M08 and M09 CNC Codes: Coolant ON and OFF Commands

The use of coolant is very important for the safety of the tool (Tool Life), and for the best cutting while working on the machine. The correct use of coolant has a direct impact on the life of the tool, surface finish and machine performance.
During machining, a lot of heat is generated due to friction between the tool and the material. If this heat is not controlled by using coolant, the tool can quickly deteriorate, the surface of the workpiece can be affected.

M08 and M09 are two important M-Codes in CNC programming. M08 is usually used to turn the coolant ON, while M09 is used to turn the coolant OFF.

Related: Coolant, Spindle, Tool Change Functions in CNC

M08 Code: Coolant On

N10 M08 (Coolant ON)

The M08 command starts the coolant pump and the coolant starts to flow from the nozzle to the tool and workpiece.

Coolant should be used during drilling, milling or turning, especially on hard materials such as steel and stainless steel.

M09 Code: Coolant Off

M09 (Coolant OFF)

This code turns off the coolant pump and stops the flow of coolant. Use this command when coolant is not needed in an operation before terminating the program.

Program example

O1001
G21 G90 G40 G80
T01 M06
G54
S1200 M03
G00 X0 Y0
G43 H01 Z50.
M08                (Coolant On)
G01 Z-5. F150 
G01 X50. F200
G00 Z50.
M09                (Coolant Off)
M05 
M30  

In this example, M08 is given before the tool descends into the cut and M09 is given after the tool is lifted up after cutting.

Important Precautions When Using M08 and M09

When using coolant commands in a CNC program, be sure to observe the following:

• Write M08 before cutting.
• Set the coolant nozzle correctly at the cutting point.
• Verify that M08 and M09 are in the correct place in the program.
• Keep checking the coolant level: Low or bad coolant causes rust and odor problems.
• Be sure to check the machine manual: M08 and M09 are the same on almost all controllers (Fanuc, Haas, Siemens, etc.).
• Keep safety doors closed and follow machine safety rules when using coolant.

Always follow your machine’s controller manual, tool requirements, and safety instructions when creating a CNC program. It is important to properly test any new program before running it on a real machine.