Milling Machine

Milling machine: A milling machine is a machine tool that removes metal as the work is fed against a rotating multipoint cutter. The cutter rotates at a high speed and because of the multiple cutting edges it removes metal at a very fast rate. Milling is the process of removing metal by a rotating multi point cutter. The work is fed past the cutter. The metal is removed in the form of small chips. As multipoint cutter is used, metal removal is very fast. One or more cutter is used at a time. Milling produces a good surface finish. The accuracy is high.

Principle of operation: The working principle employed in the metal removing operation on a milling machine, is that the work is rigidly clamp on the table of the machine and revolving multi teeth cutter mounted either on a spindle or on an arbor. The cutter revolved at a high speed and the work fed slowing, past the cutter. The milling machine has a rotating cutter. The cutter is mounted on a rotating spindle or arbor. The cutter has multiple cutting edges. The workspace is clamped on the table. The cutter rotates at the required cutting speed. The work piece is fed slowly past the cutter. The feed may be longitudinal, cross wise or vertical. Angular feed can also be given in certain milling machines. As the work is fed, the cutting edges remove metal from the work pieces in the form of chips. During the cutting, each cutting edge cuts the metal only during a part of the cutter revolution. The work can be fed in a vertical, longitudinal or cross direction. As the work advance the cutter-teeth remove the metal from the work surface to produce the desired shape.

Type of milling machine:

1. Column and knee type milling machine

1. Hand milling machine

2. Plain or horizontal milling machine

3. Vertical milling machine

4. Universal milling machine

5. Omniversal type milling machine

2. Special purpose type milling machine

1. Thread milling machine

2. Profile milling machine

3. Gear milling or gear hobbing milling machine

4. Cam milling machine

5. Planetary type milling machine

6. Double end milling machine

7. Spar and skin milling machine

3. Fixed bed type or manufacturing type milling machine

1. Plain type (having single horizontal spindle)

2. Duplex head (having double horizontal and one vertical spindle)

3. Triplex head (having two horizontal and one vertical spindle)

4. Rise and fall type (for profile milling)

4. Planner type milling machine

5. Production type milling machine

1. Rotary table or continuous type

2. Drum type

3. Tracer controlled

Column and knee type milling machine: Column and knee type milling machines are most commonly used. These types of milling has vertical column on its base. The column has machined guide ways on its front faces. The knee is mounted on this column. The knee can slide up and down on the guide ways of the column. The knee can carry the saddle and work table. It is general purpose machine. Different varieties of jobs can be done on these machines.

Plain milling machine: It is also known as horizontal milling machine, since the spindle of the machine is horizontal. There is a vertical column on the base. The column houses the main drive and the spindle. The column has vertical dovetail guide ways on its front face. The knee can move vertically on these guide ways. This is done by rotating the elevating screw. The knee at its top has horizontal dove-tail guide ways perpendicular to the front of the column. In the table travels longitudinally along these guide ways. The longitudinal travel of the table is perpendicular to the axis of the spindle. The top surface of the table is accurately machined. There are t-slots along the length of the table for holding the work. The vertical movement of knee, crosswise movement of the saddle and the longitudinal movement of table can obtained by hand or power. The front end of the spindle is called nose. The nose just projects from the column face. It has tapered holes. Arbores or various cutting toots can be inserted into this holes. There is an over arm mounted on the top of the column .it acts as support for the arbor.

Milling machine attachments: It is an important point to remember that full of use of the capacity of a milling machine can be made only when different types of attachments are available for use to deal with various type of jobs. There attachments are generally classified into two categories, viz., standard and special. Standard attachments have greater adaptability and application in general type of work. They are capable of dealing with a large variety of jobs and can be fitted to most of the standard type of milling machine. Special attachments are those that are specially designed and used on a standard milling machine to make it suitable for performing special milling operations in mass production of identical items. There attachments mainly include the various milling fixtures. Now we will study in detail the various attachments.

1. Arbors adaptors and collets: They all are used for holding the milling machine cutters during the operation. This is common method of mounting the cutters although they are mounted on the machine spindle directly also. The nose (front end) of the machine spindle, for this purpose, is made to have the following features as show in fig.

1. Two driving dogs and four threaded holes to locate and drive the adaptor and face milling cutter etc.

2. An accurate tapered hole to locate arbors and adaptors etc. and keep them in perfect alignment with the axis of spindle.

