Programming of CNC Machining
CNC Programming
CNC is the short form for Computer Numerical control. The numerical control machine tool receiving information through a punched paper tape or floppy disk and the tape is prepared in accordance with a program manuscript written for the job or operations to be carried out on the CNC machine. The program is prepared by listing the coordinate values (X, Y, Z) of the entire tool paths as suited to machine the complete component. The coordinate values are prefixed with preparatory codes to indicate the type of movement required (straight or circular) from one coordinate to another. Also, the coordinates are suffixed with miscellaneous codes for initiating machine tool functions like start, stop, spindle movement, coolant on/off and optional stop. In addition to these coded functions, spindle speeds, feeds and the required tool numbers to perform machining in a desired sequence are also given. All these elements represent a line of information and form one meaningful command for the machine to execute and are called a block of information. The number of such blocks written sequentially forms a part program for the particular component.
Haas CNC Milling Machine Control Panels
What the programmer has to do?
- Study the relevant component drawing thoroughly.
- Identify the type of material to be machined.
- Determine the specifications and functions of machine to be used.
- Decide the dimension and mode- metric or inch.
- Decide the coordinate system- absolute or incremental.
- Identify the plane of cutting.
- Determine the cutting parameters for the job or tool combination.
- Decide the feed rate programming- mm/min or mm/rev.
- Check the tooling required.
- Establish the sequence of machining operations.
Example of CNC Milling Machine Program
Job Drawing
Main Programming
- O0001
- G21 G17 G90 G40 G80 G49
- G45
- T01 D01 M06
- G00 Z100
- G00 X140 Y60
- G00 Z5
- G97 S750
- G94 F100
- M03
- G01 Z0
- M98 P00090015
- (M98 P0009 L15)
- G00 Z100
- M30
Sub Programming
| Absolute Mode | Incremental Mode |
| O0009 | O0009 |
| G90 G01 Z-1 | G91 G01 Z-1 |
| G42 G90 G01 X110 | G42 G01 X-30 |
| G01 Y110 | G01 Y50 |
| G01 X30 | G01 X-80 |
| G03 X10 Y90 R20 (I0 J-20) | G03 X-20 Y-20 R20 (I0 J-20) |
| G01 Y10 | G01 Y-80 |
| G01 X30 | G01 X20 |
| G02 X70 Y10 R20 (I20 J0) | G02 X40 Y0 R20 (I20 J0) |
| G01 X90 | G01 X20 |
| G01 X110 Y30 | G01 X20 Y20 |
| G01 Y80 | G01 Y50 |
| G01 Y140 Y60 | G01 X30 Y-20 |
| G40 G01 X140 Y60 | G40 G90 |
| M99 | G01 X140 Y60 |
| M99 |
Some Vital CNC Milling G Code List
| G code | Description |
| G00 | Rapid Motion |
| G01 | Linear interpolation Rapid Motion |
| G02 | Circular interpolation Rapid Motion CW |
| G03 | Circular interpolation Rapid Motion CCW |
| G04 | Dwell |
| G10 | Set Offsets |
| G17 | X Y plane selection |
| G18 | Z X plane selection |
| G19 | Y Z plane selection |
| G20 | Select Inches |
| G21 | Select Metric |
| G28 | Return to reference position |
| G31 | feed until skip |
| G35 | Automatic Tool Diameter Measurment |
| G36 | Automatic Work Offset Measurment |
| G37 | Automatic Tool Offset Measurment |
| G40 | Cutter compensation cancel |
| G41 | 2D Cutter compensation left |
| G42 | 2D Cutter compensation right |
| G43 | Tool length compensation + direction |
| G44 | Tool length compensation – direction |
| G49 | G43/G44 cancel |
| G51 | Scaling |
| G53 | Machine coordinate system selection |
| G54 | Workpiece coordinate system 1 selection |
| G55 | Workpiece coordinate system 2 selection |
| G68 | Rotation |
| G73 | High Speed Peck drilling cycle |
| G76 | Fine boring cycle |
| G80 | Canned cycle cancel |
| G81 | Drilling cycle |
| G82 | Stop Drilling Canned boring cycle |
| G83 | Peck drilling cycle |
| G84 | Tapping cycle |
| G85 | Boring cycle |
| G90 | Absolute command |
| G91 | Increment command |
| G92 | Setting for work coordinate system or clamp at maximum spindle speed |
| G98 | Return to initial point |
| G99 | Return to R point in canned cycle |
Some Vital CNC Milling M Code List
| M code | Description |
| M00 | Program stop |
| M01 | Optional program stop |
| M02 | End of program |
| M03 | Spindle start forward CW |
| M04 | Spindle start reverse CCW |
| M05 | Spindle stop |
| M06 | Tool change |
| M08 | Coolant ON – Flood coolant |
| M09 | Coolant OFF |
| M19 | Spindle orientation |
| M30 | End of program (Reset) |
| M41 | Low gear Override |
| M42 | High gear Override |
| M94 | Cancel mirrorimage |
| M95 | Mirrorimage of X axis |
| M96 | Mirrorimage of Y axis |
| M98 | Subprogram call |
| M99 | End of subprogram |