1) Operational principle

Drilling with a Milling Machine

Since a milling machine can perform exact positioning, a drilling process can be carried out to an exact position. It’s more efficient to process it using a drilling machine, if it’s easy drilling process. However, when correctness is required of the position of the holes, or when there are many holes, the milling machine is suitable. Moreover, it is also the characteristics of the drilling with the milling machine that the taper drill of a large diameter can be used. Generally, we make a drill with the milling machine, when the position of the holes needs high accuracy. In order to get the accuracy, it is needed to the positioning of the original point, and using a center drill is better before a drilling.

INSTRUCTIONS HOW TO USE A MILLING MACHINE
The process of machining flat, curved, or irregular surfaces by feeding the workpiece against a rotating cutter containing a number of cutting edges is milling. The usual Mill consists basically of a motor driven spindle, which mounts and revolves the milling cutter, and a reciprocating adjustable worktable, which mounts and feeds the work piece. Basically milling machines are classified as vertical or horizontal and these types of machines also classified as knee-type, ram-type, manufacturing or bed type, and planer-type. Most of the milling machines have self-contained electric drive motors, coolant systems, variable spindle speeds, and power-operated table feeds.

KNEE-TYPE
Knee-type mills are characterized by a vertically adjustable worktable resting on a saddle which is supported by a knee. The knee is a massive casting that rides vertically on the milling machine column and can be clamped rigidly to the column in a position where the milling head and milling machine spindle are properly adjusted vertically for operation.
The plain vertical machines are characterized by a spindle located vertically, parallel to the column face, and mounted in a sliding head that can be fed up and down by hand or power. Modern vertical milling machines are designed so the entire head can also swivel to permit working on angular surfaces.
The turret and swivel head assembly is designed for making precision cuts and can be swung 360° on its base. Angular cuts to the horizontal plane may be made with precision by setting the head at any required angle within a 180°arc.
The plain horizontal milling machine's column contains the drive motor and gearing and a fixed position horizontal milling machine spindle. An adjustable overhead arm containing one or more arbor supports projects forward from the top of the column. The arm and arbor supports are used to stabilize long arbors. Supports can be moved along the overhead arm to support the arbor where support is desired depending on the position of the milling cutter or cutters.
The milling machine's knee rides up or down the column on a rigid track. A heavy, vertical positioning screw beneath past the milling cutter. The milling machine is excellent for forming flat surfaces, cutting dovetails and keyways, forming and fluting milling cutters and reamers, cutting gears, and so forth. There are many special operations can be performed with the attachments available for milling machine use. The knee is used for raising and lowering. The saddle rests upon the knee and supports the worktable. Saddle moves in and out on a dovetail to control cross feed of the worktable. The worktable traverses to the left or right upon to the saddle for feeding the work piece past the milling cutter. The table may be manually controlled or power fed.
UNIVERSAL HORIZONTAL MILLING MACHINE
The most basic difference between a universal horizontal milling machine and a plain horizontal milling machine is the addition of the table swivel housing between the table and the saddle of universal machine. This permits the table to swing up to 45° in either direction for angular and helical milling operations. The universal machine can be fitted with various attachments such as the indexing fixture, rotary table, slotting and rack cutting attachments, and various special fixtures.
RAM-TYPE MILLING MACHINE
The ram-type milling machine is characterized by a spindle mounted to a movable housing on the column and to permit positioning to the milling cutter forward or rearward in a horizontal plane. Two most popular ram-type milling machines are the universal milling machine and the swivel cutter head ram-type milling machine.
UNIVERSAL RAM-TYPE MILLING MACHINE
The universal ram-type milling machine similar to the universal horizontal milling machine, the difference being, as its name implies, the spindle is mounted on a ram or movable housing.
SWIVEL CUTTER HEAD RAM-TYPE MILLING MACHINE
The cutter head containing the milling machine spindle is attached to the ram. The cutter head can be swiveled from a vertical spindle position to a horizontal spindle position or can be fixed at any desired angular position between vertical and horizontal. The saddle and knee are hand driven for vertical and cross feed adjustment while the worktable can be either hand or power driven at the operator's choice.

