have a look at how I did the rear axle on my TC project: http://www.ultimaterc.com/forums/sho...t=95710&page=4
Its machined out of 5mm mild steel (silver steel is preferred, but I didn't have enough, and messed up the first attempt), and at each end I've lathed it down to 4mm and threaded it with an M4 thread. Then I drilled a few 2mm holes to fit the axle pins. It took me a couple of hours to make (and a few attempts!), and another hour to fit properly and loctite in place inside the bearings.