UNIT-II

SHAPER MACHINE

INTRODUCTION

In a shaper, rotary movement of the drive is converted into reciprocating movement by

the mechanism contained within the column of the machine. The ram holding the tool

gets the reciprocating movement. Thus the shaper mechanism should be so designed that

it can allow the ram holding the tool to move at a comparatively slower speed during the

forward cutting stroke, the cutting speed depending upon the type of material and

machining condition, whereas during the return stroke it can allow the ram to move at a

faster rate to reduce the idle return time. This mechanism is known as quick return

mechanism. The reciprocating movement of the ram and the quick return mechanism of

the machine are usually obtained by any off of the following methods:

1. Crank and slotted link mechanism

2. Whitworth quick return mechanism

3. Hydraulic shaper mechanism

FEED MECHANISM: In a shaper both downfeed and crossfeed movements may be

obtained. Crossfeed movement is used to machine a flat horizontal surface. The rotation

of the bull gear causes the driving disc 8 to rotate in a particular direction. The driving

disc 8 is T-slotted and position of the crank pin 9 attached to the connecting rod may be

altered to give different throw of eccentricity. The other end of the connecting rod is

attached to the rocking any by a § § The rocking arm houses a spring loaded paw which

is straight on one side and bevel on the other side. As the driving disc rotates, the

connecting The amount of feed may be altered by shifted the position of crank pin with

respect to the centre. Greater the throw of eccentricity, more will be the rocking

movement of the arm and the pawl will pass through three or four teeth on the ratchet

wheel at a time imparting greater feed movement.

PLANER MACHINE

The planer like a shaper is a machine tool primarily intended to produce plane and fiat

surfaces by a single point cutting tool.

A planer is very large and massive compared to a shaper and capable of machining heavy

workpieces which cannot be accommodated on a shaper table. The fundamental

difference between a shaper and a planer is that in a planer the work which is supported

on the table reciprocates past the stationary cutting tool and the feed is supplied by the

lateral movement of the tool, whereas in a shaper the tool which is mounted upon the ram

reciprocates and the feed is given by the crosswise movement of the table.

TYPES OF PLANING MACHINE

Different classes of work necessitates designing of different types of planing machine to

suit to various requirements of our present day industry. The different types of planer

which are most commonly used are: 1. Double housing planer. 2. Open side planer. 3. Pit

planer 4. Edge or plate planer. 5. Divided table planer.

STANDARD OR DOUBLE HOUSING PLANER: The standard or double housing

planer is most widely used in workshops. A double housing planer has a long heavy base

on which a table reciprocates on accurate guide ways. The length of the bed is little over

twice the length of the table. Two massive vertical housings or uprights are mounted near

the middle of the base, one on each side of the bed.

OPENSIDE PLANER: An open side planer has a housing only on one side of the base

and the cross rail is suspended from the housing as a cantilever. This feature of the

machine allows large and wide jobs to be clamped on the table and reciprocated past the

cutting tool. One side of the planer being opened, large and wide out of the table and

reciprocate without being interfered by the housing. § In a double housing planer, the

maximum width of the job which can be machined is limited by the distance between the

two housings.

PIT PLANER: A pit type planer is massive in construction. It differs from an ordinary

planer in that the table is stationary and the column carrying the crossrail reciprocates on

massive horizontal rails mounted on both sides of the table.

This type of planer is suitable for machining a very large work which cannot be

accommodated on a standard planer and the design saves much of floor space. The length

of the bed required in a pit type planer is little over the length of the table, whereas in a

standard planer the length of the bed is nearly twice the length of the table. The uprights

and the crossrail are made sufficiently rigid to take up the forces while cutting.

EDGE OR PLATE PLANER: The design of a plate or edge planer is totally unlike that

of an ordinary planer. It is specially intended for squaring and beveling the edges of steel

plates used for different pressure vessels and ship-building works. One end of a long

plate which remains stationary is clamped with the machine frame by a large number of

air operated clamps. § § The cutting tool is attached to a carriage which is supported on

two horizontal ways of the planer on its front end. The operator can stand on a platform

extending from the carriage. The carriage holding the tool reciprocates past the edge of

the plate. The feed and depth of cut is adjusted by the tool holder which can be operated

from the platform.

DIVIDED TABLE PLANER: This type of planer has two tables on the bed which may

be reciprocated separately or together. This type of design saves much of idle time while

setting the work. The setting up of a large number of identical workpieces on the planing

machine table takes quite a long time. It may require as much time for setting up as may

be necessary for machining. To have a continuous production one of the table is used for

setting up the work, while the other reciprocates past the cutting tool finishing the work.

When the work on the second table is finished, it is stopped and finished jobs are

removed. Fresh jobs are now set up on this table while the first table holding the jobs now

reciprocates past the tool. § When a heavy and large job has to be machined, both the

tables are clamped together and are given reciprocating movement under the tool.

PLANER MECHANISMS

The two important mechanisms of a planer are: 1. Table drive mechanism. 2. Feeding

mechanism. The different mechanisms used to drive the table are:

I. Open and cross belt drive. 2. Reversible motor drive. 3. Hydraulic drive.

OPEN AND CROSS BELT DRIVE: The open and cross belt drive of the table is used in

a planer of smaller size where the table width is less than 900 mm

DRILLING MACHINE

INTRODUCTION:-

The drilling machine is one of the most important machine in workshop In a drilling

machine holes may be derived quickly and at a low cost. The hole is generated by the

rotating edge of a cutting tool known as the drill which exerts large force on the work

clamped on the table.