2) Types and construction features of milling machine

Vertical mill
The spindle axis is vertically oriented. Milling cutter are held in the spindle and rotate on its axis. The spindle can generally be extended or the table can be raised and lowered, giving the same effect, allowing plunge cuts and drilling. There are two subcategories of vertical mills; they are bedmill and the turret mill.
· Turret mills, like the ubiquitous Bridgeport, are generally smaller than bedmills, and are considered by some to be more versatile. In a turret mill the spindle remains stationary during cutting operations and the table is moved both perpendicular to and parallel to the spindle axis to accomplish cutting.
· Bedmill, however, the table moves only perpendicular to the spindle's axis, while the spindle itself moves parallel to its own axis. Also of note is a lighter machine, called a mill-drill. It is quite popular with hobbyists, due to its small size and lower price. These are frequently of lower quality than other types of machines, however.
Horizontal mill
Has the same sort of x–y table, but the cutters are mounted on a horizontal arbor across the table. A majority of horizontal mills also feature a +15/-15 degree rotary table that allows milling at shallow angles. While endmills and the other types of tools available to a vertical mill may be used in a horizontal mill, their real advantage lies in arbor-mounted cutters, called side and face mills, which have a cross section rather like a circular saw, but are generally wider and smaller in diameter. Because the cutters have good support from the arbor, quite heavy cuts can be taken, enabling rapid material removal rates. These are used to mill grooves and slots. Plain mills are used to shape flat surfaces. Several cutters may be ganged together on the arbor to mill a complex shape of slots and planes. Special cutters can also cut grooves, bevels, radii, or indeed any section desired. These specialty cutters tend to be expensive. Simplex mills have one spindle, and duplex mills have two. It is also easier to cut gears on a horizontal mill.
Different between the vertical and horizontal milling machine
• Vertical milling machines must use smaller cutting tools than horizontal
mills because they have less rigid, less massive castings, and lower
horsepower motors. Still, they can accomplish the same end results as the
horizontal mill, just more slowly.
• Vertical milling machines are less complex than horizontal machines
because the one-piece tool head eliminates the need for complicated
gearing inside the vertical column.

Other types of milling machine variants and terminology
Column mills are very basic hobbyist bench-mounted milling machines that feature a head riding up and down on a column or box way.
Turret or vertical ram mills are more commonly referred to as Bridgeport-type milling machines. The spindle can be aligned in many different positions for a very versatile, if somewhat less rigid machine.
knee-and-column mill refers to any milling machine whose x-y table rides up and down the column on a vertically adjustable knee. This includes Bridgeports.
Planer-style mills are large mills built in the same configuration as planers except with a milling spindle instead of a planing head. This term is growing dated as planers themselves are largely a thing of the past.
Bed mill refers to any milling machine where the spindle is on a pendant that moves up and down to move the cutter into the work. These are generally more rigid than a knee mill.
Ram type mill refers to a mill that has a swiveling cutting head mounted on a sliding ram. The spindle can be oriented either vertically or horizontally, or anywhere in between.
Jig borers are vertical mills that are built to bore holes, and very light slot or face milling. They are typically bed mills with a long spindle throw. The beds are more accurate, and the handwheels are graduated down to .0001" for precise hole placement.

There are two basic construction types of milling machines: the column and knee machines and the fixed bed machines. As the name indicates the column and knee mills have a knee attached to the column which is elevated by a jack screw. The fixed bed construction (found in most CNC machines) does not have a knee. Only the spindle can change elevations. This more rigid machine than the column and knee configuration.

Head - part of the drive system that transforms electrical power from a motor to mechanical power in the spindle.
Quill -moves vertically in the head and contains the spindle in which cutting tools are installed.
Quill feed hand wheel -moves the quill up and down within the head as does the quill feed lever.
Knee- moves up and down by sliding on ways that are parallel to the column.
Saddle -sits on the knee and allows translation of the worktable.
Column -main function is to hold the turret.
Turret -allows the milling head to be rotated around the column's centre.
Over arm - (ram) slides on the turret and allows the milling head to be repositioned over the table.
Longitudinal traverse hand wheel- moves the worktable to the left and right cross traverse hand wheel- moves the work table in and out.
Vertical movement crank -moves the knee, saddle, and worktable up and down in unison.

3) Milling Machine Accessories and attachments

a)Vertical heads- Vertical heads are generally attached to the face of the column or to the overarm of a horizontal milling machine. The head is a semiuniversal type, which pivots only on the axis parallel to the center line of the spindle. For a fully universal head, it can be set to cut compound angles. Both types of heads are powered by the spindle of the milling machine and accept standard arbors and collets.

b)Rack-milling attachment- Rack-milling attachment bolts to the spindle housing of the milling machine. Its spindle is at a right angle to the main spindle of the machine. Both spur and helical racks can be milled at this attachment, and it can be used to mill worms. Some rack-milling attachments have an outboard support for the spindle, which makes it possible to take heavier cuts.

c)High-speed milling attachments- High-speed milling attachments can be placed on both horizontal and vertical milling machines when spindle speed is beyond the operating range. A gear train is used to step up the speed as much as 6:1, which allows more efficient use of small cutters. A high-speed milling attachment is fully universal.

d)Plain vice- Plain milling vices are actuated by an Acme threaded screw, and the movable jaws moves on either a dovetail or rectangular slide. The vices are usually cast of high grade gray cast iron or ductile iron and can be heat-treated. Steel keys are attached by caps screws. Vices of this type are classified by the jaws width and maximum opening.

