MCMT UNIT-4

UNIT-4MILLING MACHINES

A milling machine is a machine tool that removes metal as the work is fed against a rotating multi point cutter. Thecutter rotates at a high speed, and because of the multiple cutting edges it removes the metal at a very fast rate.WORKING PRINCIPLE OF MILLING MACHINEWorking of a milling machine is based on the fact that milling cutter is fed against work piece. This is achieved bydeveloping relative motion with precise control between work piece and rotating milling cutter. Feed motion is generallygiven to the work piece through its holding device. Cutting mechanism of the work piece in milling operations is(1) Conventional(2) Partial Face Milling(3) End Milling(4) Profile Milling(5) Pocket Milling(6) Surface Contouringsame as that in turning operation on lathe. This cutting takes place due to plastic deformation of metal by the cuttingtool. Milling machine can also hold more than one cutter at a time. The holding device is supported by mechanism thatcan offer a selective portion of the work piece to milling cutter for its processing. Indexing is one of the examples of thistype of processing.SPECIFICATIONS OF A MILLING MACHINE1. The max. length of longitudinal, cross and vertical travel of the table.2. No. of spindle speeds,3. No. of table speeds and feeds4. Floor space required5. Net weight required6. Spindle nose taper (for vertical milling machine spindle and arbors)7. Total power availableTYPES(CLASSIFICATION )OF MILLING MACHINES*Give a brief classification of various milling machines used in the industry, giving a brief note on theapplications.2013RColumn and Knee Type Milling Machine(a) Head milling machine(b) Plain milling machine(c) Universal milling machine(d) Omniversal milling machine(e) Vertical milling machineFixed Bed Type Milling Machine(a) Simplex milling(b) Duplex milling(c) Triplex millingSpecial Type Milling Machine(a) Rotary table milling(b) Drum milling(c) Planetary milling(d) Tracer controlled millingIn addition to above three types there is one more type of milling machine named as planner type milling machinewhich is rarely usedHead Milling Machine: In case of head milling machine feed motion is given by hand and movements of the machineare provided by motor. This is simple and light duty milling machine meant for basic operations.Plain Milling Machine: Plain milling machine is similar to hand milling machine but feed movement can be poweredcontrolled in addition to manual control.PRINCIPAL PARTS OF A MILLING MACHINEGenerally columns and knee type milling machine is considered as typical milling machine. Principal parts of a typicalmilling machine are described as below.Base:It provides rest for all parts of milling machine including column. It is made of grey iron by casting.Column:It is a type of rigid vertical long box. It houses driving mechanism of spindle, table knee is also fixed to theguide ways of column.Knee:Knee can be adjusted at a height on the column. It houses the feed mechanism of the table and other controls.Saddle:Saddle is placed at the top of the knee. Saddle provides guide ways for the movement of the table.

Prepared by s.sanyasirao, assistant professor, VITS College of Engg., Sontyam,[email protected],9292556602/8179525072

Table: Table rests on the saddle. It consists of T shaped slots for clamping the work piece.Movements of the table (feedmotions) are given in very controlled manner be lead screw.Overhanging Arm: Over hanging arm is mounted on the column and serves a bearing support for the arbor.This arm isadjustable so that the bearing support may be provided near to the milling cutter. There can be more than one bearingsupports to the arbor.Arbor: It holds rotating milling cutters rigidly and mounted on the spindle. Sometimes arbor is supported at maximumdistance from support of overhanging arm like a cantilever, it is called stub arbor. Locking provisions are provided inthe arbor assembly to ensure its reliability.Front Brace Milling:Front base is used to adjust the relative position of knee and overhanging arm. It is also an extrasupport fixed between the knee and overhanging arm for rigidity.Spindle:Spindle is projected from the column face and provided with a tapered hole to accommodate the arbor.Performance of a milling machine depends on the accuracy, strength and rigidity of the spindle. Spindle also transfer themotive power to arbor through belt or gear from column.PRINCIPLE FEATURES OF MILLING MACHINESHorizontal Milling Machine:-*How will you classify milling machines? Using neat sketch, describe the principal parts of the horizontalmilling machine by neat sketches. 2012S*How will you classify milling machines? Using neat sketch, describe the principal parts of the horizontal millingmachine by neat sketches. 2012S

