Lathe machine Introduction: The late is one of the oldest machine tools and came into existence from the early tree lathe which was then a novel device for rotating and machining a piece of work held between two adjacent trees. It further development a strip of wood called “lath” was used to support the rope and that is how the machine came to be known as “ lathe”. It has develop in the years in 1797 hennery maudlin, an Englishman, has develop this. Lathe machine is a versatile machine, which proves to be a vital necessity in all workshops, repair shops, tanning workshops and modern tool room. Its main significance is the ability to perform variety of applications in the production of different types of job. A single job will need a number of the other machine tools for performing various operations required with production.
Function of the lathe: The main faction of a lathe is to remove metal from a piece of work to give it the required shape and size. To cut the material properly the tool should be harder than the material of the work piece, should be rigidly held on the machine and should be fed or progressed in a definite way relative to the work.
Type of lathe machine: Large variety of type and size of lathe is available that it is difficult to classify them into some definite categories. There is a large variegation in their design, construction and use. However, according to their construction and design we may broadly classify lathes as follow. Lathes of various designs and constructions have developed to suit the various conditions of metal machining. Following type is:
1. Speed lathe: There lathe may of bench type or they have the supporting legs cast and fitted to the bed. The speed lathe, it construction and operation is the simplest of all types of lathe. It consists of a bad, a headstocks, a tailstock and a tool-post mounted on an adjustable slide. There is no feed box, lead box is mounted on the adjustable slide and is fed into work purely by hand control. It is usually range from 1200 to 3600 rpm.
Light cuts and high speeds necessitate the use of this type of machine where cutting force is minimum such as in wood working, spinning, centering, polishing etc. The speed lathe has been so named because of the very high speed of the headstock spindle. There are late have most of the attachment, which the other type of lathe machine carry but have no provision for power feed. They have no gear box, carriage and the lead screw. With the result, the tool is fed and actuated by hand. Usually the tool is either mounted on a tool post or supported on a T-shaped supported. Such lathes are usually employed for wood turning, polishing, centering and metal spinning etc. Thus, they are considered as merely of a theoretical value as far as the modern machine shops are concerned.
2. Engine lathe: It is also known as “Centre lathe". It is the most important of the lathe firmly and most widely used. It has got all the basic parts. E.g. bed, headstock and tailstock. The name engine lathe is a little confusing in modern practice as all these lathes are now made to have an individual motor drive. It can feed the cutting tool both in cross and longitudinal direction with reference to the lathe axis with the help of carriage, feed rod and lead screw.
It is classified according to the various designs of the headstock and methods of transmitting power to the machine. Belt driven lathe, Motor driven lathe, geared head lathe. However, it carries a great historical significance that in the very early days of its development it was driven by a steam engine. From this, it derived its name, which is popular even today.
3. Bench lathe: This is a small lathe usually mounted on a bench. It has practically all the parts of an engine lathe or speed lathe and it is used for small and precision work. It is a very small lathe and is mounted on a separately prepared bench or cabinet.
It is used for small and precision work since it is very accurate. It is usually provided with all the attachments that a large lathe carries and is capable of performing almost all the operations, which a large lathe can do.
4. Tool room lathe: A tool room lathe having features similar to an engine lathe is much more accurately built and has a wide range of spindle speeds ranging from a very low to quite high speed up to 2500 r. p. m. the sizes of this machine is same sizes of centre lathe or engine lathe.
Its carries a wide range of speeds and feeds. The usual attachments provided on the tool room lathe are taper turning attachment, follower rest, collets and chucks etc. This lathe is made to have a comparatively smaller bed length less the usual engine lathe.
5. Capstan and turret lathe: These lathes are development of the engine lathe and are used for production work. The advantage is that several different types of operation can be done on a work piece without re-setting of work or tools, and a number of identical parts can be produced in the minimum time. These lathe from a very important and useful group and are vastly used in mass production.
These machines are actually of semi-automatic type and a very wide range of operations can be performed on them. In these machines, whatever skill is needed of the operator (setter) it is only in the setting of tools in the turret or capstan head and once this setting has been successfully accomplished future operation of these machines calls for a comparatively less skill on the part of the operator.
