JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III METROLOGY AND MACHINE TOOLS Previous Question Paper (March - 2021 - R18/R16)

Given data:

Rake angle (α) = 10°

Chip thickness ratio (r) = 0.3

Horizontal cutting force (F_c) = 1290 N

Vertical cutting force (F_t) = 1650 N

1. Calculation of Shear Angle (φ):

tan φ = (0.3 × cos 10°) / (1 - 0.3 × sin 10°) = (0.3 × 0.9848) / (1 - 0.3 × 0.1736) = 0.29544 / 0.94792 = 0.3117

φ = tan⁻¹(0.3117) = 17.31°

2. Calculation of Coefficient of Friction (μ):

μ = (1650 + 1290 × tan 10°) / (1290 - 1650 × tan 10°) = (1650 + 1290 × 0.1763) / (1290 - 1650 × 0.1763) = (1650 + 227.43) / (1290 - 290.89) = 1877.43 / 999.11 = 1.879

Friction angle (β) = tan⁻¹(1.879) = 61.98°

3. Calculation of Force Components:

Friction force (F) at chip-tool interface:

F = 1290 × sin 10° + 1650 × cos 10° = 1290 × 0.1736 + 1650 × 0.9848 = 223.94 + 1624.92 = 1848.86 N

Normal force (N) at chip-tool interface:

N = 1290 × 0.9848 - 1650 × 0.1736 = 1270.39 - 286.44 = 983.95 N

Shear force (F_s) along shear plane:

F_s = 1290 × cos 17.31° - 1650 × sin 17.31° = 1290 × 0.9547 - 1650 × 0.2975 = 1231.56 - 490.88 = 740.68 N

Normal force (F_n) on shear plane:

F_n = 1290 × 0.2975 + 1650 × 0.9547 = 383.78 + 1575.26 = 1959.04 N

A lathe is a machine tool used for removing metal from a workpiece by rotating it against a stationary cutting tool. Lathes are classified based on their configuration, purpose, and degree of automation.

The primary types of lathes include:

1. Speed Lathe: The simplest form, used for wood turning and metal spinning.
2. Engine Lathe (Center Lathe): The most common type, used for a wide range of operations like turning, facing, and thread cutting.
3. Bench Lathe: A small version of the engine lathe mounted on a workbench for precision work on small parts.
4. Tool Room Lathe: A high-precision engine lathe equipped with extra accessories for tool and die making.
5. Capstan and Turret Lathes: Semi-automatic lathes used for mass production, featuring a hexagonal turret instead of a tailstock.
6. Special Purpose Lathes: Designed for specific tasks, such as wheel lathes, gap-bed lathes, and T-lathes.
7. Automatic Lathes: Fully automated machines where the entire machining cycle is pre-programmed.
8. CNC Lathe: Computer Numerical Control lathes that offer high precision and repeatability through digital control systems.

Engine Lathe (Center Lathe) Description:

The engine lathe is the most versatile machine tool in a workshop. It consists of a bed that supports all major components, a headstock housing the main spindle and gear train for rotating the workpiece, and a tailstock used to support long workpieces or hold drilling tools. The carriage moves along the bed and carries the cross-slide and tool post, allowing the cutting tool to move both longitudinally and transversely. The feed mechanism provides the required movement to the tool relative to the rotating workpiece.

Sketch Description: The lathe layout features the headstock on the left end of the bed, with the tailstock positioned on the right. The carriage assembly is located between the headstock and tailstock, mounted on the bed ways. The workpiece is held between the headstock chuck and the tailstock center, while the cutting tool is secured in the tool post mounted on the compound rest atop the carriage.