Select the formula for finding rpm (1/min) for drilling where v = cutting speed in m/min; d = diameter of drill in mm
1
\(N=\frac{\pi d}{1000\times v }\)
2
\(N=\frac{1000\times v}{ \pi d}\)
3
\(N=\frac{1000}{ \pi dv}\)
4
\(N=\frac{dv}{ 1000\times \pi }\)