Question

Metric thread of 0.8 mm pitch is to be cut on a lathe. Pitch of the lead screw is 1.5 mm. If the spindle rotates at 1500 rpm, the speed of rotation of the lead screw (rpm) will be ________

Answer 1

Concept:

RPM of lead screw = \(\frac {Pitch~ of Metric ~thread}{Pitch ~of ~lead ~screw}\times Spindle ~RPM\)

Calculation:

Pitch = 0.8 mm

Lead screw pitch = 1.5 mm

Spindle speed = 1500 rpm

In one rotation of lead, it should advance 0.8 mm.

Fraction of revolution in one rotation of spindle \( = \frac{{0.8}}{{1.5}}\)

RPM of lead screw \( = \frac{{0.8}}{{1.5}} \times 1500 = 800\;rpm\)

Alternate Solution

Pitch of thread, P_t = 0.8 mm

Speed of spindle, N_t = 1500 rpm

Pitch of screw (P_s) = 1.5 mm

Now N_s × P_s × Z = N_t × P_t × Z_t

N_s × 1.5 × 1 = 1500 × 0.8 × 1

N_s = 800 rpm