Question

The ratio between two consecutive spindle speeds for a 8 speed drilling machining using drills of diameter 6.25 to 25 mm size and at cutting velocity of 188 m/min.

• A. 1.22
• B. 2.22
• C. 0.22
• D. 1.42

Answer 1

The correct option is A 1.22

$\pi DN=18m/min$

$\pi D_{min}\times N_{max}=18$

$N_{max}=\frac{18}{\pi \times 6.25\times {10}^{-3}}=916.732rpm$

$\pi D_{max}\times N_{min}=18$

$N_{min}=\frac{18}{\pi \times 25\times {10}^{-3}}=229.183rpm$

$N_{min}=N_1$

$N_{max}=N_1{r}^{3-1}$

$916.73=229.183r^7$

$r=\sqrt{\frac{916.73}{229.183}}$

$r=1.219\simeq 1.22$

$\frac{N_1}{N_2}=1.22$