*Describe the working and constructional features of column & knee type milling machine. 2013S1. Column & knee type: Most commonly used for general shop work. The table is mounted on the knee casting, whichin-turn is mounted on the vertical slides of the main column. The knee is vertically adjustable on the column, so that thetable can be moved up and down to accommodate work of various heights. The table can be moved longitudinally andcross wise on the knee casting. Classification of this type is based on methods of supplying power to the table, diff.movement of the table and diff. axis of rotation of the main spindle.(a)Hand milling machine: Feeding is done by hand and used for light and simple operations like slots, grooves,keyways. This is available in both horizontal & vertical models Table movements are as above.(b) Plain milling machine : This is a horizontal type milling m/c. This is more rigid and sturdy, for heavy work, can befed by hand or power.Table can be fed as above.(c) Universal millingmachine :*Explain the principle features of Universal milling machine. 2014RThis is also a horizontal type milling m/c. In addition to 3movements in plain milling machine the table has a fourthmovement i.e. it is fed at an angle to milling cutter. This enable it to perform helical milling. This machine can producespur, spiral, bevel gears,twist drills, reamers, milling cutters etc.(d) Omniversal milling machine : This is a horizontal type milling m/c. The extra fifth movement is the table can betilted in vertical plane by providing a swivel arrangement at the knee. This enables milling in any plane. Taper spiralgroves in reamers, bevel gears etc can be done.(e) Vertical milling machine*With the help of a neat sketch explain vertical type milling machine and name its main parts. 2012S*Sketch and describe a vertical milling machine. 2015S*Discuss the principle features of vertical milling machines. 2014RHere the position of the spindle is vertical and – to the work table. The spindle head is clamped to the vertical columnand can be swiveled at an angle . Also the spindle head can be adjusted up / down relative to work. The tablemovements are same as plain milling machine.

2. Plano Miller:It resembles a planer. It is having two spindle heads adjustable in vertical and transverse directions. Ithas a cross rail which can be raised or lowered along with cutters. Hence no. of work surfaces can be machinedsimultaneously, there by reducing production time. Ina plano miller, the table has feed movement instead ofreciprocation. Hence the table movement here is much slower than planning machine.

3. Rotary table Machine : A modification of vertical milling machine adopted for machining flat surfaces. A No. ofwork pieces can be mounted on a circular table which rotates about vertical axis. The face milling cutters can bemounted on tow (or) more vertical spindles and can be set at diff .heights relative to work so that when one cutter isroughing the other is finishing them. Continuous loading and unloading of work pieces can be done by the operatorwhile milling is in progress.*Whatarethedifferencesbetweenbedtypeandplanartypemillingmachine?Discuss withneatsketches 2014S4.Planetary milling machine: Here the work is held stationary while the revolving cutter /cutters move in a planetarypath to finish a cylindrical surface on the work either internally / externally /simultaneously. This machine isparticularly adopted for milling internal/ external threads of different pitches.

5. Pantograph milling machine : It can duplicate a job by using a pantograph mechanism which permits the size othe work piece reproduced to be smaller than, equal to or greater than the size of a template or model used for thispurpose. A pantograph is a mechanism that is generally constructed of four bars or links joined in the form ofparallelogram. Pantograph machines are available in 2D or3D models. 2-D models are used for engraving lettersor other designs, 3-D models are used for copying any shape and contour of the work piece. The tracing stylus is movedmanually on the contour of the model to be duplicated and the milling cutter mounted on the spindle moves in a similarpath on the work piece, reproducing the shape of the model.







6.Fixed Bed Type Milling MachineIt is also known as manufacturing type milling machine. Its table is mounted directly on the ways of fixed bed. Tablemovement is restricted to reciprocation only. Cutter is mounted on the spindle head which can move vertically on thecolumn. Duplex milling machine has double spindle heads, one on each side of the table. Triplex milling machinehas three spindle heads one each side of the table and third one is mounted on the cross rail. Bed type milling machine isshown.

MILLING MACHINE OPERATIONS*Explain various types of milling operations using neat sketches. 2012S*What machining operations can be done on a milling machine? 2014R*Describe the various operations that can be performed on a milling machine with neat sketches. 2013S*What are the different operations that can be performed on a milling machine? Explain. 2013SMilling operations described earlier were based on major categorization of milling. These were differentiated on thebasis of relative position of milling cutter and work piece. Their detailed description is given below. Following differentoperations can be performed on a milling machine :(a) Plain milling operation (b) Face milling operation (c) Side milling operation (d) Straddle milling operation(e) Angular milling operation (f) Gang milling operation (g) Form milling operation (h) Profile milling operation(i) End milling operation (j) Saw milling operation (k) Slot milling operation (l) Gear cutting operation(m) Helical milling operation (n) Cam milling operation (o) Thread milling operation*Describe the following operations with sketches. 2012R

i) Peripheral milling and ii) Face milling*Write a short notes on following milling operations. 2012R

a)Straddle milling b) Gang milling c) String milling*With the help of neat sketches, explain the following with reference to milling: 2013R

(i) Straddle milling (ii) Gang millingPlain Milling OperationProducing plain, flat horizontal surface.This is called slab milling if performed with a peripheral cutter and called faceMilling if a face milling cutter is used.

