74 Questions
What is the main function of a lathe machine?
To remove material from a work piece
Who is credited with designing the first screw cutting lathe?
Henry Maudslay
Which type of lathe is most common for ergonomic conveniences?
Horizontal lathe
What material is removed from the work piece in the form of chips during turning on a lathe machine?
Chips
Which type of lathe occupies less floor space?
Vertical lathe
In which year did Henry Maudslay design the first screw cutting lathe?
1797
What is the part of the carriage hanging in front of the bed called?
Apron
Which movement is achieved by moving the cross slide on a lathe?
Cross feed
What is the purpose of the lead screw in a lathe?
Cutting threads
Which mechanism is used to vary the feed rate for both turning and threading on a lathe?
Gear quadrant in FGB
What motion allows the tool to move axially for longitudinal feed on a lathe?
Feed motion
Which part is engaged with the rotating lead screw to cause travel of the carriage during threading on a lathe?
Half nuts
What is used to shift the tailstock along the lathe bed when required?
Clamping bolt
What part is connected to the small end of the cone pulley in a back geared headstock?
Pinion gear P1
What motion is attained by rotating the job in a lathe?
Cutting motion
What part is used to move the carriage or cross-slide for various operations in a lathe?
Feed rod
What is the purpose of a capstan lathe?
Performing specific operations repeatedly over a long time
Which type of lathe is most versatile and commonly used for medium duty work?
Medium duty lathe
What is the main function of the tailstock on a centre lathe?
Supporting the end of the workpiece and holding tools
Which part of a centre lathe moves in a direction parallel to the lathe axis?
Saddle
In terms of precision, which type of lathe is meant for high accuracy and finish?
Precision lathe
What distinguishes a bar type lathe from a chucking type lathe?
Bar type lathes handle slender rod-like jobs, while chucking type lathes handle disc-type jobs.
Which type of automation is considered modern in lathes?
Flexible automation
What distinguishes single spindle lathes from multi-spindle lathes?
Single spindle lathes have one spindle, while multi-spindle lathes have multiple spindles.
On a center lathe, what is the function of the carriage?
Giving various movements to the tool by hand or power
What does the compound rest on a center lathe carry?
Compound slide and swivel plate
What is the purpose of back gears B1 and B2 in the lathe mechanism described?
To further reduce the spindle speed
Why is the all geared headstock preferred in modern lathes?
Because it eliminates the need for belt shifting
In the context of feed mechanisms, what is the purpose of the tumbler gear reversing mechanism?
To change the direction of lead screw and feed rod
How does changing the position of the lever in the tumbler gear reversing mechanism affect the direction of movement of the carriage?
Reverses the direction of movement
What is one advantage of using a cone pulley mechanism in lathes?
Provides a wider range of spindle speeds
Why are gears G4, G5, and G6 on the all geared headstock mounted on an intermediate shaft and cannot be moved axially?
To ensure they mesh with G1, G2, and G3 individually
What happens when back gear is engaged in lathe operations?
The speed of the spindle is reduced
Why does the all geared headstock mechanism result in almost constant power available at the tool for all spindle speeds?
Because power is transmitted through a splined shaft
In a lathe, what does engaging back gears do to the power flow in the mechanism?
Reduces power flow from P1 to B1
What purpose does the lock pin serve when locking the step cone pulley with the main spindle?
Prevents slipping between cone pulley and spindle
What is the purpose of a quick-change gearbox in a lathe?
To obtain various power feeds in the lathe
How many different speeds can Shaft C receive in a lathe equipped with a quick-change gearbox?
36
In which mechanism is power transmitted from the feed rod to the worm wheel?
Apron mechanism
What is the function of the splined shaft in a lathe's apron mechanism?
To always be engaged with gears F and G
How are various speeds obtained in a tumbler gear quick-change gearbox?
By sliding the sliding gear to different positions and engaging the tumbler gear
What happens when the feed check knob 'E' is in a neutral position in an apron mechanism?
Hand feed is given
How does the carriage move towards the tailstock?
By disconnecting the engagement of tumbler gears with the spindle gear
Which shaft is connected to lead screw by a clutch and feed rod by a gear train in a lathe?
'C' shaft
What is the function of Shaft B in a lathe equipped with a quick-change gearbox?
To receive different speeds from Shaft A by sliding gear
How are various power feeds obtained in a lathe equipped with a quick-change gearbox?
