Lathe Machine MCQ Quiz - Objective Question with Answer for Lathe Machine - Download Free PDF

Explanation:

Taper Turning by Swiveling the Compound Rest:

• Taper turning by swiveling the compound rest is a machining process used to create tapered surfaces on a workpiece. The compound rest, which is part of the lathe, is swiveled to a specific angle relative to the lathe axis to achieve the desired taper.
• In this method, the compound rest is set at an angle corresponding to the taper angle to be produced. As the tool moves along the compound rest, it cuts the workpiece to create a taper. The angle of the compound rest determines the taper angle of the workpiece.
• Due to the limited travel of the compound rest, this method is only suitable for producing short tapers. The compound rest can only move a limited distance, restricting the length of the taper that can be produced. For longer tapers, other methods such as taper turning attachments or tailstock offset methods are more appropriate.

Limitations:

• Limited to short tapers due to the constraints of compound rest travel.
• Not suitable for high production efficiency as the setup and operation are relatively slow.
• Surface finish may not be optimal compared to other taper turning methods.

Explanation:

Tailstock in a Lathe:

• The tailstock is an essential component of a lathe machine, primarily used to provide support and bearing for the rotating workpiece during machining operations. It is located at the opposite end of the headstock on the lathe bed and can be adjusted along the bed to accommodate different workpiece lengths.
• During machining operations, especially when working with long or slender workpieces, the tailstock plays a critical role in maintaining stability and alignment. It houses a spindle (or quill) that can hold tools such as centers or drills. When the workpiece is mounted between the headstock and tailstock, the tailstock ensures that the workpiece remains securely supported, preventing deflection, wobbling, or bending under cutting forces.

Advantages:

• Provides stability to long workpieces during machining, ensuring accurate results.
• Prevents deflection and bending caused by cutting forces, allowing for precise machining.
• Facilitates operations such as drilling, reaming, and tapping by holding the necessary tools.
• Adjustable along the lathe bed, accommodating a wide range of workpiece lengths.

Disadvantages:

• Requires careful alignment with the lathe’s spindle to ensure proper operation.
• Can limit access to certain areas of the workpiece during machining, depending on its position.

Applications: The tailstock is widely used in various machining operations such as turning, drilling, reaming, and tapping. It is particularly beneficial for machining long shafts, rods, or other components that require support to maintain alignment and stability.

Explanation:

Primary Function of the Tool Post in a Lathe Machine

Definition: The tool post in a lathe machine is a crucial component designed to hold the cutting tool securely and allow precise adjustments of the tool position during machining operations. This component is fundamental in ensuring the tool's stability and precision, which are critical for achieving the desired machining results.

Working Principle: The tool post is mounted on the carriage of the lathe machine, and it typically consists of a base plate, a tool holder, and a clamping mechanism. The tool holder can accommodate various types of cutting tools, and the clamping mechanism secures the tool in place. The tool post allows the operator to adjust the tool's position in multiple directions, ensuring it is set at the correct angle and height relative to the workpiece.

Advantages:

• Provides a secure and stable platform for the cutting tool, reducing vibrations and improving machining accuracy.
• Allows for precise adjustments of the tool position, facilitating the machining of complex shapes and features.
• Enhances the versatility of the lathe machine by accommodating various types of cutting tools and tool holders.

Disadvantages:

• Requires careful setup and adjustment to ensure optimal tool positioning and machining accuracy.
• Improper clamping or adjustment can lead to tool deflection or breakage, affecting the quality of the machined part.

Applications: The tool post is used in various machining operations on a lathe machine, including turning, facing, threading, and parting-off. It is an essential component for both manual and CNC lathes, providing the necessary support and adjustability for precise machining.

Explanation:

The Primary Function of the Headstock in a Lathe Machine

Definition: The headstock is a critical component of a lathe machine, which is primarily responsible for holding and rotating the workpiece at various speeds during machining operations. It is located at the left-hand end of the lathe bed and houses the main spindle, speed change mechanism, and the drive motor. The headstock's ability to rotate the workpiece is crucial for performing various turning operations, which involve cutting, facing, threading, and drilling.

Working Principle: The headstock works by transmitting power from the drive motor to the spindle, which in turn rotates the workpiece. The speed and direction of the spindle rotation can be adjusted using the speed change mechanism within the headstock. This adjustment allows the machinist to select the appropriate spindle speed for different materials and types of cutting operations. The headstock ensures that the workpiece is held securely and rotated precisely, providing a stable platform for the cutting tools to remove material efficiently and accurately.

