We recently upgraded a VMC to one using through coolant. A couple of days ago the machine started playing up with spindle drive errors. While checking the drive status I noticed a drip of coolant from inside the top of the control cabinet falling into the drive!!! We killed the power and started checking what had happened.
The spindle coolant line has a connection for air blast when changing tool. This line is fitted with a check valve (only 3 weeks old) to prevent coolant ingress to the air system but the check valve had failed and coolant got back to the soleniod valve that was mounted on top of the control cabinet. Because the valve was shut the coolant got dumped out the exhaust port on to the top of the cabinet then through the top cooling fan into the spindle drive.

We managed to stop the machine before damage was done and after a day drying out it was back in action. We have now moved the valve to the top of the column where all the other valves are mounted and if they leak they are well away from the electronics.

This could have been very expensive. I suggest anyone running a VMC with thro coolant have a look on top of their machine to see where the valves are mounted and if any are on top of the control cabinet move them just in case.