3. An accurately machined and ground front face. 

The arbors used on milling machines are mainly of two types; the long supported arbor and the stub arbor. The former is also known as standard arbor and is relatively larger than the later type. It is provided with a set of spacing collars that help in adjustable the position of the cutter or the distance between cutters when more than two cutter are mounted simultaneously. A larger number of such collars, usually ranging from 1 mm to 50 mm in with are supplied with the machine. In addition to these, two or three collars of relatively large diameter are also supplied which act as bearing sleeves when the arbor is supported in the yokes or arbor supports. The slots provided on the flange of the arbor engage the driving dog of the spindle. A key runs for the whole length of the arbor that fits in the corresponding key-way in the cutter is provide a positive driver. Rear end of the draw bar. Stub arbors are used to hold face and side milling cutters that do not need a large overhang. The end of the arbor that fits in the spindle nose carries a tapered shank as shown. A draw bar is usually provided in the spindle to pull in or push out the arbor as desired. The rear end of the draw bar is provided with a collar that is abutted against the retaining nut fitted on the rear side of the spindle. The arrangement prevents the draw bar from having an axial movement when rotated. The square shape made at the rear end of the draw bar is rotated, since its axial movement is checked as started above it either pulls the arbor in or pushes it out, depending upon the direction of its rotation.

Milling cutters that carry straight shanks are held in collets chuck carrying a spring collet. This chuck is made to have a tapered shank that fits in an adaptor. The straight shank cutter is gripped in the chuck and the later inserted in the adaptor, the assembly being secured to the spindle as usual. Collets of different sizes are available to suit various corresponding sizes of the cutter shanks.

2. Vices: Vices are the common devices used for holding the workpiece on milling machine. The common type of the vice used are the following:

1. Plain or parallel vice: A plain vice is the most simple of all the types. The vice may have a single screw or double screws for actuating the moveable jaw. The double screws add gripping strength while taking deeper cuts or handling heavier jobs. It consists of a solid cast base carrying a fixed jaw at one end an elevated projection at the other. The later carries internal threads and acts as a nut for the screwed spindle that, while rotating in it, moves the adjustable jaw.

It is commonly employed for holding the work in all plain milling operations that involve heavy cuts such as in slab milling, its especially low construction enable the work to remain quite close to the table and thus reduces the chances of vibrations to a minimum. The base carries slots to accommodate T-slots to fix the vice on the table.

2. Swivel vice: In a swivel vice the base is graduated in degrees and the body of the vice may be swiveling arrangement at any desired angle on a horizontal plane. The swiveling arrangement is useful in beveling the end of workpiece. The swivel vice consists of a swivel base on which is mounted the body which can be clamped in any angular position by means of the clamping bolt. The graduated scale provided on the swivel base help in adjusting the body at any desired angle relative to that of a plain vice. This vice facilities milling of an angular surface on the work piece without disturbing its setting. The clamping bots operate in a circular T-slot provided in the base.

3. Universal swivel vice: A universal vice may be swiveled like a swivel vice. In addition to that, the body may be tilted in a vertical plane upto 90° from the horizontal. An inclined surface may be machined by a universal vice. The universal machine vice, enables milling of various surface, at an inclination to one another, without removing the work piece from the some. The vice, apart from being swiveled in a horizontal plane, can also be tilted vertically to be set at a desired angle and can thus be adopted for milling of compound angle. It is vastly used in tool room work and should not be used where heavy cuts are to be employed since it does not have the required clamping rigidity.

4. Vertical vice: The vertical vice very much resembles a plane vice in construction and operation both. The only difference is that it carries vertical jaws instead of the horizontal jaws. It is specific use is in holding those jobs on which milling is to be done at the ends.

5. Precision angle vice: The Precision angle vice consists of a cast base carrying two small vertical projections. One end of the body is hinged about those projections and other end can be adjusted in a vertical direction. It, thus, enables a precision angular adjustment of the job in a vertical plane. The marks provided on the body near the hinge enable a quick adjustment through the required angle.

6. Compound vice: The compound machine vice is very important and Precision vice which a compound slide similar to the one used on a center lathe. The work piece is held on the table provided at the top of the vice. This table can be swiveled in a horizontal plane to any desired angle, thus eliminating the use of a swivel vice. The Compound slide enables the adjustment of the work from front to back, back to front, left to right and right to left. Thus, the work can be adjusted in any desired position.

3. Circular table: It is also called the circular milling attachment and is employed for indexing as well as providing continuous rotary motion to the work. It can be either manually operated or power driven. It consists of a heavy base that is secured to the machine table by means of T-bolts.