Face Milling Operation*What are the differences between face milling and end milling? Explain their applications. 2015S*Distinguish between face milling and end milling. 2014RThis operation produces flat surface at the face o the work piece. This surface is perpendicular to the surface prepared inplain milling operation. This operation is performed by face milling cutter mounted on stub arbor of milling machine.Depth of cutis set according to the need and cross feed is given to the work table.Side Milling OperationThis operation produces flat and vertical surfaces at the sides of the work piece. In this operation depth of cut is adjustedby adjusting vertical feed screw of the work piece.













*Explain the following milling operations: 2015Si)Straddle milling ii)Gang milling

Straddle Milling OperationThis is similar to the side milling operation. Two side milling cutters are mounted on the same arbor. Distance betweenthem is so adjusted that both sides of the work piece can be milled simultaneously. Hexagonal bolt can be produced bythis operation by rotating the work piece only two times as this operation produces two parallel faces of boltsimultaneously.

Angular Milling Operation

Angular milling operation is used to produce angular surface on the work piece. The produced surface makes an anglewith the axis of spindle which is not right angle.Production of V shaped groove is the example of angular millingoperation. Angular milling is shown.Gang Milling Operation

As the name indicates, this operation produces several surfaces of a work piece simultaneously using a gang of millingcutters. During this operation, the work piece mounted on the table is fed against the revolving milling cutters. Thisoperation is illustrated.Form Milling Operation

Form milling operation is illustrated in below figure.This operation produces irregular contours on the work surface.These irregular contours may be convex, concave, or of any other shape. This operation is done comparatively at verylow cutter speed than plain milling operation.Profile Milling Operation

In this operation a template of complex shape or master die is used. A tracer and milling cutter are synchronizedtogether with respect to their movements. Tracer reads the template or master die and milling cutter generates the sameshape on the work piece.Profile milling is an operation used to generate shape of a template or die. This operation is demonstrated in the belowfigure.

End Milling Operation

End milling operation produces flat vertical surfaces, flat horizontal surfaces and other flat surfaces making an anglefrom table surface using milling cutter named as end mill.This operation is preferably carried out on vertical millingmachine. This operation is illustrated in the below figure.Saw Milling Operation*How can sawing be done on milling machine? 2015SSaw milling operation produces narrow slots or grooves into the work piece using saw milling cutter. This operation isalso used to cut the work piece into two equal or unequal pieces which cut is also known as “parting off”. Incase ofparting off operation cutter and work piece are set in a manner so that the cutter is directly placed over one of the slot ofthe worktable as illustrated in Figure .

Slot Milling OperationThe operation of producing keyways, grooves, slots of varying shapes and sizes is called slot milling operation. Slotmilling operation can use any type of milling cutter like plain milling cutter, metal slitting saw or side milling cutter.Selection of a cutter depends upon type and size of slot or groove to be produced. Right placement of milling cutter isvery important in this operation as axis of cutter should be at the middle of geometry of slot or groove to be produced.The operation is illustrated in the below figure.

Gear Cutting Operation*How do you perform gear cutting on a milling machine? 2014R

The operation of gear cutting is cutting of equally spaced, identical gear teeth on a gear blank by handling it on auniversal dividing head and then indexing it. The cutter used for this operation is cylindrical type or end mill type. Thecutter selection also depends upon tooth profile and their spacing. Gear cutting operation is illustrated in Figure.Indexing is explained in detail later in this unit.