TYPES OF DRILLING MACHINE: - Drilling machines are made in many different

types and sizes, each designed to handle a class of work or specific job to the best

advantage. The different types of drilling machines are

1. Portable drilling machine.

2. Sensitive drilling machine. (a) Bench mounting, 3. Upright drilling machine. (a) Round

column section,

4. Radial drilling machine. (a) Plain (c) Universal

5. Gang drilling machine.

6. Multiple spindle drilling machine.

7. Automatic drilling machine.

8. Deep hole drilling machine. (a) Vertical (b) Flour mounting

GANG DRILLING MACHINE:-When a number of single spindle drilling machine

columns are placed side by side on a common base and have a common worktable, the

machine is known as the gang drilling machine. In a gang drilling machine four to six

spindles may be mounted side by side.

MULTIPLE SPINDLE DRILLING MACHINE:-The function of a multiple spindle

drilling machine is to drill a number of holes in a piece of work simultaneously and to

reproduce the same pattern of holes in a number of identical pieces in a mass production

work. Once the work is loaded at the first machine, the work will move from one

machine to the other where different operations can be performed and the finished work

comes out from the last unit without any manual handling. § This type of machine is

intended purely for production purposes and may be used for milling, honing and similar

operations in addition to drilling and tapping.

DEEP HOLE DRILLING MACHI:-The machine is operated at high speed and low feed.

Sufficient quantity of lubricant is pumped to the cutting points for removal of chips and

cooling the cutting edges of the drill. A long job is usually supported at several points to

prevent any deflection. The work is usually rotated while the drill is fed into the work.

This helps in feeding the drill in a straight path. In some machines both the work and the

drill are rotated for accurate location. § The machine may be horizontal or vertical type.

In some machines step feed is applied. The drill is withdrawn automatically each time

when it penetrates into the work to a depth equal to its diameter. This process permits the

chip to clear out from the work.

THE SIZE OF A DRILLING MACH:-

The size of a drilling machine varies with the type of machine being considered The

sensitive and upright drilling machines are specified by the diameter of the largest piece

that can be centered under the spindle. § Thus in the case of a 600 mm size upright

drilling machine, the spindle placed at a distance is slightly greater than 300 mm from the

front face of the column.

UPRIGHT DRILLING MACHINE :-

The different parts of an upright drilling machine are as follows: 1. Base 2. Column 3.

Table 4. Head 5. Spindle, quill and drill head assembly 6. Spindle drive and feed

mechanism

Base: The base is that part of the machine on which vertical column is mounted. Column:

The column is the vertical member of the machine which supports the table and the head

containing all the driving mechanism. Table: The table is mounted on the column and is

provided with T-slots for clamping the work directly on its face Spindle drive

mechanism: The spindle drive mechanism of a drilling machine incorporates an

arrangement for obtaining multiple speed of the spindle similar to i lathe to suit to various

machining conditions. Multiple speed of the spindle may be obtained as follows: 1. By

step cone pulley drive. 2. By step cone pulley drive with one or more back gears. 3. By

gearing. Step cone pulley drive illustrates a spindle driving mechanism incorporating a

step cone pulley. The motion is transmitted from an overhead line shaft to the

countershaft mounted on the base of the machine.. § Step cone pulley drive with back

gear In order to obtain larger number of spindle speeds back gears are incorporated in the

machine in addition to the step cone pulley. § With backgears “out” the speed of the

spindle is increased and the machine is used for drilling smaller boles. For drilling larger

diameter holes or for tapping, the spindle speed is reduced by engaging the backgears.

Spindle drive by gearing: § Modem heavy duty drilling machines are driven by individual

motor mounted on the frame of the machine. The multiple speeds may be obtained by

sliding gear or sliding clutch mechanism or by the combination of the above two

methods. § The sliding gear and sliding clutch mechanism in drilling is similar to that

described in Art. 3/7.

FEED MECHANISM

§ § In a drilling machine, the feed is effected by the vertical movement of the drill into

the work. The feed movement of the drill may be controlled by hand or power. The hand

feed may be applied by two methods: I. Quick traverse hand feed 2. Sensitive hand feed

RADIAL DRILLNG MACHINE PARTS

The different parts of a radial drilling machine have been illustrated in Fig.5.3. They are

as follows:

1. Base 2. Column 3. Radial arm

4. Drill head 5. Spindle speed and feed mechanism

BASE: The base of a radial drilling machine is a large rectangular casting that is finished

on its top to support a column on its one end and to hold the work table at the other end

COLUMN : The column is a cylindrical casting that is mounted vertically at one end of

the base RADIAL ARM : The radial arm that is mounted on the column extends

horizontally over the base. ]DRILL HEAD : The drill head is mounted on the radial arm

and drives the drill spindle. It encloses all the mechanism for driving the drill at multiple

speed and at different feed. SPINDLE DRIVE AND FEED MECHANISM: There are

two common methods of driving the spindle. A constant speed motor is mounted at the

extreme end of the radial arm which balances partially the weight of the overhanging

arm.

WORK HOLDING DEVICES

Before performing any operation in a drilling machine it is absolutely necessary to secure

the work firmly on the drilling machine table. The work should never be held by hand,

because the drill while revolving exerts so much of torque on the work piece that it starts

revolving along with the tool and may cause injuries to the operator. The devices

commonly used for holding the work in a drilling machine are 1. T-bolt and clamps. 2.

