The oak turntable bridge was trimmed to its appropriate final length, and narrowed to approximately 2.5", with the exception of each end as seen in the above photo.
The Upper Shaft must be perfectly “squared and centered” to the oak, or the top of each end of the bridge will change height, tilt up and down as it rotates.
The bottom portion of the Rev-A-Shelf center shaft (with nylon fitting) was cut to approximately 12.25" in length. The exact length of this cut is dependent on how deep you build your drive mechanism platform. When this shaft is connected to the turntable bridge and mounted in the turntable pit, the nylon bushing at the bottom end of the shaft needs to fit over the Rev-A-Shelf bottom pivot. The length of the shaft should be long enough so that most of the weight of the finished rotating bridge rests on the nylon bushing and rotates on the bottom pivot.
The bottom pivot's height can be adjusted later if necessary by using sheets of poster board or other material as shims to very slightly raise its height. These will be among the last adjustments you make. They will be necessary to achieve a balance of friction-free bridge rotation on the pit rail coupled with a minimum of bridge tilting.
As can be seen in the following photo of the Final Drive Mechanism design, the bottom pivot has been "shimmed" approximately 1/8".
Last Update - June 16, 2015
A slide show of all photos in this article is available at the end of the column.
BPSouthwestern.com is a noncommercial model railroading project dedicated to promoting the enjoyment of toy trains by sharing lessons-learned as we build and operate the B&P South-Western O Gauge Model Railroad.
To see Videos of the B&P South-Western Model Train Layout in action and information about recent activities, go to our YouTube and Facebook pages.
To preview the B&P South-Western Railroad click on the following photo.
Once we had completed and finished the pit wall, we made final adjustments to the circular pit rail’s length. During this process, all of the spikes failed causing the plastic ties to separate from the rail.
In frustration with the Atlas track, Bob carefully cut the wood ties of two unused 36" sections of Gargraves Flexible Stainless Steel Track lengthwise. After discarding the center rails, we wound up with four 36" sections of single rail and ties. The Gargraves ties are held to the rails by grooves cut in the wood ties, allowing them to slide along the underside of the steel rail. After re-spacing the ties evenly along each rail, Bob used both Gargraves rail pins, and Split-Jaw rail joiners in an effort to join the rails. After some slight Dremel tool modification to the Gragraves rail, the Split-Jaw rail joiners worked best.
However, without the structural integrity of all three rails, joined by wooden ties, the single Gargraves tubular rails proved to be prone to distortion with only slight provocation. The unused Rev-A-Shelf 28" shelf was used as a form around which to curve the Gargravesrail. After several attempts resulted in the collapsing and kinking of the tubular rail, Bob conceded defeat and resurrected the Atlas rail.
With the pit wall in place, final adjustments of the Atlas pit rail length were completed. These adjustments were made in very small increments, with as little as 1/8" being trimmed at a time. After each adjustment, the rail was rejoined into a circle with a rail clamp and laid back in place to determine fit. This process was repeated many times.
Because there was no tie/rail integrity with the Atlas product, Bob decided to secure the ties in their appropriate location on the pit step, then remove the rail. This was done by placing the rail and separated ties in place atop the pit step as precisely as possible. Clear drying Gorilla Wood Glue was then floated around the entire circumference, following photo.
As seen in the above photo, you can now determine the approximate height for the pit wall. In our case it worked out to be 3-7/8" above the plywood base.
The pit floor was spray painted with gray primer. After additional sanding, a second application of spotting putty was applied to the pit step. The pit floor was then centered and glued to the 36" X 36" piece of plywood, following photo.
This motor assembly was mounted to the drive mechanism platform, with the drive wheel mounted to the center shaft for testing. With as little as 1.5 volts DC from a D-battery, this motor ran smoothly and turned the turntable bridge. However, even with this low voltage, the bridge’s rotational speed was too great.
To address this, Bob purchased a used HO Transformer (variable DC output) on eBay hoping to be able too more precisely control the DC voltage. Unfortunately, its rheostat speed control was faulty. Fifteen volts of DC current was either all on, or all off. The eBay seller was very good, providing a full refund (including shipping), without us having to return the item. Unfortunately, we still had the problem.
We then purchased a Motorized Planetary Gearbox System from Micro-Mark for $30.00. This is a small DC motor with four separate planetary gear sets that allow the user to adjust the motor’s output shaft speed from a very slow 13.8 rpm up to 6,500 rpm. We have set the motor up for its slowest 13.8 rpm shaft speed.
A 3/8" aluminum fitting was purchased at a local hobby shop to lock to the Micro-Mark motor’s 4mm output shaft. A short piece of 3/8" rubber hose was purchased from an auto supply store to finish the shaft and increase the shaft’s traction on the drive wheel.