6. Automatic lathe: These are high speed, heavy duty, mass production lathes with complete automatic control. It have, the tool are set and the machine is stared it performs automatically all the operations to finish the jobs. The changing of tools speeds and feeds are also done automatically.
They are so designed that all the working and job handing movements of the complete manufacturing process for a job are also done automatically, no participation of the operation is required during the No. operation. Another variety of this type of the lathe includes the semi-automatic lathe in which the mounted and removal of the work done by operator whereas the machine performs all the operations automatically. Automatic lathe are available having single spindles.
7. Special purpose lathe: A large number of lathes are designed to suit a definite class of work and to perform certain specified operations only.
They obviously prove more efficient as compared to the common engine lathe as far this specified class of the work is concerned. The classification of lathes; however cannot be confined merely to the broad outlines gives they above. They cannot be future classified according to the type of drive they posses and their sizes, Etc. According to the swing of center (above the bed) lathe can be grouped as.
i). Small lathes - having swing up to 150 mm.
ii). Medium size lathe - having swing of center from 150 to 300 mm.
iii). Heavy duty lathe - having swing of center above 300 mm.
The sizes of a lathe:-
1. The height of the centers measured from the lathe bed.
2. The swing diameters over bed.
3. The sing diameter over carriage.
4. The length between centers.
5. The maximum bar diameters.
6. The length of bed.
Principle of lathes machine: The lathe is defined as a machine tool, which holds the work between two rigid and strong supports called center or in a chuck or face plate and the work revolves. The chuck or the faceplate is mounted on the projected end of the machine spindle. The cutting tool is rigidly held and supported in a tool post and is fed against the revolving work. While the work revolves about its own axis, the tool is made to move either parallel to or at an inclination with this axis to cut the desired material. In doing so, it produces cylindrical surface, if it fed parallel to this axis, or will produce a tapered surface if it is fed at fed an inclination.
Principle parts of lathes machine: Following are the main principle parts:-
Bed: The lathes bed forms the base of the machine. The headstock and tailstock are located at either end of the bed and the carriage rest over the lathe bed and slides on it. Many lathes are made with a gap in the bed. This gap is used to swing extra large diameter pieces. The bed material should be wear resistance and absorb vibration.
Carriage: The carriage of lathes machine have several parts that serves to support, control and move the cutting tool. It consists of saddle, cross slide, compound rest, tool post and apron.
Saddle: Saddle is h- shaped casting and mounted over the bed and slides to the ways. It consists and cross slide and compound rest.
Cross slide: It is over the saddle and slides with the guides ways provided. it is made up of cast iron . Compound rest is mounted upon it.
Compound rest: It is very important parts of carriage. It is just over the cross- slide and is made from cast iron. It has a circular base graduated in degree for cutting tapper.
Tool post: It is mounted at the top of the compound rest the main function of tool post is to hold the tool at convenient position.
Headstock: It is mounted over the bed at left hand side inner ways of the bed. The head stock is secured spindle. The spindle is made up of carbon or nickel chromium steel. All the parts of lathes machine is housed within the main casting of headstock. Live centre is inside of hollow spindle. The main function of headstock spindle is to rotate a work at multi
Tailstock: It is also called loose- headstock, because it is not permanently secured on the lathe bed. It is mounted over the right hand side of lathe bed and is adjusted as per requirement at any convenient position. The main function of tailstock:-
1. To support the long cylindrical type of work when it is being machined between two centers i.e. - live centre and dead centre.
2. It is also used to holding the tool for performing drilling, reaming, boring, tapping, etc.
Lathe operation: The following operations are performed in lathe machine:
Filling, Thread cutting, Polishing, Grooving, Spinning, Spring winding, Forming, Drilling, Reaming, Boring, Internal thread cutting, Tapping, Undercutting, Parting off, Milling, Grinding, taper boring, counter boring.
Facing: Facing is the operation of machining the end of a work pieces to produce flat Surface Square with the axis. It is also used to cutting the work at the required length. This is done by different types of facing tool.
