What is a knee-type milling machine?

The milling machine is a machine tool used to machine workpieces by swarf removal, through the action of a cutting tool called a milling cutter. In metalworking, milling is used to shape different materials: metal, steel, wood, iron, and so on. A milling machine can machine workpieces with complex shapes.

Types of milling machine

Milling machines machine workpieces by swarf removal, through the rotary movement of the cutter, which has several cutting edges. The milling machine is a very versatile machine that can machine different workpieces made of all kinds of materials; in addition, depending on its type, a milling machine can carry out various kinds of machining. A milling machine can mill, drill, bore, slot, and so on.

Because of the needs of industry, milling machines have diversified and adapted to new technologies, so you can find different types of machine tools for milling workpieces. Although these milling machines share a common basis, they differ from one another according to the sector in which they are used.

Milling machines can be classified in different ways, the most common being by the orientation of the tool or axis of rotation, and by the number of axes in the operation. Here we focus on the classification by tool orientation, because this is where knee-type milling machines are found.

By tool orientation

Following the orientation of the cutter's axis of rotation, you can find three different types of milling machine:

• Horizontal: with cylindrical cutters mounted on a horizontal arbor driven by the head of the machine, supported at one end by the head and at the other end by a bearing on the ram or sliding bridge. It is mainly used for slotting.
• Vertical: where the spindle axis is positioned vertically and perpendicular to the worktable. The cutters are mounted on the spindle and rotate about their own axis. Vertical milling machines can in turn be bed-type and knee-type or turret milling machines.
• Universal: this milling machine has a main spindle that allows horizontal tool arbors to be fitted, as well as a head that attaches to the spindle and means that the milling machine can be converted into a vertical one.

What is a knee-type or turret milling machine used for?

The vertical milling machine is characterised by having the spindle axis positioned vertically and perpendicular to the table. The cutters are mounted on the spindle and rotate about their own axis, and both the spindle and the table can move vertically; this movement increases the depth of cut. The knee-type or turret milling machine is a vertical milling machine in which the spindle stays stationary, without moving, while cutting operations are carried out; the worktable, however, can move horizontally and vertically.

Thanks to the orientation of the axis, this type of milling machine is used for step milling of workpieces, and for cutting straight or shaped slots and cavities. In addition to these operations, with a knee-type milling machine it is possible to machine workpieces by swarf removal.

A knee-type milling machine can work different flat surfaces, as well as gears and even decorative elements; this means that turret milling machines are used in many industries. These machines also accept many different materials for machining: wood, metal, steel, plastics and tiles, among others.

Features and operation of the turret milling machine

The knee-type milling machine is characterised by a sort of arm that allows the table to move along the vertical axis: up and down. This allows the machine to make deep or shallow cuts in the workpiece; as a result, workpieces with very complex finishes can be machined.

When the operator actuates the arm and the lever under the table, they can make the various vertical cuts that the workpiece requires. Thanks to this function, the knee-type milling machine means that the workpieces to be machined need less pre-cutting work, since the operator does not have to worry about spindle and table movements, only about operating the table.

Today you can find manual and automatic turret milling machines. On manual machines, the operator has to move the table so that it moves up or down; on automatic knee-type milling machines, you only need to enter the required information so that the tool knows how and where to cut. The movement of the table, whether manual or automatic, makes it possible to obtain rapid variations in power.