OK, it's like I was saying. These spindle motors will NOT work for you. These are for machining at high speed, in soft materials like wood etc. If the original spindle motor was one of these then Sybil sold you a wrongly configured machine. You need a low speed spindle motor, something that has torque at maybe 1500 rpm for a 1/2" mill cutter. Chip size is an indication of what is going wrong there, I bet you had aluminium wool coming off the mill, far too fine, there were no real chips. Guessing you were trying to run the spindle at low speeds and that is right, there is NO torque down there, which is why a knee mill has mechanical gearing with belts etc.