MILLING CUTTERS: Plain Milling Cutters, Side Milling Cutters, End Milling Cutters, Face Milling Cutters, Metal slitting Cutters (Slitting Saws), Angle Milling Cutters, Formed Milling Cutters,T-slot Milling Cutters, Wood ruff-key Milling Cutters, Fly Cutter

MILLING CUTTERS

The milling cutters may have either straight tooth i.e. parallel to the axis of rotation or in helical shape. The helix angle may be right hand or left hand and this will decide the direction of rotation of the cutter for performing the cutting operation. 

A milling cutter may be made of single piece of steel or having the cutting portion welded to a tough shank or having removable cutting teeth (bits) inserted in a solid body. The broad classification of milling cutter is according to the shape of the teeth they carry, such as plain, inserted, formed or saw teeth etc.

Common types of milling cutters are the following:

1. Plain Milling Cutters 

2. Side Milling Cutters

3. End Milling Cutters 

4. Face Milling Cutters

5. Metal slitting Cutters (Slitting Saws) 

6. Angle Milling Cutters

7. Formed Milling Cutters 

8. T-slot Milling Cutters

9. Wood ruff-key Milling Cutters 

10. Fly Cutter

1. PLAIN MILLING CUTTERS: 

These milling cutters may have the cutting teeth on their periphery and they may be either straight or helical. 

Their end faces are either ground square with the axis or slightly concave to reduce friction. Thus, no cutting action is provided by the side faces. These cutters are employed for milling flat surfaces parallel to the axis of rotation.

The milling cutters are made to have either fine pitch or coarse pitch. Fine pitch teeth cutters are used for light work and finishing workThe coarse pitch teeth cutters are called heavy duty slab milling cutters. They carry less number of teeth, having a steep helix angle.

They are commonly used where very heavy cuts are to be used, since they are capable of removing more material with less power consumption.

2. SIDE MILLING CUTTERS: 

these cutters, apart from having teeth on the periphery, also have cutting teeth on one side or both sides. They are always provided with central hole for the purpose of mounting them on the arbor. They are also called staddle mills when used in pairs. The main types of side milling cutters are the following.

a) Plain side Milling Cutters: 

They are made to have cutting teeth on the periphery as well as on both sides. They are normally used for cutting slots or in face milling. These cutters are in different widths from 5mm to 25mm and dia up to 200mm.

b) Half side Milling: 

These cutters have teeth on the periphery and on one side only. They can be used for face milling. The teeth may be either straight or helical. Also they can be either left hand or right hand. Actual cutting action is performed by the teeth provided on the periphery while side teeth do the finishing and sizing work.

c) Staggered teeth side Milling Cutters: 

The cutters carry alternate teeth on the periphery only. These alternate teeth are of opposite helix angle, staggered from side to side, just as the teeth of wood saw, and cut alternately on one side and then on the other. They are commonly used for key-way cutting and slot cutting.

d) Interlocking side Milling Cutters: 

These cutters are similar in design to the side milling cutters but are used as a unit, consisting of two cutters joined together such that their teeth interlock. They can be adjusted to aquire the required width by inserting shims or spacers between them to make good the reduction in width of the cutters due to wear and frequent sharpening of the teeth. These cutters are used for milling wider slots to exact width.

3. END MILLING CUTTERS: 

These are solid circular cutters which are manufactured in two different varieties; those having shank and others which do not have shank. They carry teeth on the periphery as well as on the end. These teeth may be straight or helical. Helical teeth may be right hand and left hand. End milling cutters are used for milling slots, key ways, grooves and irregular shaped surfaces. Shank type end mills may have either taper shank or straight shank and diameters from 3mm to 50 mm.

4. FACE MILLING CUTTERS: 

These cutters are made in two common forms. The smaller type is known as shell-type-face milling cutter. It carries teeth on periphery as well as on end face. Maximum cutting is done by the teeth on the periphery and those on the end face perform finishing operation. The larger type of cutter, called the built up face milling cutter, consists of a steel body, along the periphery of which are inserted cutting teeth. The shell type face milling cutters are used for small work where as built up face milling for larger surfaces.

The shell type cutter is usually held in a stub arbor and larger type can be mounted directly on the spindle.

5. METAL SLITTING CUTTERS: 

These cutters are also called metal slitting saws. They are used for cutting thin slots or parting off. They are very thin. They are in two varieties.

a) Plain Slitting Saws: 

They are plain milling cutters, which are very thin. Their teeth are provided with some side relief in order to prevent rubbing. They are made in different widths 1mm to 5mm.

b) Staggered teeth Milling Cutter (Saw): 

These saws are used for comparatively heavier work. They have their teeth staggered alternately and have side teeth also. These saws are in different widths, ranging between 4 mm and 10 mm.

