[Vogavt]

Just curious if anyone happens to know what the average temperature is for your mill where the spindle motor was upgraded to a treadmill motor that doesn't have a built in fan.

I've made the change myself and am very happy with the results with one exception..there is no fan to cool the spindle. I've got a section of 4" rigid vent duct coming up off the spindle motor followed to a shroud via flex duct where a 4" fan is at.

I'm blowing from the top downward through the flex duct as opposed to drawing air from the bottom up. I'd read somewhere that this was a better approach as it prevents fine swarf from being drawn into the motor body.

Anyway, I want to have the fan come on automatically before a certain scary temperature is getting close. I don't want the fan to run all the time. I supposed it could but where's to coolness with that? LOL!

I'm contemplating a PID unit to regulate the temperature which in turn activates a solid state relay which of course turns on the fan.

All I need to know now is what would be an average number that I needed to be looking at. This is needed for purchasing the correct thermocouple with the correct temperature range.

Also, I don't want to control this fan via some output off the cnc controller. I definitely want a totally separate power up of the fan in case something fails. This way when the board shutdown for whatever reason the fan will continue to cool the spindle motor even if it's not turning.

Thanks in advance,
Vogavt

[Al_The_Man]

With a DC motor, the source of heat originates in the armature, because this is isolated from the stator to a certain degree, the heat is radiated out to the stator, so when the temperature of the case is detected this means the armature is usually at a very much higher temperature.
And due to the mass of the armature having a high degree of copper, the time taken to reduce this heat can be lengthy.
It is usually wise to allow the fan to run continuously if high temperatures are found to occur with normal running.
Al.