Quote Originally Posted by mactec54 View Post
Why don't you set the correct Parameter so it won't go below the 8,000 RPM it's as simple as that
I asked about how can i automaticaly enable cooling under 8000 RPM, not how to prevent going under 8000 RPM completely. I am already doing this. Reason why i added external cooling is that i want to use my spindle in low RPM, because it's very useful when cutting plastics (even with 1 flute endmill and fast). I can simply set relay to switch the fan on, when the spindle is running, but i have very powerful fan (from 1U server) and it's loud, so i don't want to run it when over 8000 RPM and spindle fan is sufficient.

Quote Originally Posted by mactec54 View Post
That's because you have programed decelerating and it is pulsing the relay, that would be controlling a Brake on / off to slow down a rotating mass
Not really. It happens even on accelerating and it does not have anything to do with braking. It's just auxiliary relay configured to switch when spindle is at defined frequency...