I built my own turntable some time ago, so I don't remember all the details. The area where it was built had plywood on the tabletop, so the first step was to cut out the area for the pit. Then, working from beneath the layout, I first installed strips of plywood of suitable thickness to the underside of the tabletop around the pit, then installed a new pit bottom of 3/4" plywood (that's what happened to be on hand). I then cut some 1/8" Masonite to the proper size and installed it, using carpenters glue, as the pit wall. When the glue had dried, I cut the "concrete" base for the ring rail from a piece of 1/4" maple plywood (nice smooth finish) and glued it in place. After determining the centre of the pit, I used the same material to make a circular foundation for the centre bearing and glued it in place. The ring rail is made from a piece of code 83 flextrack, the ties cut on the inside of one rail to a length equal to the amount that was sticking out on the other side. The turntable is near the edge of the layout and was originally designed to use the mechanism from an electric hand mixer, turned by a hand crank, to move the table. Unfortunately, this was not very satisfactory, so the table is an Armstrong one. (Actually, it's a fingerstrong one, but it's good enough for my purposes.)
The bridge is a block of pine with a cut-down freight truck on the underside of each end. Two axles are used in each truck, the inner ends have no wheels, while the outer ends each have two Athearn metal passenger car wheels installed, face-to-face, forming a pair of extra-wide double-flanged wheels on each end of the bridge. These ride on, and pick up current from, the ring rail to power one of the bridge rails. The bridge rotates on a beater shaft, an electical wiper under the table powers the other bridge rail. The bridge is supported at the centre by a metal washer and the shaft turns in a brass bearing. The sides of the bridge are covered with built-up pieces of the sides from a couple of Atlas through girder bridges. The track on the bridge is Atlas code 83 flextrack with the connecting webs between the ties removed, and then real wooden ties (extra long, to support the deck and handrails) inserted between the plastic ones. The deck is basswood, and once installed, the flextrack ties became unnoticeable. The handrails are brass wire in Athearn diesel handrail stanchions. The control cab is scratchbuilt from styrene. I do intend to install a power arch eventually. The picture only partially shows the turntable, since I just learned today how to do photos and had taken this mainly to show the loco.
Wayne