Knurling: It is the operation of embossing diamond shape pattern on the work pieces .it is provided for the effective gripping of .when it is operated by hand. It provides from slipping, it is done by special knurling tool.
The tool id rigidly held in tool post and the roller are pressed against the revolving work piece.
Centering: Where the work is required to be turned between centers or between a chuck and a centre, conical shaped holes must be provided at the ends of the work piece to provide bearing surface for lathe centers. It is the operation of producing conical holes in work pieces.
Turning: Turning in a lathe is to remove excess material from the work pieces to produce a cone- shaped or a cylindrical surface.
1. Straight turning: The work is turned straight when it is made to rotate about the lathe axis and the tool is fed parallel to the lathe axis. The straight produces a cylindrical surface by removing excess metal from the work piece.
2. Rough turning: It is the process of removal of excess material from the work pieces in a minimum time by applying high rate of feed and heavy depth of cut. The depth of cut roughing operations in average machine shop work is from 2 to 5 mm and the rate of feed is from 0.3 to 1.5 mm per revolution of the work.
3. Finish turning: It has requires high cutting speed, small feed and a very small depth of cut to generate a smooth surface. The depth of cut ranges from 0.5 to 1mm and feed 0.1 to 0.3 mm per revolution of the work pieces.
4. Shoulder turning: When a work pieces having different diameter is turned the surface forming the step from one diameter to the other is called the shoulder and machining this parts of the work pieces is called ‘shoulder turning’.
Taper and taper turning: A taper may be defined as a uniform increase or decrease in diameter of a piece of work measured along its length. Taper turning means to produce a conical surface by gradual reduction in diameter from a cylindrical work piece.
This tapering of a part has wide applications in the construction of machines.
Taper elements:-a tapered piece may be designated by following symbols:-
D = large diameter of taper.
d = small diameter of taper.
L = length of taper.
Alfa= angle of taper or half taper angle.
2 Alfa = full taper angle. {K= D-d /L}
Standard tapers: Tapered surface which follow standard dimensions are called standard tapers. Metric tapers are sometimes used as standard tapers.
Eccentric turning: If a cylindrical work pieces has two separate axis of rotation one being out of centre to the other, the work pieces is termed eccentric and turning of different surface of the work pieces is known as “ eccentric turning”. Ex. Crank shaft turning.
Chamfering: Chamfering is the operation of beveling the extreme and of a work pieces. This is done to remove the burrs to protect the end of the work pieces.
The operation may be performed after knurling rough turning, boring, drilling or thread cutting.
Feed mechanism of lathe machine: The movement of tool relative to the work is termed as “feed”. A lathe tool may have three types of feed i.e. longitudinal, cross and angular feed. When the lathe tool moves as longitudinal feed. It is affected by the carriage of lathe machine. When the tool moves right angle to the axis and is affected by cross- slide the movement is turned as cross- feed. But when the movement of tool is effected or provided by compound rest and the tool is swiveled at any required angle then it is called angular feed. The longitudinal and cross feed both hand and power operated, but angular feed is only hand operated. There is no power feed for angular operation. Otherwise our job will be damaged.
Following are the units of feed mechanism: End of bed gearing, Feed gear box, Feed rod and lead screw, Apron mechanism.
Thread –cutting mechanism: the rotation of the lead screw is used to transverse the tool along the work to produce screw thread. The half nut mechanism makes the carriage to engage or disengage with the lead screw. It comprises a pair of half nuts capable of moving in or out of mesh with the lead screw. The two halves of the nut are of connected in the cam slots in a circular disc by two pins. When the disc is rotated by a hand lever attached to it. The*+- split nuts and thus engages or disengages with the lead screw. The half nuts slide within the guide or frame. Closing the half nuts causes the carriage to move a fixed distance for each revolution of the spindle. The direction in which it moves depends upon the position of the fed reverse lever on the headstock. The split nut is used only for thread cutting and never for any other operation.
Differentiate between lathe accessories and lathe attachments:
Lathe accessories: It include centers, catch plates, carries, chucks, collets, face plate, angle plate mandrels, rests. They are used either for holding and supporting the work or for holding the tool.
