I would like to know if I am pushing my mill too far. I was making a part yesterday (an adapter for the T-Slot that could take a gooseneck for making a custom machine chip shield). Some pieces of it I milled with a 1/4" carbide end mill and spun the spindle at about 4.5k RPM. (set the VFD to 100 Hz) It milled fine, however, I noticed that the top of the spindle (the area where there is a cam to lock the spindle, above the belts) heated up to being quite warm to the touch. I still could hold my hand on it, but it was very warm. I want to know if I pushed the mill too much.