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°. The angle (&dgr;) 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:P P125° &dgr; (57°-&ohgr;)·K+90. degree., PPwhere: &ohgr; is the angle of helix of the helical flute (3) relative to the twist drill axis at the point under consideration.PPK=1.4-2.1.
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