Derek,
Essentially, a metal lathe is a “programmable” lathe but the wood lathe is not. What I mean by that is that you have mechanical help in describing a trajectory for the cutting head, without the need to hold the tool in your hand.
Advantages of metal lathes:
1. You do not need a very steady hand or a very strong grip to machine any material, no matter how hard
2. You can machine perfect (simple) curves. For example, a perfect cone or cylinder
Disadvantages of metal lathes:
1. Expensive
2. Much lower capacity (swing over bed) than wood lathes
3. Complicated machines. Too many things to worry about
The wood lathe is a lot more appropriate for artistic work, in which you do not want to work with a prescribed shape but to follow your instinct. For example, it is fairly hard to do a perfect cylinder or a sphere (you basically need jigs to do that), but the turning is a lot more straightforward. I almost never think about the shape when I turn wood, I just do along with the “feeling”.
I can see two ways to use a metal lathe to turn wood:
1. Do what Blake did and play with the X-Y controls to get a shape. While it will work to some extent, the shape will be choppy (unless you have extraordinary skills).
2. Retrofit the metal lathe with a tool rest used for a wood lathe so you can use it like a normal wood lathe (not sure if you can find such a toolrest).
Unless you are very space constrained, I would strongly suggest you buy a wood lathe and a metal lathe. It is very likely that the metal lathe will cost you 5-10 times more than the wood lathe of the same capacity. If you are unsure you want to do a lot of metal work, go with the wood lathe for now.
Alin
-- -- Alin Dobra, Gainesville, Florida