M08 Coolant On

M08 turns on flood coolant. It is called once the tool is about to cut and switched off with M09 before the program ends or a tool change. Some machines add M07 for mist coolant.

Format

M08 (flood coolant on)
M09 (coolant off)

How it works

  • M08 starts the flood pump; M09 stops all coolant.
  • Turn coolant on after the spindle starts and off before the spindle stops.
  • M07 is mist coolant on machines that support it.

Example

S2000 M03
M08 (coolant on)
G01 Z-0.25 F5.0

FAQ

Should M08 come before or after the spindle start command? Common practice is to start the spindle with M03 or M04 first, then turn on coolant with M08, so coolant isn’t wasted on a stationary tool and the cutting edge is already spinning before coolant hits it.

Is M08 the same as through-spindle coolant? No, M08 typically controls flood coolant delivered externally through nozzles at the tool. Through-spindle coolant usually has its own separate M-code, since it requires a different plumbing path through the spindle itself.

Related: the Coolant Selection Guide and Coolant & Lubrication calculators.

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