Helical Milling OperationHelical milling produces helical flutes or grooves on the periphery of a cylindrical or conical work piece. This isperformed by swiveling the table to the required helix angle, then rotating and feeding the work piece against revolvingcutting edges of milling cutter. Helical gears and drills and reamers are made by this operation.Cam Milling Operation*What are the various methods by which a cam can be cut? 2014SThe operation cam milling is used to produce the cam on milling machine. In this operation cam blank is mounted at theend of the dividing head spindle and the end mill is held in the vertical milling attachment.Thread Milling OperationThe operation thread milling produces threads using thread milling centres. This operation needs three simultaneousmovements revolving movement of cutter, simultaneous longitudinal movement of cutter, feed movement to the workpiece through table. For each thread, the revolving cutter is fed longitudinal by a distance equal to pitch of the thread.Depth of cut is normally adjusted equal to the full depth of threads.1. Peripheral Milling: It is the operation performed by a milling cutter to produce a machined surface parallel to theaxis of rotation of the cutter. Here the cutting force is not uniform throughout the length of cut by each tooth. Due tothis reason, a shock is developed in the mechanism of the machine that leads to a vibration. The quality of surfacegenerated and the shape of the chip formed is dependent upon the rotation of the cutter relative to the direction of feedmovement of the work. According to the relative movement between the tool and work, the peripheral milling isclassified into two types:*Describe the relative characteristics of climb milling and up milling. 2013R*Describe the relative characteristics of climb milling and up milling and their importance in machining operations.2012S(a) Up milling/ Conventional milling: The metal is removed by the cutter which is rotated against the travel of the W.P.The thickness of the chip is min. at the beginning of cut max.when the cut terminates. The cutting force is directed upwards and this tends to lift the work from the fixtures. This is used for roughing operations. The chips accumulate at thecutting zone, and may be carried over with the cutter, spoiling the work surface.It generates a poor finish. Cutting force and power are more.(b) Down milling/ Climb milling: The metal is removed by the cutter which is rotated in the same direction of travel ofthe W.P. The thickness of the chip is max. when the tooth begins its cut and it reduces to the min. when the toothleave the work. The cutting force is directed down wards &this tends seat the work firmly in the work holding devices.Hence fixture design is easier. This operation cannot be used on old machine as the back lash error present in the screwelements that may cause vibration and damages the work surface considerably. Hence this operation should beperformed on rigid machines provided with back last eliminator. This is used for finishing operations. The chipsare also disposed off easily and do not interfere with the cutting. This results in improved surface finish. Cuttingforce and power are less.

Types of cutters*Discuss various types of milling cutters in detail. 2014R*Describe the construction of milling cutters. 2015S*Discuss different types of milling cutters used in milling machine. 2015SMetal Slitting Saw

These cutters are like plain or side milling cutters having very small width. These are used for parting off or slottingoperations. Metal slitting saw is shown in Figure .It is of two types. If teeth of this saw resembles with plain millingcutter, it is called plain milling slitting saw. If its teeth matches with staggered teeth side milling cutter, it is calledstaggered teeth slitting saw.Angle Milling CutterThese cutters have conical surfaces with cutting edges over them. These are used to machine angles other than 90o. Twotypes of angle milling cutters are available single angle milling cutter and double angle milling cutter.End MillWhat are the various types of end mills used in milling? Draw the simple sketches and explain briefly. 2013REnd mills are used for cutting slots, small holes and light milling operations. These cutters have teeth on their end aswell as an periphery. The cutting teeth may be straight or helical. Depending upon the shape of their shank, these arecategorized as discussed below.Taper Shank Mill: Taper shank mill have tapered shank.Straight Shank Mill :Straight shank mill having straight shankShell End MillsThese are normally used for face milling operation. Cutters of different sizes can be accommodated on a single commonshank.‘T’ Slot Milling CuttersThese are the special form of milling cutters used to produce „T_ shaped slots in the work piece. These have cuttingedges on their periphery and both sides.Fly CutterFly cutters are the simplest form of cutters used to make contoured surfaces. These cutters are the single cutting pointcutting tools.Formed CuttersFormed cutters may have different types of profile on their cutting edges which can generate different types of profileon the work pieces. Depending upon tooth profile and their capabilities formed cutters are categorized as given below.Convex Milling CuttersThese cutters have profile outwards at their circumference and used to generate concave semicircular surface on thework piece.Concave Milling CuttersThese milling cutters have teeth profile curve in words on their circumference. These are used to generate convexsemicircular surfaces.Corner Rounding Milling CuttersThese cutters have teeth curved inwards. These milling cutters are used to form contours of quarter circle. These aremain used in making round corners and round edges of the work piece.Gear CutterThese cutters are used in making gears on milling machine. Gear cutting is an operation which cannot be doneotherwise. These cutter have shape of the teeth which are to be reproduced on the gear blank.Different gear cutters are used to make teeth with involute profile or cycloidal profile. A gear cutter is used to cut arange of gear size with a fixed tooth profile.Thread Milling CutterThese cutters are designated to mill threads of specific form and size on the work piece. These cutters may be withparallel shank of tapered shank and mainly used to make worms.Top and Reamer CutterTop and reamer cutters are the cutters of double angle type, these are normally used to make grooves and flutes in tapsor reamers. Taps and reamers are used as thread cutting tools for softer material work pieces.GEOMETRY OF MILLING CUTTERS*Explain the geometry of a milling cutter with a neat sketch. 2013SPeripheral cutter: As the cutting edges are arranged radially on the periphery the rake angle is called radial rake whichis the cutting edges angle w.r.t to the periphery of the cutter. +ve radial rake gives better performance in peripheralmilling.Face cutter: Two rake angles are defined here.*Show with sketches and explain the following milling cutter angles 2014S

(i)Radial rake angle (ii)Axial rake angle (iii)Approach angle (iv)Side clearance angle(a) Radial rake is the cutting insert’s angle w.r.t the periphery of the cutter(b) Axial rake is the cutting insert’s angle w.r.t the central axis of the cutter.Axial Rake has significant effect on axial force and thrust applied to the spindle. Radial rake has major effect ontangential and radial forces. +ve axial rake, - ve radial rake gives best performance.


