DigiKey has Cantherm R20 snap-disc thermostats in a wide variety of temps.

For instance, an 80C Normally-closed switch is DigiKey part no. 317-1086-ND,  $6.60 ea.

Not truly cheap, but not expensive either...when you consider the cost of a cooked motor!

Oh, yes...I forgot to mention...

Thermal Protectors, such as referenced below, are a kind of fuse. Once tripped, they have to be replaced.

Snap-disc thermoswitches, on the other hand, reset themselves when cooled down.

This would be a good reason to use a cubloc!

You could display Motor Temp as well as program a  automatic Emergency Stop,
Or a G-Code Pause till the motors cool to a safe temp then start G-Code again.

http://cubloc.com/product/01_01.php

Hi guys,

Just a couple of comments. You didn't say if they were servos or steppers.  Steppers are designed to run hot, like hotter than you think they should be but if you are burning out coils than you need to back down the current to the motor. Cooling won't help with a over current coil open.
Now you might be saying if I turn down the current than the motor is not fast/strong enough. In this case you need to fit bigger motors. If you are  running them so hard as to burn them up/out to get the performance then you just need to get into a bigger motor and lower the safe operation area.
Same goes for servos.

One of the strange things with steppers is they pull pretty much the same amount of current at a stand still as they do at full speed. Knowing this a thermal alarm for mach won't do any good unless it actually cuts power to the stepper drivers. Again steppers do run HOT but if yo are burning them out you are just running them TOO hard!

.02c

Chad
 

well to answer alot of questions. Im running servo's. but turns out that my overheating was due to an overtightened bearing retainer. the feed screw was nearly binding so the motor burned up because of that. I loosened everything up and it should be running real cool as soon as I get the replacement motor. I guess Im still somewhere on the learning curve eh. .
shouldnt have any over heating problems now. so I guess an alarm is a bit uneccisary if everything is as it should be.