e)Swivel-based vise- A swivel-based vise is less rigid in construction. The base graduated in degrees is slotted for keys that align it with the T slot in the table. The upper part of the vise is held to the base by T bolts that engage a circular T slot. When it is used on milling machine with semiuniversal head, makes possible milling compound angles on a workpiece.

f)Arbors-
· Style A arbors consists of the tapered portion that fits the spindle, the shaft on which the cutter fits the spacers and nuts. The shaft has a keyway along its entire length. The outboard end of the arbor has a pilot that fits into a bronze bushing in the outboard support of the milling machine overarm. One or more cutters can mount on the arbor, either adjacent to each other or separated by spacer and shims. This type of arbor is used primarily for light and medium-duty milling operations.
· Style B arbors are used heavy milling operations, especially where it is necessary to provide support close to a milling cutter, such as instraddle milling operations. One or more bearing may be place on the arbors as near to the cutters as possible. An outboard bearing support is used for each bearing sleeve on the arbor.
· Style C arbors are use to hold and drive shell end mills and some type of face milling cutters. In some cases, they can also be fitted with adapters for mounting other types of cutters.


g)Special tool holders- For some operations that require the use of tools with nonstandard shank sizes, chucks can be use to hold the tool. These chucks are available with Morse taper or straight shanks. Either type can be use in milling machines when the proper adapters or collets are available.

4) Milling Cutters

Milling cutters are cutting tools used in milling machines or machining centres. They remove their material by their movement within the machine (eg a ball nose mill) or directly from the cutter shaper (a form of tool such as Hobbing cutter).

Feature of milling cutter
Milling cutters come in several shape and many size. There is also a choice of coatings, as well as rake angle and the number of cutting surface.
Shape: Several standard shapes of milling cutter are used in industry today, which are explained in more detail below.
Flutes / teeth: The flutes of the milling bit are the deep helical grooves running up the cutter, while the sharp blade along the edge of the flute is known as the tooth. The tooth cuts the material, and chips of this material are pulled up the flute by the rotation of the cutter. There is almost always one tooth per flute, but some cutters have two teeth per flute. Often, the words flute and tooth are used interchangeably. Milling cutters may have from one to many teeth, with 2, 3 and 4 being most common. Typically, the more teeth a cutter has, the more rapidly it can remove material. So, a 4-tooth cutter can remove material at twice the rate of a 2-tooth cutter.
Helix angle: The flutes of a milling cutter are almost always helical. If the flutes were straight, the whole tooth would impact the material at once, causing vibration and reducing accuracy and surface quality. Setting the flutes at an angle allows the tooth to enter the material gradually, reducing vibration. Typically, finishing cutters have a higher rake angle (tighter helix) to give a better finish.
Center cutting: Some milling cutters can drill straight down (plunge) through the material, while others cannot. This is because the teeth of some cutters do not go all the way to the centre of the end face. However, these cutters can cut downwards at an angle of 45 degrees or so.
Roughing or Finishing: Different types of cutter are available for cutting away large amounts of material, leaving a poor surface finish (roughing), or removing a smaller amount of material, but leaving a good surface finish (finishing). A roughing cutter may have serrated teeth for breaking the chips of material into smaller pieces. These teeth leave a rough surface behind. A finishing cutter may have a large number (4 or more) teeth for removing material carefully. However, the large number of flutes leaves little room for efficient swarf removal, so they are less good for removing large amounts of material.
Coatings: Tool coatings can have a great influence on the cutting process The right coating can increase cutting speed and tool life, and improve the surface finish. Polycrystalline Diamond(PCD) is an exceptionally hard coating used on cutters which must withstand high abrasive wear. A PCD coated tool may last up to 100 times longer than an uncoated tool. However the coating cannot be used at temperatures above 600 degrees C, or on ferrous metals. Tools for machining aluminums are sometimes given a coating of Tialn. Aluminums is a relatively sticky metal, and can weld itself to the teeth of tools, causing them to appear blunt. However it tends not to stick to TiAlN, allowing the tool to be used for much longer in aluminums.
Shank: The shank is the cylindrical (non-fluted) part of the tool which is used to hold and locate it in the tool holder. A shank may be perfectly round, and held by friction, or it may have a Weldon Flat, where a grub screw makes contact for increased torque without the tool slipping. The diameter may be different from the diameter of the cutting part of the tool, so that it can be held by a standard tool holder.

