Milling MachinesMilling is the process of machining flat, curved, or milling machines are basically classified as vertical or irregular surfaces by feeding the work piece against a rotating horizontal.Milling is the process of cutting away material by feeding a work piece past a rotating multiple tooth cutter. The cutting action of the many teeth around the milling cutter provides a fast method of machining. The machined surface may be flat, angular, or curved. The surface may also be milled to any combination of shapes. The machine for holding the work piece, rotating the cutter, and feeding it is known as the milling machine.

Types of Milling MachinesKNEE-TYPE MILLING MACHINEKnee-type milling machines 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.UNIVERSAL HORIZONTAL MILLING MACHINEThe basic difference between a universal horizontal milling machine and a plain horizontal milling machine is the addition of table swivel housing between the table and the saddle of the 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 fixturesRAM-TYPE MILLING MACHINEThe ram-type milling machine is characterized by a spindle mounted to a movable housing on the column to permit positioning the milling cutter forward or rearward in a horizontal plane. Two popular ram-type milling machines are the universal milling machine and the swivel cutter head ram-type milling machine.UNIVERSAL RAM-TYPE MILLING MACHINEThe universal ram-type milling machine is 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 MACHINEThe 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 operators choice.

Milling Machine Parts and their FunctionBaseThe 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.ColumnThe column is the main supporting frame mounted vertically on the bage. The column is 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.KneeThe 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, and in 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.

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.TableThe 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 by fixing trip dogs on the side of the table. In universal machines, the table may also be swivelled 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. 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 may be 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.

Milling Cutters A milling cutter is a cutting tool that is used on a milling machine. Milling cutters are available in many standard and special types, forms, diameters, and widths. The teeth maybe straight (parallel to the axis of rotation) or at a helix angle. The helix angle helps a slow engagement of the tool distributing the forces .The cutter may be right-hand (to turn clockwise) or left-hand (to turn counter clockwise).The figure shows a typical end milling cutter.Helical Milling Cutters The helical milling cutter is similar, to the plain milling cutter, but the teeth have a helix angle of 45 to 60. The steep helix produces a shearing action that results in smooth, vibration-free cuts. They are available for arbor mounting, or with an integral shank with or without a pilot. This type of helical cutter is particularly useful for milling elongated slots and for light cuts on soft metal.Metal Slitting Saw Milling CutterThe metal slitting saw milling cutter is essentially a very thin plain milling cutter. It is ground slightly thinner toward the center to provide side clearance. These cutters are used for cut off operations and for milling deep, narrow slots, and are made in widths from 1/32 to 3/16 inch.Side Milling CuttersSide milling cutters are essentially plain milling cutters with the addition of teeth on one or both sides. A plain side milling cutter has teeth on both sides and on the periphery. When teeth are added to one side only, the cutter is called a half-side milling cutter and is identified as being either a right-hand or left-hand cutter. Side milling cutters are generally used for slotting and straddle milling.Interlocking tooth side milling cutters and staggered tooth side milling cutters are used for cutting relatively wide slots with accuracy.End Milling Cutters The end milling cutter, also called an end mill, has teeth on the end as well as the periphery. The smaller end milling cutters have shanks for chuck mounting or direct spindle mounting. End milling cutters may have straight or spiral flutes. Spiral flute end milling cutters are classified as left- hand or right-hand cutters depending on the direction of rotation of the flutes. If they are small cutters, they may have either a straight or tapered shank.T-Slot Milling Cutter The T-slot milling cutter is used to machine T-slot grooves in worktables, fixtures, and other holding devices. The cutter has a plain or side milling cutter mounted to the end of a narrow shank. The throat of the T-slot is first milled with a side or end milling cutter and the headspace is then milled with the T-slot milling cutter.Woodruff Key slot Milling Cutters Cutters The Woodruff key slot milling cutter is made in straight, tapered-shank, and arbor-mounted types. The most common cutters of this type, under 1 1/2 inches in diameter, are provided with a shank. They have teeth on the periphery and slightly concave sides to provide clearance. These cutters are used for milling semi cylindrical keyways in shaft.Gear Hob The gear hob is a formed tooth milling cutter with helical teeth arranged like the thread on a screw. These teeth- are fluted to produce the required cutting edges. Hobs are generally used for such work as finishing spur gears, spiral gears, and worm gears. They may also be used to cut ratchets and spline shafts.Concave and Convex milling cutterConcave and convex milling cutters are formed tooth cutters shaped to produce concave and convex contours of 1/2 circle or less. The size of the cutter is specified by the diameter of the circular form the cutter produces.Corner Rounding Milling CutterThe corner-rounding milling cutter is a formed tooth cutter used for milling rounded corners on workplaces up to and including one-quarter of a circle. The size of the cutter is specified by the radius of the circular form the cutter produces, such as concave and convex cutters generally used for such work as finishing spur gears, spiral gears, and worm wheels. They may also be used to cut ratchets and spline shafts. Special Shaped-Formed Milling CutterFormed milling cutters have the advantage of being adaptable to any specific shape for special operations. The cutter is made especially for each specific job. In the field, a fly cutter is formed by grinding a single point lathe cutter bit for mounting in a bar, holder, or fly cutter arbor. The cutter can be sharpened many times without destroying its shape.

CLASSIFICATION OF MILLING Peripheral Milling In peripheral (or slab) milling, the milled surface is generated by teeth located on the periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel to the work piece surface to be machined.Face Milling In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the work piece surface. The milled surface results from the action of cutting edges located on the periphery and face of the cutter. End Milling The cutter in end milling generally rotates on an axis vertical to the work piece. It can be tilted to machine tapered surfaces. Cutting teeth are located on both the end face of the cutter and the periphery of the cutter body.

METHODS OF MILLING Up Milling Up milling is also referred to as conventional milling. The direction of the cutter rotation opposes the feed motion. For example, if the cutter rotates clockwise , the work piece is fed to the right in up milling.Down Milling Down milling is also referred to as climb milling. The direction of cutter rotation is same as the feed motion. For example, if the cutter rotates counter clockwise , the work piece is fed to the right in down milling.