| 摘要 |
PCT No. PCT/SU88/00193 Sec. 371 Date May 25, 1990 Sec. 102(e) Date May 25, 1990 PCT Filed Sep. 29, 1988 PCT Pub. No. WO90/03238 PCT Pub. Date Apr. 5, 1990.A twist drill for deep hole drilling comprises a cutting portion, margins (2) and helical flutes (3) designed for chip removal. The front-end wall (4) of the helical flute (3) comprises two conjugate sections (7, 8). The first section (7) intersecting with the margin (2) forms with the generatrix of the twist drill outer cylindrical surface an angle ( psi ) which is smaller than 90 DEG . The angle ( delta ) of inclination of the tangent at any point of the second sections (8) of the front-end wall (4), to the generatrix (9) of the twist drill outer cylindrical surface is selected proceeding from the relationship: 125 DEG > delta >(57 DEG - omega )xK+90 DEG , where: omega is the angle of helix of the helical flute (3) relative to the twist drill axis at the point under consideration. K=1.4-2.1.
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