As a general rule, wood working tools are capable of machining Aluminum and other Non-Ferrous metals such as brass and copper. While a 4-pole 800hz motor, as found in our ATC systems, is not designed for mild steel this customer reported success, albeit slow but success, nonetheless. 

Largely speaking we have not experimented enough with machining aluminum or like metals to say what speeds can be used before the motor stalls out.

Spindles are induction motors which are opposed to electric motors. 

An induction motor is brushless by design, which is why there are not brushes to replace in our spindles, but it is also given rotational force by magnets.

Electric motors are driven directly by electricity via direct drive and utilize brushes to cool the motor mechanisms (hence people burning out routers, but not spindles)

The number of electro-magnets is referred to as poles. 

The stator core is where the electromagnets are housed, the rotor gives the rotational movement, and the shaft is along for the ride. 

We offer 2-pole and 4-pole motors, and additional poles give higher torque at lower rpms. 

Our traditional Spindle System comes with a 2-pole motor, unless you opt for the 2.2kw 800 hz metal working spindle

Our ATC Systems only come with a 4-pole motor with ceramic bearings which is still capable of 24k RPM.

Theoretically, the 2-Pole spindle motors can go as slow as 6,000 RPM and our 4-pole motor can go as low as 4,000 RPM.

We haven't fully tested the lower end of the spectrum but have utilized 10,000 with great success with an 'O' Flute bit on aluminum. 

Adhere to feeds & speeds of bit manufacturer, and adjust one of the values from there at a time.