To improve a structure of a gundrill such that the gun drill can drill a variety of products made of metals from relatively brittle cast iron to soft and ductile aluminum.
A method for forming a deep hole and a gundrill therefore is disclosed. The gun drill has a tubular shank 200 and a cutting tip. They are provided with a tubular central region 210 for supplying pressurized drilling fluid and a non-circular cross section 232 defining a drilling fluid return passage together with a hole being formed. The longitudinal flute 206 at the cutting tip end portion defines a main rake face 202 which terminates at an offset point and a secondary flank 204 which forms an exit of the drilling fluid together with the hole being formed and has the size that cools the cutting surface and effectively discharges the formed chips by keeping the pressure of the fluid within a bottom end space. A local discharge passage 232, whose relative size with respect to the exit passage 206 is set so as to make a lot of the drilling fluid flow there through, is formed behind the main rake face 202 such that the drilling fluid flows out from the bottom end space and cools the tip.
VAL YEFIM
ASTAKHOV VIKTOR P
Hiroshi Koyama
Hiroshi Takeuchi
Yuji Takeuchi
Katsumi Imae
Tomoo Harada
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