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INTRODUCTION OF MILLING MACHINES

Milling is one of the most common machining processes because it is capable

of economically producing a variety shapes on workpieces.

Milling machines are very versatile. They are usually used to machine flat

surfaces, but can also produce irregular surfaces. They can also be used to drill,

bore, cut gears, and produce slots. The type of milling machine most commonly

found in student shops is a vertical spindle machine with a swiveling head. Although

there are several other types of milling machines, this document will focus only on the

vertical milling machine.

A milling machine removes metal by rotating a multi-toothed cutter that is fed into the

moving workpiece. The spindle can be fed up and down with a quill feed lever on thehead.

The bed can also by fed in the x, y, and z axes manually. In this clip the z axis isadjusted first, then the y, than the x.

Once an axis is located at a desired position and will no longer be fed, it should belocked into position with the gibb locks.

Most milling machines are equipped with power feed for one or more axes. Powerfeed is smoother than manual feed and, therefore, can produce a better surface

finish. Power feed also reduces operator fatigue on long cuts. On some machines,the power feed is controlled by a forward reverse lever and a speed control knob.


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1.0 MACHINES

Milling machines are tools designed to machine metal, wood, and other solid

materials. Often automated, milling machines can be positioned in either vertical orhorizontal orientation to carve out materials based on a pre-existing design. These

designs are often CAD directed, and many milling machines are CNC-operated,

although manually and traditionally-automated milling devices are also common.

Milling machines are capable of dynamic movement, both of the tool and the

workpiece, and many milling machines can perform multi-axis machining. Because of

variations in orientation, operation and application, milling machines have varying

functions and different operating principles.

1.1 The principle parts of milling machine are given:

Base

The base of the machine is Grey iron casting accurately machined on its top and

bottom surface and serves as a foundation member for all the other parts which rest

upon it. It carries the column at its one end. In some machines, the bage is hollowed

and working as a reservoir for cutting fluid.

Column

The column is the main supporting frame mounted vertically on the bage. The columnis box shaped. Heavily ribbed inside and houses all the driving mechanisms for the

spindle and table feed. The front vertical face of the column is accurately machined

and is provided with dovetail guide ways of supporting knee. The top of the column is

finished to hold an over-arm that extends outward at the front of the machine.

Knee

The knee is the rigid gray iron casting that slides up and down on the vertical way of

the column face. The adjustment of height is effected by elevating screw on the base

that also supports the knee. The knee houses the feed mechanism of the table, andin different controls to operate it. The top face of the knee forms slid way for the

saddle to provide cross travel of the table.

Saddle

The saddle is placed on the top of the knee, which slides on guide ways set exactly

at 90 to column face. A cross feed screw near the top of the knee engages a nut of

the bottom of the saddle to move it horizontally, by hand or power, to apply cross

feed. The top of the saddle is accurately machined to provide guide ways for the

table.


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Table

The table rest on ways on the saddle and travels longitudinally. The top of the table is

accurately finished and T-slots are provided for clamping the work and other fixtures

on it. A lead screw under the table engages a nut on the saddle to move the table

horizontally by hand or power. The longitudinal travel of the table may be limited byfixing trip dogs on the side of the table. In universal machines, the table may also be

swiveled horizontally. For this purpose the table is mounted on a circular bage which

in its turn is mounted on the saddle. The circular bage is graduated in the degree.

Over hanging arm

Over hanging arm is mounted on the top of column extends beyond the column face

and serve as a bearing support may be provided nearest to the cutter. More than one

bearing support may be provided for the arbor.

Front Brace

The front brace is an extra support that is fitted between the knee and over arm to

ensure further rigidity to the arbor and the knee. The front brace is slotted to allow for

adjustment of the height of the knee relative to over arm.

Spindle

The spindle of the machine is locates in the upper part of the column and receive

power from the motor through belts, gears and clutches and transmit it to the

arbor the front end of the spindle just projects from the column face and it is

provided with a tapered hole into to which various cutting tools and arbors maybe inserted. The accuracy in metal machining by the cutter depends on primarily

accuracy, strength and rigidity of the spindle.

Arbor

An arbor is considered as an extension of the machine spindle on which cutters

are securely mounted and rotated. The arbors are made with taper shanks for

proper alignments with machine spindles having taper hole on their nose. The

taper shank of the arbor conforms to the Morse taper or self release taper whose

value is 7:24. The arbor may be supported at the farthest end from the overhanging arm or may be of cantilever type which is called stub arbor.