PERIPHERAL CUTTER

NOMENCLATURE OF PLAIN MILLING CUTTERThe principal parts and angles (elements) of a plain milling cutter are1.body of the cutter: The part of the cutter excluding the teeth portion is called body.2.land:the edge formed by the intersection of the face and the land.3.face : it is the front portion of tooth. The chip removed during cutting impinges on the face.4.gash: the space between the back of one tooth and the face of the next tooth.5.Fillet: The curved surface at the bottom of the gash.6.outside diameter: the diameter of the circle passing through the peripheral cutting edges.,7.rootdiameter:The diameter of the circle passing through the bottom of the fillet.8.reliefangle:It is the angle between the land of a touth and tangent to the out side diameter of cutter at the cutting edge.9.primary clearance angle:The angle formed by the back of the tooth with a line drawn tangent to the periphery of thecutter at the cutting edge.10.Secondary clearance angle:The angle formed by the secondary clearance surface of the tooth with a line drawntangent to the periphery of the cutter at the cutting edge.11.rake angle: The angle measured in the diametral plane between the face of the tooth and a radial line passing throughthe tooth cutting edge.12.Lip angle: The included angle between the land and the face of the tooth.Plain Milling Cutters

These cutters are cylindrical in shape having teeth on their circumference. These are used to produce flat surfacesparallel to axis of rotation. Plain milling cutter is shown in Figure. Depending upon the size and applications plainmilling cutters are categorized as light duty, heavy duty and helical plain milling cutters.Side Milling CuttersSide milling cutters are used to remove metals from the side of work piece. These cutters have teeth on the peripheryand on its sides. These are further categorized as plain side milling cutters having straight circumferential teeth.Staggered teeth side milling cutters having alternate teeth with opposite helix angle providing more chip space. Halfside milling cutters have straight or helical teeth on its circumference and on its one side only.Circumferential teeth dothe actual cutting of metal while side teeth do the finishing work .Interlocking side milling cutter has teeth of two halfside milling cutter which are made to interlock to form one unit.

PERIPHERAL CUTTER



PERIPHERAL CUTTER



Tool signatureTool angles and elements of a milling cutter are given in a definite sequence as follows

1. Axial rake angle2. Radial rake angle3. Face relief angle4. Peripheral relief angle5. Face cut edge angle6. Peripheral cutting edge angle7. chamfer

INDEXINGIt is the operation of dividing the periphery of a piece of work into any No. of equal parts. This is adopted forproducing hexagonal and square headed bolts cutting splines on shafts, flutes in milling cutters, drills, taps andreamers, cutting of Gears, cams etc. Indexing is accomplished by using a special attachment known as dividing head orIndex head. They are of 3 types1) Plain / Simple dividing head 2) Universal Dividing head3) Optical Dividing headUsing these dividing heads, the work can be set in vertical, horizontal or in inclined positions relative to the tablesurface. There are several methods of indexing. The choice of any one method depends upon the No. of divisionsrequired and the type of dividing head used.Universal Dividing Head*Explain the functions of a universal dividing head. 2013R*Describe the universal diving head with neat sketch. 2013S

It is most popular and common type of indexing arrangement. As indicated by its name “universal”, it can be used to doall types of indexing on a milling machine. Universal dividing head can set the work piece in vertical, horizontal, or ininclined position relative to the worktable in addition to working principle is explained below with the help ofillustration in Figure. The worm gear has 40 teeth and the worm has simple thread. Crank is directly attached with theworm. If we revolve crank by 40 revolutions the spindle attached with worm gear will revolve by only one revolutionand one complete turn of the crank will revolve the spindle only by 1/40th revolution (turn). In order to turn the crankprecisely a fraction of a revolution, an indexing plate is used. An indexing plate is like a circular disc having concentricrings of different number of equally spaced holes.Normally indexing plate is kept stationary by a lock pin. A spring loaded pin is fixed to the crank which can be fixedinto any hole of indexing plate. The turning movement of the work piece is stably controlled by the movement of crankas explained below.METHODS OF INDEXING*What you mean by indexing? Explain the types. 2014R*Explain the various methods of indexing. 2013R*Describe any one indexing method with its merits and demerits. 2015S*What is indexing? Describe direct indexing, with example.2012SThere are different indexing methods in popularity. These are :(a) Direct indexing(b) Simple indexing(c) Compound indexing(d) Differential indexing(e) Angular indexing

