[Rickertsen2]

I'm no machining expert, but my guess would be that you are using a spindle speed that is way too high. As a general rule, use faster spindle speeds for aluminum and VERY slow ones for metals like steel. In addition, the bigger the bit you are using the slower the speed should be. Also, it might be a good idea to work your way up to 1/2" rather than tackling it in one step.