Difference between NC and CNC Machine

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Today we will discuss about difference between NC and CNC machine. NC stands for numerical control whereas CNC stands for computer numerical control. Both of these are automatic machines which are used for machining any metal with accurate dimensions. These both machines work on feeding mechanism in which we command the machine in some defined code language and the machine compile and convert it into machine language and perform the predefine operation. Today we will learn about both of these machines and also differentiate them in later portion of this article. Now let’s start the discussion.

Numerical Control (NC) Machine:

Numerical Control (NC) refers, the method of controlling the manufacturing operation by directly inserted numerical codes into the machine tool. It is important to realize that it is not a machining method, rather, it is a concept of machine control.

In a Numerical Control machine, the program is fed to the machine through punched card, magnetic tapes and other such media. The program consists of precise instructions about the manufacturing method as well as the movements. It has no memory storage and it run off of the “tape” each time the machine cycles.


The essential features of numerically controlled machines have been established for many years. They comprise a controller, known as the machine control unit MCU, capable of reading and interpreting a stored program and using the instructions in this to control a machine via actuation devices.


The detailed step-by-step commands that direct the actions of the processing equipment called program of instructions. In machine tool applications, the program of instructions is called a part program, and the person who prepares the program is called a part programmer. In these applications, the individual commands refer to positions of a cutting tool relative to the worktable on which the workpart is fixtured. Additional instructions are usually included, such as spindle speed, feed rate, cutting tool selection, and other functions. The program is coded on a suitable medium for submission to the machine control unit.


NC Coordinate System:


In machine tools the cutter may typically move in multipledirections with respect to the workpiece, or vice versa, and therefore the controller normally drives more than one machine axis. Examples of machine applications and numbers of axes are as follows:


1.) 2-axis motion, generally in two orthogonal directions in a plane, which applies to most lathes as well as punch presses, flame and plasma-arc and cloth cutting machines, electronic component insertion and some drilling machines.


2.) 3-axis motion, which is generally along the three principal directions (x, y and z) of the Cartesian coordinate system, and applies to milling, boring, drilling and coordinate measuring machines.


3.) 4-axis motion typically involves three linear and one rotary axis, or perhaps two x-y motions, as for example for some lathes fitted with supplementary milling heads.


4.) 5-axis machines normally involve three linear (x, y and z) axes, with rotation about two of these, normally x and y.


Computer Numerical Control (CNC) Machine:

It is the next method of NC machine. In a Computer Numerical Controlled machine, the machines are interfaced with computers. This makes them more versatile in the sense that, suppose a change in dimension of a part is required. In a NC machine, you would have to change the program in the tape and then feed it to the machine again. But in a CNC machine, you just change a variable in the computer and you can modify the program. It has the memory storage and the programs can be stored in its control. In modern CNC systems, the design of a mechanical part and its manufacturing program is highly automated. The part’s mechanical dimensions are defined using computer-aided design (CAD) software, and then translated into manufacturing directives by computer-aided manufacturing (CAM) software. The resulting directives are transformed (by “post processor” software) into the specific commands necessary for a particular machine to produce the component, and then loaded into the CNC machine. Consists of main memory and secondary memory. Main memory (Primary storage) consists of ROM (read-only memory) and RAM (Random access memory) devices.Operating system software and machine interface programs are generally stored in ROM. Numerical control part programs are stored in RAM devices. Current programs in RAM can be erased and replaced by new programs as jobs are changed. High-capacity secondary memory (also called auxiliary storage or secondary storage) devices are used to store large programs and data files, which are transferred to main memory as needed. In NC machine if an error occurs in the program than its debugging and modification is not easy. In CNC machine the debugging and modification is very easy. High skilled operator is required to operate the NC machine whereas to operate a CNC machine, a semiskilled operator may work. The cost of the NC machine is less as compared with the computer control machines.

Difference Between NC and CNC Machine:



Input method: Punched tape, punched card and other such media.
Input method: programs are fed directly into the computer by small key board similar to our traditional key board.
Programs should be changed in punched card and then fed to machine.
We can modify the program in computer.
Operation parameters could not be changed.
Operation parameters can be changed.
It has no memory storage.
We can store programs using the memory storage in computer.
Run off the “Tape” each time of machine cycle.
It have the facility of running the program without actually running it ON the machine tool.
NC machine cost is less.
CNC machine cost is high.
Maintenance is less.
Maintenance is high.
Accuracy is less.
It has more accuracy.
High skill operator required.
High skilled not required.
It is less flexible.
It is highly flexible.
It required more time to perform a operation.
It requires less time.

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