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NC vs CNC vs DNC: Differences Explained



John Abraham
Hey I'm John. I write about Manufacturing, Metalworking, CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com


NC vs CNC vs DNC

NC, CNC, and DNC are programming techniques used in manufacturing to automate operational processes.

These three terms are often used interchangeably, but they represent different machine operation techniques.

In the evolutionary chain of machining, NC was invented first. Then came its computerized version – CNC, and its advanced industrial version, DNC.

This article looks at these techniques individually and then compares them in detail by discussing their differences.

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NC, CNC, and DNC – What are they?

NC is a machine programming technique that uses punch tapes and tape readers. CNC uses a computer to program the code and a machine controller unit to read the code fed to the machine. DNC is a network of multiple CNC machines that connect to a single mainframe computer.

These machine programming techniques help create parts with more precision and accuracy than traditional (manual machining) approaches.

Today these machines are regularly used in manufacturing industries such as woodworking, metalworking, etc.

What is NC?

Rolled punch tape
A set of rolled punch tapes (Source: Wikipedia)

Numerical Control (NC) is a computer-controlled machining process that uses punched tape to provide machining instructions to the cutting tool.

The punched tape is fed into a tape reader, and the instructions are read and analyzed by the NC controller.

The NC controller then converts these instructions into cutting tool movements by activating the machine transmission.

A typical NC machine generally has a three-axis system (X, Y, and Z) to move in a three-dimensional space.

What is CNC?

Design to part workflow in CNC
Design to part workflow in CNC

Computer numerical control (CNC) is a technology that allows you to control the motion of a machine by inputting commands through an electronic interface, usually through the combination of a computer and a microcontroller onboard the machine.

A computer is used to create a digital design of the part you need to make and convert it into a part program that machine controllers can read and implement.

CNC programming is generally performed by using CAD/CAM software. However, you must be familiar with basic G-code language to manually tweak the program, which slightly increases the difficulty of CNC programming.

computer numerical control system
Basic components of a computer numerical control system

What is DNC?

illustraction of a direct numerical control system
A DNC setup

Direct numerical control (DNC) is a type of automation technology used in manufacturing industries to link multiple CNC machines to a centralized computer.

The part programs are stored on this mainframe computer, which is usually a powerful computer that can carry out multiple processes simultaneously.

The main advantage of using a DNC system is that it allows you to run the same part program on different machines at the same time.

Moreover, certain part programs, required to machine complex parts, can be memory-intensive, and loading these programs on individual machine control units of different machines can be time-consuming.

DNC solves this dilemma by storing and sending these programs through a localized server.

In most setups, these machines are connected to the main computer through networking cables.

However, these are now being replaced by wireless technology as it allows to easily switch networks to other central computers.

DNC is primarily implemented through either switching networks or Local Area Networks (LAN).

Different DNC networks
Different DNC network setups

In a switching network DNC, the master computer sends the data packet to a data switching box. From there, the data is individually sent to different machine control units connected to the machines.

The local area network (LAN) DNC has a hierarchical or branched setup. Here the mainframe computer is connected to different satellite computers, which process the data and send it to different machines.

LAN-DNC is best suited when working with different types of machines like mills, lathes, etc., as you can easily branch a machine type under one satellite computer.

DNC is actively being used in many production-intensive industries like automobile, aerospace, food processing, packaging, textile, etc.

Difference Between NC, CNC, and DNC

Input MethodPunch TapeComputer SystemComputer System
Number of machines under each control system11Multiple machines
Ability to modify an existing programLowHighVery High
Machine feedback from the toolNoYesYes
ApplicationLow-volume productionLow and medium volume productionHigh volume production

Difference between NC, CNC, and DNC

In terms of how the program is fed to the machine

Of the three, NC is the oldest machine programming setup.

Since old programmable manufacturing machines were run using hardwired control units, they used punch tapes and tape readers to provide the input program to the machine.

CNC and DNC systems use computers to operate, and so the program codes are software generated and fed to them using different software programs.

Machinists operating these machines use CAD software to generate the design, CAM software, such as DeskProto, to convert the design into code, and CNC control software to send the design to the machine.

In terms of program revisions

You can easily modify the part program on CNC and DNC setups by editing it on the computer, allowing much more flexibility in the manufacturing process.

In addition, on DNCs, you only have to modify the program on one computer (i.e., the central computer). From there, the program can be sent to different machines.

But on NC and CNC systems, you have to individually store the edited program in each machine to run it. This requires you to spend more time preparing the machine for the job.

Since NC machines use a physical input like punch tape, you can’t make changes to the existing tape.

Instead, you’ll have to use a new tape to punch the revised program. This is the major disadvantage of using an NC-integrated machine tool.

In terms of the number of machines

The DNC system is the best option for managing multiple machines at once. This is because it only requires one computer to connect with many machine tools.

Comparatively, CNCs require dedicated computers or storage devices to send program code to the machine controller.

In terms of the machine control unit

Each machine will have its own dedicated machine control unit in NC, CNC, and DNC setups.

On NC machines, the tape reader that reads the punched tape is part of the control unit. In comparison, CNC and DNC systems use dedicated microcontrollers on each machine control unit.

In terms of machine feedback

Since CNC and DNC systems use microcontrollers in the machine controller unit, they can receive feedback data from the machine tool.

Feedback from the machine is an important aspect of the manufacturing process.

It helps the controller to detect any abnormality in the machining process and make adjustments to rectify the program code and overcome the abnormality.

Final Thoughts – Which is better?

After comparing NC, CNC, and DNC, It’s clear that the DNC setup is more flexible and the NC configuration has many limitations in the manufacturing process.

NC is an outdated system. Today, only a handful of machines use them, mostly old-school machines employed in the military.

CNC is the most widely used machine control system today. It’s equally used by hobbyists, small businesses, and large industries.

Their wide usage is attributed to their cost-effectiveness, operational simplicity, accuracy, and highly customizable workflow.

DNC systems are employed to control multiple machines at the same time. Therefore, they are best suitable for large businesses that manufacture repeated parts or objects.

Frequently Asked Questions

What are the advantages of DNC over CNC?

The advantage of DNC over CNC is that it is a cost-effective way of manufacturing for large-scale industries working with many machines. It cuts investment costs spend on multiple computers and machine operators by implementing a centralized system with one computer and one machine operator handling multiple machines.

What are the disadvantages of CNC machines?

The disadvantages of using CNC machines include their high initial investment and routine maintenance. Also, these machines need to be programmed and operated by skilled technicians.

What components are needed for a CNC or DNC system?

CNC or DNC machine control systems use components like a Central Processing Unit (CPU), immediate access memory (ROM and RAM), input/output devices, control interfaces, cutting tools, etc.

John Abraham
Hey I'm John. I write about Manufacturing, Metalworking, CNCs and Lasers at Mellowpine. If you have any questions related to CNCs or Lasers, I'd be happy to answer them. Reach me at mail@mellowpine.com