Sawtooth structure with reversed cutting function and its drill series

A sawtooth structure with reversed cutting function has characteristics as below:

• the sawtooth structure is constructed by sawteeth (1-1) and grooves (1-2) located on cutting edges of a drill;
• the sawteeth (1-1) and the grooves (1-2) are helically arranged around a drill axis;
• the sawtooth structure is classified as left-hand helix sawtooth structure and right-hand helix sawtooth structure based on a helix angle (1-β) of the sawtooth structure;
• the sawteeth (1-1) with the helix angle (1-β) larger than 60° and smaller than 90° _are categorized as right-hand sawteeth, and top edges (1-3) of the right-hand sawteeth are additional cutting edges that are ground into positive rake angles (1-γ0u);
• the sawteeth (1-1) with the helix angle (1-β) smaller than 150° and no less than 90° are categorized as left-hand sawteeth, and bottom edges (1-4) of the left-hand sawteeth are additional cutting edges that are ground into positive rake angles (1-γ0d);
• the sawtooth structure is located on cutting edges of which diameters are equal to 0.6 to 1 time of the diameter of a drill, and for step a drilling structure, the sawtooth structure is located on a step minor cutting edge;
• a length of sawteeth (1-Lt) is not larger than the length of a drilling margin and is at least 0.8 mm;
• a width of grooves (1-Wg) is at least 0.3 mm;
• a width of sawteeth (1-Wt) is at least 0.5 mm;
• a depth of grooves (1-Dt) is at least 0.8 mm, and the sawteeth (1-1) at a minimum diameter position cannot interfere with a drilling core.