I used to use ram in dowel for the axles but now I have moved to turning my own axles from beech. This is a harder wearing wood and looks better.
I cut squares off the block and turn them down by hand, measuring with callipers to get the right diameter.

I then either leave them plain, or for a better finish I make a brass ferrule that I fit on the end of the shaft. The axle is held in a collet chuck to turn the ferrule fitting.

A nice transformation.

Showing the axle fitted into the frame. The brass sockets at each end hold the ferrules. This make a neat way of taking the axle out for adjustments. The dockets are retreated into the frame and the axle is then free to slide out.