Drill press vise. 3. Step blocky 4. V-block. 5. Angle plate. 6. Drilljigs

DRILLING MACHINE OPERATIONS

The different operations that can be performed in a drilling machine are:

1. Drilling. 2. Reaming. 3. Boring. 4. Counterboring. 5. Countersinking.

6. Spot facing. 7. Tapping. 8. Lapping. 9. Grinding. 10. Trepanning.

DRILLING: Drilling is the operation of producing a cylindrical hole by removing metal

by the rotating edge of a cutting tool called the drill. REAMING: Reaming is an accurate

way of sizing and finishing a hole which has previously drilled. In order to finish a hole

and to bring it to the accurate size, the hole is drilled slightly undersize. BORING: Boring

is performed in a drilling machine for reasons stated below 1. To enlarge a hole by means

of an adjustable cutting tool with only one cutting edge. This is necessary where suitable

sized drill is not available or where hole diameter is so large that it cannot be ordinarily

drilled. 2. To finish a hole accurately and to bring it to the required size. 3. To machine

the internal surface of a hole already produced in casting. 4. To correct out of roundness

of the hole. 5. To correct the location of the hole as the boring tool follows an

independent path with respect to the hole. LAPPING: § § Lapping is the operation of

sizing and finishing a small diameter hole already hardened by removing a very small

amount of material by using a lap. There are many kinds of lapping tools. The copper

head laps are commonly used. The lap fits in the hole and is moved down while it

revolves. GRINDING: Grinding operation may be performed in a drilling machine to

finish a hardened hole. TREPANNING: It is the operation of producing a hole by

removing metal along the circumference of a hollow cutting tool.

NOMENCLATURE OF DRILL TOOL:

The following are the twist drill elements.

Axis: The longitudinal centre line of the drill.

Body: That portion of the drill extending from its extreme point to the commencement of

the neck, if present, otherwise extending to the commencement of the shank.

Body clearance : That portion of the body surface which is reduced in diameter to

provide diametric clearance.

Chisel edge : The edge formed by the intersection of the flanks. The chisel edge is also

sometimes called dead centre. The dead centre or the chisel edge acts as a flat drill and

cuts its own hole in the workpiece. § A great amount of axial thrust is required to cut a

hole by the chisel edge. In some drills chisel edge is made spiral instead of a straight one.

This reduces the axial thrust and improves the hole location. Chances of production of

oversize holes are also reduced.

Chisel edge corner: The corner formed by the intersection of a lip and the chisel edge.

Face: The portion of the flute surface adjacent to the lip on which the chip impinges as it

is cut from the work.

Flank: That surface on a drill point which extends behind the lip to the following flute.

Flutes: The groove in the body of the drill which provides lip The functions of the flutes

are:

1. To form the cutting edges on the point.

2. To allow the chips to escape.

3. To cause the chips to curl.

4. To permit the cutting fluid to reach the cutting edges.

Heel: The edge formed by the intersection of the flute surface and the body clearance.

Lands: The cylindrically ground surface on the leading edges of the drill flutes. The

width of the land is measured at right angles to the flute helix. The drill is full size only

across the lands at the point end. Land keeps the drill aligned.

Lip (cutting edge): The edge formed by the intersections of the flank and face. The

requirements of the drill lips are: 1. Both lips should be at the same angle of inclinatory

with the drill axis, I

2. Both lips should be of equal length. 3. Both lips should be provided with the correct

clearance. Neck : The diametrically undercut portion between the body and the shank of

the drill. Diameter and other particulars of the drill are engraved at the neck.

DRILL MATERIAL

The materials for the manufacture of twist drills are as follows 1. One piece construction’

: High speed steel or carbon steel. 2. Two piece construction: Cutting portion —High

speed steel. Shank portion — Carbon steel with a minimum tensile strength of 70 kg per

sq mm.

High speed drills are more widely used due to its greater cutting efficiency. Cemented

carbide tipped drills are also used in mass production work.

BORING MACHINES

The boring machine is one of the most versatile machine tools used to bore holes in large

and heavy parts such as engine frames, steam engine cylinders, machine housings, etc.

which are practically impossible to hold and rotate in an engine lathe or a drilling

machine. Boring machines have, therefore, been developed primarily to do this. In

addition to its primary purpose of boring the range of speeds and feeds provided to the

various traversing components allow drilling, milling and facing to be performed with

equal facility. § By the fitting of simple attachments, the use of the machine can be

extended still further to include screw cutting, turning, planetary grinding, or gear cutting.

TYPES OF BORING MACHINES

The boring machines may be classified under the four headings:

1. Horizontal boring machine. (a) Table type. (b Floor type. (c) Planer type. (d Multiple

head type.

