I’ve machined nickel silver with down to a .010" (.25mm) flat-ended mill, and a .009" (.23mm) ball-end mill. Not on the Nomad, but using a Proxxon 20,000 RPM hand tool clamped to the spindle on the Tormach. I don’t doubt the Nomad will do just as well, and in the next month or two I plan to machine some wheels on the Nomad.
http://www.prototrains.com/fine_n/fine_n.html for reference.
.020" (.50mm) is not a small cutter at all…remembering where I got the small cutters is not a small challenge though… 
I think I’ve dealt with all these three:
http://www.microcutusa.com/decimal2flute.php
http://bitsbits.com/index.php?main_page=index&cPath=2_70
http://www.microendmill.com/decimal2flute.php
Randy