Rotary motion to the worm wheel at the bottom of the circular table, through a worm provided on the shaft on which this hand wheel is mounted. The workpiece can be mounted on the table either directly by means of clamps and bolts or held in a vice clamped to the table. Alternatively, a specially designed milling fixture can be used to hold the work. The power driven circular milling attachment usually has a provision for hand drive as well as power drive. The mechanism for hand driving is the same as in the same as in the manually operated circular milling attachment. For power drive, a bracket is attached to the machine table that carries a train of gears driven by a gear mounted on the screwed shaft driving the machine table worm wheel mechanism.

4. Dividing or indexing head: 

1. Dividing head: These head, help in changing the angular position of the component in relation to the cutter. With their use it is possible to divide the periphery of the workpiece into any number of equal parts. These heads are generally of the following types:

1. Plain dividing head

2. Universal dividing head.

2. Indexing method: By indexing, we wean division of the job periphery into a desired number of divisions. A controlled movement of the crank accomplishes it such that the job rotates through a definite angle after each cut is over. The following methods of indexing are commonly used:

1. Direction indexing 2. Plain or simple indexing 3. Compound indexing 4. Differential indexing 5. Angular indexing 

5. Vertical milling attachment: It is also sometime called swivel head. It is used both on horizontal as well as universal milling machine. For fixing it on the machine, the over arm of the later is pushed back and the attachment bolted on the front face of the column as show in fig. With the use of this attachment, the horizontal and universal milling machine can be made to act as vertical milling machines.

An important point that needs attention here is that the attachment cannot be adjusted in the vertical direction. As such, the depth of the cut has to be adjusted by raising the table of the machine. However, it has an advantageous feature that it can be swiveled to a desired angle in a vertical plane to make the spindle and hence, the cutter rotates at an angle. For providing the drive to vertical spindle of the attachment, an adapter is fitted to the horizontal spindle of the machine. It drives a horizontal spindle in the attachment. Than through a train of spur gear and finally a pair of bevel gears, the drive is transmitted to the vertical spindle. It may however, be noted that even through the horizontal and universal milling machines can be converted into vertical milling machines by using this attachment, still it will not be as efficient as a regular vertical milling machine. Operations like face milling, grooving, T-slot cutting etc. can easily be performed with this attachment.

Milling Cutters: The milling cutter may have either straight tooth, i.e., parallel to the axis of rotation or in helical shape. The helix angle may be right hand or left hand and this decide the direction of rotation of the cutter for performing the cutting operation. Further, a milling cutter may be made of single piece of steel or having removable cutting teeth inserted in a solid body. The broad classification of milling cutter is according to the shape of teeth they carry such as plain, inserted, and formed or saw-teeth etc. Under this classification are covered a large number of milling cutters. Common types of these cutters are described below.

1. Plain milling cutter               7. Face milling cutters

2. Side milling cutters              8. Gear milling cutters

3. End milling cutters               9. Thread milling cutters

4. Angle milling cutters.         10. Tslot milling cutters

5. Metal milling cutters.         11. Fly milling cutters

6. Foamed milling cutters      12. Woodruff-key milling cutters

1. Plain milling cutter: These milling cutter may have the cutting teeth on their periphery, the teeth may be either straight i.e., parallel to the axis, or helical. Their end faces are either ground square with the axis, or slightly concave to reduce friction. Thus, the side faces provide no cutting action. These cutters are employed for milling flat surface parallel to the axis of rotation. These cutters include the light duty plain milling cutter or key way cutter and the helical or slab milling cutters.

The former type is available up to 20mm in width and carries straight teeth. It is usually employed for key way and slot cutting. The latter type. i.e., slab milling cutter are enough long and carry helical teeth. These cutters are used for light work and finishing work. The coarse pitch teeth cutter are called heavy-duty slab milling cutters. They carry less number of teeth having a steep helix angle. They are commonly used where very heavy cut are to be employed since they are capable for removing more materials with less power consumption. A recommended practice is not to be use very long cutter. If at all very big length is needed, A preferable practice is to have the desired length built up with a number of short length cutter with their teeth running alternately right and left hand to neutralize the end thrust.

2. Side milling cutters: These cutters, apart from having teeth on the periphery also have cutting teeth on one or both side; they are always provided with a central hole for a purpose of mounting them on the arbor.

