I know
this link is talking about applying this concept to a failing hard drive.
However, when grinding through a kilo of bark, I used this and feel it greatly reduced the chance of overheating or breaking the motor.
Between every 100-250g of bark, place the blender base or grinder motor in the freezer or refrigerator for 10 minutes (or until cool) and continue. It takes longer to do, but it worked for me.
I've heard of people going through multiple blender motors/bases when processing bark and I feel more people should be aware of this trick if they want to try extending the life of whatever it is you are processing your bark with.
Mods move this if it does not belong.