Lathe Machine MCQ Quiz in తెలుగు - Objective Question with Answer for Lathe Machine - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Concept:

When the diameter of the bar either increases or decreases along the length of the bar then it is called a taper.

This operation is performed on a lathe machine with the help of a taper-turning attachment.

The formula for taper angle α is

\(\tanα = \frac{{D \ - \ d}}{2L}\)

where, α = taper angle, D = large diameter of the bar, d = small diameter of the bar, L = length of the bar.

The amount of taper is given by,

\(Taper = \frac{{D \ - \ d}}{L}\)

Calculation: 

Given: 

D = 80 mm, d = 70 mm, tan α = 1/20

\(\frac{1}{{20}} = \frac{{80 \;-\; 70}}{{L}}\)

L = (80 - 70) × 20

L = 10 × 20

L = 200 mm

Hence the length of the workpiece will be 200 mm.

Explanation:

Jobs requiring no support from the tailstock are usually mounted in the following ways:

• Three-jaw self-centring chuck.
• Four-jaw independent chuck.
• Face-plate.
• Jigs and fixtures.

Three-jaw	Four-jaw
Pre-machined round bars are quickly and co-axially fitted in the three-jaw chuck by simultaneously moving the three jaws radially by rotating the scroll (disc with radial thread) using a key.	They are available in various sizes and are generally used for strongly holding non-circular bars both with and without pre-machining at the gripping portion. The jaws are moved radially and independently by rotating the corresponding screws.
The depth of the cut is comparatively less.	More depth of cut can be given.
Work-piece cannot be set for eccentric turning.	Work-piece can be set for eccentric turning.
3-jaw chuck centring accuracy is lower.	4-jaw chuck centring accuracy better than 3-jaw chuck.
Less gripping power.	More gripping power.
Setting up of work is simple.	Setting up of work is complex.
Heavier jobs cannot be turned.	Heavier jobs can be turned.

Face-plate:

For turning, facing, boring, threading, and similar operations, jobs of odd shape and size are usually mounted on a large face-plate (instead of the chuck) which is fitted on a spindle nose. The job maybe-

• directly clamped on the face-plate.
• in a fixture which is clamped on the face-plate.

The carriage is the part of the lathe which slides over the bed-ways between the head stock and the tail stock.

It provides various movements for the cutting tool manually as well as by power feed.

The carriage can be locked on the bed at any desired position by tightening the carriage lock screw.

The carriage consists of the following parts:

• Saddle
• Cross – slide
• Compound rest swivel and top slide
• Tool post
• Apron

Saddle: It is a 'H' shaped casting having 'V' guide grooves at the bottom face, corresponding to the lathe bed-ways for mounting on the lathe bed and for sliding.

Cross Slide: The cross-slide is mounted on the top of the saddle, and it provides cross movement for the tool. This is fitted at right angles to the bed and is moved by means of a screwed spindle, fitted with a handle.

Compound rest: The compound rest is fitted on the top and to the front of the cross-slide. The compound rest can be swivelled horizontally through 360°.

Apron: The apron is bolted to the front of the saddle. It contains mechanism for moving and controlling the carriage.

Tool Post: The tool post holds the tool meant for the operation to be performed on the work. The tool post is assembled to the top slide.

The tool is provided with the following three movements by the carriage.

• Longitudinal feed – with the help of the carriage movement (parallel to the axis of work)
• Cross feed – with the help of the cross-slide movement (perpendicular to the axis of the work)
• Angular feed – With the help of the compound slide movement positioned at an angle to the axis of the work.

Concept:

Speed of lead screw = \(\frac {Pitch~ of Metric ~thread}{Pitch ~of ~lead ~screw}\times Spindle ~Speed\)

Calculation:

Pitch = 2 mm

Lead screw pitch = 6 mm

Spindle speed = 60 rpm

In one rotation of lead, it should advance 2 mm.

Fraction of revolution in one rotation of spindle \( = \frac{{2}}{{6}}\)

RPM of lead screw \( = \frac{{2}}{{6}} \times 60 = 20\;rpm\)

Alternate Solution

Pitch of thread, Pt = 2 mm

Speed of spindle, Nt = 60 rpm

Pitch of screw (Ps) = 6 mm

Now Ns × Ps × Z = Nt × Pt × Zt

Ns × 6 × 1 = 60 × 2 × 1

Concept:

Contour turning:

• In this operation of the lathe machine, the tool is not feed in a straight path.
• Instead, the tool follows a contour, a contoured form is created in the turned part.

Taper turning:

• The turning operation used for producing the taper on the cylindrical component is called a taper turning operation.

Facing:

• The turning operation used for reducing the length of the component is called the face turning operation.
• Facing is mostly used to finish the edges in necklines, armholes, hems, and openings. They are also used widely in all other sewings like quilts and home decor items like curtain hems.
• Shaped facings are cut to match the outside shape of the piece to provide a neat finish, and are often cut from the same pattern pieces.

Form Turning:

• It is a method of taper turning in which a broad nose tool having a straight cutting edge is set on to the work at half taper angle and is feed straight into the work to generate a tapered surface.
• With this method, tapers of only short lengths can be turned.

Concept:

Lathe: In a lathe, a work-piece is held in a chuck or between centers and rotated about its axis at a uniform speed.

The cutting tool held in tool post is fed into the work-piece for desired depth and in desired direction:

Parts of lathe:

• Bed
• Headstock
• Tailstock
• Carriage
• Feed mechanism

An accurate lathe in India is identified as Grade I. 

Concept:

When the diameter of the bar either increases or decreases along the length of the bar then it is called a taper.

This operation is performed on a lathe machine with the help of a taper-turning attachment.

The formula for taper angle α is

\(\tanα = \frac{{D \ - \ d}}{2L}\)

where, α = taper angle, D = large diameter of the bar, d = small diameter of the bar, L = length of the bar.

The amount of taper is given by,

\(Taper = \frac{{D \ - \ d}}{L}\)

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

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.

Apron: It is attached to the saddle and hangs in front of the bed. It has gears, levers, and clutches for moving the carriage with the lead screw for thread cutting.

Explanation:-

The lead screw is used to move the carriage automatically during threading.

• The lead screw is a long threaded shaft used as a master screw.
• It is brought into operation during thread cutting to move the carriage to a calculated distance
• Mostly lead screws are acme threaded.

Important Points

The bed is mounted on the legs of the lathe which are bolted to the floor.

• It is made of cast iron and its top surface is machined accurately and precisely.

The feed rod is placed parallel to the lead screw on the front side of the bed.

• It is a long shaft which has a keyway along its length,

The carriage handwheel is used to manually position and/or hand feed the carriage in the longitudinal or  axis.

Explanation:

Lathe Accessories:

Lathe accessories are devices used for holding or supporting a job on a lathe during machining. These include lathe center, faceplate, dog-carrier, chucks, angle plate, mandrel, etc.

The lathe center

• It is used for turning jobs between the centers.
• The center which is fitted in the spindle nose and which revolves with the job is called the live center.
• The one which is fitted with tailstock is called dead center as it does not revolve with the job.
• The job is held between two lathe centers and can be tightened or loosened by advancing or retreating the dead center by revolving the tailstock handwheel.
• Some of its types are mentioned below:

Ordinary center:

• The ordinary center is used for general purpose turning with included angle 60° for light work and 90° for heavy work.

Ball center:

• The ball center is employed for taper turning with a tail-stock set-over method to minimize wear and strain on centers.

Revolving center:

• The revolving center is used in the tailstock for supporting a heavy job revolving at high speed and wherein this center (unlike dead center) revolves with the job.