They are also called straddle mills when used in pairs. The main types of side milling cutters are the following:

(i.) Plain side milling cutters: They are made to have cutting teeth on periphery as well as on both the side. They are normally used for cutting slots or in face milling. They can also be used in pairs for straddle milling. These cutters are available in different widths ranging from 5 mm to 25 mm and diameters up to 200 mm.

(ii.) Half side milling machine: These cutters have teeth on the periphery and one side only. They can be used for face milling. The teeth may be either straight or helical. In addition, they can be either right hand or left hand. The teeth provided on the periphery perform actual cutting while the side teeth do the finishing and sizing work. A distinct feature of these cutters is that their teeth are longer than those of the plain milling cutters. They are frequently used in pairs (one left hand and one right hand) for milling two parallel surfaces simultaneously; the operation being known as straddle milling.

(iii.) Staggered teeth side milling cutters: These cutters carry alternate teeth on the periphery only. These alternate teeth are of opposite helix angle, staggered from side just as the teeth of a wood saw, and cut alternately on one side and then on the other. They are commonly used for keyways cutting and slot cutting. They prove very efficient in milling deep slots but narrow in width. A typical type of staggered tooth side milling cutter is show in fig.

(iv.) Interlocking side milling cutters: These cutters are similar in design to the side milling cutters but are used as a unit consisting of two cutters joined together such that their teeth interlock as show in fig. They can be adjusted to acquire the required width by inserting shims or spacers between them. These shims or spacers are also used to make good the reduction in the width of the cutter due to wear and relatively wider slots to exact width. Also, they find a wide use in gang milling.

3. End milling cutters: These are solid circular cutters that are manufactured in two different varieties; those having the shank and others that do not have the shank. They carry teeth on the periphery as well as on the end. These teeth may be straight, parallel to the axis of rotation or helical as in slab milling cutters. Helical teeth may be right hand or left hand.

End milling cutters are used for milling slots, keyways, grooves and irregular shaped surface. Shank type end mils are either mounted directly on the spindle, or held in collets (straight shank type mills only) or in an adapter. The following are the main classification of these end mills. 

(i.) Common type: These milling cutters carry multiple teeth on their periphery and on the end. The teeth may be straight or helical; the former type is, however, available in small only, say below 8 mm dia. A typical design of this type is show in fig.

(ii.) Two-lipped end mill: These milling cutters are also know as slotting mills. These cutters have two straight or helical teeth on the periphery and the corresponding two teeth on the end that meet at the end center. The main advantage of these cutters is that they can be fed straight into the material like a drill and the feed longitudinally to produce a groove of desired length and depth. In addition, they can be used for taking heavy cuts in solid stock. These cutters may have either a straight shank or a taper shank. The latter type is however, more commonly used.

(iii.) Shell end-milling cutters: These cutters are larger and heavier than most of the other type of end mills. They have teeth on the periphery and the end both. Generally, they are made in over 50 mm size (diameter). The end face of these cutters is provided with a recess to receive a cap screw. They are held in a stub arbor. Two slots are made across the back of the cutter that engages the collar key of the arbor to get the driver. Generally, helical teeth are provided on these cutters. These teeth may be right hand or left hand. These cutters are employed of heavy-duty work. Milling of flat surface using the end or face and cutting slots etc. are the common operations performed by them. The former operation is called facing.

4. Face milling cutter: These cutters are made in two common forms. The smaller type almost resembles a small end-milling cutter and is known as well-type face milling cutter. It carries teeth on the periphery as well as the end face.

The teeth on the periphery do maximum cutting and those on the end face perform a type of finishing operation. The larger type of cutter called the built-up face-milling cutter consists of a steel body along the periphery of which are inserted the cutting teeth. The former type is used for small work whereas the later for larger surfaces. The shell-type cutter is usually help in a stub arbor and the larger type can be mounted directly on the spindle nose.

5. Metal slitting cutter: These cutters are also frequently called metal slitting saws.

They are used for cutting thin slots or parting off. They are commonly manufacturing in the following varieties:

(i.) Plain slitting saws: They are plain milling cutters that are very thin as compared to other of milling cutters. Their teeth are provided with some side relief in order to prevent rubbing. They are made in different widths ranging between approximately 1 mm to 5 mm. A plain slitting saw is show in fig.

(ii.) Staggered teeth milling cutter (saw): These saw are used for comparatively heavy work. They have their teeth staggered alternately and have side teeth similar to the staggered teeth side-milling cutter. These saws are generally made in different widths ranging between 4 mm and 10 mm.

