Machine Tools MCQ Quiz - Objective Question with Answer for Machine Tools - 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:

Broaching Operation

• Broaching is a machining process that uses a toothed tool, called a broach, to remove material. There are two main types of broaching: linear and rotary. In both processes, the broach is used to machine internal holes, splines, keyways, or other shapes in a workpiece.
• In a broaching operation, the broach is drawn or pushed through the workpiece to shape or enlarge a hole. The broach has a series of progressively larger teeth that cut the material in a single pass, producing a precise and smooth finish. The operation can be performed on a broaching machine, which is specifically designed for this purpose.
• In internal broaching operations, the broach is typically pulled through the workpiece using a puller. The pilot is a cylindrical portion at the front of the broach that helps in aligning and guiding the tool through the hole before the cutting teeth engage. The puller attaches to the pilot to draw the broach through the component, ensuring proper orientation and control during the cutting process.

Applications: Broaching is widely used in industries such as automotive, aerospace, and manufacturing to produce internal gears, keyways, splines, and other precise shapes.

Explanation:

The correct option is option 4, which states that pairs (ii) and (iii) are correctly matched. To understand why this is the case, let's delve into each pair and analyze them thoroughly:

(i) Drill press: Trepanning

A drill press is a tool used for drilling holes in various materials. Trepanning, on the other hand, is a specific type of drilling operation that involves cutting a hole by removing a disk-shaped piece from the workpiece rather than drilling out the entire hole. Trepanning is typically used for creating large diameter holes that are not practical to drill using conventional drilling techniques.

While trepanning can be performed on a drill press, it is not exclusively associated with drill presses. Trepanning is a distinct process that can be carried out using various types of machinery, including lathes and specialized trepanning machines. Therefore, the statement that "Drill press: Trepanning" is not entirely accurate, as it implies an exclusive association that does not exist.

(ii) Centreless grinding: Through feeding

Centreless grinding is a machining process that removes material from the outside diameter of a workpiece using abrasive cutting. In centreless grinding, the workpiece is supported by a blade and rotated by a regulating wheel while being ground by a grinding wheel. Through feeding is a method used in centreless grinding where the workpiece is fed continuously through the grinding wheels, allowing for the grinding of long workpieces or producing high volumes of parts.

This pair is correctly matched because through feeding is a common method used in centreless grinding operations.

(iii) Capstan lathe: Ram type turret

A capstan lathe is a type of lathe used for repetitive production of small and medium-sized parts. One of the defining features of a capstan lathe is the turret, which holds multiple cutting tools and can be rotated to bring each tool into position for machining operations. The ram type turret is a specific type of turret used in capstan lathes, where the turret is mounted on a ram that can slide longitudinally, allowing for rapid tool changes and efficient machining.

This pair is correctly matched because capstan lathes typically use ram type turrets for holding and changing tools.

Important Information:

Now that we have established why option 4 is the correct answer, let's briefly analyze the other options to understand why they are incorrect:

• Option 1: This option states that pairs (i) and (ii) are correctly matched. However, as we discussed, pair (i) is not entirely accurate, making this option incorrect.
• Option 2: This option states that pairs (i), (ii), and (iii) are correctly matched. While pairs (ii) and (iii) are correct, pair (i) is not, making this option incorrect.
• Option 3: This option states that pairs (i) and (iii) are correctly matched. While pair (iii) is correct, pair (i) is not, making this option incorrect.
• Option 5: This option does not specify any pairs, making it irrelevant to the question.

In conclusion, the correct option is option 4, which accurately identifies the correctly matched pairs (ii) and (iii). Understanding the principles and applications of various machining processes is essential for selecting the appropriate tools and techniques for specific tasks, and this knowledge can greatly enhance efficiency and productivity in manufacturing operations.

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.

Concept:

Cutting speed of shaper is given by,

 $V=\frac{\mathrm{N}\mathrm{L}\left(1+\mathrm{m}\right)}{1000}m/min$

Where, V = Cutting speed of shaper, N = Number of double stroke per minute, L = l ength of stroke

m = Quick return ratio = $\frac{\mathrm{T}\mathrm{i}\mathrm{m}\mathrm{e}\mathrm{o}\mathrm{f}\mathrm{r}\mathrm{e}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{n}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{k}\mathrm{e}}{\mathrm{T}\mathrm{i}\mathrm{m}\mathrm{e}\mathrm{o}\mathrm{f}\mathrm{c}\mathrm{u}\mathrm{t}\mathrm{t}\mathrm{i}\mathrm{n}\mathrm{g}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{k}\mathrm{e}}$

Given:

Calculation:

N = 40, L = 240 mm

m = $\frac{2}{3}$= 0.667

$V=\frac{\mathrm{N}\mathrm{L}\left(1+\mathrm{m}\right)}{1000}m/min$

$V=\frac{40\times 240\times \left(1+0.667\right)}{1000}$

= 16 m/min

Explanation:-

Clearance angle (γ):

• The angle of inclination of clearance or flank surface from the finished surface.
• The clearance angle is essentially provided to avoid rubbing of the tool (flank) with the machined surface which causes loss of energy and damages to both the tool and the job surface.
• Clearance angle is a must and must be positive (3° - 15°)  depending upon tool-work materials.