Type Of Milling Cutters
Plain milling cutters – Plain milling cutters cut only on the periphery and are used to machine flat surfaces and slots. The surface that is produced by the teeth of the cutter is always parallel to the spindle of the machine. Plain milling cutters range in width from about 0.032 in to as much as 8 in. and are almost always made of high speed steel.

a)Side-milling cutters – side milling cutters have teeth on the periphery of the cutter and on one or both sides. The sides of the teeth are relieved so that only the cutting edge contacts the work. Separate chips can be cut by the teeth on the periphery and sides, although this is not the case in simple slotting operations.
b)End mill - End mills are those tools which have cutting teeth at one end, as well as on the sides. The words end mill are generally used to refer to flat bottomed cutters, but also include rounded cutters (referred to as ball nosed) and radiused cutters (referred to as bull nose, or torus). They are usually made from high speed steel(HSS) or carbide, and have one or more flutes. They are the most common tool used in a vertical mill.
c)Slot drill - Slot drills (top row in image) are generally two (occasionally three or four) fluted cutters that are designed to drill straight down into the material. This is possible because there is at least one tooth at the centre of the end face. They are so named for their use in cutting keyway slots. The words slot drill are usually assumed to mean a two fluted, flat bottomed end mill if no other information is given. Two fluted end mills are usually slot drills, three fluted sometimes aren't, and four fluted usually aren't.
d)Roughing end mill - Roughing end mills quickly remove large amounts of material. This kind of end mill utilizes a wavy tooth form cut on the periphery. These wavy teeth form many successive cutting edges producing many small chips, resulting in a relatively rough surface finish. During cutting, multiple teeth are in contact with the workpiece reducing chatter and vibration. Rapid stock removal with heavy milling cuts is sometimes called hogging. Roughing end mills are also sometimes known as ripping cutter.
e)Ball nose cutter - Ball nose cutters (lower row in image) are similar to slot drills, but the end of the cutters are hemispherical. They are ideal for machining 3-dimensional contoured shapes in machining centres, for example in molds and dies. They are sometimes called ball mills in shop-floor slang, despite the fact that that term also has another meaning. They are also used to add a radius between perpendicular faces to reduce stress concentrations.
f)HSS slab mill – Slab mills are used either by themselves or in gang milling operations on manual horizontal or universal milling machines to machine large broad surfaces quickly. They have been superseded by the use of Carbide tipped face mills that are then used in vertical mills or machining centres.
g)Side and face cutter - The side-and-face cutter is designed with cutting teeth on its side as well as its circumference. They are made in varying diameters and widths depending on the application. The teeth on the side allow the cutter to make unbalanced cuts (cutting on one side only) without deflecting the cutter as would happen with a slitting saw or slot cutter (no side teeth).

h)Involute gear cutter - The image shows a Number 4 cutter from an involute gear cutting set. There are 7 cutters (excluding the rare half sizes) that will cut gears from 12 teeth through to a rack (infinite diameter). The cutter shown has markings that show it is a

-10 DP (diametrical pitch) cutter
-That it is No. 4 in the set
-that it cuts gears from 26 through to 34 teeth
-It has a 14.5 degree pressure angle
i)Hobbing cutter - These cutters are a type of form tool and are used in hobbing machines to generate gears. A cross section of the cutters tooth will generate the required shape on the workpiece, once set to the appropriate conditions (blank size). A hobbing machine is a specialised milling machine.
j)Face mill (indexable carbide insert) - face mill consists of a cutter body (with the appropriate machine tapper) that is designed to hold multiple disposable carbide or ceramic tips or inserts, often golden in color. The tips are not designed to be resharpened and are selected from a range of types that may be determined by various criteria, some of which may be: tip shape, cutting action required, material being cut. When the tips are blunt, they may be removed, rotated (indexed) and replaced to present a fresh, sharp face to the workpiece, this increases the life of the tip and thus their economical cutting life.
k)Fly cutter - A fly cutter is composed of a body into which one or two tool bits are inserted. As the entire unit rotates, the tool bits take broad, shallow facing cuts. Fly cutters are analogous to face mills in that their purpose is face milling and their individual cutters are replaceable. Face mills are more ideal in various respects (e.g., rigidity, indexability of inserts without disturbing effective cutter diameter or tool length offset, depth-of-cut capability), but tend to be expensive, whereas fly cutters are very inexpensive.
l)Woodruff cutter - Woodruff cutters make the seat for woodruff keys. These keys retain pulleys on shafts and are shaped as shown in the image.
m)Hollow mill - Hollow milling cutters, more often called simply hollow mills, are essentially "inside-out endmills". They are shaped like a piece of pipe (but with thicker walls), with their cutting edges on the inside surface. They are used on turret lathes and screw machines as an alternative to turning with a box tool, or on milling machines or drill presses to finish a cylindrical boss (such as a trunnion).

