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 _____________

Internal gears are manufactured by

The following data is applicable for a turning operation. The length of job is $$900$$ $$mm,$$ diameter of job is $$200$$ $$mm,$$ feed rate is $$0.25$$ $$mm/rev$$ and optimum cutting speed is $$300$$ $$m/min.$$ The machining time (in $$min$$) is _____________

In a machining operation, if the generatrix and directrix both are straight lines, the surface obtained is