M08 CNC Code Explained: An Easy Intro for Beginners [Flood Coolant]

What does the M08 CNC code do?

M08 is a modal command which turns on flood coolant.

Flood coolant is literally flooding or washing the cutter and/or workpiece in liquid coolant. The coolant helps remove chips from the cutting area.

If chips are not moved from the cutting area, then they can end up being recut which tends to cause heat buildup and can damage your cutting tool.

Flood coolant also cools the cutter and workpiece and lubricates the cutter. 

Both of these things help extend the life of your cutter as well.

cnc machine table with coolant lines and spindle shown
Flood coolant in action

M08 [flood coolant] vs M07 [mist coolant]

The most common type of coolant used in CNC machining is flood coolant with the M08 code.

The second most common option is mist coolant using the M07 code.

Mist coolant combines the coolant fluid with compressed air and sprays it on the cutting area. 

Mist coolant uses less coolant fluid and can be less messy depending on your CNC setup, but it isn’t as good at reducing heat buildup as flood coolant is.

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Advantages of using coolant

The three main advantages of using coolant with your CNC machine are:

  • Lubricate the cutter
  • Clear chips
  • Reduce heat buildup

What are the other options for using coolant?

We discussed mist and flood coolant above but there are other options available as well including:

  • Air: This type of coolant reduces heat and clears the chips, but it does not lubricate the workpiece. This type of coolant is used more often with sensitive materials.
  • High pressure: High pressure coolant is similar to flood coolant. The only difference is that it hits the workpiece at greater than 1000psi. The higher pressure and higher quantity of coolant helps cool the cutter better and remove more chips.
  • Through spindle: Through spindle coolant delivers the coolant directly where it is needed. It is better at clearing chips in many cases because the coolant from the spindle pushes the chips out of a hole or pocket.

How to turn off coolant

The M-code to turn coolant off is M09.

However, there are other commands that turn off coolant as part of their function including:

Frequently asked questions about the M08 code

Does every CNC machine have coolant capabilities?

Yes and no.

You can expect that industrial level CNC machines will have coolant capabilities.

Home or hobbyist level machines such as CNC routers often do not have coolant capabilities, but they can usually be added on if needed.

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CNC routers do not usually come equipped with coolant functions

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