The blank and the support piece are glued with a sheet of paper in the joint
The blank and the support, ready for turning
The assembly is held against the chuck by pressure from the tailstock
A spigot is formed at the bottom of a hole in the support (of somewhat unusual shape)
The spigot is used to mount the assembly. The top of the discus is roughly shaped
A faceplate is screwed over the top of the spigot (in its depression)