The thing you'll come to realise, is making hobby money machining something for somebody else, is likely to bring more headaches than profit.

I do do occasional jobs for other people, but they're mostly because I either want to help a mate, or just fancy doing something a bit different knowing full well it'll not likely to be profitable.
The vast majority of stuff I machine is stuff I sell directly myself, and while it is nice being able to load a length of bar into the lathe, hit run, and come back an hour later and retrieve a couple hundred pound worth of parts from amongst the swarf, it is good to exercise the brain cells and do something more involved occasionally.