5) Alignment involved in milling operation

a)Machine Alignment
-Alignment is needed for the worktable and head of those milling machines.
-Alignment is not needed for the plain milling machines, both vertical and horizontal because the table cannot be swiveled.
-Overarm typer vertical milling machine does not need it because the head can move only up or down.
b)Table alignment
-The table on universal milling machines must be checked for alignment whenever it is being returned to the 0 degree position.
-Do not trust the graduations on the saddle or any other part.
-A rigid mounting for the dial indicator is necessary so that flexing and slippage do not alter the readings.
-Dial indicator must be mounted to the table of the machine because the motion of the table relative to the face of the column is being checked.
-The following eight step should be followed:
· Clean the table and column face and make sure there are no nicks that rise above the surface.
· Attach the dial indicator.
· Make sure the dial indicator is in contact with one edge of the column face.
· Move in one-fourth of the indicator’s operating range,and zero the dial by turning the bezel.
· Move the table manually and note any changes in the dial indicator reading.The gribs on the knee,saddle,and table must be in good condition and properly adjusted to eliminate lost motion.
· Table cannot be adjusted accurately if there are any loose mating surfaces.
· If any error is noted,loosen the saddle clamps and move the table one and a half of the error in the proper direction and retighten.
c)Head alignment
-Semiuniversal or universal heads must be checked before doing jobs requiring accurate alignment between the head and table.
-The spindle must be aligned perpendicularly to the table when drilling,boring and flycutting operations are performed.
-The dial indicator must be rigidly attached to a fixture held in a collet in the spindle.
-The diameter of the circle that the dial indicator makes should be slightly smaller than the width of the table.
-Table must be clean and free of nicks before the aligning operation is started.
-Steel or cast iron known as flatness and parallelism can be placed on table to avoid plunger on the dial indicator from drop into the Tslots.
-The following procedures is suggested for aligning the head of vertical milling with semiuniversal or universal heads:
· Clean the table and place a flat a parallel plate on it.
· Attach the dial indicator to the spindle.
· Feed the spindle down,with the dial plunger at the operator’s right or left side until it registers about one-fourth of its operating range,and zero it.
· Rotate the spindle one revolution and for this if the head is universal type,the reading may vary on both axes.
· Adjust a semiuniversal head by loosening the head and swiveling it so that the dial indicator reading is out in half.
· Universal heads should be adjusted in one plane at a time.
· Securely tighten all head locking bolts and recheck.



Vise and fixture alignment
-Solid jaw of the vise is always the reference surface.
-The dial indicator is attached to the arbor of a horizontal milling machine or held in the collet of a vertical milling machine.
-The following procedures is suggested for aligning plates and other fixture with major flat surfaces:
· Clean all parts thoroughly and make sure that there are no burrs or nicks on mating surfaces.
· Lightly clamp the vise or fixture in approximately the correct position.
· Bring the dial indicator in contact with one end of the part to be aligned.
· Move the table or cross slide the full length of the jaw or fixture.
· Note the variation in indicator reading and move the vise or fixture in the appropriate direction using a soft hammer.
· When the indicator shows no deviation,retighten all bolts and recheck.

6) Basic Milling operations

The success of any milling operation depends, Before setting up a job, be sure that the to a great extent, upon judgment in setting up the job, workpiece, the table, the taper in the spindle, selecting the proper milling cutter, and holding the cutter by the best means under the circumstances. Some fundamental practices have been proved by experience to be necessary for and the arbor or cutter shanks are all clean and good results on all jobs.

a)Plain Milling:The milling cutter axis parallel to the surface being milled. Generally, plain milling is done with Plain milling, also called surface milling or slab milling, is milling flat surfaces with the workpiece surface mounted parallel to the surface of the milling machine table and the milling cutter mounted on a standard milling machine arbor. The arbor is well supported in a horizontal plane between the milling machine spindles and one or more arbor supports.The workpiece is generally clamped directly to the table or supported in a vise for plain milling. The milling machine table should be checked for alignment before starting to cut. If the workpiece surface to be milled is at an angle to the base plane of the piece, the workpiece should be mounted in a universal vise or on an adjustable angle plate. The holding device should be adjusted so that the workpiece surface is parallel to the table of the milling machine.

b)Angular Milling:Angular milling, or angle milling, is milling flat surfaces which are neither parallel nor perpendicular to the axis of the milling cutter. A single angle milling cutter is used for angular surfaces, such as chamfers, serration’s, and grooves.When milling dovetails, the usual angle of the cutter is 45°, 50°, 55°, or 60° based on common dovetail designs. When cutting dovetails on the milling machine, the workpiece may be held in a vise, clamped to the table, or clamped to an angle plate. The tongue or groove is first roughed out using a side milling cutter, after which the angular sides and base are finished with an angle milling cutter. In general practice, the dovetail is laid out on the workpiece surface before the milling operation is started. To do this, the required outline should be inscribed and the line prick-punched. These lines and punch marks may then be used as a guide during the cutting operation.

