I'm pretty sure it has been written up in the ME, although I can't remember when. It is certainly not uncommon to twist a flat blank in model sizes, and was done in full size steam practice too. Professor Chaddock many years back suggested using a milling machine to remove as much as possible of the stock, with the shaft mounted between centres. I have done this a few times, including making a shaft for a Stuart Triple from one piece, including all the eccentrics. A two throw shaft for a Double Ten went from a three pound blank to a three ounce shaft.

For larger shafts you can make a pattern and have it cast in Spheroidal Graphite iron. I did this for my Leak Compound, which greatly reduced the amount to be machined away.

Back when I used to write for Model Engineer an article of mine about milling crankshafts was published.

John