What is the speed ratio between lathe spindle and lead screw?

Question

It is required to cut screw threads withdouble start and 2 mm pitch on a lathe having lead screw pitch of 6 mm. What is the speed ratio between lathe spindle and lead screw?           

(a) 1 : 3                           (b) 3 : 1

(c) 2 : 3                           (d) 3 : 2

Answer 1

(D)  pitch of thread*no. of start* speed of thread =pitch of screw*no. of start *speed of screw