现介绍一种宜于钻削铸铁的钻头——双后角麻花钻。它的外刃锋角2φ、横刃斜角ψ、内刃斜角τ的修磨与图1(是标准麻花钻常用的修磨形式)相同。磨出过渡刃AB后(图2),形成双重锋角2φ′约65～75°。磨窄横刃b,使内刃前角γ_τ约为-10°。在外刃和过渡刃上各磨出双后角为:α=12～14°,α_R=16～18°,α′=10～12°,α_C′=14～16°。 Now introduce a drill suitable for drilling cast iron - double posterior twist drill. Its outer blade edge angle 2φ, chisel angle ψ, taper angle φ internal grinding and Figure 1 (which is commonly used in standard twist drill grinding form) the same. After grinding out the transitional edge AB (Fig. 2), a double frontal angle of 2φ ’is formed about 65-75 °. Grind the chisel b so that the rake angle γ_τ of the inner blade is about -10 °. In the outer edge and the transition edge on the grinding of the double posterior horn: α = 12 ~ 14 °, α_R = 16 ~ 18 °, α ’= 10 ~ 12 °, α_C’ = 14 ~ 16 °.