minor cutting edge at the margin is zero, which causes the friction between the minor relief surface and the hole wall to increase. The cutting temperature increases and the corner of the outer edge of the drill is greatly worn. The machined surface roughness is deteriorated.