JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III MACHINE TOOL DESIGN Previous Question Paper (February/March - 2022 - R16)

The machining time for a lathe turning operation is determined by the length of the cut and the feed rate of the tool. The fundamental formula is:

Where T is the machining time in minutes, L is the total length of the cut in mm (including approach and overtravel), f is the feed rate in mm/rev, and N is the spindle speed in revolutions per minute (RPM).

To calculate N, the cutting speed (V) in m/min is used: N = (1000 × V) / (π × D), where D is the diameter of the workpiece in mm. For multiple passes, the total time is the sum of the times for each pass, accounting for the depth of cut and material removal rate.

Mechanical transmission relies on rigid components like gears, belts, chains, and shafts to transmit power and motion. It offers high efficiency, precise synchronization, and is cost-effective for high-speed applications, but it is susceptible to vibrations and wear under heavy loads.

Hydraulic transmission uses pressurized fluid to transmit power through cylinders and motors. It provides smooth, stepless speed variation, high torque capacity, and inherent overload protection, but is less efficient due to heat generation and requires complex maintenance to prevent leaks.

For a boring operation, hydraulic transmission is generally more suitable. Boring requires high precision, smooth feed motion to achieve superior surface finish, and the ability to handle varying cutting forces without chatter. The damping characteristics of hydraulic systems effectively absorb vibrations, ensuring the stability required for accurate hole sizing and finishing.