CNC Procedure: 5 Basic Steps – CNC Programming

CNC Procedure: 5 Basic Steps – CNC Programming

To run a CNC machine in a productive manner, one has to follow a basic CNC procedure.

A typical CNC Procedure includes the following 5 basic steps:-

  • NC Coordinate System
  • Process Planning
  • Part programming
  • Verification of Part Program
  • Production

In this article, we will discuss all the above steps in details.

To know more about NC System Click here

NC Coordinate Drawing

An NC Coordinate Drawing is the first requirement to run a CNC machine. A CAD Drawing of any product is not directly acceptable in any CNC machine. Thus, a CAD drawing needs to be converted into a machine-readable format that is NC Coordinate Drawing.

A Typical Drawing

A CNC machine makes use of any one of the following coordinate system.

Absolute Coordinate System (ACS)

It is also known as Absolute Dimensioning System or Absolute Positioning System or Reference Dimensioning System. In this Coordinate System, all the part’s coordinates are measure about a single reference point or zero-point.

In other words, all the tool’s movements/locations are defined with respect to a single reference point or zero-point.

The reference point or zero-point is set fixed and remains the same throughout the tool’s movement.

Drawing using ACS

Note:- To activate Absolute Coordinate System (ACS), G90 word is used in the part program.

Incremental Coordinate System

It is also known as Incremental Dimensioning System or Incremental Positioning System or Relative Dimensioning System. An Incremental Dimensioning System makes use of the tool’s current position to find out the tool’s next position. 

In other words,  Tool’s current position works as a reference point for the next position.

The Reference point or zero-point keeps changing throughout the tool’s movement.

Drawing using ICS

Note:- To activate Incremental Coordinate System (ICS), G91 word is used in the part program.

Process Planning

Process Planning is the second step in the CNC procedure. A number of manufacturing operations are required to manufacture a product. So it becomes quite important to schedule all the required manufacturing operations in a logical sequence to reduce the non-productive time. To write a part program for a given product, a part programmer also follow the same procedure.

A Process Planning basically involves:-

  • Selection of manufacturing processes
  • Scheduling/sequencing of manufacturing processes
  • Selection of required tooling, etc.

 To know more about Process planning Click here

Note: Route Sheet is the listing of the scheduled manufacturing processes with their sequence.

Part Programming

This one is the most important step in CNC procedure. In this step, the part programmer writes the part program for a given part/product. A part program consists of all the required machining instructions to be followed by the machine in an appropriate format.

There are at least two type of part programming :-

Online Part Programming

Online part programming refers to the writing the part program directly into the MCU of the CNC through Control panel. Sometimes it is also known as Manual Data Input (MDI). Online part programming is used only for the simple part program. To make a complex part program, part programmers usually use the Off-line part programming method.

Off-line Part programming

Offline part programming is all about writing the part program in any computer system with the help of appropriate software. Then the part program is transferred to the respective machine using any available data transfer mechanism like pen drive, blue tooth, wifi, etc.

Verification of Part Program

The most important step in CNC Procedure is to verification the part program. Some errors or mistakes may be included in a part program which may further lead to the major or minor breakdown in the CNC machine. To avoid any kind of accident or breakdown, a part programmer verifies part program using any available methods.   

Visual Inspection

This one is the simplest and cheapest method available to verify a part program. An experienced part programmer verifies the part program only by reading it. It is the least reliable method available and usually uses for the simple part program only.


This one is the most advanced feature available to any CNC machine or part programming software.  This feature is capable to plot the tool path graphically. Part programming software runs the part program to check the tool path. If the tool follows the desirable path, the part program is said to be ready.   

Single Block Execution

This type of verification is carried out over the CNC machine itself. As we know, a part program is a set of numbers of the block. A block consists of sufficient instructions either to setup machine setting or to move machine tool.

In this method, MCU sends the signal to the machine in single blocks. Once a Single block executed properly, the next block is fed to the machine. If any thing goes wrong during the execution of any block, it can be easily short out without any major breakdown or accident.

Dry Run

In this part program verification method, the part program is fed into the MCU and machine is set to run. The main difference between the actual run and dry run of the machine is the workpiece. During a dry run, a cheap material like wood, plastics, etc is used in place of the actual workpiece. Some time machine is run without any workpiece to check out the tool’s path only.


This one is the last and the final step in the CNC Procedure.  In this step, the verified part program is fed into the MCU and machine is set to run for production.

This is all about the CNC Procedure: 5 Basic Steps – CNC Programming

Hope you find it useful

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