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

Explanation:

Special-Purpose Lathe:

• A special-purpose lathe is designed for specific machining applications that cannot be efficiently performed using standard lathes. These machines are tailored for specialized tasks, offering enhanced precision, productivity, and functionality in handling unique or heavy-duty machining requirements. Among the various types of special-purpose lathes, a wheel lathe stands out for heavy-duty applications, particularly in machining railway components like wheels, journals, and treads.

Key Features of Wheel Lathes:

• Heavy-Duty Design: Wheel lathes are robust and designed to machine large, heavy components, ensuring stability and precision during operation.
• Specialized Machining: They are equipped with tools and features specifically for machining railway wheels, including their journals and treads.
• Precision and Efficiency: These lathes ensure accurate machining of components, which is critical for the safe operation of railway systems.
• Automated Functions: Many modern wheel lathes come with automation features for enhanced productivity and reduced manual intervention.

Applications:

• Machining railway wheels to maintain dimensional accuracy and surface finish.
• Repairing worn-out journals and treads of railway wheels.
• Ensuring the safety and reliability of railway components by maintaining strict tolerances.

Explanation:

Lead Screw Engagement in a Lathe:

• A lead screw is a critical component in a lathe machine, primarily used for transmitting motion to the carriage during machining operations. Its engagement depends on the type of operation being performed. The lead screw is specifically utilized during thread-cutting operations to ensure precise and synchronized motion between the workpiece and the cutting tool. This synchronization is essential for creating accurate threads with consistent pitch.
• In a lathe, the lead screw is engaged by a mechanism called the half-nut, which locks onto the lead screw and allows the carriage to move at the same rate as the rotation of the spindle. This precise movement ensures that the cutting tool traces the desired helical path on the workpiece, which is a fundamental requirement for thread cutting.

Why is the Lead Screw Only Used for Thread-Cutting Operations?

• The lead screw is designed with a specific pitch and thread profile that matches the requirements of thread-cutting operations. Unlike the feed rod, which is used for general-purpose feeding of the carriage during turning, facing, or knurling operations, the lead screw ensures the exact pitch of the thread being cut. Using the lead screw for other operations, such as turning or facing, would result in excessive wear and tear on this critical component, as it is not designed for continuous or general-purpose motion transmission.

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:

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:

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:

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.

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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.