lathe work on heavy part

Because in any machine, it's going to be under cyclic loads, and always in the same direction. I have made some machine parts using aluminum, and have never found it satisfactory. When we make riser blocks for some strange lathe mods, they are always steel or cast, the ones we tried from aluminum proved to fail, to become unusable far too soon. When we measured them, we found that the thing I call sag, there is probably another term, was predictable and always in the direction the load on it would dictate. Not that the same doesn't happen with steel, it does, but normally only 10% or so as much as with aluminum.

To answer Tim, if cast iron was not the best material for the job, Hardinge wouldn't use it. It has the damping, strength and mass that is required for a solid machine, can be hardened for wear properties and is still easy to machine. It's an old material, but like many others, it's still with us because nothing has been found that will do the same jobs as efficiently, cheaply and easily.

Karl,

Your method will work also, but I think you are worrying too much about the centers failing. Lathes are designed to turn between centers a chunk of solid metal with a diameter equal to the lathe swing over the cross slide. Remember prior to the advent of lathe chucks almost everything was turned using centers and dogs. Your chances of shearing off a lathe center is extremely remote as long as you turn at reasonable spindle speeds and feeds. The shear strength of a center is also dependent on how deep you drill the countersink. Drill it deep and lubricate it well. If you do the calculations, I think that with only 200 lbs. you will be nowhere near the shear strength of the centers. Another safety advantage of turning between centers is that there is no chance of axial creep. Although extremely unlikely with a properly tightened chuck, it is theoretically possible. I think the bigger issue here is the hernia potential when loading the assembly on the lathe:).

Best of Luck