Originally Posted by
ninefinger
I wouldn't make the chuck adapter / backplate of aluminum, especially if you are using a larger chuck on the machine. Couple of reasons: 1. aluminum is not as stiff as steel and the lathe needs as much rigidity as it can get, so you would need to increase the thickness of the backing plate to compensate, pushing the work further from the supporting bearings and still reducing overall rigidity.
2. If the aluminum does flex, even a little it will crack eventually, and a spinning over sized chuck is the best way I can think of to get through the thousands of cycles needed to make that happen when you least expect it. This is one of the reasons the highly stressed bits on engines, lathes etc are steel.
Mike