L₃— total length of brazed PCBN superhard drill; l₃— length of working part of brazed PCBN superhard drill; H₃— width of the spiral groove; h₃— depth of the spiral groove; β₃— helix angle of the spiral groove; ht₃— substrate protrusion height of cutting edge; d₃— substrate diameter of brazed PCBN superhard drill; D₃— diameter of brazed PCBN superhard drillFig. (6) Geometric structure of Brazed PCBN Superhard drill.