A simple way to chuck pistons into the lathe is to make a draw rod assembly that goes through the head stock of the lathe. I made a bushing to locate it and give the draw nut a place to seat. Sometimes you may have to make a ring adapter for the pistons. You might just have to get inventive if they do not sit on the chuck jaws level. It might not work for all pistons, but it is a nice option if you don’t want to set up a vice on the mill.
North Branch, MN