c)Straddle Milling:When two or more parallel vertical surfaces are machined at a single cut, the operation is called straddle milling. Straddle milling is accomplished by mounting two side milling cutters on the same arbor, set apart at an exact spacing. Two sides of the workpiece are machined simultaneously and final width dimensions are exactly controlled.Straddle milling has many useful applications introduction machining. Parallel slots of equal depth can be milled by using straddle mills of equal diameters The workpiece is usually mounted between centres in the indexing fixture or mounted vertically in a swivel vise. The two side milling cutters are separated by spacers, washers, and shims so that the distance between the cutting teeth of each cutter is exactly equal to the width of the workpiece area required. When cutting a square by this method, two opposite sides of the square are cut, and then the spindle of the indexing fixture or the swivel vise is rotated 90°, and the other two sides of the workpiece are straddle milled.

d)Face Milling:Face milling is the milling of surfaces that are perpendicular to the cutter axis. Face milling produces flat surfaces and machines work to the required length. In face milling, the feed can be either horizontal or vertical. In face milling, the teeth on the periphery of the cutter do practically all of the cutting. However, when the cutter isproperly ground, the face teeth actually remove a small amount of stock which is left as a result of the springing of the workpiece or cutter, thereby producing a finer finish.It is important in face milling to have the cutter securely mounted and to see that all end play or sloppiness in the machine spindle is eliminated.When face milling, the workpiece may be clamped to the table or angle plate or supported in a vise, fixture, or jig. Large surfaces are generally face milled on a vertical milling machine with the workpiece clamped directly to the milling machine table to simplify handling and clamping operations. Angular surfaces can also be face milled on a swivel cutter head milling machine. In this case, the workpiece is mounted parallel to the table and the cutter head is swiveled to bring the end milling cutter perpendicular to the surface to be produced. During face milling operations, the workpiece should be fed against the milling cutter so that the pressure of the cut is downward, thereby holding the piece against the table.Whenever possible, the edge of the workpiece should be in line with the center of the cutter. This position of the workpiece in relation to the cutter will help eliminate slippage.

e)Gang Milling:Gang milling is the term applied to an operation in which two or more milling cutters are mounted on the same arbour and used when cutting horizontal surfaces. All cutters may perform the same type of operation or each cutter may perform a different type of operation. For example, several workplaces need a slot, a flat surface, and an angular groove. All the completed workplaces would be the same. Remember to check the cutters carefully for proper size.

f)Form Milling:Form milling is the process of machining special contours composed of curves and straight lines, or entirely of curves, at a single cut. This is done with formed milling cutters, shaped to the contour to be cut. The more common form milling operations involve milling half-round recesses and beads and quarter-round radii on workplaces. This operation is accomplished by using convex, concave, and corner rounding milling cutters ground to the desired circle diameter. Other jobs for formed milling cutters include milling intricate patterns on workplaces and milling several complex surfaces in a single cut such as are produced by gang milling.

g)Single Point Milling:Single point milling, is one of the most versatile milling operations. It is done with asingle-point cutting tool shaped like a lathe tool bit. It is held and rotated by a fly cutter arbor. You can grind this cutter to almost any form that you need. Formed cutters are expensive. There are times when you need a special form cutter for a very limited number of parts. It is more economical to grind the desired form on a lathe-type tool bit than to buy a preground form cutter, which is very expensive and usually suitable only for one particular job.The single-point or fly cutter can be used to great advantage in gear cutting. A II that is needed is enough of the broken gear to grind the cutting tool to the proper shape. It can also be used in the cutting of splines and standard and special forms. Another type of fly cutter, which differs mainly in the design of the arbor, can be used to mill flat surfaces as in plain or face milling. The arbor can easily be manufactured in the shop using common lathe tool bits. This type of fly cutter is especially useful for milling flat surfaces on aluminum and other soft nonferrous metals, since a high quality finish can be easily obtained. Boring holes with this type of fly cutter is not recommended. The arbor is so short that only very shallow holes can be bored.

