Drill structure

A drill structure comprising:

• a shank part;
• and
• a flute part arranged on one end of the shank part, a chisel edge arranged at a front end of the flute part, a first drill blade and a second drill blade with tilt directions toward the shank part formed on two sides of the chisel edge, a first outer circumference edge of the first drill blade and a second outer circumference edge of the second drill blade respectively helically extended around a periphery of the flute part toward the shank part to form a first helical groove and a second helical groove respectively, the first drill blade comprising a first primary relief surface and a first secondary relief surface, the first primary relief surface and the first secondary relief surface connected to each other through a first ridge edge, the first primary relief surface having a first cutting edge, the first secondary relief surface having a first knife-back edge, the second drill blade comprising a second primary relief surface and a second secondary relief surface, the second primary relief surface and the second secondary relief surface connected to each other through a second ridge edge, the second secondary relief surface having a second knife-back edge, wherein the first cutting edge of the first primary relief surface and a portion of the second knife-back edge of the second secondary relief surface near the chisel edge extend and form a first assist relief surface that extends to an inner wall of the first helical groove.