I'd be surprised if you'll be able to cut steel with the colt. Or for that matter, any wood router based machine. You need torque (read: lower rpm and more power) and LOTS of rigidity to cut steel. At 15000 rpm and low feed rates you'll put so much heat into a end mill it will destroy it very quickly, even with coolant. Aluminum is a different story, you should be able to cut aluminum. Keep the spindle rpm low and feed rates as high as your machine will allow. Take shallow depth of cuts until you feel confident how your machine will react.