G Code in CNC Programming

G-codes are also called preparatory codes, and are any word in a CNC program that begins with the letter "G". Generally it is a code telling the machine tool what type of action to perform, such as:
- Rapid move
- Controlled feed move in a straight line or arc
- Series of controlled feed moves that would result in a hole being bored, a workpiece cut (routed) to a specific dimension, or a decorative profile shape added to the edge of a workpiece.
- set tool information such as offset.


A number following address G determines the meaning of the command for the concerned block.
G codes are divided into the following two types.

1. One-shot G code
    The G code is effective only in block in which it is specified
    Example :
      N011 G00 X0 Y0 M5; 
        N012 G49 Z250.0 T15 M6;
        N013 G43 Z0 H15;
        N014 S20 M3;
        N015 G99 G82 X550.0 Y–450.0 Z–130.0 R–97.0 P300 F70;
      The G82 also known as drilling cycle is use only one shot.

2. Modal G code
    The G code is effective until another G code of the same group is specified
    Example :
      N010 G01 X0.0 Y0.0 F500 ;
        N020 Z50.0;
        N030 X20.0;
        N040 X25.0 Y15.0;
        N050 GO X0.0 Y0.0:
  
       The G01 is effective in range N010 - N040, until there is another G comand or program end.
     

GENERAL FLOW OF OPERATING CNC MACHINE

When machining the part using the CNC machine tool, first prepare the program, then operate the CNC machine by using the program.

1) First, prepare the program from a part drawing to operate the CNC machine tool.
How to prepare the program is described in the Chapter PROGRAMMING.

2) The program is to be read into the CNC system. Then, mount the workpieces and tools on the machine, and operate the tools according to the programming. Finally, execute the machining actually.



How to operate the CNC system is described in the Chapter OPERATION.

Before the actual programming, make the machining plan for how to machine the part.
Machining plan
1. Determination of workpieces machining range
2. Method of mounting workpieces on the machine tool
3. Machining sequence in every machining process
4. Machining tools and machining
Decide the machining method in every machining process.

Tool coordinate system

If you want to create a CNC Program, you must know also about tool coordinate system.

dont forget to adjust the tools.

Coordinate system

There are easy ways to remember the coordinate system in programming Cnc.
1. Cartesian Coordinate Systems

2. Right hand rule

Kind of axis coordinate in CNC Machine

Before we go to create a cnc program, we must know that every machine have a axis coordinate.
If the machine only have 3 axis coordinate, then it should be look like this

and axis coordinate in lathe machine, generally look like this

and this

You must know the philosophy of the axis coordinate

Information needed in CNC programming

There are information needed in CNC programming, such as :

1. Preparatory Information: units, incremental or absolute positioning

2. Coordinates: X,Y,Z, RX,RY,RZ

3. Machining Parameters: Feed rate and spindle speed

4. Coolant Control: On/Off, Flood, Mist

5. Tool Control: Tool and tool parameters

6. Cycle Functions: Type of action required

7. Miscellaneous Control: Spindle on/off, direction of rotation, stops for part movement

This information is conveyed to the machine through a set of instructions arranged in a desired sequence – Program

Information needed by a CNC Machine