This part of the turntable represents the ground that surrounds the table's pit and everything "underground". I wanted to create a stand-alone diorama of sorts so that I could remove the turntable when the layout needed to be taken down. The turntable base was made out of 3/4" MDF board. I cut out a circle matching the diameter I wanted for the turntable. I used a jig and the router to make this circular cut (see my article about the jig). Keep the circular cut-out, and make note of the center nail hole in it, because these are important later on.
I then cut a matching piece of 1/8" Masonite board and glued it to the bottom of the entire MDF base.
The pit walls are made out of strips of styrene to resemble concrete. I cut three strips of 0.010"-thick styrene to line the walls of the pit. These can then be easily painted and weathered later on.
I glued the styrene to the MDF pit walls using Loctite "Handy Man's Choice" adhesive & sealant. This is a nice general-purpose glue that dries clear, but shiny. When I took this photo, I had already sanded away some of the excess glue that squeezed out. Five-minute epoxy would work just as well.
The next step is to install the rail on which the turntable rides. In the modeling world, all we need the rail for is to transfer electricity to the tracks on the bridge. I used the left-over "disk" to help pre-bend the code 40 rail.
I cut the rail in half (for different polarities), and spread a thin layer of the glue on the pit floor. The rail was held in place by some metal weights while the glue dries.
I left a gap between the two rail halves to prevent shorts later on. Each rail will have its own polarity.
Drilling an accurate center hole in the pit floor is critical to the good operation of the turntable. I placed the left-over "disk" in the center of the pit (as best as possible). It rested on the rails. In retrospect I should have done this before I installed the rails. I clamped the disk to the floor and used the drill press to drill a small hole in the center of the pit. The hole in the disk was created by the circle cutter jig (mentioned above) where its pivoting nail was placed. This makes sure that the hole is in the center of the pit.
The center hole then needed to be drilled out more to accommodate the brass sleeve to be inserted here. This brass sleeve came from my Diamond Scale kit, but I believe they can be bought at most hardware stores. The inside diameter needs to the match the bridge drive rod that will be used later. Using 5-minute epoxy I glued the brass sleeve in the center hole.
Through experimentation I discovered that it is best to have two bushings through which the bridge shaft rotates. The shaft remains more stable. The photo below shows the parts necessary to build a second support point for the shaft. I glued the two 1.5"x3" pieces of MDF to the 3"x4" piece of Masonite board after the center hole was drilled in the board. Just like above, I then glued the bushing in the center hole with some 5-minute epoxy. Note that I used a locking bushing, but I removed the locking screw from it before installation. I didn't have anything else to use at the time.
I then glued this assembly to the bottom of the turntable base. I put the shaft in there and made sure it turned smoothly while the glue was drying.
It is finally time to complete the turntable pit. In the real world these can be made out of exposed dirt, or covered with sand or gravel. More modern ones tend to have a sloping concrete base for drainage. Mine will simulate gravel. The first thing I did was paint the pit floor with a flat black acrylic paint. The brush strokes are visible with the camera's flash, but once covered with gravel, they will be hidden.
Before coating the surface with gravel, I needed to drill two holes and run some wire to the rails. The gravel will help hide the wire.
The motor assembly (see other article) can now be installed. I glued a block of MDF in position such that the motor assembly could be connected to it and sit relatively straight to the bridge shaft. After the glue dried I installed the motor assembly via two screws through the plastic hinges on the case (hidden from view here). I tested the assembly and everything seems to work just fine.