When machining aluminum on a milling machine, it is important to use the correct RPM (revolutions per minute). If the RPM is too high, the cutting tool will overheat and damage the workpiece. If the RPM is too low, the tool will simply bounce off the surface of the metal and will not create a clean cut. The best way to determine the optimal RPM for milling aluminum is to consult a machining reference chart. These charts list the recommended speeds for various materials based on the cutting tool used. By choosing the correct RPM, you can ensure that your aluminum parts are machined accurately and with high precision.