6. Angle milling cutter: These cutters carry sharp angular teeth, which are neither parallel nor normal to their axes.

Their specific use is in milling V-grooves, notches, dovetail slots, reamer teeth and other angular surfaces. The following two type’s angle cutters are in common use:

(i.) Single angle cutter: These cutters may have teeth either only on the angular face or on both the angular face and side. The latter type enables milling of both the flanks of the included angular groove simultaneously. Their teeth may have an included angle of 45° or 60°.

(ii.) Double- angle cuter: These cutters differ from the single cutter in that they have two angular faces which join to from V-shaped teeth. The included angle of this “V” is either 45°, 60° or 90°, Through it is not necessary that the angle of both the face should be equal.

7. Formed milling cutters: They are also known as form relieved milling cutter or radius cutters. This category includes a large variety of milling cutter used for producing different shaped contours.

Their teeth are provided with a certain angle of relief so that there from and size are retained even after resharpening. The following are common types of relieved cutters:

(i.) Corner rounding cutters: These cutters are used for milling the edge and corner of the job to a required radius. They are manufactured separately as single cutters or double cutters. Single cutter may be right hand or left hand. The double cutter has a combination of both right and left hand in a single unit.

(ii.) Concave and convex cutter: These cutters are very commonly used type of from-relieved cutters. They are used for milling convex surface or circular contours of half-circular contours or half circle less. The names concave or convex given to the cutters do not indicate the shape of the surface to be produced but shape of the cutter teeth. As such, a convex cutter will be used for used for milling a convex surface and a convex cutter for milling a concave surface.

(iii.) Gear cutter: They are also designed as involutes gear cutters. They are used for milling gear teeth on a milling machine. The two common grades are roughing and finished, show in fig down first diagram.

(iv.) Tap and reamer fluting cutter: These formed cutters are used for milling flutes on reamer and tapes. In appearance, they look like double angle cutters such that their two inclined face meet to from a rounded corner. A typical tap and reamer fluting cutter is show in 2figure next page.

(v.) Gear hobs: A gear hob is a formed milling cutter which carries helical cutting teeth on its periphery. It is used for a number of different milling operations such as cutting teeth of worm wheels, helical and spur gear and spline shafts etc. A standard form of such a cutter is show in figure.

(vi.) Thread milling cutters: These are also formed cutter used milling different type of threads, mostly for worm and type. These cutters can be single or having multi-teeth. The included angle of the cutting teeth will correspond to the angle of the threads to be produced.

8. Woodruff-key milling cutter: It is a small type of end milling cutter that resembles with plain and side mills. Smaller size, say up to 50 mm diameter and made to have solid shank to be fitted in the machine spindle whereas the large size are provided with a hole for mounting the same on arbor.

Smaller sizes generally have straight teeth on the periphery with the side having teeth both on the periphery as well as on the sides. A small size woodruff-key milling cutter is show in figure.

9. T-slot milling cutter: It is a single operation cutter that is used only for cutting T- slots. In smaller it is made to have the shank integral with the cutter as show in figure. The large size cutters are mounted on a separate shank. In operation, the narrow groove at the top is first milled by means of a slotting cutter or end-milling cutter.

The T-slot milling cutter is then employed for milling the wider groove. Note the thin neck provided between the shank and the cutter. It facilities an unhindered movement of the cutter through the upper groove as the cut produced.

10. Fly cutter: It is actually a single point tool. It is either mounted on a cylindrical body held in a stub arbor or held in a bar exactly in same way as a boring tool in a boring bar. Screws are used for tightly holding the tool in the above holders.

Cutting edge of the tool can be ground to any desired shape. It can thus be considered as a formed tool. It is generally used for experimental producing a very accurate surface.

Milling processes: The various milling processes performed by different milling cutters may be grouped under two separate headings: peripheral milling and face milling. The cutter actions milling cutters to perform the above processes are described below:

(1) Peripheral milling: The peripheral milling is the operation performed by a milling cutter to produce a machined surface parallel to the axis of rotation of the cutter. In peripheral milling, the cutting force is not uniform throughout the length of the cut by each tooth. Due to this reason, a shock is developed in the driving mechanism of the machine that leads to a vibration. The quality of surface generated and the shape of the chip formed is dependent upon the rotation of the cutter relative movement between the tool and the work, the peripheral milling is classified under two heading: up milling and down milling. The cutting processes involved in up milling and down milling are described below:

