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

Explanation:

The centre lathe is the most common of the lathes, which derives its name from the way a workpiece is clamped by centres in a lathe.

This is sometimes also called engine lathe because early lathes were driven by steam engines.

This is generally used for more general application.

Engine lathe can feed the cutting tool both in the cross and longitudinal directions with reference to lathe axis, with the help of carriage, feed rod and lead screw.

The machining operations generally carried out in centre lathes are:

• Facing
• Cantering
• Rough and finish turning
• Chamfering, shouldering, grooving, recessing etc
• Axial drilling and reaming by holding the cutting tool in the tailstock barrel
• Taper turning
• Boring (internal turning): straight and taper
• Forming: external and internal
• Cutting helical threads: external and internal
• Parting off
• Knurling

Explanation:

Shaper Machine: It is a reciprocating type of machine tool used for producing flat surfaces, which may be horizontal, vertical or inclined. Sometimes irregular or curved surfaces are also produced by shapers. In shaping, the tool is given a reciprocating motion. It is generally not used as a production machine. But widely used in the machine shops and tool rooms since it is very easy to set up and operate.

Advantages of a shaper machine

• A comparatively lighter and cheaper machine.
• Requires less floor area.
• Tool reciprocates horizontally and has a definite stopping point.
• Work is stationary during cutting.
• Clamping of work is simple, quick and easy.

Disadvantage

• Usually, one tool is used on a shaper.
• Cutting speed is low
• Very heavy cuts and coarse feeds cannot be employed.
• Used for machining small size workpieces comparatively

Explanation:

Turret Lathes:

• Turret lathes are capable of performing multiple cutting operations, such as turning, boring, drilling, thread cutting, and facing on the same workpieces.
• But Turret lathe is not used for broaching operation.
• Several cutting tools are mounted on the hexagonal main turret, which is rotated for each specific cutting operation.
• The lathe usually has a square on the cross slide, with as many as four cutting tools mounted on it.
• The workpiece, generally a long round rod, is advanced a preset distance through the chuck.
• After the parts are machined, it cut off by a tool mounted on the square turret which moves radially into the workpiece.
• The rod is then advanced the same present distance into the work area and the next parts machined.
• Turret lathes (bar type or bucking type) are versatile and operations may be carried out either by hand, using the Turnstile (Capstain wheel), or automatically set up properly by a setup person, these machines do not require highly skilled operations.
• The turret lathe is also known as a ram-type turret lathe, one in which the ram turret lathe, one in which the ram slides in a spate base on the saddle.
• The sort stroke of the turret slides this machine to relatively short workpieces and light cuts in both small and medium quantity production.
• In another style, called saddle type, the main turret is installed directly on the saddle, which slides directly on the bed.
• The length of the stroke is limited only by the length of the bed.
• This type of lathe is more heavily constructed and is used to machine large workpieces.
• Because of the heavyweight of the components, saddle-type lathe operations are slower than ram-type lathe operations.
• Vertical turret lathes are also short, heavy, workpieces with diameters as large as 102m.
• Turret lathe can be tape controlled using Numerical controlled lathes.

Broaching (Slotting):

• Broaching (Slotting) is a machining process in which a keyway or a profile is created by cutting movements on the Z-axis.
• The cutting depth is determined with movements of the X-axis.
• With the working stroke on the Z-axis, the material is removed depending on the cutting depth.
• The return movement is an idle stroke where no material is removed because there is only one cutting direction

• Lathe centre is a lathe accessory which is used to support lengthy jobs to carry out lathe operations
• Lathe centres are generally made of high carbon steel which is hardened, tempered and ground
• The centre which is accommodated in the main spindle sleeve is known as the ‘live sleeve’ and the centre fixed in the tailstock spindle is known as the ‘dead centre’
• In construction, both centres are identical, made as one unit that consists of a conical point of 60° included angle, a body provided with a Morse taper shank and a tang
• The dead centre is made out of high carbon steel, hardened and ground whereas the live centre need not have its conical tip hardened as it revolves with the work
• A good lubricant should be used for the dead centre

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 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:

• It gives the approximate floor area that the lathe can occupy.