Components of the Headstock:

• Main Spindle: The main spindle is the central part of the headstock. It holds the workpiece and rotates it during machining. The spindle is designed to accommodate various work-holding devices such as chucks, collets, and faceplates.
• Speed Change Mechanism: This mechanism allows the operator to change the spindle speed to suit different machining operations and materials. It can include a combination of gears, belts, and pulleys.
• Drive Motor: The drive motor provides the necessary power to rotate the spindle. The motor's power and speed are transferred to the spindle through the speed change mechanism.
• Spindle Bearings: These bearings support the spindle and ensure its smooth and precise rotation. High-quality bearings are essential for maintaining the accuracy and stability of the machining process.
• Chuck: A chuck is a work-holding device attached to the spindle. It grips the workpiece securely and can be adjusted to hold different sizes and shapes of workpieces.

Advantages:

• Provides precise control over the rotation of the workpiece, enabling accurate machining operations.
• Allows for the adjustment of spindle speed to match the requirements of different materials and cutting conditions.
• Ensures the workpiece is held securely, reducing the risk of slippage or movement during machining.
• Facilitates the use of various work-holding devices, increasing the versatility of the lathe machine.

Applications: The headstock's primary function is essential for various turning operations in manufacturing and metalworking industries. It is used in the production of cylindrical parts, such as shafts, bolts, and screws, as well as in the creation of intricate shapes and threads. The ability to rotate the workpiece at different speeds makes the headstock a vital component in both manual and CNC lathes.

Analysis of Other Options:

Option 1: To provide support for cutting tools during operation

The headstock does not provide support for cutting tools. Instead, this function is performed by the tool post and the carriage assembly. The tool post holds the cutting tools and allows for their precise positioning, while the carriage assembly moves the tool post along the length of the workpiece.

Option 2: To adjust the feed mechanism for thread-cutting

The feed mechanism for thread-cutting is controlled by the carriage and the lead screw, not the headstock. The carriage moves the cutting tool along the workpiece to create threads, and the lead screw ensures the accurate translation of the tool to produce the desired thread pitch.

Option 3: To control the movement of the carriage and tailstock

The movement of the carriage and tailstock is controlled by separate mechanisms. The carriage is moved along the bed of the lathe by the lead screw and feed rod, while the tailstock can be manually adjusted to support the end of the workpiece or to hold drilling tools.

In conclusion, the headstock's primary function in a lathe machine is to hold and rotate the workpiece at different speeds, making it an essential component for various machining operations. Other functions, such as supporting cutting tools, adjusting the feed mechanism for thread-cutting, and controlling the movement of the carriage and tailstock, are performed by different parts of the lathe machine.

Explanation:

Key Advantages of CNC Lathes in Turning Operations

Definition: Computer Numerical Control (CNC) lathes are advanced machining tools used in manufacturing to perform turning operations with high precision and automation. These machines are controlled by computer programs, allowing them to execute complex machining tasks with minimal human intervention.

Working Principle: CNC lathes operate based on a computer program that dictates the movements of the cutting tool and the workpiece. The program is created using CAD/CAM software and then loaded into the CNC machine. The machine's controller interprets the code and drives the motors to move the cutting tool along the specified paths, producing the desired shape on the workpiece.

Advantages:

• Higher Automation and Complex Machining Cycles: CNC lathes can perform highly automated operations, significantly reducing the need for manual intervention. This automation allows for complex machining cycles, including intricate geometries and multiple operations in a single setup, which are challenging or impossible with conventional lathes.
• Precision and Repeatability: CNC lathes offer exceptional precision and repeatability, ensuring consistent quality across multiple parts. The computer control eliminates human error, resulting in higher accuracy and fewer defects.
• Efficient Production: The automation and speed of CNC lathes lead to increased productivity and shorter production times. These machines can operate continuously, further enhancing efficiency and throughput.
• Flexibility: CNC lathes can be easily reprogrammed to produce different parts, making them highly versatile. This flexibility is particularly beneficial in industries with varying production needs and custom requirements.
• Reduced Labor Costs: With CNC lathes, fewer operators are needed to oversee the machining process. This reduction in labor costs, combined with increased efficiency, leads to significant cost savings for manufacturers.

Disadvantages:

• Initial Investment: CNC lathes require a substantial initial investment in machinery and software, which can be a barrier for small businesses. However, the long-term benefits often outweigh the initial costs.
• Maintenance and Repairs: CNC machines require regular maintenance to ensure optimal performance. Additionally, repairs can be complex and costly, necessitating specialized knowledge and tools.
• Programming Skills: Operating CNC lathes requires skilled programmers who can create and modify the machining programs. Training and retaining such skilled personnel can be challenging.

Applications: CNC lathes are widely used in various industries, including automotive, aerospace, medical device manufacturing, and precision engineering, where high precision and complex geometries are critical.

Analysis of Other Options:

Option 2: They are limited to simple machining operations.

