Great Guy and Great Info
Craig is one of the very few that under advertise and deliver far more than promised!
As he stated the key is what is the wood's natural state. A lot of wood, even good looking wood, should never be shaft wood. Even after babying it along and turning it slowly to size over years it still wants to warp. This very dry maple makes pretty good kindling.
Which brings us to the point Craig mentioned several times, why the wood is warped is key. If it warped due to stress, abuse of some kind, there is a very good chance it can be straightened and stay straight. If it warped due to stress relief, it returned to it's natural state, it will probably always have a tendency to warp. Beating a dead horse to keep straightening it. I have a playing shaft I use down here in a very humid climate that warps very slightly with the seasons and straightens back out on it's own when cool dryer weather returns. I just let it do it's thing.
Never hurts to try straightening a shaft once or twice but if it warps over and over it is likely that is it's natural state. A good woodworking forum might give you some ideas about dealing with that but the shaft is going to be out of action for a long long time or some pretty fancy equipment is going to be needed. After all of that, the shaft may still warp. A shaft is unique in woodworking in that we are asking a piece of wood to stay straight without support while abusing it with just normal use. The beating is one thing, the atmosphere inside pool halls and bars another.
Hu