I found this amusing video on you tube. The ultimate cheap milling machine. I've used a similar setup to cut slots in plastic. Also some of the comments illustrate why one should not use a drill press as a miller.
Using a router on (soft) aluminum is pretty common, and it does look dangerous. Modern cnc machining centers often run at 10~20,000 rpm, but with flood cooling. The guy's making parts for homemade Gingery machine tools. http://www.lindsaybks.com/dgjp/djgbk/series/index.html