A $$\phi $$ $$20$$ $$mm$$ through hole is to be drilled in a $$30$$ $$mm$$ thick plate using a double fluted, $${120^ \circ }$$ lip angle drill. The drill tip is at a distance of $$3$$ $$mm$$ from the plate surface when cutting is started and an over travel of $$2$$ $$mm$$ is recommended as a margin to ensure drilling through the full thickness of the plate. If the drill rotates at $$500$$ $$rev/min$$ and the feed per tooth is $$0.01$$ $$mm,$$ the machining time of the operation (in sec) will be

A non standard thread of pitch $$3.175$$ $$mm$$ is to be cut on a lathe having lead screw of pitch $$6$$ $$mm.$$ A change gear set provided with the lathe has one gear each with the following number of teeth: $$20, 30, 40, 50, 60, 70, 80,$$ $$90, 100, 110, 120, 127.$$ The correct pairs of change gears $$\left( {a/b\,\,x\,\,c/d} \right)$$ for machining the given thread are (assuming that the transmission ratio of the rest of the kinematic train between the lathe spindle and lead screw is equal to

The cutting portion of a drill is to be welded to its shank. The process best suited for this is

Two identical cylindrical jobs are turned using (a) a round nosed tool of nose radius $$2$$ $$mm$$ and (b) a sharp corner tool having principal cutting edge angle $$ = {45^ \circ }$$ and auxiliary cutting edge angle $$ = {10^ \circ }$$. If the operation is carried out at a feed of $$0.08$$ $$mm/rev,$$ the heights of micro irregularities on the machined surfaces (in $$mm$$) in the two cases will be