2 Vertical boring machine. (a) Vertical turret lathe. (b) Standard vertical boring machine.

3. Precision boring machine.

4. Jig boring machine. (a) Vertical milling machine type. (b)Planer type.

HORIZONTAL BORING MACHINE

In a horizontal boring machine, the work is supported on a table which is stationary and

the tool revolves in a horizontal axis. A horizontal boring Multiple head type horizontal

boring machine: The machine resembles a double housing planer or a piano-miller. The

table is supported on a long bed on which it reciprocates. There are two vertical columns

at two sides of the bed, nearly at the middle of the bed. The two columns are bridged by a

crossrail. The machine may have two, three or four headstocks. This type of machine

may be used both as a horizontal and vertical machine. The machining operations can be

performed simultaneously at different work surfaces

PARTS OF A HORIZONTAL BORING MACHINE

The different parts of a horizontal boring machine are Bed: The bed is that part of the

machine which is fitted on the floor of the shop and has a box like casting. The bed

supports the columns, tables and other parts of the machine. Headstock supporting

column : § § The column provides support to the headstock and guides it up and down

accurately by the guide ways provided on the face of the column. The column which is

hollow houses the counterweights of the headstock, and is heavily ribbed to add rigidity.

Some columns are stationary, others may be made to slide along the bed. End supporting

column : § § The end supporting column situated at the other end of the bed houses the

bearing block for supporting a long boring bar. The column may be adjusted on the

sideways of the bed towards or away from the spindle for supporting different lengths of

boring bars or it may be moved at right angles to the spindle as. in the case of a floor type

machine. Headstock: § The headstock mounted on the column supports, drives, and feeds

the tool. The spindle revolves within a quill. The spindle provides rotary movement to the

tool and the quill may be moved longitudinally to provide feeding movement of the

boring cutter or any tool mounted on the spindle.

The spindle nose is provided with a taper hole for receiving taper shanks of the boring bar

or any other tool. The headstock may be moved up and down on the column for setting

the tool for different heights of the work. The headstock and the end supporting bearing

block arc raised or lowered in unison by the help of screws.

Saddle and table : The table supports the work and is therefore provided with T-slots for

clamping the work or for holding various devices. The saddle permits the work to be

moved longitudinally on the bed. The table may be moved crosswise on the saddle. These

movements may be slow or rapid and is performed by hand or power. Boring bars: The

boring bar supports the cutter for boring operations on jobs having large bore diameters.

For short holes the bar may be supported on the headstock spindle end only, whereas for

long work the bar is supported on the spindle end and on the column bearing block.

BORING MACHINE MECHANISM

The machine contains different controls for movements of the different parts of the

machine. A table type machine has the following movements: 1.The headstock and the

end supporting block may be moved up and down. 2. The spindle may be rotated. The

spindle has different speeds.The spindle may be, moved in or out by hand or power for

feeding. The saddle and the table may be moved by hand or power. The columns may be

moved by hand or power.

JIG BORING MACHINE

The jig boring machine is the most accurate of all machine tools.The machining accuracy

is very high, within a range of 0.0025 mm. A jig boring machine resembles in appearance

to a vertical milling machine, but so far its operation and accuracy are concerned there

cannot be any comparison between the two. This machine are extremely rigid to resist

deflection and the vibration is minimum. The spindle runs in preloaded antifriction

bearings. The spindle housings are made of invar having a very low coefficient of linear

expansion. The jig boring machine requires to be operated in temperature controlled

rooms where temperature can be maintained constant. This is essential to prevent

inaccuracy in Jig boring machine the machine and in the work being.

Types of jig boring machines: There are mainly two types of jig boring machines: 1.

Vertical milling machine type. 2. Planer type.

Vertical milling machine type:

It resembles in construction to a vertical milling machine. The spindle rotates on a

vertical column and the horizontal table rests on the bed in front of the column The

positioning of the work mounted on the table may be obtained by compound movements

of the table, perpendicular and parallel to the column face.

Planer type:

It consists of two vertical columns at the two sides of the table and is mounted on the

base. The table has reciprocating movement for adjustment of the work. § The spindle is

mounted on the crossrail bridging the two vertical columns. In a planer type jig borer,

two co-ordinate movements for hole location are provided by the longitudinal movement

of the table and the cross movement of the spindle along the crossrail.

BROACHING MACHINE

Broaching is a method of removing metal by pushing or pulling a cutting tool called a

broach which cuts in fixed path. The tool may be pulled or pushed through the surfaces to

be finished. Surfaces finished by broaching may be flat or contoured and may be either

internal or external. Broaching is generally limited to the removal of about 6 mm of stock

or less. § The term broaching may have derived from an ancient Roman word braces,

which meant an object having projecting teeth. § The operation itself dates only to the

1850’ s when broaching tools, then called “drifts” were hammered in blacksmith shops

through the work or pushed through with an arbor press.

BROACHES A broach is a multiple-edges cutting tool that has successively higher

cutting edges along the length of the tool.

TYPES OF BROACHES : Broaches may be classified in various ways, according to: 1.

Type of operation: internal or external. 2. Method of operation: push or pull.

3. Type of construction: solid, built-up, inserted tooth, progressive cut, rotor cut, double

jump, or overlapping tooth.’ 4. Function : surface, keyway, round hole, splint, spiral,

burnishing, etc.

BROACH MATERIAL: Most broaches are made from 18-4-1 tungsten chromium

vanadium steel ground after hardening. Carbide broaches are. used extensively in the

broaching of cast iron in the automotive field. They are also used for surface broaches,

for high production and for finishing broaches.

BROACHING METHODS: Broaching, according to the method of operation, may be

classified as follows 1.Pull broaching: The work is held stationary and the broach is

pulled through the work. Broaches are usually long and are held in a special head. Pull

broaching is used mostly for internal. broaching but it can do some surface broaching.

2.Push broaching: The work is held stationary and the broach is pushed through the work.

