This will also be part of the demo I'm doing in Minneapolis. I just us a 2" square block and remove 2 jaws from my chuck so the block can be tilted, left right or up and down and move off center or each of those depending on your design. The simplest technique is to first turn it round. Then tilt it out and turn a wedge shape. Then move it off center to turn the hole. My chuck is the Vicmarc with dovetail jaws so just the corners bite in when gripping the square blank. This makes indentation marks that make it really easy to go back to one of the settings if you want to refine a shape previously done. This works really well when making smaller earrings since you need to make 2 just alike.