1.  Drives

Basic function of a CNC machine is to provide automatic and precise motion control to its elements such work table, tool spindle etc. Drives are used to provide such kinds of controlled motion to the elements of a CNC machine tool. A drive system consists of drive motors and ball lead-screws. The control unit sends the amplified control signals to actuate drive motors which in turn rotate the ball lead-screws to position the machine table or cause rotation of the spindle.

2.  Power drives

Drives used in an automated system or in CNC system are of different types such as electrical, hydraulic or pneumatic.

• Electrical drives
  
  These are direct current (DC) or alternating current (AC) servo motors. They are small in size and are easy to control.
  
• Hydraulic drives
  
  These drives have l arge power to size ratio and provide stepless motion with great accuracy. But these are difficult to maintain and are bulky. Generally they employ p etroleum based hydraulic oil which may have fire hazards at upper level of working temperatures. Also hydraulic elements need special treatment to protect them against corrosion.
  
  
• Pneumatic drives
  
  This drives use air as working medium which is available in abundant and is fire proof. T hey are simple in construction and are cheaper. However these drives generate low power, have less positioning accuracy and are noisy.

In CNC, usually AC, DC, servo and stepper electrical drives are used. The various drives used in CNC machines can be classified as:

1. Spindle drives to provide the main spindle power for cutting action
   
2. Feed drives to drive the axis