(i.) Up milling: The up milling, which is also called conventional milling, is process of removing metal by a cutter that is rotated against the direction of travel of the work piece. The up milling operation is show in figure. The thickness of the chip in up milling is minimum at the beginning of the cut and it reaches to the maximum when the cut terminates. As the thickness per tooth is not uniform, the cutting force in up milling increases from zero to the maximum value per tooth movement of the cutter. The cutter force is directed upwards and this tends to lift the work from the fixtures. In up milling due to the typical nature of the cut, difficulty is experienced in pouring coolant just on the cutting edge from where the chip begins. As the cutter progresses, the chips accumulate at the cutting one, and may be carried over with the cutter spoiling the work surface. The surface milled by up milling appears to be slightly wavy, as the cutter teeth do not begin their cut as soon as they touch the work surface. The teeth slide through a minute distance at the beginning and then the cut is started. The up milling processes, begin safer, is still commonly used inspite of having so many disadvantage.

(ii.) Down milling: The downmilling, which is also called climb milling, is the process of removing metal by a cutter that is rotated in the same direction of travel of the work piece. The thickness of the chip is maximum when the tooth begins its cut and it reduces to the minimum when the cut terminates. The cutter tooth start removing metal immediately on reaching the workpiece, without sliding, as it can apply a sufficient bite on the work.

Milling machine operation:

1. Plain milling:

2. Face milling:

3. Side milling:

4. Straddle milling:

5. Angular milling:

6. Gang milling:

7. Form milling:

8. Profile milling:

9. End milling:

10. Saw milling:

11. Gear cutting milling:

12. Helical milling:

13. Cam milling:

14. Thread milling:

15. Milling keyways, Grooves and slots:

Mandrels: A mandrels is a devices for holding and rotating a hallow pieces of work that has been previously drilled or bored. The work revolves with the mandrel which is mounted between two centers. It is made of high carbon steel.

The ends of mandrels are slightly smaller in diameter. The mandrel is rotated by the lathe dog and the catch plate and it drives the work by friction. There are many different types of mandrels:

Plain mandrels: this type of mandrels is most commonly used in shops and finds wide application where a large number of identical pieces having standard sizes holes are required to be mounted on it. The lengths from 55 to 430 mm. the taper is provided for proper gripping of the work piece. This type of mandrel is suitable for only one size of bore.

Step mandrels: Step mandrels having steps of different diameter may be employed to drive different wok piece having different sizes of holes without replacing the mandrel each time. It is suitable for turning collars, washers and odd sizes jobs used in repairing workshops.

Collar mandrel: a collar mandrel having solid collars is used for turning work pieces having holes of larger diameter usually above 100 mm. this construction reduces weight and fits better than a solid mandrel of equal sizes.

Screwed mandrel: It is threaded at one end with a collar. Work pieces having internal threads are screwed on to it against the collar for machining. It may be right or left hander, square, ‘V’ or any other type. External surface of screwed flanges, holding them on the screwed mandrel. 

Cone mandrel: It consist of a solid attached to the one end of the body, and a sliding cone which can be adjusted by turning a nut at a threaded end. This type of mandrel is suitable for holding work-pieces having different whole diameter by a placing the work piece on two cones and tightening the nut. 

Gang mandrel: This has a fixed collar at one end and a movable collar at the threaded end which may be adjusted to this position by a nut. These mandrels are used to hole a set of hollow work pieces between two collars by tightening the nut. 

Expansion mandrel: There are different types of expansion mandrel. It consists of a tapered pin which is driven into a sleeve that is parallel outside and tapered inside. To use this mandrel, the sleeve is first placed within the work with pin removed. The diameter ranges from 0.5 to 2 mm. this range may be increased with different sizes of the sleeve. 

Rests: A rest is a mechanical device which supports a long slider work piece, which is turned between centers or by a clutch.

A rest should always be used when the length is 10 to 12 times the diameter of work piece. There are two types’ mandrels:-

Steady rest: It consists of a cast iron base, which may be made to slide on the lathe bed ways and clamped at any desired position where a support in necessary. the three jaws on the steady rest, two on the lower base and one on the upper frame.

It is to provide supports to a long slender work for this purpose one or more study rests may be used to support the free end of a long work piece.

Follower rest: It consists of a ‘C’ like casting having two adjustable jaws which support the work pieces. Te rest is bolted to the back end of the carries and moves with it .it is used in finish turning operations.