This statement is incorrect. CNC lathes are capable of performing complex machining operations that are difficult or impossible to achieve with conventional lathes. The advanced computer control allows for intricate geometries, multi-axis movements, and complex cutting paths, making CNC lathes highly versatile and suitable for a wide range of applications.

Option 3: They are less accurate than conventional chucking machines.

This statement is incorrect. CNC lathes are generally more accurate than conventional chucking machines. The precision of CNC lathes is enhanced by computer control, which eliminates human error and ensures consistent quality. The repeatability of CNC lathes allows for the production of parts with tight tolerances and high precision, making them superior in accuracy compared to conventional machines.

Option 4: They rely mainly on mechanical devices for control.

This statement is incorrect. CNC lathes rely on computer control rather than mechanical devices for operation. The movements of the cutting tool and workpiece are dictated by a computer program, which provides precise control over the machining process. This digital control allows for greater flexibility, automation, and complexity in machining operations.

Important Information:

The key advantage of CNC lathes in turning operations lies in their ability to provide higher automation and complex machining cycles. This capability significantly enhances productivity, precision, and versatility in manufacturing processes. By leveraging computer control, CNC lathes overcome the limitations of conventional lathes, offering a range of benefits that include increased efficiency, reduced labor costs, and the ability to produce intricate and high-precision parts. While the initial investment and maintenance requirements may be higher, the long-term advantages make CNC lathes an essential tool in modern manufacturing industries.

Explanation:

Apron mechanism

It contains the mechanism for moving and controlling the carriage which is the feature of lathe that provides the method of holding and moving the tool.

The main parts of apron are:

• Traversing hand wheel
• Feed lever
• Feed selector
• Lead screw engagement lever

Important Points

Headstock 

• The headstock is the main body parts that are placed on the left side of the bed.
• The headstock supports the central spindle in the bearings and aligns it correctly.
• It supports the main spindle in the bearings and aligns it properly.
• It also houses a necessary transmission mechanism for different speeds.
• Accessories mounted to the headstock gear mechanism, driving pulley, spindle, etc.

Tailstock 

• The tailstock fits on the inner ways of the bed and can slide towards any position the headstock to fit the length of the workpiece.
• An optional taper turning attachment would be mounted to it.

The carriage holds the tools and provides movement of the tool in both cross and longitudinal directions.

Feed rod 

• It is a power transmission mechanism that provides precise longitudinal movement of the carriage.
• For turning the operation movement of the feed, the rod is mandatory.
• In some lathes feed may not be available and lead screw serves the purpose of the feed rod.

• Cross slide in a lathe moves perpendicular to the axis of rotation.
• Apron gives horizontal feed in a lathe machine.

Explanation:

Three Jaw Chuck:

• It is also known as three jaws universal chuck, self-centering chuck, and concentric chuck having three jaws that work at the same time.
• The 3 jaws, which are generally made of high-quality steel, are arrogated at an angle of 120° to each other. During the operation, the jaw teeth are made to mesh with scrawl spiral teeth (Bevel’s teeth).
• The meshing causes a moment of all 3 jaws either towards or away from the chuck center, depending upon the direction of rotation of the bevel pinion.
• Three jaw chucks are used to hold only perfect round and regular jobs, workpieces of circular and hexagonal shapes.

Face Plate:

• It is a circular plate threaded at its center with plain and T-slots which are machined rapidly.
• It is fitted to the lathe spindle with its central threaded portion.
• The job on the workpiece is held by the faceplate using bolts and clamps in the slots.
• The faceplate is suitable to hold both regular and irregular shaped workpieces, which cannot help conveniently by chucks or on centers.

Four Jaw Chuck:

• The four-jaw chuck is also called an independent chuck since each jaw can be adjusted independently.
• Four jaw chucks are used for a wide range of regular and irregular shapes.

Explanation:

Centre Lathe → Knurling

Milling → Slotting

Grinding → Dressing

Drilling → Counter-boring

Knurling

Knurling is the operation of producing a straight-lined, diamond-shaped pattern or cross lined pattern on a cylindrical external surface by pressing a tool called knurling tool. Knurling is not a cutting operation but it is a forming operation.

A lathe is used for many operations such as turning, threading, facing, grooving, Knurling, Chamfering, centre drilling

Counter - boring

Counter - boring is an operation of enlarging a hole to a given depth, to house heads of socket heads or cap screws with the help of a counterbore tool.

Dressing:

When the sharpness of grinding wheel becomes dull because of glazing and loading, dulled grains and chips are removed (crushed or fallen) with a proper dressing tool to make sharp cutting edges.

The dressing is the operation of cleaning and restoring the sharpness of the wheel face that has become dull or has lost some of its cutting ability because of loading and glazing.

Slot Milling:

Slot milling is an operation of producing slots like T - slots, plain slots, dovetail slots etc.