Hand and hydraulic arbor presses are popular for push broaching, This method is used

mostly for sizing holes and cutting keyways. 3.Surface broaching: § Either the work or

the broaching tool moves across the other. This method has rapidly become as important

means of surface finishing. Fixtures are most important in broaching operations. § They

are used particularly for two reasons first, because of the high pressures used and because

of the manner in which the cutting is done ; second, broaching being essential a mass-

production operation, fixtures speed up the operation and help to keep it accurate.

BROACHING OPERATION § Broaching is applied for machining various internal and

external surfaces, for round or irregular shaped holes from 6 to 100 mm in diameter, for

external flat and contoured surfaces. Certain types of surfaces, for example, splint holes,

are machined at the present time only by broaching due to the exceptional difficulties in

machining such surfaces by other methods. § Most broaching operations are completed in

one pass, but some are arranged for repeated cuts to simplify the design of the broach. §

The teeth of a gear or splint may be broached altogether or one or a few at a time. A

comparatively simple broach can be made to cut one or a few tooth spaces, After one

pass, the gear blank is indexed, and more of its teeth are cut. Successive passes are made

until all the teeth are finished.

ADVANTAGES AND LIMITATIONS OF BROACHING:-

Broaching has been adopted for mass production work because of the following

outstanding features and advantages: 1. Rate of production is very high. With properly

applied broaches, fixtures, and machines, more pieces can be turned per hour by

broaching than by any other means, 2. Little skill is required to perform a broaching

operation. In most cases the operator merely loads and unloads the workpiece. 3. High

accuracy and a high class of surface finish is possible. A tolerance of ± 0.0075 mm and a

surface finish of about 0.8 microns (1 micron =0.001mm) can be easily obtained in

broaching. 4. Both roughing and finishing cuts are completed in one pass of the tool. 5.

The process can be used for either internal or external surface finishing. 6. Any form that

can be reproduced on a broaching can be machined. 7. Cutting fluid may be readily

applied where it is most effective because a broach tends to draw the fluid into the cut.

Certain reasons, however, limit the application of the broaching process. They are: 1.

High tool cost. A broach usually does only one job and is expensive to make and sharpen.

2. Very large workpieces cannot be broached. 3. The surfaces to be broached cannot have

an obstruction. 4. Broaching cannot be used for the removal of a large amount of stock. 5.

Parts to be broached must be capable of being rigidly supported and must be able to

withstand the forces that set up during V Cutting.

GRINDING MACHINES

INTRODUCTION § Grinding is metal cutting operation performed by means of a

rotating abrasive wheel that acts as a tool. This is used to finish workpieces which must

show a high surface quality, accuracy of shape and dimension. § Mostly grinding is the

finishing operation because it removes comparatively little metal, 0.25 to 0.50mm in

most operations and the accuracy in dimensions is in the order of 0.000025 mm. KINDS

OF GRINDING Grinding is done on surfaces of almost all conceivable shapes and

materials of all kinds. Grinding may be classified broadly into two groups I. Rough or

non-precision grinding. 2. Precision grinding.

Rough grinding: § The common forms of rough grinding are snagging and off-hand

grinding where the work is held in the operator’ s hand. The work is pressed hard against

the wheel, or vice -versa. The accuracy and surface finish obtained are of secondary

importance. § Snagging is done where a considerable amount of metal is removed

without regard to the accuracy of the finished surface. Examples of snag grinding are

trimming the surface left by sprues and risers on castings, grinding the parting line left on

castings, removing flash on forgings, the excess metal on welds, cracks, and

imperfections on alloy steel billets.

Precision grinding: This is concerned with producing good surface finish and high degree

of accuracy. The wheel or work both are guided in precise paths. Grinding, in accordance

with the type of surface to be ground, is classified as 1. External cylindrical grinding. 3.

Surface grinding.

2. Internal cylindrical grinding. 4. Form grinding. External cylindrical grinding §

produces a straight or tapered surface on a workpiece. The workpiece must be rotated

about its own axis between centers as it passes lengthwise across the face of a revolving

grinding wheel. It produces internal cylindrical holes and tapers. § The workpieces are

chucked and precisely rotated about their own axis. The grinding wheel or, in the case of

small bore holes, the cylinder wheel rotates against the sense of rotation of the workpiece.

Surface grinding produces flat surface. The work may be ground by either the periphery

or by the end face of the grinding wheel. The workpiece is reciprocated at a constant

speed below or on the end face of the grinding wheel. Form grinding is done with

specially shaped grinding wheels that grind the formed surfaces as in grinding gear teeth,

threads, splined shafts, holes, and spheres, etc. In Grinding machines, according to the

quality of surface finish, may be classified as: 1. Rough grinders. 2. Precision grinders.

ROUGH GRINDERS: Rough grinders are those grinding machines whose chief work is

the removal of stock without any reference to the accuracy of the results. They are mainly

of the following types:

1. Floor stand and bench grinders. 2. Portable and flexible shaft grinders. 3. Swing frame

grinders. 4. Abrasive belt grinders. PRECISION GRINDERS: Precision grinders are

those that finish parts to a very accurate dimensions. According to the type of surface

generated or work done they may be classified as follows 1. Cylindrical grinders (a)

Centre-type (Plain) (b) Centre-type (Universal) (c) Centreless 2. Internal grinders (a)

Chucking (i) Plain (ii) Universal (b) Planetory (c) Centreless 3. Surface grinders (a)

Reciprocating table (i) Horizontal spindle (ii) Vertical spindle (b)Rotating table (i)

Horizontal spindle (ii) Vertical spindle 4. Tool and cutter grinders (a) Universal (b)

Special 5. Special grinding machines

FLOOR-STAND AND BENCH GRINDERS

The simplest type of grinder is the floor-stand grinder. A floor-stand grinder has a

horizontal spindle with wheels usually at both ends and is mounted on a base or pedestal.