6. ANGLE MILLING CUTTERS: 

These cutters carry sharp angular teeth which are neither parallel nor normal to their axes. Their specific use is in milling V-grooves, notches, dovetail slots, reamer teeth and other angular surfaces. The following two types of angular cutters are in common use:

a) Single Angle Cutter: 

these cutters may have their teeth either only on the angular face or on both, the angular face and side, which enables milling of both flank of the included angular groove simultaneously. Their teeth may have an included angle of 45or 600.

b) Double angle cutters: 

These cutters differ from the single angle cutters in that they have two angular faces which join together to form V-shaped teeth. The included angle of this ‘V’ is either 450, 600, or 900, though it is not necessary that the angle of both the faces should be equal.

7. FORM MILLING CUTTERS: 

These are also known as form relieved milling cutters or radius cutters. This category includes large variety of milling cutters used for producing different shaped contours. Their teeth are provided with a certain angle of relief, so that their form and size are retained even after resharpening. The common types of form relieved cutters are:

a) Corner rounding cutters: 

For milling edges and corners of the jobs

b) Concave and convex cutters: 

Concave cutter for milling convex surface and convex cutter for milling concave surface

c) Gear cutters: 

For milling gear teeth

d) Tap and reamer fluting cutters: 

For milling flutes on reamers and taps

e) Gear hobs: 

For cutting teeth of worm wheels, helical and spur gears

f) Thread milling cutters: 

For milling different types of threads.

8. WOOD RUFF-KEY MILLING CUTTER: 

It is a small type of end milling cutter, up to 50mm dia. are to have solid shank, to be fitted in the machine spindle, where as larger sizes are provided with a hole for mounting the same on an arbor. Smaller sizes have straight teeth on the periphery with the sides having little clearance. Larger sizes are usually made to have staggered teeth both on the periphery as well as the sides.

9. T-SLOT MILLING CUTTER: 

It is a single operation cutter, which is used only for cutting T-slots. In similar sizes it is made to have the shank integral with the cutter. Large size cutters are mounted on a separate shank. In operation, the narrow groove at the top is first milled by means of a slotting cutter or end mill cutter. The T-slot milling cutter is then used for milling the wider groove.

10. FLY CUTTER: 

It is a single point tool, mounted on a cylindrical body, held in a stub arbor or held in a bar. Screws are used for tightly holding the tool in the holders. Cutting edge of the tool can be ground to any desired shape and is capable of producing a very accurate surface.

MATERIALS FOR MILLING CUTTERS

Materials used for manufacturing the milling cutters are the same as for lathe tools.

The common materials used are:

1. High Carbon Steel

2. High Speed Steel

3. Stellite

4. Cemented Carbides

5. Ceramics

High carbon steel is used for small scale production.

High speed steel is extensively used for solid type cutters.

Stellite is used for milling cutters for machining hard metals, forgings, castings etc.

Cemented Carbides are used in the form of bits for milling cutters when high speeds are used.

Ceramics are used for milling bronze and cast Iron. Twice the speed of Carbides.

ANGLES OF A PLAIN MILLING CUTTER:

A milling cutter can be considered as a built up unit of a number of single point cutting tools, such that each tooth of the cutter is a single point cutting tool. 

The relief angle is the angle between the plain P1, which is normal to the axial plane PP at a point on the cutting edge, and the tangent to the relieved land of the outer tooth. This angle is measured in a plane perpendicular to the axis of the cutter. Higher the value of this angle, lessor will be the friction and hence less wear on the land.

A larger relief angle will increase the tool life between two grinds and ensure better surface finish, but at the same time, due to consequent reduction in the lip angle, it will make the tooth weak. Normally relief angle ranges between 10to 300.

The rake angle is the angle between the axial plane PP and the face of the cutter tooth, measure in a plane normal to the cutting edge. Rake angle facilitates free cutting by the tool by allowing the chips to flow smoothly. 

This ensures the less consumption of power, better surface finish, less wear on the tool face and consequently a greater life of the tool between two grinds. However, it should not be increased beyond 20otherwise, the resulting smaller lip angle will again weaken the tool.

The angle between the face and the land of the cutter tooth is called lip angle. It value depends upon the values of rake and relief angles. Larger lip angle ensures stronger tooth and helps in milling harder metals and when deeper cuts are used.

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