MF,
that is a bit tricky as it is a case of just tacking on and off not something I would try too early, you just have to go slowly and watch the temperature and if it starts getting too hot leave it to cool down and start again. I find 2mm rods best and keep the amps down just enough for it to melt the rod. It takes practice but don't practice on something that is important till you get an idea how it works. Then there is the problem where the axles have worn down and I just run welds along the axle where it has worn and then grind it back to be somewhere near round