By transmitting power from spindle to feed shaft through tumbler gear
What material is used to manufacture forged cutting tools?
High carbon steel
How are ceramic inserts in tool holders fastened?
By clamping using a bolt
In precision boring on a center lathe, where is the tool fitted?
On the tailstock quill
Which method is used to attach tipped tools to carbon steel shanks?
Brazing
What is the general material used for making solid tools?
High carbon steel
How are ceramic inserts mounted in the tool post?
By brazing
What is the primary reason for using a solid tool?
Rigidity
What is the purpose of tipped tools fastened mechanically to carbon steel shanks?
To ensure rigidity
Where are solid tools typically mounted in a lathe?
On the tool post
How are tool bits usually secured in tool holders?
By bolting
How is longitudinal feed achieved in a lathe?
By engaging pinion I with rotating gear G
What happens when the feed check knob 'E' is pulled-out?
Power is transmitted to cross feed screws
Which mechanism provides rigidity in construction for feed reversing in modern lathes?
Clutch operated bevel gear feed reversing mechanism
What type of chuck is used for holding non-circular bars in a lathe?
4 jaw independent chuck
What is the purpose of an angle plate in a lathe setup?
To provide two faces at right angles to each other
How are the jaws of a 4 jaw chuck in a lathe moved radially?
Independently by rotating corresponding screws
Which component of a lathe setup consists of radial, plain, and T slots for holding work pieces?
Face plate
What happens when the half nut is engaged with the carriage in a lathe?
The carriage moves along the axis of the lathe
What is the purpose of using an angle plate with the faceplate in a lathe machine?
To hold eccentric or unsymmetrical jobs
What is the function of a catch plate or driving plate in a lathe machine?
To drive the workpiece through a carrier or dog
What are carriers or dogs used for in a lathe machine?
Transferring motion from the driving plate to the workpiece
Why are mandrels made of high carbon steel in a lathe machine?
To hold and rotate hollow workpieces
When is a revolving centre preferably used in a lathe machine?
To avoid sliding friction between the job and the centre
What is the function of a pipe centre in a lathe machine?
To support pipes and hollow end jobs
How does a tipped centre differ from an ordinary centre in a lathe machine?
The hard tip is brazed into steel shank for wear resistance
What additional support is provided for long slender jobs like feed rod, lead screw etc. in a lathe machine?
A follow rest that moves along with the cutting tool
How are tools usually mounted in a center lathe according to the information provided?
In a tool post
What is the purpose of using an angle plate with the face plate in a lathe machine?
To hold eccentric or unsymmetrical jobs
Study Notes
Centre Lathe
- A centre lathe is a machine tool used to remove material from a work piece to produce the required shape and size.
- It is the oldest machine tool invented, dating back to the Egyptian tree lathes.
- The main function of a centre lathe is to hold the work piece securely and rigidly on the machine and turn it against a cutting tool, which removes material from the work piece in the form of chips.
Components of a Centre Lathe
- Apron: The lower part of the carriage attached to the saddle and hangs in front of the bed. It contains gears, clutches, and levers for moving the carriage.
- Feed mechanism: The movement of the tool relative to the work piece is termed as "feed". There are three types of feed: longitudinal, cross, and angular.
- Feed rod: A long shaft used to move the carriage or cross-slide for turning, facing, boring, and other operations except thread cutting.
- Lead screw: A long threaded shaft used as a master screw and brought into operation only when threads have to be cut.
Kinematic System and Working Principle
- The job and the cutting tool need to be moved relative to each other.
- The tool-work motions are: formative motions (cutting motion, feed motion) and auxiliary motions (indexing motion, relieving motion).
- In lathes, cutting motion is attained by rotating the job, and feed motion is attained by linear travel of the tool.
Headstock Driving Mechanisms
- There are two types of headstock driving mechanisms: back geared headstock and all geared headstock.
- Back geared headstock: Used for reducing the spindle speed, necessary for thread cutting and knurling.
- All geared headstock: Commonly used in modern lathes due to its advantages, such as providing a wider range of spindle speeds, being more efficient and compact, and reducing vibration.
Feed Mechanisms
- The feed mechanism is used to transmit power from the spindle to the carriage.