Explanation:

The swing and distance between centers define the capacity of a lathe.

Specification of Lathe

• The length between the centers → this expresses the maximum length of job that can be mounted between the lathe centers ie.e between head stock and tail stock.
• The length of the bed → gives the approximate floor area that the lathe can occupy.
• The height of the centers → is measured from the lathe bed.
• The maximum diameter → is the diameter of the work or bar that may pass through the hole of the headstock spindle.
• The swing diameter of the bed → indicates the maximum diameter of the work that may revolve over the bed ways.
• The swing diameter over carriage → indicates the maximum diameter of the work that may rotate over the saddle. This is normally less than the swing diameter over the bed.

​

Explanation:

Capstan Lathe:

• This is also known as a ram-type lathe. It consists of a hexagonal turret on a ram that slides longitudinally on a saddle positioned and clamped on the lathe bed ways.
• This type of machine is light in construction and suitable for the machining bars of small diameter.
• The tools are mounted on all the faces of the turret (commonly square or hexagonal).
• The saddle movement is suitably controlled in such a way that the saddle need not be moved back and forth appreciably to bring the tool to a cutting position.
• When the ram is moved back a little and then moved forward, the next tool indexes automatically for the next operation.

Concept:

A lathe is a machine tool that holds the job in between the center and base and rotates the job on its own axis.

Main parts of Lathe:

The carriage has the following five major parts:

Saddle: It is an H–shaped casting fitted over the bed. It moves along the guideways.

Cross–Slide: It carries the compound slide and tool post. It can be moved by power or by hand.

Compound rest: It is marked in degrees. It is used to support the tool post and the cutting tool. It is used during taper turning to set the tool for angular cuts.

Tool Post: The tool is clamped on the tool post.

Concept:

Set over = L × \(\rm \frac{D-d}{2l}\) and K = \(\rm \frac{D-d}{l}\)

Where, K is taper ratio, D = large diameter, d = small diameter, L = length of work, l =  Taper length

Calculation:

Given:

 L = length of work, 1:50 is the taper ratio.

we know that, Set over = L × \(\rm \frac{D-d}{2l}\) and K = \(\rm \frac{D-d}{l}\)

∴ Set-over = L × \(\rm \frac{K}{2}\)

It is given that, taper is 1 ∶ 50. It mearns,

K = \(\rm \frac{1}{50}\)

∴ Set-over = \(\rm \frac{200\times \frac{1}{50}}{2}\) = 2 mm

Additional Information

Set-over on lathe

• Work-piece that can be set up between centres (live and dead centre) can be tapered externally by setting the tailstock of the lathe off-centre.
• If the live centre and the dead centre of the machine are set-over (out of alignment), a turned work-piece will be tapered.
• Work-piece turned will have a taper proportional to the amount of the set-over.
• The method is applicable only to long tapers on long work-pieces.
• But if the work is not too short and if the dead centre is carefully set over very accurate results are obtainable.

Explanation:

lathe chuck:

• A lathe chuck is a holding device which is used for holding the job firmly against the cutting tool.

There are two types of chuck:

Four Jaw Chuck:

• The four-jaw chuck is also called an independent chuck since each jaw can be adjusted independently.
• Four jaw chucks are used for a wide range of regular and irregular shapes.
• A work can be trued to within 0.02 mm accuracy, using this chuck.
• This type of chuck is much more heavily constructed than the self-centering chuck, and has much greater holding power.
• Each jaw is moved independently by a square thread screw.
• The jaws are reversible for holding large diameter jobs.
• The independent four-jaw chuck has four jaws each working independently of the others in its own slot in the chuck body and actuated by its own separate square threaded screw.
• By suitable adjustment of the jaws, a workpiece can be set to run either true or eccentric with the machine centre.
• Finished jobs when held in a four-jaw chuck can be trued with the help of a dial test indicator.

Three Jaw Chuck:

• It is also known as three jaws universal chuck, self-centring chuck and concentric chuck having three jaws which work at the same time.
• Three jaw chucks are used to hold only perfect round and regular jobs

Concept:

Offset in tailstock is given by;

\(sin\frac{α}{2}=\frac{S}{L_w}\)

where, S = Tail offset, α = Taper angle, L_w = workpiece length,

Calculation:

Given:

α = 60°, Lw = 1 m,

\(sin(\frac{60}{2})=\frac{S}{1}\)

S = 1 × sin 30° 

S = 1 sin 30° 

Velocity (V) = ΠDN

Where D is diameter of object

N is spindle speed in revolution per minute

By turning operation diameter of object decreases i.e. cutting velocity decreases.

Chattering is too and fro motion of cutting tool during their operation. Chattering force is directly proportion to the cutting velocity. Since cutting velocity decreases therefore chattering reduces.