1) Direct Indexing: Also called rapid indexing, is used making small No. of divisions. This can be performed inboth plain and universal dividing head. The spindle and index crank are connected by bevel gears. The required No. ofdivisions on the work is obtained by means of the rapid index plate generally fitted to the front end of the spindle nose.The plate has 24 equally spaced holes, into any one of which a spring loaded in is pushed to lock the spindle withthe frame. While indexing, the pin is first taken out and then the spindle is rotated by hand, and after the requiredposition is reached, it is again locked by pin. when the plate is turned throughout the required part o a revolution,the dividing head spindle and the work are also turned through the same part of the revolution.With a rapid index plate having 24 holes, it is possible to divided the work into equal divisions of all factors of 24 i.e.2,3,4,6,8,12,24Rule:No. of holes = No. of holes in the direct index plate to be moved No. of divisions reqd.Q) Find out the index movement required to mill a hexagonal bolt by direct indexing.Ans. No. of holes to be moved = 24/6 = 4After machining one side of the bolt the index plate will have to be moved by 4 holes for 5 times to machining theremaining 5 faces of the bolt.2) Simple Indexing: Also called plain indexing, is more accurate and suitable for numbers beyond the range of rapidindexing. The bevel gears are replaced by a worm and worm wheel. The shaft carrying the crank has a single threadedworm and it meshes with the worm wheel on spindle having40 teeth. 40 turns of crank are necessary to rotate thespindle thro' one revolution ,i.e one complete turn of the index crank will cause the worm wheel to make 1/40of arevolution. For indexing fractions of a turn, various index plates are used.Rule:Index crank movement = 40/N,where N = No. of divisions required.Three indexing plates are used. These plates have concentric circles of holes withtheir different numbers as described below :Plate No. 1 15 16 17 18 19 20Plate No. 2 21 23 27 29 31 33Plate No. 3 37 39 41 43 47 49These are the standard indexing plates followed by all machine tool manufacturers.If the crank movement obtained from the formula is a whole No. the index crank should be rotated equal to thewhole No. derived. If the crank movement obtained from he above formula is a whole No. and a fraction then, thenumerator and denominator of the fraction are multiplied by a suitable common No. which will make the denominatorof the fraction equal to No. of holes in the index plate. The new numerator now stands for the No. of holes to be movedby index crank in the hole circle derived from denominator, in addition to the complete turns of crank.Eg: Index plates- 12, 14, 16, 18, 21 hole circles etc.2. A Gear is to have 19 teeth. What is the indexing movement required?

Indexing movement =

= = =

1. Select the index plate with 19- holed circle plate.2. The brown and Sharpe plate no:1 is required.3. The whole number ‘2’ represents two complete rotations of the index crank and fraction 2/19 denotes

another ‘2’ holes are to be bypassed in the 19-holed circle by the crank.4. This entire movement is to be repeated for ‘19’ times.

Index for 35 divisionsThe index crank movement = =

Here, ‘35’ in the denominator denotes the 35 holed circle is to be used. But we don’t have35 holed circle in anyof the three plates, so Modify the fraction

Index crank movement = = = = =

Now the denominator is made 21 instead of 31 without changing the value of the fractionIndexing is done by 1 complete revolution + 3 holes in a 21- holed circle.This is to be done for 21 times to index the job completely.

*What are the differences between compound indexing and differential indexing? 2013R3) Compound indexing:-*Obtain the compound indexing for 87 divisions. 2013S*Explain how compound indexing of 51equal divisions can be obtained on a cylindrical job. 2013S

N40

1940

19

22

3540

N40

35

40 51

35 7

11

37

311

21

31

The indexing method is called compound due to the two separate movement of the index crank in two diff. hole circlesof one index plate to obtain a crank movement not obtainable by plain indexing.The word compound indexing is an indicative of compound movements of indexing crank and then plate along withcrank. In this case indexing plate is normally held stationary by a lock pin, first we rotate the indexing crank through arequired number of holes in a selected hole circle, then crank is fixed through pin. It is followed by another movementby disengaging the rear lock pin, the indexing plate along with indexing crank is rotated in forward or backwarddirection through predetermined holes in a selected hole circle, then lock pin is reengaged.Necessary crank movement is obtained by combination of two movements. Simple index movement of the crank. Movement of the index plate itself with the handle.

This also known as ‘hit and trail’ method.