Mil l ing Machine Construc i ton

Milling machine may be defined as the type of machine in which the metal is

removed by causing the job to be fed against a revolving cutting tool called the

milling cutter, which has one or more cutting.
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2.0 Process or Types

Types of Milling Machines

Milling machines are among the most versatile and useful machine tools due to their

capabilities to perform a variety of operations. They can be broadly classified into the

following types:

Column and knee type of milling machines

Bed type

Rotary table

Tracer controlled

Horizontal Milling Machine Vertical Milling Machine


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Column & Knee type Milling Machines

Used for general purpose milling operations, column and knee type milling machinesare the most common milling machines. The spindle to which the milling cutter is maybe horizontal (slab milling) or vertical (face and end milling). The basic components

are:

Work table, on which the workpiece is clamped using the T-slots. The tablemoves longitudinally with respect to the saddle.

Saddle, which supports the table and can move transversely.

Knee, which supports the saddle and gives the table vertical movements for

adjusting the depth of cut.

Overarmin horizontal machines, which is adjustable to accomadate different

arbor lengths.

Head, which contains the spindle and cutter holders. In vertical machines thehead may be fixed or vertically adjustable.

Bed type Machines

In bed type machines, the work table is mounted directly on the bed, whichreplaces the knee, and can move only longitudinally. These machines have highstiffness and are used for high production work.

Planer Machines

Planer machines are similar to bed type machines but are equipped with severalcutters and heads to mill various surfaces.

Rotary Table Machines

Rotary table machines are similar to vertical milling machines and are equipped withone or more heads to do face milling operations.

Tracer Controlled Machines

Tracer controlled machines reproduce parts from a master model. They are used inthe automotive and aerospace industries fro machining complex parts and dies.

Computer Numerical Control(CNC) Machines

Various milling machine components are being replaced rapidly with computer

numerical control(CNC) machines. These machine tools are versatile and arecapable of milling, drilling, boring and tapping with repetitive accuracy.


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Milling Operations

Facing: removes material across the top surface

Contouring: removes material to a specified depth along a CAD geometry

Drilling: uses points identified on a CAD layer to drill holes to a specified depth

Pocketing: removes all material within the outline of a CAD geometry

Surface of Revolution: removes all material within a surface generated by revolvinggeometry about the X or Y axis


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3.0 Tools and Equipment

Tool ing

Milling machines can be outfitted with a number oftool headsto accomplish differentmachining needs. Some of these tool heads include cutters, roundingmills,flutedmills and ball end mills. Some milling machines have rotating tool ends that canchange depending on the needed task computer programming communicates withthe machine when to change its tooling.

The different tooling used in milling machines is based on material and desiredshape. Because materials like wood and steel have different physical properties,different tool bits are needed to properly machine the materials. If a milling machineuses a tool bit that is not strong enough to machine steel, the tooling and even themachine itself can be damaged. Tooling that is too strong for softer materials candamage the workpiece.

The basic tooling bit on a milling machine is called the cutter. A cutter is a shaped barthat has saw teeth. The cutter rotates rapidly to cut down and shape materials. Thecutter is attached to an arbor, which is sometimes called a mandrel or mandril, ashaped bar that varies in size, length and ending, and is used to hold the cutterfirmly.

A milling cutters saw ending can be spaced, sized and oriented in many ways.Generally, the teeth are either positioned in a straight up-and-down orientation, or

angled in a helical orientation. Straight teeth are preferable in operations on densermaterials, while helical teeth can create very smooth cuts on softer materials. Thereare a variety of cutters within these categories, including dense end cutters, t-slotcutters, and angle cutters. Cutters are subject to different standardized sizes, withCAT sizes as the most commonly-used standardization category in the United States.

ATTACHMENTS AND ACCESSORIES

The attachment and standard or special auxiliary devices intended to be fastened to

or joined with one or more components of the milling for the purpose of augmenting

the range, versatility, productivity or accuracy of operation.

The following are the different attachments used on universal milling machine.

