It is required to cut screw threads of 2 mm pitch on a lathe. The lead screw has a pitch of 6 mm. If the spindle speed is 60 rpm, then the speed of the lead screw will be
- A. 10 rpm
- B. 20 rpm
- C. 120 rpm
- D. 180 rpm
Answer: B. 20 rpm
Explanation: $N_L / N_S = P_{thread} / P_{lead} \Rightarrow N_L / 60 = 2 / 6 \Rightarrow N_L = 20$.