Looking back at the third picture in Post #36 of the inside of the turn-table pit. It is flat and just the MDF wood base. All turn tables I've seen in pictures have the pit slope towards the center. This area could be concrete, gravel or even grass.
I want a sloped gravel with grass/weeds so need to fill to center of the pit.
1st pic- shows some fill using 'light weight joint compound'. This is just a rough fill.
Also the "ring rail' is glued in. This operation went very well by following the instructions. I pre-curved the rail, ME weathered Code 70, by running it through my fingers so it has a slightly larger radius than required. Then deceased the radius for about 3 inch at one end so it exactly matched the tie notches (see picture in post #36). I cut off about an inch of this end that didn't take the proper curve. Then spotted CA glue on about a dozen ties and laid in the rail. Once the glue set pulled the unglued rail towards the center and applied CA to the next dozen rails and set the rail against the tie notches. Keep going around until the last dozen ties are un-glued. Placed the rail in position and marked where the rail over lapped then cut with rail cutters. Finally applied glue to the last ties and finished setting the rail in place.
2nd pic- shows the second fill layer being smoothed using contour template cut from a piece of cardboard. This will not be perfectly smooth but that will work out since I'll be covering the surface with gravel and weeds.
3rd pic- is the bottom of the turn table with the gears, shafts, coupler and motor. Under the turn table is the sub-roadbed and the turn-table will be installed just at the right hand edge of the picture.
4th is a side view of the motor/gears. The motor drive a worm which turns a 50 tooth worm gear. The motor is a small gear motor from Pololu Robotics