The ATC spindle cooling fan is always on, never turns off.
It makes noise even when the machine is idle, when SLB-EXT is powered on.
The blog post “Everything You Need to Know about the ATC” from 12/03/25 says:
“Additionally, since we can turn the fan on and off as needed, this impacts the overall noise of the spindle as well. It should be noted that the fan will primarily turn on when the spindle is running and cutting, where the sound of the spindle is masked by the sound of cutting anyway.”
So, I expect the cooling fan to be off when there is no need for a cool-down.
Here is the response I got from Sienci Labs support.
"
The cooling fan always being on is intensional for safety, the information you found on our website isn’t correct, i will have it edited right away.
Thank you,
Danial
"
That is rather disappointing for those of us who leave their Altmill powered up always. What aspect of safety requires the fan to be on all the time? Could there not be a choice in the setup to allow the fan action be ‘constant’ (default) or ‘when spindle is on’ ?
I just built a 2x4 AltMill with Sienci’s 2.2kW spindle. No sound from spindle when at idle. Unless I’m missing something, I thought the spindle fan is attached to rotating part within spindle–i.e., the cooling fan rotates as the armature does…?
