Introduction to Milling Machines

Milling Process

• Milling is a process of removing metal by feeding the work against a rotating multipoint cutter.
• The machine tool intended for this purpose is known as a milling machine.

Types of Milling Machines

• Classified according to the general design of the machine:
• Column and knee type
• Table type
• Planer type
• Special type

Column and Knee Type Milling Machine

• The column is mounted vertically upon the base.
• Knee is mounted on the accurately machined guide ways of the column.
• Saddle and table are mounted on the knee.
• Different types of column and knee type machines:
• Plain milling machine (rigid and sturdy, used for heavy workpieces)
• Universal milling machine (table can be swivelled by 45º, used for helical milling works)
• Omniversal milling machine (knee can be tilted to a required angle, used for machining helical grooves, reamers, and bevel gears)
• Vertical milling machine (spindle is positioned at right angles to the table, used for machining slots and flat surfaces)

Main Parts of Column and Knee Type Milling Machine

• Base: supports all the other parts of the machine tool, made of cast iron.
• Column: mounted upon the base, box shaped, houses the mechanism for providing drive for the spindle.
• Knee: slides up and down on the guide ways of the column, movements obtained by elevating screw mounted on the base.
• Saddle: mounted on the guide ways of the knee, moves in a cross direction.
• Table: moved longitudinally either by power or manually on the guide ways of the saddle, top surface has 'T' - slots.
• Spindle: located in the upper part of the column, receives power from the motor through belt, gears, and clutches.
• Overhanging arm: supports the arbour from the top of the column.
• Front brace: an extra support fitted between the knee and the overhanging arm.
• Arbor: supports different types of cutters used in the machine, drawn into the taper hole of the spindle by a draw bolt.

Size of a Milling Machine

• Specified by:
• Size of the table (length and width)
• Maximum lengths of longitudinal, cross, and vertical travel of the table
• Number of spindle speeds, number of feeds
• Spindle nose taper
• Power required
• Net weight of the machine
• Floor space required
• Type of the machine

Milling Operation - Peripheral Milling

• Classified into two types:
• Up milling (workpiece mounted on the table is fed against the direction of rotation of the milling cutter)
• Down milling (workpiece mounted on the table is moved in the same direction as that of the rotation of the milling cutter)

Cutter Holding Devices

• Depending on the design of the cutter, there are several methods of supporting milling cutters on the machine spindle:
• Arbor
• Collet
• Adapter
• Screwed on cutters

Milling Machine Attachments

• Intended for developing the range of operations, versatility, production capacity, and accuracy of machining process:
• Vertical milling attachment
• Universal milling attachment
• High speed milling attachment
• Slotting attachment
• Rotary table attachment
• Indexing head attachment

Indexing Head

• Indexing is the method of dividing the periphery of a piece of work into any number of equal parts.
• The attachment used for performing indexing is known as an indexing head.
• Three different types of indexing heads:
• Plain or simple dividing head
• Universal dividing head
• Optical dividing head