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

Two separate slab milling operations, $$1$$ and $$2,$$ are performed with identical milling cutters. The depth of cut in operation $$2$$ is twice that in operation $$1.$$ The other cutting parameters are identical. The ratio of maximum uncut chip thicknesses in operations $$1$$ and $$2$$ is ___________