Dividing head

Vertical head

Rotary table

Slotting attachment

Rack milling attachment
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Dividing head

Dividing head

Dividing head or indexing head is a special work holding device, which is bolted onthe machine table. The work may be mounted on a chuck fitted on the dividing head

spindle or may e supported between a live and dead center. The dead center is

mounted on a foot stock as in a lathe tail stock that is bolted on the machine table

after correctly aligning its spindle axis with the dividing head spindle. The attachment

is principally used for dividing the periphery f a work piece in equal number of

divisions for machining equally spaced slots, or groves. The worm and worm gear

driving mechanism of the attachment can be linked with the table lead screw for

cutting equally spaced helical grooves on the periphery of a cylindrical work piece.

Vertical head

Vertical head

The vertical milling attachment can converted a horizontal milling machine into a

vertical milling machine by orienting the cutt9ing spindle acids from horizontal to

vertical for performing specific operation. The attachments consist of a right anglegearbox, which is attached to the nose of the horizontal milling machine spindle by


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bolting it on the column face. The speed of the vertical spindle is same as that of the

machine spindle. The attachment with the spindle can also be swiveled at any angle

other that at right angles to the table for machining angular surfaces.

Rotary table

Rotary table

Rotary table or circular milling attachment is especial work holding device, which is

bolted on the top of the machine table. It provides rotary motion to the table. The

attachment consists of a circular table having T-Slots mounted on the graduated

base. The circular table may be rotated by hand, and in special case by power by

linking the rotary table driving mechanism with the machine lead screw

Slotting attachment

Slotting attachment

A slotting attachment converts the rotary motion of the spindle into reciprocating

motion of the ram by means of an eccentric or crank housed with in the attachment,

thus a milling machine can be converted into a slotter by accepting a single pointslotted tool at the bottom end of the ram and is conveniently used for cutting internal


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or external key ways, spines, etc. The attachment is bolted on the face of the column

and can also be swiveled at an angle for machining angular surfaces. The length of

stroke of the ram can also be adjusted.



A rack milling attachment is bolted to the face of the column and is used for cutting

rack teeth on a job mounted on the table. The attachment consisting of a gear trainenables the spindle axis to be oriented at rightly angles to the machine spindle. In a

horizontal plan. The successive rack teeth are cut by using a rack indexing

attachment. The slanted rack teeth or skew rake may be machined when the

attachment is mounted on universal milling when the table may be swiveled to the

required helix angle


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4.0 Product sample

Using advance milling machines, woodworkers, who once used a hammer and chisel

to form and shape a block of wood into a work of art, can now perform the same workwith ease. Woodworking crafts is a highly skilled form of art dating back to ancient

civilization. Evidence of woodworking is found carved on the walls of caves and

ancient tombs in Egypt and elsewhere. Since then, the craft of woodworking has

dramatically evolved due to the invention of milling machines.

Operation

Computer numerical controlled (CNC) milling machines possess a set of unique

cutting tools designed to create intricate patterns in various wood materials. Besidesmanual operation, the entire milling job can be performed by specialized computer

software. Since this type of milling machine is able to refer motion directions to a

router, woodworkers can give the machine step by step instructions, resulting in the

production of nearly any wood pattern.

Mill Cutters

In order to carve wood with intricate design features, the machine mill utilizes a

number of milling cutters, including plain mill cutters, corner rounding mill cutters,

dovetail mill cutters, four fluted end mill cutters, ball end mill cutters and two flutedend mill cutters. These cutters are designed to automatically cut gears, produce slots,

drill and bore holes in any piece of wood stock. Woodworkers will discover that such

tools make the hammer and chisel obsolete.

Product ion

One advantage of machine mills is that it allows the woodworker to create a mass

number of the same woodcraft patterns over and over again. The old way of creating

the same wood craft involved a laborious and repetitive work. All the wood craft

maker has to do is properly set up the machine and watch it produce hundreds of

identical woods patterns. With a chisel and hammer, this process would have taken

months if not years.

Ease of Use

Woodworkers will have little difficult operating this machine. Even if she possesses a

limited number of skills, all she is required to do is load the machine and receive the

finish product. The computerized software that translates wood pattern ideas into

designs to be produced by the machine mill makes her job that much easier. The

bottle line is that, with a machine mill, a woodworker will be able double or triple the

number of woodworking crafts he would normally make during the course of a day.


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5.0 Pictures and diagram related

Milling

machine

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cadcam end of chapter 2

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