The height of the centers: 

• It is measured from the lathe bed.

The maximum diameter: 

• It is the diameter of the work or bar that may pass through the hole of the headstock spindle.

The swing diameter of the bed: 

• It indicates the maximum diameter of the work that may revolve over the bed ways.

The swing diameter over carriage: 

• It 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:

Bench vice:

• A bench vice is a work-holding device used to hold work for operations such as sawing, filing, chipping, tapping, threading, etc.
• Vices have two parallel jaws, one fixed and the other movable, threaded in and out by a screw and lever.
• The size is indicated by the width of the jaw.

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 Acme thread :

• This thread is a modification of the square thread.
• It has an included angle of 29°
• Acme threads are used in lathe lead screws and brass valves etc. 

Buttress Thread: 

• In this thread, one flank is perpendicular to the axis of the thread and another flank is at 45°. These threads are used in power presses, carpentry vices, bench vice and gun breeches, ratchets etc.
• They are generally used in bench vice as they withstand heavy loads in one direction and still unscrew easily in the opposite direction as they are designed specifically to withstand extreme axial thrust in one direction.

Square thread :

• In this thread, the flanks are perpendicular to the axis of the thread
• Square threads are used for transmitting motion or power
• Eg. screw jack, vice handles, cross-slide and compound slide, activating screwed shafts

Concept:

The bed is the base or foundation of the lathe. It is massive (heavy) and rigid casting made in one piece to resist deflection and vibrations.

It holds or supports all other parts, that is, headstock, tailstock, and carriage, etc.

Explanation:

• A lathe is a machine tool on which surfaces of revolution can be produced.
• Generally, the workpiece rotates, and the cutter moves relative to the workpiece.

• A lathe is a machine tool that holds the job in between the centre and rotates the job on its own axis.
• Due to this quality of holding the job from the centre and rotating the job, it is called the centre lathe.
• There are different types of the lathe:
  • Speed lathe
  • Engine lathe or Centre lathe
  • Bench lathe
  • Toolroom lathe
  • Capstan and turret lathe
  • Special purpose lathe
  • Automatic lathe
  • CNC machine
  • Precision Lathe

Capstan and turret lathe:

• These are developed from engine lathe, used for production work.
• The tailstock of an engine lathe is replaced by a hexagonal turret where a number of tools can be mounted.
• A number of identical parts can be produced in a minimum time.
• The capstan and turret lathe machine is used for Mass production (large Quantity) and is a modified version of the engine lathe machine.

​Bench Lathe:

• It is so small that it can be mounted on a bench.
• It is used for small and precise work.

Speed lathe:

• The spindle of a speed lathe operates at very high speeds (approximately at a range of 1200 to 3600 rpm) and so it is named so.
• It consists of a headstock, a tailstock, a bed and a tool slide only. Parts like a lead screw, feed rod and apron are not found in this type of lathe.
• The wood lathe is the type of speed lathe.

​Engine lathe:

• It is the most common type of lathe and is widely used in workshop.

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;

\(V = \frac{{{\rm{NL\;}}\left( {1{\rm{\;}} + {\rm{\;m}}} \right)}}{{1000}}\;m/min\)

where

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

m = Quick return ratio = \(\frac{{{\rm{Time\;of\;return\;stroke}}}}{{{\rm{Time\;of\;cutting\;stroke}}}}\)

Given:

  \(C=\frac{{Cutting~time}}{{Total~time}}=\frac{{Cutting~time}}{{Return~time\;+\;Cutting~time}}\)

\(\frac{{1}}{{C}}=\frac{{Cutting~time\;+\;Return~time}}{{Cuttting~time}}=1+m\)

\(\therefore V = \frac{{{\rm{NL\;}}\left( {1{\rm{\;}} + {\rm{\;m}}} \right)}}{{1000}}=\frac{{NL}}{{1000C}}\) m/min.