1.There is provision for driving the wheel spindle by belt from motor at the rear, at floor

level. 2. The headstock can be swiveled at an angle in a horizontal plane. 3. The wheel

head and slide can be swivelled and traversed at any angle. The wheelhead can also be

arranged for internal grinding by the addition of an auxiliary wheelhead to revolve small

wheels at high speeds.

CENTRELESSS GRINDERS

Centreless grinding is a method of grinding exterior cylindrical, tapered, and formed

surfaces on workpieces that are not held and rotated on centres. The principal elements of

an external centreless grinder are the grinding wheel, regulating or back up wheel, and

the work rest. Both wheels are rotated in the same direction. The work rest is located

between the wheels. The work is placed upon the work rest, and the latter, together with

the regulating wheel, is fed forward, forcing the work against the grinding wheel. § The

axial movement of the work past the grinding wheel is obtained by tilting the regulating

wheel at a slight angle from horizontal.

Centreless grinding may be done in one of the three ways :

(a) through feed,

(b) infeed and

(c) end feed. Internal grinders of chucking type may be classified as plain and universal

grinders. In a plain internal grinder, the workhead can be swivelled to grind a straight

hole tapers upto 450 included angle. The wheel head is moved into and away from the

bole and can be cross fed into the work. § In a universal grinder, which is basically the

same as a plain internal grinder, the workhead is mounted on a cross-slide as in the wheel

head, and can be swivelled through a 9O0angle

SURFACE GRINDERS

Surface grinding machines are employed to finish plane or flat surfaces. They are also

capable of grinding irregular, curved, convex, and concave surfaces. § Conventional

surface grinders may be divided into two classes One class has reciprocating tables for

work ground along straight lines, while the other covers the machines with rotating work

tables for § The first two are most commonly used for repetitive work by hand operation

or with simple fixtures. The third type is widely used for production operations where

parallel surfaces are ground simultaneously.

TOOL AND CUTTER GRINDERS

Tool and cutter grinders are used mainly to sharpen and recondition multiple tooth

cutters like reamers, milling cutters, drills, taps, hobs and other types of tools used in the

shop.

With various attachments they can also do light surface, cylindrical, and internal grinding

to finish such items as jig, fxture, die and gauge details and sharpen single point tools.

They are classified according to the purpose of grinding, into two groups:

Universal tool and cutter grinders. purpose tool and cutter grinders.

Single -Universal tool and cutter grinders are particularly intended for sharpening of

miscellaneous cutters. Single-purpose grinders are used for grinding tools such as drills,

tool-bits etc in large production plants where large amount of grinding work is necessary

to keep production tools in cutting condition. In addition, tools can be ground uniformly

and with accurate cutting angles proper

Universal tool and cutter grinders The universal tool and cutter grinders made by

different manufacturers vary more or less as to details, but they are similar in their

general arrangement and operate on the same general principle. The grinder has the

following principal parts. Base: The base 4 gives rigidity and stability to the machine. It

is heavy, rugged and box-type. Tapered face straight wheels primarily used for grindiag

thread, gear teeth, etc. Cylinder or wheel ring is used for producing flat surfaces, the

grinding being done with the end face of the wheel. Cup wheel No. 6 is used for grinding

flat surfaces by traversing the work past the end or face of the wheel. Flaring cup wheel

No.11 is used for grinding in tool room. Dish wheel No. 12 is also used for tool room

work. The thinness of the wheel permits it grind the surface at narrow places. Saucer

wheel No. 13 is generally used for sharpening of circular or band saws. The principal

dimensions of a grinding wheel are the outside diameter, bore diameter, and the width.

Segmented wheels are used chiefly on vertical spindle, rotary, and reciprocating-table

surface grinders and way grinders. Grinding wheels of the straight wheel type can be

supplied with a large variety of face : flat, pointed, concave, convex, etc. These faces are

used for grinding special contours and sharpening saws.

MOUNTED WHEELS Mounted wheels are small shaped wheels (50 mm dia and below)

mounted securely and permanently to steel spindle or mandrel by cementing or other

means. Mounted wheels and points are shown Great care should be taken in using

mounted wheels and points.

Pressure between wheel and work small at no time be so heavy that any considerable

springing of the spindle will result. It is particularly important to observe this rule in

connection with small wheels and points where the end of the mandrel entering the wheel

is of reduced diameter.

STANDARD MARKING SYSTEM The Indian standard marking system for grinding

wheels (IS: 551-1954) has been prepared with a view to establishing a uniform system of

marking of grinding wheels to designate their various characteristics, to give a general

indication of the hardness and grit size of any wheel as compared with another. Each

marking shall consist of six symbols, 1. Abrasive type 2. Grade 3. Grain size 4. Structure

5. Bond type 6. Manufacturer’ s record

SELECTION OF GRINDING WHEELS § It is customary for grinding wheel

manufactures to provide, through their published literature, information on the selection

and use of grinding wheels, but it may not always be possible or convenient for users to

take advantage of such consultative service. § The need for ready to use general guide on

grinding wheels hp been keenly felt and the Indian Standard (IS:1249-1958) gives

recommendations on the general considerations which should guide the selection of

grinding wheels for different applications. In selecting a grinding wheel there are four

constant factors and four variables given in table grinding wheel selection factors

1. The material to be ground This influences the selection of (a) abrasive, (b) grain size,

(c) grade, (d) structure, and (e) bond.

