Well, despite the funk, I’m pressing on. A handful of supportive words from Mike Chandler at Scott Calvert’s operating session last night encouraged me. When I told him of my concern that the pit is not round enough, he opined, “a lot of them weren’t very round.” Well, okay, let’s go for it then.
The critical engineering detail is that the ring rail needs to be actually circular and centered on the turntable pivot; otherwise the wheels will fall off the track. The way I am planning to accomplish this is pictured below. The piece of wood, which is simply CAed to the side of the turntable, will act as a gauge to locate the rail the same distance from the centre all the way around.
The rail pictured is a scrap; the actual ring rail is upside down on the workbench with Pliobond setting on its foot. I will make the attempt tomorrow.