CNC stands for “Computer Numerical Control”, a computer-controlled cutting machine which mounts a spindle which is used to cut out different materials. The tool path is automated by means of software containing numerical data.

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CNC machine Classification

CNC machines can be classified according to the functionality, number of axes, and control loop:

Functionality:

CNC machines can be classified according to its functionality parts into types: milling, lathes, drilling, plasma cutters, and grinders. CNC milling machines use rotary tool to remove material from the surface of a stationary work piece in order to create slots, shapes, notches, pockets, and grooves,

Number of Axis:

CNC machines can be classified according to the number of control axes into: 2-axis, 2.5-axis, 3-axis, 4-axis, and 5-axis CNC machines. An axis is what the machine operates along/around. A 3-axis CNC machine moves in 3 dimensions (X, Y and Z). It is the most used and cheaper than other which made it typical for hobbyist use. It is used for milling, drilling, cutting, and engraving. It mounts typically a cutting tool or leaser head. Typical applications are Printed Circuit Board (PCB) prototyping, engraving on materials such as woods, acrylics, leathers, and laser-cutting acrylic or woods.

Control loop:

CNC machines can be classified according to the control loop into closed-loop and open-loop.

In closed-loop, the controller sends the motor direction, velocity, and acceleration signal and gets back information about the actual movements, calculate the error (difference between desired and actual) and changes the signal accordingly. Typically, servomotors are used in such high-end machines. Its advantage is precision control, while the disadvantage is the cost.

On the other hand, in open-loop CNC machines, the controller determines the desired motor step and direction signals and sends them to the motor (typically a stepper motor) and no signals are fed-back to the controller about the actual motor step. It’s much cheaper than the closed-loop but less precise.