Lathe attachments: They are the additional equipments used for specific purpose they includes stops, ball turning rests, threads chasing dials and taper turning , milling, grinding, gear cutting. Etc.
Type of tool post: There are following of tool post:-
1) Single screw tool post: This type of tool post consists of a round bar with slotted hole in the centre for fixing he tool by means of a set screw. The tool post with concave ring and convex rocker slides in a t- slot on the top of the compound rest.
2) Four bolts tool post: In this tool post the tool is held in position by two straps and four bolts. Loose coiled springs are fitted to each bolt to keep the straps in place and hold the tool easily. This type of tool post is often fitted in heavy duty lathe.
3) Open side tool post: The open tool post is held quite independent of the main fixing bolt and clamped in position by two set screw. This arrangement ensures quick replacement of the tool.
4) Four way tool post: These types of tool post sides are open to accommodate four tools at a time. The tool is held in position by separate screws and a locking bolt is located at the centre. The tool post swiveled exactly through 90 degree.
Type of work holding devices:
1. Lathes centers: The most common method of holding the work in lathe Is between the two centers- live centre and dead center. They are made of a very hard material to resist deflection of wear. The included angle of the center Is usually 60 degree for general purpose of work and 75 degree for heavy work.
2. Carries and catch plates: They are used to drive a work pieces when it is held between two centers. Carries or driving dogs are attached to the end of the work pieces by a set screw. Catch plates are either screwed or bolted to the nose of the headstock spindle.
3. Chuck: A chuck is one of the most important devices for holding and rotating a piece of work in a lathe. It is attached to the lathe spindle. There are many different types of chucks:
4. Four jaw independent chucks: four jaw chucks also know as independent chuck. This chuck has four jaws which may be made to slide within the slots provided in the body of the chuck for gripping different sizes of work pieces. Each jaws made of tough steel has three inner and one outer gripping surface. The outer gripping surface is used for holding larger sizes of work pieces by reversing the jaw. This type of chuck is particularly used in the setting up of heavy and irregular shaped articles. The diameter of the body specifies the sizes of the chucks.
5. Three jaw universal chuck: It also known as universal or self centering chuck. The chuck has three jaws may be made to slide simultaneously by an equal amount within the slots provided on the body by rotating anyone of the three pinions. When the disc is made to rotate by any one of the pinions all the three jaws move backward or forward by equal amount. The chuck is suitable for holding round or hexagonal, and other similar shaped work pieces, and the job is centered automatically and quickly. But it has less gripping capacity as only three jaws are used and centering accuracy is soon lost due to wear.
6. Combination chuck: It may be used both as a self centering and independent chuck to take advantage of both the types. The jaws may be operated individually by separate screws or simultaneously by the scroll disc. The screws mounted on the frame have teeth cut on its underside.
7. Magnetic chucks: The chuck is used for holding a very thin work pieces made of magnetic material which cannot be held in an ordinary chuck. The holding power of the chuck is obtained by the magnetic flux ordinary either from the electro- magentas.
8. Collect chucks: They are used for holding bar stroke in production work where quick setting and accurate centering is needed. The inside bore of the collets may be cylindrical , hexagonal, square etc. depending on the shape of the works that will pass through it. Different sizes of collets are used for holding different sizes of collets are used for holding different sizes of the bar stock.
9. Air or hydraulic operated chuck: It is used in mass production work for its fast and effective gripping capacity. The mechanism incorporates a hydraulic or air cylinder mounted at the back end of the headstock spindle and rotates with it.
10. Drill chuck: A drill chuck is sometimes used in a lathe for holding straight shank drill, reamer or tap for drilling, reaming or tapping operations. The chuck may be held either in headstock or tailstock spindle. It has self centering jaws which may be operated by rotating a key.
11. Face plate: A face plate consists of a circular disc bored out and threaded to fit the nose of the lathes spindle. This has the radial, plain and t-slot for holding work by bolts and clamp. It is used for holding work pieces which cannot be conveniently held between centers or by chucks.
12. Angle plates: This is a cast iron plate having two faces machined to makes them absolutely at right angles to each other. Angle plates are used in conjunction with a face plate when the holding surface of the work piece should be kept horizontal.
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