A Dome Chuck (sometimes called a Spherical Chuck) is used for holding the object perpendicular to the axis of rotation (or at some other angle which is not aligned with the axis of rotation).
If you want to buy one, Lindow Machine Works makes a very nice one. But, if you would rather make one, Bill Ooms and Jon Magill have some nice designs.
Bill Ooms made what he calls a Super Dome Chuck, and has published his plans. It is a combination of a dome chuck and an oblique chuck. He has built two very nice ideas into his design:
Jon Magill made a combination dome chuck, eccentric chuck, and oblique chuck which he showed at the 2016 AAW Symposium in Atlanta. (Images below are courtesy Jon Magill.)
|Used as a dome chuck ...||... or as an eccentric chuck|
|... or as an oblique chuck||This is the back.|