Important Points

Rake angle (α):

• The angle of inclination of the rake surface from the reference plane.
• Rake angle is provided for ease of chip flow and overall machining. Rake angle may be positive, or negative, or even zero.
  • Positive rake – helps reduce cutting force and thus cutting power requirements.
  • Negative rake – to increase edge-strength and life of the tool
  • Zero rake – to simplify the design and manufacture of the form tools. Clearance angle is essentially provided to avoid rubbing of the tool (flank)

Explanation:

Cutting speed in a shaper is the average linear speed of the tool (m/min) during the cutting stroke. It depends on the number of ram strokes per minute and the stroke length.

Cutting speed of shaper is given by;

$V=\frac{\mathrm{N}\mathrm{L}\left(1+\mathrm{m}\right)}{1000}m/min$

where

V = Cutting speed of shaper, N = Number of double stroke per minute, L = length of stroke

m = Quick return ratio = $\frac{\mathrm{T}\mathrm{i}\mathrm{m}\mathrm{e}\mathrm{o}\mathrm{f}\mathrm{r}\mathrm{e}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{n}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{k}\mathrm{e}}{\mathrm{T}\mathrm{i}\mathrm{m}\mathrm{e}\mathrm{o}\mathrm{f}\mathrm{c}\mathrm{u}\mathrm{t}\mathrm{t}\mathrm{i}\mathrm{n}\mathrm{g}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{k}\mathrm{e}}$

Given:

  $C=\frac{Cuttingtime}{Totaltime}=\frac{Cuttingtime}{Returntime+Cuttingtime}$

$\frac{1}{C}=\frac{Cuttingtime+Returntime}{Cutttingtime}=1+m$

$\therefore V=\frac{\mathrm{N}\mathrm{L}\left(1+\mathrm{m}\right)}{1000}=\frac{NL}{1000C}$ m/min.

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:

Cutting tools may be classified according to the number of major cutting edges (points) involved as follows:

• Single point Tools (One dominant cutting edge): e.g., turning tools, shaping, cutoff/parting tool, planning and slotting tools and boring tools
• Multiple Cutting Edge Tools (More than one cutting edge): e.g., Drill, milling cutters, broaching tools, hobs, gear shaping cutters, grinding wheel, Hacksaw Blade. 

Turning

• Turning is an operation which reduces the diameter of a workpiece to a desired dimension and length of the workpiece remains the same.
• Turning is done with the help of single-point cutting tool.

Important Points

Milling is a process of producing flat and complex shapes with the use of a multi-point (or multi-tooth) cutting tool.

A drill is a multipoint cutting tool used for making the cylindrical holes of definite diameters.

Broaching is a machining process for removal of a layer of material of desired width and depth usually in one stroke by a slender rod or bar type cutter having a series of cutting edges with gradually increased protrusion. 

Explanation:

Lathe accessories:

• Lathe accessories are used for supporting the work or holding the tool.
• They include lathe centres, catch plates, collet chucks, face-plates, angle plates, mandrels.

Chucks:

• Chucks are the most important device for holding a workpiece in a lathe.
• Following are some of the most important types of chucks and work holding devices:

Explanation:

• Vices are used for holding the work-pieces. They are available in different types.
• The vice used for bench work is the bench vice or called Engineer’s vice.
• A bench vice is made of cast iron or cast steel and it is used to hold or clamp work for filing, sawing, threading and other hand operations. 
• The size of the vice is stated by the width of the jaws. e.g. 150 mm parallel jaw bench vice

Clamping devices

• In jigs and fixtures, the workpiece or blank has to be strongly and rigidly clamped against the supporting surface and also the locating features so that the blank does not get displaced at all under the cutting forces during machining.
• A clamp is a device that holds the workpiece firmly against the locators provided and also resists all the force generated by the cutting action of the tool on the workpiece.
• The most common example of a clamp is the bench vice, where the movable jaw of the vice exerts a force on the workpiece thereby holding it in the correct location in the fixed jaw of the vice.
• A clamping device ensures proper location and centering of the workpiece.

Basic requirements of clamping devices

1. To force the workpiece to remain in firm contact with locating pins or surfaces.
2. To rigidly hold the workpiece in a jig or fixture against all forces.
3. To exert just sufficient pressure on the workpiece.
4. To not damage the workpiece it holds.