I've seen several people replace their spindles with AXI outrunner motors, but haven't been able to find much information on what materials they were cutting afterwards. I'd like to not lose my ability to cut stainless and titanium. I'm not so much interested in higher spindle speeds, just the ability to change speeds faster. Thing is, I have spare brushless outrunner motors lying around... that's why this is so appealing. As far as driving the motors goes, I was planning on using a switch mode power supply and a micro controller to generate the pulse train to chose speeds.
Also, how noisy is the machine after installing the new motor?