As general guide the grit and grade ranges given in Table would be suitable for the class

of work shown against each (a) Aluminum Oxide abrasive is recommended for materials

of high tensile strength and silicon carbide for low tensile strength. (b) Fine grain is used

for hard and brittle materials and coarse grain for soft ductile metals. (c) Hard wheel is

used for soft materials and soft wheel for hard materials. (d) Generally, close spacing is

required for hard and brittle materials and wide for soft and ductile. (e) The class of work

usually dictates the bond to be used. Bond selection, of course, can be safely left to the

manufacturers, if the class of work for which the wheel is required is clearly stated.

However, majority of wheels are manufactured with vitrified bonds.

2. Amount of stock to be removed: This involves accuracy and finish. Coarse grain is

used for fast cutting and fine grain for fine finish; wide spacing for rapid removal and

close for fine finish; resinoid, rubber, and shellac bond for high finish.

3. Area of contact: Area of contact influences the selection of (a) grit size, (b) grade, and

(c) structure number. Fine grain and close grain spacing are useful where the area of

contact involved is small, and coarse grain and spacing are employed where a large area

of contact is concerned.

4. Type of grinding machine: Type of grinding machine determines to an extent the grade

of the wheel. Heavy rigidly constructed machines take softer wheels than the lighter more

flexible types. The combination of speeds and feeds on some precision machines may

affect the grade of wheel desirable for best results. (i) Wheel speed : The wheel speed

influences the selection of grade and bond. The higher the wheel speed with relation to

work speed, the softer the wheel should be. Vitrified bond is usually specified for speeds

upto 2000 s.m.p.m. (or 6~00 s.f.p.m.) and rubber, shellac or resinoid bonds for speed

over 2000 s.m.p.m. (or 6500 s.f.p.m.). (ii) Work speed: The work speed with relation to

the wheel speed determines the hardness of the wheel. The higher the work speed with

relation to the wheel speed, the harder the wheel should be. Variable work speed are

often provided on grinding machines to preserve the proper relative surface speeds

between the work and wheel as the wheel diameter decreases because of wear.

MOUNTING THE GRINDING WHEELS

Great care must taken in mounting the grinding wheels on the spindle because of the high

cutting speeds of the grinding wheel.. The following points are important in connection

with mounting the wheel. I. All wheels should be closely inspected just before mounting

to make sure that they have not been damaged in transit, storage, or otherwise. The wheel

must first be subjected to the ringing test. For this purpose, the grinding wheel is put on

an arbor while it is subjected to slight hammer blows. A clear, ringing, vibrating sound

must be heard. If a grinding wheel contains fine cracks, discordant sound that fail to

vibrate will be emitted. This test is applicable to vitrified and silicate wheels. Shellac,

resinoid or Rubber loaded wheels will not ring distinctly. 2. The abrasive wheels should

have an easy fit on their spindles or locating spigots. They should not be forced on.

BALANCING GRINDING WHEELS

If wheels become out of balance through wear and cannot be balanced by truing or

dressing, they should be removed from the machine and discarded. Wheels should be

tested for balance occasionally and rebalanced if necessary. Wheels that are out of

balance not only produce poor work but may put undue strains on the machine. Small

wheels may be balanced by milling a short recess on the inside of the flanges and filling

with lead. Large wheels should be placed on a balancing stand and balanced by moving

weights around a recessed flange. Now-a-days, grinding wheel mounts are provided with

devices to enable balancing to be done whilst the wheel is running and between grinding

operations.

SURFACE FINISHING PROCESSES

INTRODUCTION:- In a manufacturing plant, a product may be shaped, turned, milled or

drilled, and left in that condition as being satisfactory for use. However, If a better finish

is desired, for looks, for accuracy, for wearing qualities, or for any other reasons, one of

the micro finishes that include lapping, honing, super finishing, polishing, buffing, may

be employed. § In some cases other operations are done only -to get durable finishes.

LAPPING

Lapping is an abrading process that is used to produce geometrically true surfaces,

correct minor surface imperfections, improve dimensional accuracy, or provide a very

close fit between two contact surfaces. Very thin layers of metal (0.005 to 0.01 mm) are

removed in lapping and it is, therefore, evident that lapping is unable to correct

substantial errors in the form and sizes of surfaces.

It is, however, low efficiency process and is used only when specified accuracy and

surface finish cannot 1e obtained by other methods.

Small flat surfaces may be lapped by holding the work against a rotating disc, or the

work may be moved by hand in an irregular path over a stationary faceplate lap. In

equalizing lapping the work and lap mutually improve each others surface as they slide

on each other. § There are three important types of lapping machines. The vertical axis

lapping machine laps flat or round surfaces between two opposed laps on vertical

spindles. The centreless lapping machine is designed for continuous production of round

parts such as piston pins, bearing races and cups, valve tappets and shafts. The centreless

lapping machine operates on the same principle as centreless grinding. The abrasive belt

lapping machine laps bearings and cam surfaces by means of abrasive coated clothes.

