Machine Design MCQ Questions & Answers | Mechanical Engineering

The correct answer is (C) Spindles of bench vices.

Let's break down why:

Buttress threads are special types of threads designed to handle heavy loads in one direction.
Think of them like a ramp on one side and a vertical wall on the other.
* Option A: Screw cutting lathes: Lathes use various threads, but not typically buttress threads for their main operation.
* Option B: Feed mechanisms: While feed mechanisms require movement, they don't usually need the one-directional, high-load capacity of buttress threads.
* Option C: Spindles of bench vices: Bench vices are all about applying a strong force in one direction to hold an object securely. The buttress thread is perfect for this! When you tighten a vice, you want a strong, secure grip *without* the vice easily loosening. The ramp allows for easy tightening, and the vertical face prevents slipping under load. This is the most common and ideal application for buttress threads.
* Option D: Railway carriage couplings: Railway couplings require a strong connection, but other thread types (like ACME threads) are generally preferred due to their ease of manufacture and suitability for bidirectional forces.

The correct answer is (A) Spindles of bench vices, (C) Feed mechanism of machine tools, and (D) Screw cutting lathes.
Here's why:
* Square Threads: Square threads are known for their high efficiency and ability to transmit power with minimal friction. This makes them ideal for applications requiring significant force or precise movement.
* Option A: Spindles of bench vices: Bench vices need to apply a large clamping force. Square threads on the spindle allow for efficient force transmission when tightening the vice.
* Option B: Railway carriage couplings: Railway carriage couplings typically use knuckle threads or other specialized designs for quick and secure connections, not square threads.
* Option C: Feed mechanism of machine tools: Machine tools require precise and controlled movement for cutting operations. Square threads are well-suited for the feed mechanisms because they provide smooth, efficient, and accurate linear motion.
* Option D: Screw cutting lathes: Screw cutting lathes use square threads in lead screws for achieving axial motion of cutting tools.
Therefore, square threads are commonly found in spindles of bench vices, feed mechanisms of machine tools, and screw cutting lathes due to their efficiency and ability to handle high loads.