Drill structure

A drill structure comprising

• a shank part;
• and
• a bit part disposed on one end of the shank part, having a bit core, which is a cylindrical body along a central axis of the bit part, and having a web at one end of the bit part, which is away from the shank part, wherein two sides of the web are tilted toward the shank part to form a first cutting face and a second cutting face, and wherein a first outer face of the first cutting face is extended helically around a surface of the bit part and along the bit core toward the shank part to form a first flute,
• wherein the first cutting face includes a first primary cutting face and a first secondary cutting face;
• the first primary cutting face has a first cutting edge, a first prismatic web edge, a first connection edge, and a first outer edge;
• the shortest distance between two ends of the first outer edge is defined as an outer-side width of the first primary cutting face;
• the first connection edge is connected with the first secondary cutting face;
• the first secondary cutting face includes a first blade back;
• wherein the second cutting face includes a second primary cutting face and a second secondary cutting face;
• the second primary cutting face is in form of a triangle;
• the second primary cutting face has a second prismatic web edge, a second connection edge, and a second outer edge;
• the second connection edge is connected with the second secondary cutting face;
• the second secondary cutting face includes a second blade back, a third outer edge, and a fourth outer edge;
• the first prismatic web edge and the second prismatic web edge jointly form the web;
• the first prismatic web edge is connected with the second secondary cutting face;
• the second prismatic web edge is connected with the first secondary cutting face;
• wherein the first cutting edge of the first primary cutting face is not parallel with the first connection edge;
• a width of the first prismatic web edge is smaller than the outer-side width of the first primary cutting face;
• a first auxiliary cutting face is extended to a wall of a chip-discharge groove from the first cutting edge and a portion of the second blade back, which is near the first prismatic web edge.