HONING

Honing is grinding or a abrading process mostly for finishing round holes by means of

bonded abrasive stones, called hones. Honing is therefore a cutting operation and has

been used to remove as much as 3 mm of stock but -is normally confined to amounts less

than 0.25 mm. § Honing is done on general purpose machines, such as the lathe, drill

press, and portable drills, as an expedient. But more economical results can be obtained

by honing machines for production work. There are two general types of honing

machines Horizontal and vertical. A honing machine rotates and reciprocates the hone

inside holes being finished. The two motions produce round and straight holes that have a

very fine surface finish of random scratches. Vertical honing machines are probably more

common. Horizontal honing machines are often used for guns and large bores.

SUPERFINISHING

Supervising is an operation using bonded abrasive stones in a particular way to produce

an extremely high quality of surface finish in conjunction with an almost complete

absence of defects in the surface layer. § A very thin layer of metal (0.005 to 0.02 mm) is

removed in super finishing. This operation may be applied for external and internal

surfaces of parts made of steel, cast iron and non-ferrous alloys, which have been

previously ground or precision turned. It is most frequently used to obtain very fine

surface finish. In super finishing, a very fine grit (grain size 400 to 600) abrasive stick is

retained in a suitable holder and applied to the surface of the work piece with a light

spring pressure. The stick is given a feeding and oscillating motion, and the work piece is

rotated or reciprocated according to the

requirements of the shape being super finished, In this process, the work rotational speed

is low (2 to 20 in/mm.) the longitudinal feed ranges from 0.1 to 0.15mm per work piece

revolution, the abrasive stick oscillates rapidly in short strokes (2 to 5mm) with a

frequency from 500 to 1,800 strokes per minute and the springs hold the stick against the

work with a force from 2 to 10 kg. A special lubricant, usually a mixture of kerosene and

oil, is used to obtain a high quality of surface finish, § Special general-purpose machine

tools are available for super finishing. Other types of ordinary machines, in particular,

lathes, are sometimes employed for this purpose. Single purpose machine tools for

example, for finishing crankshaft journals, camshafts, etc. are also used. PART-A 1. The

one and only basic machine is________ 2. State any two other basic machines. 3.

Mention the types of other basic machine, which are w 4. What is shaper? 5.List any four

important parts of a shaper. 6. Define one pass of the cutting tool 7. In which stroke, the

speed of the ram is faster? 8. Define cutting ratio of a shaper. 9. List any two types of

quick return mechanism. 10. How the feed and depth of cut is given to the shaper? 11.

State the various types of flat surface produced on a shaper. 12. What are the various

types of shaper according to various conditions? 13. What are the other types of shaper?

14. Mention any four-shaper speafications. 15. Why the apron is fitted away from the

machined surface machining? 16. State the important part to control and divert the flow

of oi4 17. State any two advantages of hydraulic drive?

18. State the type of mechanism followed on a shaper and how it works? 19. What are the

precautions to be carried out before machining anp surfaces? 20. State any two reasons

for making the stroke length greater than work length. 21. List any four types of work

holding devices? 22. What are the various types of tool? 23. How the tool is fitted on the

tool head for machining inclined surfaces? 24.How the dovetail is machined? 25. What

are the various types of recessing that can be made by 1h 26.How the fred and depth of

cut are given to the shaper while machining irregular surfaces? 27.Define feed and depth

of Cu I. 28. Write down the formula for calculating no. of strokes and passes required in a

shaper. 29.Define the metal removal rate. PART-B 1. Describe the principle of operation

of a shaper with a neat sketch. 2. Explain briefly the various parts of a shaper with neat

sketches. 3. Write short notes on a. Universal shaper b. Draw cut shaper 4. Describe the

working of a hydraulic drive quick return mechanism. 5. Explain crank and slotted link

mechanism and how quick return principle is achieved. 6. 1-low the stroke length and

position are adjusted? Explain briefly with a neat sketch. 7. Describe the automatic feed

of the shaper table with a suitable sketch. 8. List all work holding devices and explain any

two in detail. 9. Explain with neat sketches the machining of inclined and irregular

surfaces. 10. Write a short notes on machining shots, grooves and keyways.

11. A shaper is operated at 130 cutting strokes per minute and is used to machine a work

piece of 300mm in length and 122mm in widtlt Use a feed of 0.7mm per stroke and a

depth of cut of 5mm. Calculate the total machining time for machining the component

The forward stroke is completed in 220°. Calculate the percentage of the time when the

tool is not contacting the work piece. 12. Calculate the power required for shaping steel

with a depth of cut of 2.6mm, cutting speed 73 rn/mm and the work length 54 mm. The

feed rate is 0.6mm/rev. Take machining constant k as 79x 10 13. Estimate the shortest

machining time required in a shaper to machine a plate of 220 x 80mm under the

following conditions. Cutting speed = 13.3m/min Feed = 0.67mm/double stroke Ratio of

cutting speed to rapid return 14. The cross-feed on a shaper consists of a lead screw

having 0.25 threads per mm. A ratchet and pawl on the end of the lead screw is driven

from the shaper crank such that the pawl indexes the ratchet by one tooth during each

return stroke of he ram. Ratchet has 23 teeth. (a)Find the cross feed in mm. (b) If a plate

120mm wide has to be machined in 15 minutes. Find the cutting speed in rn/s. The ratio

of return to cutting speed is 2.5:1 and the length of the stroke is 130mm.