What material to use for geared shaft

[Sunset Machine]

My final vote is for scrap iron and welding. The weld and keyway are bound to cause warping though. If you're not so handy with that, then you might want another look at 1-1/2" 1045 in the hot roll form and turn it to size. Speedy wants $20 + shipping for 18" of it, not so bad after all.

Of greater concern is the worm. You really don't want to make one of those, so can the old one be rescued?