From Academic Kids
A Milling machine is a power-driven machine used for the complex shaping of metal (or possibly other materials) parts. Its basic form is that of a rotating cutter or bit which rotates concentric to the spindle axis (like a drill), and a worktable that can move in three dimensions relative to the workpiece (in contrast to the drill which can only move in one dimension while cutting). The motion across the surface of the workpiece is usually accomplished by having a moveable table on which the workpiece is mounted, so arranged to move in two dimensions. Milling machines may be operated manually or under computer numerical control (see CNC).
Milling machines can perform a vast number of complex operations, such as slot cutting, planing, drilling, rebating, routing, etc.
Types of milling machines
There are two main types of mill, the vertical mill and the horizontal mill. The vertical mill has a vertical spindle, like the drill press, but with an X-Y table that permits positioning the work. Milling cutters are held in the spindle and rotate on its axis. The spindle generally has the ability to be extended, allowing plunge cuts and drilling. Milling cutters are designated in several groups; end mills, facing mills and form cutters. End mills can cut slots, steps and pockets. Face mills are used to cut flat surfaces. Form mills can cut dovetails, bevels and t-slots. A combination machine, called a mill-drill, is quite popular with amateurs as it takes the place of the drill press and a vertical mill.
A horizontal mill has the same sort of X-Y table, but the cutters are mounted on a horizontal arbor across the table. Cutters, called side mills, have a cross section like a circular saw, but are generally wider and smaller in diameter. 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.
A more complex form of the milling machine is the Universal milling machine, in which the rotating cutter can be oriented vertically or horizontally increasing the flexibility of the machine tool.
CNC Milling Machines
Most CNC milling machines, also known as engraving machines, are computer controlled vertical mills with the ability to move the spindle vertically along the Z axis. This extra degree of freedom allows for creating 2.5D surfaces, like relief sculptures, and when combined with the use of conical tools, significantly improves milling precision without impacting speed, providing a cost-efficient alternative to most flat-surface hand-engraving work.
CNC machines can exist in virtually any of the forms of manual machinery, like horizontal mills. More advanced CNC milling machines add even more degrees of freedom, i.e. tilting the spindle or rotating the workpiece, allowing production of extremely complex 3D objects with very little refixturing, i.e. prototype machinery parts.
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