The central collar is a tin of something that was epoxied to the pan. The sweep arm assembly can be treated as a monolithic unit. This allows a thicker or larger mirror to be used later. The eccentric uses a piece of threaded rod as a lead screw. The brass block slides in the aluminum ways.
Shoulder bolts hold the pushrod in place.
The little white disc is a Delrin washer to keep the brass and aluminum from wearing each other. The brass hex handle lets me adjust the total sweep amplitude. However, I didn't have any left hand taps on hand, so it will do.