Tracker John posted:
I wanted a turntable to take to modular layout shows that was large enough for the articulated engines that club members were running. The turntable module had to be light to be lifted solo into my van for transport to shows, thin to allow additional modules and gear to be piled on in the van, durable to withstand handling, and simple to setup the morning of a show (less than an hour). The turntables demonstrated at York didn't satisfy those criteria.
With my previous experience cutting circles (AKA "router on a stick") in plywood while building Dobsonian telescopes, a turntable was just another circle cutting exercise, so I broke out the router. The turntable is 34.5" (Big Boy size) in a 4ft x 4ft module frame. The module sides frames are 1x4s with Luan plywood decking, selectively reinforced with a double layer. The assembled weight is at the limit of what I can manage. Construction uses a Dobsonian-inspired Formica + Teflon bearing. The floor of the turntable well (half the bearing) rotates (yes, its not prototypical unless you consider the B&O roundhouse turntable, but works well for this module). Appearance is tinplate with an Erector set operator's house, no fragile handrails, etc.
I motorized the turntable using a friction drive gear motor but discovered that large locomotive weights caused slipping (this IS prototypical) of the drive system. I considered a stepper motor, gear drive, and indexing but a solution that would eliminate slipping added unacceptable weight. I also found that casual operators at shows needed practice to control the motor for precise positioning. So, the motor was removed and the KISS principle now works. Operators can use the ever-reliable Armstrong motor and optical alignment techniques for rotating the bridge to the desired track.
Slip rings on the turntable bearing for bridge track power were considered but the initial solution (a quick hack) of extra length wires that could twist and untwist has lasted nearly two decades unchanged.
Wiring toggle switches to 16 tracks was a PITA.
If you are have woodworking skills (especially with a router), building a manual turntable for Big Boys is straight forward. Making it light and portable is an additional challenge. Wiring is always tedious. You can do this for $100 in materials and your labor. Scale appearance and detailing are up to you. The difference between a DIY manual drive solution and the $$$$ turntables shown at York are in the reliable motorization and indexing systems the vendors offer, plus the nice scale details. Having a turntable in your layout is a real plus. At our modular shows, turntable operations always draw a crowd of spectators and, with the slow speed operation of today's locomotives, running locos in out of storage tracks is fun. You really need one on your layout - DIY or buy one - you won't be disappointed.
I just saw this thread. I just wanted to point out with our TT the circular hole is great for tight installations where you don't have room for a large square top. Our TT has all the support it needs since it is welded aluminum. One feature you will like for a traveling layout is our bridge lifts out of out tables with one wire disconnect. This allows you to put the bridge in a separate travel case from the pit so the details on the bridge don't get damaged during transit. 2nd point on circular hole, it is easy to install. remove bridge from TT, flip TT over on top of layout and trace outside of pit wall onto plywood, slide TT up through hole in layout and install mounting bolts in welded tabs. Done
Most people have it installed and running in about an hour.
Oh, and if layout design changes, or if it was installed into a permanent layout. To remove TT simply remove mounting bolts and drop out for next house or layout spot without any damage or chiseling scenery from TT where our tables with wood tops have all the scenery material attached to them. Ours, the scenery only touches the outside of the aluminum pit wall.
I just thought I would point out the design benefits of our table over the wood square top tables.