Rule for compound indexing =1. Consider +ve sign, for index crank and plate rotate in the same direction.2. For -ve sign, they are rotated in opposite direction3. a = no of holes to be bypassed in ‘A’ circle4. A = ‘A’ number hole- circle5. b = no of holes to be bypassed in ‘B’ circle6. B = ‘B’ number hole- circle7. N = number of divisions required

4) Differential Indexing:*Explain how differential indexing of 119 equal divisions can be obtained on a cylindrical job. 2013S*Sketch and explain the differential method of indexing. 2015S*Explain the principle of differential indexing. 2012SThe differential indexing may be considered as an automatic method of performing compound indexing. Here the Indexcrank is connected to milling machine feed rod through a set of gears to get continuous rotation for spindle for makinghelical grooves as shown.The change gears may be obtained by the relation, where 40/A is index crank movement and A is the selected numberthat can be plain indexed

1. If (A-N) is positive ,the index plate rotates in the same direction as the crank2. If (A-N) is negative ,the index plate rotates in the opposite direction as the crank

5)Angular indexing:In angular indexing job is rotated through an angle. Since the crank andspindle ratio is40: 1 and hence when crank moves through one revolution. The spindle or the jobmoves through 410ofrevolution i.e the job will revolve through an angular movement of 9°.Rule For Angular IndexingOne revolution of the crank, work rotates by = 90

Index crank movement =

Calculate the indexing required for an angle 19˚40’.

Index crank movement = = = .

i.e., Crank moves through 2 complete turns and 5 holes in 27 hole-circle.Working Principle of Indexing MechanismIf the pin is moved by one hole on the indexing plate in the circle of 20 holes, the spindle will revolve by1/40 X 1/20= 1/800th turn of one revolution.ACCESSORIES TO MILLINGMACHINESWork Holding Devices*Explain the various work holding devices used in milling. 2013RA milling machine table comes with precision parallel T-slots along the longitudinal axis. The work piece can thereforebe mounted directly on the table using these T-slots. Alternatively a variety of work holding devices can be used forholding the work piece, depending upon the type of work piece and the type of milling to be done. Vice is the mostcommon form of work holding devices used for holding small and regular work pieces. The vice is mounted on the tableusing the T-slots. A variety of vice jaws are available to suit different work piece geometries .Universal chuck is usedfor holding round work pieces for machining of end slots, splines, etc. Fixtures are the most common form of workholding devices used in production milling operations. They are used to reduce the set-up time and increase thelocational accuracy and repeatability. For large and irregular work pieces, clamps in a variety of shapes are available

9degreesinntdisplacemeAngular

5401180

2752Angle in minutes

540

Milling attachementsMilling Machine Attachment :Some classes of milling machine attachments are used for positioning and driving thecutter by altering the cutter axis and speed, whereas other classes are used for positioning, holding and feedingthe work along a specified geometric path, the following are the different attachments used on standard columnand knee type milling machine.Vertical Milling Attachment:A vertical milling attachment can convert a horizontal milling machine into a verticalmilling machine by orienting the cutting spindle axis from horizontal to vertical for performing specific operations. Theattachment consist of a right angle gear box which is attached to the nose of the horizontal milling machine spindle bybolting it on the column face. The attachment with the spindle can also be swivelled at any angle other than atright angles to the table for machining angular surfaces.Universal Milling AttachmentIt is similar to the vertical milling attachment but it has an added arrangement for swivelling the spindle about twomutually perpendicular axes. This feature of the attachment permits the cutting spindle axis to swivel at practically anyangle and machine any compound angular surface of the work. The attachment is supported by the over arm is bolted tothe column and enables the cutters to be operated at speeds beyond the scope of the machine.Slotting AttachmentThe attachment is bolted on the face of the column and can also be swivelled at an angle for machining angular surfaces.The length of stroke of the ram can also be adjusted. It converts the rotary motion of the spindle in to reciprocatingmotion of the ram by means of an eccentric crank housed within the attachment. Thus a milling machine can beconverted in to a slotter by accepting a single point slotter tool at the bottom end of the ram and is conveniently used forcutting internal or external keyways, splines, etc.Universal Spiral milling AttachmentThe universal spiral milling attachment may be used in a plain milling machine or n a universal milling machine forcutting a spiral grooves on a cylindrical work iece. The attachment is bolted on the face of the column and its spindlehead may be swivelled in avertical or horizontal plane. While using on a plain milling machine, the cutter mountedon the attachment may be swivelled to the required helix angle for cutting a spiral similar to the swivelling of the tableof a universal milling machine.Rack Milling AttachmentA rack milling attachment is used for cutting rack teeth on a job mounted on the table.The attachment consisting of agear train enables the spindle axis to be at right angles to the machine spindle in a horizontal plane. The successive rackteeth are cut by using a rack indexing attachment. The slanted rack teeth or a skew rack may be machined whenthe attachment is mounted on a universal milling machine where the table may be swivelled to the required helix angle.Circular Milling AttachmentA circular milling attachment is bolted on the top of the machine table. It. Provides rotary motion to the work piece inaddition to the longitudinal cross and vertical movements of the table. The attachment consist of a circular table havingT-slots mounted on a graduated base. The circular table may be rotated by hand, and in special cases by powerby linking the rotary table driving mechanism with the machine lead screw. The surfaceof any profile of a work piececan be generated by combining three or four moments of the table and rotary movement of the attachments.In some of the circular milling attachments an index plate is provided on the horizontal worm shaft for milling equallyspaced slots or grooves on the periphery of a work piece.Dividing Head AttachmentA dividing head attachment is bolted on the machined table. The work may be mounted on a chuck fitted on thedividing head spindle or may be supported between a live and a dead centre. The dead centre is mounted on a footstock.The attachment is principally used for dividing the periphery of a work piece in equal number of divisions formachining equally spaced slots or grooves. The worm and worm gear driving mechanism of the attachment can belinked with the table lead screw for cutting equally spaced helical grooves on the periphery of a cylindrical I workpiece.Tool Holding Devices:

