I have been experimenting making metal mirrors and decided to try roughing the parts on the lathe so I built this very large radius attachment. The white piece on the pivot is teflon sheet as a bearing. The spring is a valve spring so is plenty strong. The rider on the cross slide is machined on the bottom to fit the same as the top slide and is locked in the same way. It also serves as a nice solid tool post when the top slide isn't needed or gets in the way.
The red glow on some parts is from my "you left the drives on" warning lamp.
The attachment produces a spherical mirror and is used to rough out the shape for the final parabolizing step on the milling machine.