h)Keyway Milling:Keyways are grooves of different shapes cut along the axis of the cylindrical surface of shafts, into which keys are fitted to provide a positive method of locating and driving members on the shafts. A keyway is also machined in the mounted member to receive the key. The type of key and corresponding keyway to be used depends upon the class of work for which it is intended. The most commonly used types of keys are the Woodruff key, the square-ends machine key, and the round-end machine key. The Woodruff keys are semicylindrical in shape and are manufactured in various diameters and widths. The circular side of the key is seated into a keyway which is milled in the shaft. The upper portion fits into a slot in a mating part, such as a pulley or gear. The Woodruff key slot milling cutter must have the same diameter as that of the key.Woodruff key sizes are designated by a code number in which the last two digits indicate the diameter of the key in eighths of an inch, and the digits preceding the last two digits give the width of the key in thirty-seconds of an inch. Thus, number 204 Woodruff key would be 4/8 or 1/2 inch in diameter and 2/32 or 1/16 inch wide, while a number 1012 Woodruff key would be 12/8 or 1 1/2 inches in diameter and 10/32 or 5/16 inch wide. For proper assembly of the keyed members to be made, a clearance is required between the top surface of the key and the keyway of the bore. This clearance may be from a minimum of 0.002 inch to a maximum of 0.005 inch. Positive fitting of the key in the shaft keyway is provided by making the key 0.0005 to 0.001 inch wider than the keyway.

i)T-Slot Milling:Cutting T-slots in a workpiece holding device is a typical milling operation. The size of the T-slots depends upon the size of the T-slot bolts which will be used. Dimensions of T- slots and T-slot bolts are standardized for specific bolt diameters. Two milling cutters are required for milling T-slots, a T- slot milling cutter and either a side milling cutter or an end milling cutter. The side milling cutter (preferably of the stag- gered tooth type) or the end milling cutter is used to cut a slot in the workpiece equal in width to the throat width of the T- slot and equal in depth to slightly less than the head space depth plus the throat depth). The T-slot milling cutter is then used to cut the head space to the prescribed dimensions.

j)Helical Milling:A helix may be defined as a regular curved path. such as is formed by winding a cord around the surface of a cylinder. Helical parts most commonly cut on the milling machine include helical gears. spiral flute milling cutters, twist drills. and helical cam grooves. When milling a helix. a universal index head is used to rotate the workpiece at the proper rate of speed while the piece is fed against the cutter. A train of gears between the table feed screw and the index head serves to rotate the workpiece the required amount for a given longitudinal movement of the table. Milling helical parts requires the use of special formed milling cutters and double- angle milling cutters, The calculations and formulas necessary to compute proper worktable angles, gear adjustments. and cutter angles and positions for helical milling are beyond the scope of this manual.

k)Spline Milling:Splines are often used instead of keys to transmit power from a shaft to a hub or from a hub to a shaft. Splines are. In effect. a series of parallel keys formed integrally with the shaft. mating with corresponding grooves in the hub or fitting. They are particularly useful where the hub must slide axially on the shaft, either under load or freely. Typical applications for splines are found in geared transmissions, machine tool drives. and in automatic mechanisms. Splined shafts and fittings are generally cut by bobbing and broaching on special machines. However. when spline shafts must be cut for a repair job. the operation may be accomplished on the milling machine in a manner similar to that described for cutting keyways. Standard spline shafts and splint fittings have 4, 6, 10, or 16 splines, and theirdimensions depend upon the class of tit for the desired application: a permanent fit, a sliding fit when not under load, and a sliding fit under load. The shaft to be splined is set up between centers in the indexing fixture. Two side milling cutters are mounted to an arbor with a spacer and shims inserted between them. The spacer and shims are chosen to make space between the inner teeth of the cutters equal to the width of the spline to be cut . The arbor and cutters are mounted to the milling machine spindle. and the milling machine is adjusted so that the cutters are centered over the shaft.

7)Operational Safety Precautions

There are two kind of milling machine that we using in workshop during our practical class, the first one is Vertical Milling Machine, and another one is Horizontal Milling Machine. All milling machines contain hazards from rotating parts, belts and pulleys, high voltage electricity, noise, and compressed air. When using CNC machines and their components, basic safety precautions must always be followed to reduce the risk of personal injury and mechanical damage.

Horizontal and Vertical Milling Machine Safety Guidelines
The Horizontal Mill is use for boring, drilling, face milling, tapping, and similar operations. The principle hazards associated with the operation of horizontal machine are :
· Tools or materials dropped on the feet and toes.
· Flying chips or scale from boring and facing operations and flying fragments from a broken tool. · Contact with unguarded moving parts or with pinch point between a tool and a work.Work pieces thrown from the worktable if they are not secured properly

1. Always keep safety in mind. Accidents on milling machines usually occur when the operator loads or unload or makes adjustments to the milling operation. The major hazard is injury to hands, arms or fingers by contact with the cutter, other sharp object, or by pinching. Unsafe can be due to :
· Lack of essential guarding.
· Unsafe work practices.
· Failure to withdraw the job to a safe distance from the cutter while loading or unloading the machine, measuring the parts or checking the finish.
· Attempting to remove chips by hand.
· Adjusting coolant while cutters are revolving.
· Using wipes or rags near revolving cutters.
· Wearing gloves or loose clothing near revolving cutters or machine parts.
· Unsafe workplace.
· Poor housekeeping around machine (wet or slippery floor).