- There are several types of feed mechanisms, including:
- Tumbler gear reversing mechanism
- Quick-change gearbox
- Tumbler gear quick-change gearbox
- Apron mechanism
- Bevel gear feed reversing mechanism
Tool Holding and Mounting
- Different types of tools are used in centre lathes, including:
- HSS tools (shank type)
- HSS form tools and threading tools
- Carbide and ceramic inserts
- Drills and reamers
- Boring tools
- Tools are mounted in various ways, including:
- HSS tools in tool post
- Carbide and ceramic inserts in tool holders
- Drills and reamers in tailstock
- Boring tools in tool post
Cutting Tools
- Single point cutting tools are used in centre lathes.
- Tools are classified according to:
- Method of manufacturing
- Method of holding
- Method of using
- Method of applying feed
- Types of cutting tools include:
- Forged tools
- Tipped tools brazed to the carbon steel shank
- Tipped tools fastened mechanically to the carbon steel shank
- Solid tools
- Tool bits inserted in tool holders### Classification of Lathes
- Lathes can be classified according to their special purpose, size or capacity, configuration of the jobs being handled, precision, and number of spindles.
- Special purpose lathes include capstan lathe, turret lathe, and gear blanking lathe.
- Lathes can be classified by size or capacity as small (up to 1.1 kW), medium (up to 11 kW), large (heavy duty), and mini or micro lathe.
Configuration of Jobs
- Lathes can be classified according to the configuration of the jobs being handled as bar type, chucking type, and housing type.
- Bar type lathes hold slender rod-like jobs in collets.
- Chucking type lathes hold disc-type jobs in chucks.
- Housing type lathes hold odd-shaped jobs in face plates.
Precision and Number of Spindles
- Lathes can be classified according to precision as ordinary and precision (high accuracy and finish).
- Lathes can be classified according to the number of spindles as single spindle (common) and multi-spindle (2, 4, 6, or 8 spindles).
Type of Automation
- Lathes can be classified according to the type of automation as fixed automation (conventional) and flexible automation (modern).
- Examples of fixed automation include single spindle automat and Swiss type automatic lathe.
- Examples of flexible automation include CNC lathe and turning centre.
Degree of Automation
- Lathes can be classified according to the degree of automation as non-automatic, semi-automatic, and automatic.
- Non-automatic lathes require manual handling operations.
- Semi-automatic lathes require some manual handling operations.
- Automatic lathes require minimal manual handling operations.
Constructional Features of Centre Lathes
- Centre lathes are the most versatile and commonly used lathes.
- Major parts of a centre lathe include headstock, tailstock, bed, carriage, saddle, cross-slide, compound rest, and tool post.
Headstock
- The headstock holds the spindle and transmits power and rotation to the job at different speeds.
- The headstock can hold various work-holding attachments such as three-jaw chucks, collets, and centres.
Tailstock
- The tailstock can be used to support the end of the workpiece with a centre, to support longer blanks, or to hold tools for drilling, reaming, threading, or cutting tapers.
- The tailstock can be adjusted in position along the ways to accommodate different length workpieces.
Bed, Carriage, and Saddle
- The bed is fixed on columns and the carriage travels on it.
- The carriage is used for giving various movements to the tool by hand and by power.
- The saddle carries the cross-slide, compound rest, and tool post.
Cross-Slide, Compound Rest, and Tool Post
- The cross-slide carries the compound rest and tool post.
- The compound rest is used during taper turning to set the tool for angular cuts.
- The tool post is fitted over the compound rest.
Quick-Change Gearbox and Tumbler Gear Quick-Change Gearbox
- The quick-change gearbox is used to get various power feeds in the lathe.
- The tumbler gear quick-change gearbox is simpler than the quick-change gearbox.
- Both types of gearboxes are used to obtain various speeds of the driving shaft.
Apron Mechanism
- The apron mechanism is used to transmit power from the spindle gear to the feed rod through tumbler gears.
- The apron mechanism is used for automatic feeds.
Mounting of Jobs in Centre Lathes
- Jobs can be mounted in centre lathes using chucks, face plates, and angle plates.
- Chucks can be 3-jaw self-centring or 4-jaw independent.
- Face plates have radial, plain, and T slots for holding work by bolts and clamps.
- Angle plates have two faces at right angles to each other with holes and slots for holding work.
Learn about the centre lathe, the oldest machine tool invented with origins dating back to Egyptian tree lathes. Understand its main function of removing material from a workpiece to produce the required shape and size by turning it against a cutting tool.
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