1. Proper devices are designed to hold milling cutters2. Some of the devices are arbor ,collets, adapter and spring collets

Necessity Of Tool Holding Devices1. To obtain a higher metal removal rate2. To get higher spindle speeds which drive the cutters.3. To overcome all machining a mechanism to hold the cutting tool is essential

Tool Holding Devices - Arbor1. Cutter is directly mounted on it with key2. One end is tapered and fits in the spindle nose3. Spacing collars are used to position number of cutters4. Arbors are available in different diameters,16mm,22mm,27mm,32mm,and 40mm

5. The other end of the arbor is supported by a yoke6. It is designated by the taper number, diameter and length7. For example, ISO 40 x Φ22 x 500mm

Tool holding Devices - Collets1. A taper sleeve fitted to the nose of the spindle2. It can secure an arbor end or taper shank of cutter3. Spring collets used to secure straight shank cutters4. The front end is split into three equal-spaced slots and act like jaws to the shank

Tool Holding Devices - Adapters1. Attached to the spindle by a draw bolt2. Used for cutters having shanks that cannot be mounted on arbor

Tool Holding Devices - Vertical Milling attachment1. It facilitates facing and groove cutting on horizontal surfaces2. It may be swiveled to machine inclined surfaces3. Spindle speed remains the same

Slotting Attachment1. It can machine slots and key ways internally2. Converts the rotary motion of the spindle into reciprocating3. Slotting head is capable of tilting to desired angle4. For slotting , the work is to be clamped on two parallel bars

CUTTING PARAMETERS*What are the machining parameters of a milling machine? 2012RThere are three major cutting parameters to be controlled in any milling operation. These three parameters are cutting,speed, feed rate and depth of cut. These parameters are described below.Cutting SpeedCutting speed of a milling cutter is its peripheral linear speed resulting from operation. It is expressed in meters perminute. The cutting speed can be derived from the above formula.V=πdn/1000where d = Diameter of milling cutter in mm,V = Cutting speed (linear) in meter per minute, andn = Cutter speed in revolution per minute.Spindle speed of a milling machine is selected to give the desired peripheral speed of cutter.Feed RateIt is the rate with which the work piece under process advances under the revolving milling cutter. It is known thatrevolving cutter remains stationary and feed is given to the work piece through worktable. Generally feed is expressedin three ways.Feed per ToothIt is the distance traveled by the work piece (its advance) between engagement by the two successive teeth. It isexpressed as mm/tooth (ft).Feed per RevolutionTravel of work piece during one revolution of milling cutter. It is expressed as mm/rev. and denoted by f(rev).Feed per Unit of TimeFeed can also be expressed as feed/minute or feed/sec. It is the distance advances by the work piece in unit time (fm).Above described three feed rates are mutually convertible.Fm= n X f(rev)where n = rpm of cutter.It can be extended further as fm =n X f(rev) =z X n X ftwhere z = Number of teeth in milling cutter.Depth of CutDepth of cut in milling operation is the measure of penetration of cutter into the work piece. It is thickness of thematerial removed in one pairs of cutter under process. One pairs of cutter means when cutter completes the millingoperation from one end of the work piece to another end. In other words, it is the perpendicular distance measuredbetween the original and final surface of work piece. It is measured in mm.


Documents

MCMT UNIT-4