What is the spindle feed (vf) when the feed per revolution is 0.2mm/rev and main axis spindle speed is 1350min-1? (Answer) Substitute fr=0.2,n=1350 into the formula vf=fr×n=0.2×1350=270mm/min The spindle feed is 270mm/min. Drilling time (Tc) Tc (min) : Drilling Time n (min-1) : Spindle Speed ld (mm) : Hole Depth fr (mm/rev): Feed per Revolution i