1. Before starting the machine, the operator will make certain that conditions are such that neither she/he nor a fellow worker will be injured by the operation of the machine. Among the items to be checked are :
· All guard are in good condition and in place.
· Proper cutting tool , correctly sharpened , is used.
· Tool is securely fastened.
· Machine has been properly lubricated.
· Work has been properly secured in place, and bolts and other holding devices are such that they will not be caught or come into contact with moving parts of the machine.
· Table feeds, proper cutting speed and all machine attachments are correctly set and in proper working order.
· Tools or other loose objects are not lying about where they may fall or be caught n thrown ,injury to the operator or other or with damage to the machine or to the work.



2. Before leaving the machine for any reason, the operator is to make sure the machine is stopped and the power shut off.



3. Wear eye protection and safety shoes at all times.



4. Do not wear neckties, wristwatches, rings, jewelry, gloves, etc. When operating the machine. Long sleeve shirts will be rolled above the elbows. Do not wear loose clothing.



5. The area around the machine should be free of oil or coolant spills (avoid a slippery floor) and as free as possible from obstructions. Keep the area clean at all times.



6. Do not use compressed air to blow chips from the spindle or table machine surfaces, cabinets, controls, or the floor around the machine.



7. For normal lifting, use leg, not back muscles. For heavy lifting, use a hoist.



8. Illuminating lamps should be adjusted so light is not directed into operator’s eyes.



9. When work platforms are used around the machine, they should be extremely sturdy, safe, and with anti-slip surfaces.



10. Wrenches, tools, and other miscellaneous equipment should be kept off all moving units of the machine.



11. Be mentally alert on the job, always sober, and never dulled by the influence of drugs, prescribed or otherwise.



12. Use the proper hand tools for each job.



13. Only qualified personnel should perform maintenance repair work.



14. Report any unsafe conditions to yr supervisor.



15. Keep machinery clean.



16. Clean machine and area after each use.



17. Before starting clear area and table of obstructions.



18. Use appreciate lifting device for fixtures, rotary tables, angle plates and large work pieces.



19. Always remember to remove wrench after tightening bolt for collets and arbors.



20. Use soft hammer (plastic or rawhide) to loosen collets, not a wrench or steel hammer.



21. Always pay attention and never walk away when machine is in use.



22. Make sure all changeable tooling is properly secured.



23. Remove levers, handles, and cranks before engaging feed or rapid traverse.



24. Stop spindle when removing chips, changing or measuring parts or adjusting setups.



25. Use a magnetic shield when necessary.



26. To check workpiece – shut machine off & move cutter away from workpiece, do not check
workpiece while spindle is moving.



27. Use appreciate PPE for the job.



28. Do not operate under restrictive medications or use of alcohol or drugs.



29. Report any safety discrepancies to the shop supervisor.


Do’s and Don’ts
1.DO get thoroughly familiar with the STOP lever or button.
2.DO make sure that the work is held securely before engaging the cutter with it.
3. DO make sure that all tools and machine parts are clear of the cutter before starting the machine.
4.DO keep your hands away from the revolving items (cutters, spindles, work pieces, etc)
5.DO handle all cutters carefully to guard against injury to yourself and others.
6.DON’T under any circumstances attempt to operate any machine unless you are thoroughly familiar with it.
7.DON’T move any lever unless you know exactly what is going to happen when it is moved.
8.DON’T play around with the lever of any machine.
9.DON’T go away, even a moment, and leave the machine running.
10.DON’T try to operate the machine and engage fellow workers in conversation at the same time. Keep your mind on your work and let the other fellow do the same.
11.DON’T attempt to oil the machine while it is in operation.


The Cautions and Symbol
1. Do not operate without proper training.
2.Always wear safety goggles.
3.Never place your hand on the tool in the spindle and press ATC FWD, ATC REV,
4.NEXT TOOL, or cause a tool change cycle. The tool changer will move in and crush your and.
5.To avoid tool changer damage, ensure that tools are properly aligned with the spindle drive lugs when loading tools.
6.The electrical power must meet the specifications in this manual. Attempting to run the machine from any other source can cause severe damage and will void the warranty.
7.DO NOT press POWER UP/RESTART on the control panel until after the installation is complete.
8.DO NOT attempt to operate the machine before all of the installation instructions have been completed.
9.NEVER service the machine with the power connected.
10.Improperly clamped parts machined at high speeds/feeds may be ejected and puncture the safety door. Machining oversized or marginally clamped parts is not safe.
11.Windows must be replaced if damaged or severely scratched - Replace damaged windows immediately.
12.Do not process toxic or flammable material. Deadly fumes can be present. Consult material manufacturer for safe handling of material by-products before processing.
13.The spindle head can drop without notice. Personnel must avoid the area directly under the spindle head.