Motor shaft pressure against the drive wheel is maintained by the motor’s hinge mounting and spring tension as illustrated in, following three photos.
B&P South-Western Railroad Facts
Layout Room Size: 21.5" X 16.5"
Layout Size: 21.5' X 15.5' Folded Dog-Bone
Layout Surface Area: 270 Square Feet
Track Type: Atlas O Nickel Silver
Track Running Length: 389 Feet
Upper Mainline Length: 51 Feet
Perimeter Mainline Length: 64 Feet
Folded Dog-Bone Mainline Length: 100 Feet
Track Curves: Three Mainlines 072 - 099
Track Curves: Sidings/Yards 054 - 072
Turnouts: 23, Ross-Custom (16), Atlas (7)
Turnout Control: Blue Point Switch Machines - Manually Operated
Turntable: Scratch-Built 120' Scale (30")
Track Power: Lionel TMCC, MTH DCS, 720 watts
Motive Power: Lionel, K-Line, MTH
Rolling Stock: Lionel, K-Line, MTH, Weaver, Menards
Structures: Ameri-Towne, Plasticville, Scratch-Built
Vehicles: Lionel, Historic Rail, MTH, Match Box
Figures: Woodland Scenics, Model Power, WeHonest
The B&P South-Western’s model railroading philosophy is that we are builders and operators, not collectors. We try to stay reasonably close to O Gauge’s 1:48 scale, without being obsessive with every minute detail.
Our layout design philosophy is to maximize the amount of track devoted to railroad mainlines, sidings and rail yards within the given space we have available. While we use Lionel TMCC and MTH DCS to control all of our locomotives, our 23 turnouts (switches) are manually controlled. This requires train operators to move about the layout as they operate their locomotives.
Additionally, we cut off or rounded layout corners to facilitate movement around the layout. These priorities limit the space available for buildings, street scenes, etc.
Finally, where we can, we try to scratch-build and/or kitbash layout features.
The following is a description of how we scratch-built the B&P South-Western Railroad's O Scale 120 foot turntable.
B&P's O Gauge Turntable
A major feature on the B&P South-Western's California side will be the locomotive servicing facility and what has evolved into a 30" O-Gauge Toy Train Turntable. Several O Gauge/O-Scale model train turntables are on the market. Their prices’ range from approximately $200 for the not too realistic Atlas 24" model, to more than a thousand dollars for prototypical models 30" or larger in diameter.
Not wanting to spend $thousands, Bob originally thought he might try to use the Atlas model. However, we worried that its 24" diameter might be too small for some of our larger steam locomotives. Additionally, the Atlas product was unavailable to dealers for several months in 2010.
A Google search identified several efforts to “scratch” build turntables. Bob also studied as much data as possible about the construction of commercially available turntables.
Armed with a lot of ideas, Bob set out to build his own High-Rail O Gauge Model Train Turntable. Originally we thought we would be able to complete the job in two or three months of aggressive modeling and approximately $250 in materials. Our efforts have resulted in what we believe is a fairly realistic looking turntable with a 120' scale (30") bridge.
The aluminum bogie frames were painted and assembled, following photo.
Continued, Top of Center Column.
Precise placement of the bottom pivot on the drive mechanism platform is critical for the same reason care was needed whenepoxying the 4" upper shaft assembly to the oak bridge base. The tolerances of the pit floor’s metal collar allow slight side-to-side movements of the center shaft. Care needs to be taken when placing the bottom pivot to ensure that the turntable remains level throughout its 360 degrees of travel. Otherwise, the top of each end of the bridge will change height, tilt as it rotates, following photo.
The top edge (future pit step) was wrapped first with 10mm X 10mm PVC strips, and then 10mm X 3mm strips, following photo.
Bob’s concept consisted of using one of the two round shelves for the turntable pit floor and pit step. The second shelf is used as part of the turntable’s drive mechanism. Each shelf has a cast metal center collar that allows the steel center shaft to either freely rotate (e.g., turntable pit floor), or be locked to the shaft (e.g., drive wheel).
The final step of completing the turntable pit is the installation of a pit rail around the inside of the pit wall atop the pit step. In real life, each end of the turntable bridge is equipped with bogies that ride atop the pit rail. The bogies are designed to partially support the significant weight of, and move the turntable bridge and any locomotive it carries. In our model, much of the weight of the bridge and any locomotive it carries will be supported by the oak bridge and its epoxied steel Rev-A-Shelf center shaft riding on its attached center shaft collar.
Continued, Top of Right Column.
We made an online purchase of a Rev-A-Shelf 6012, 28" two shelf, dependent system from Bold Hardware Company, Sacramento, California, for approximately $75. Rev-A-Shelf does sell a less expensive version of this product, however, it does not have the precision metal shaft, and metal shaft and shelf collars of the 6000 Series, following two photos.
The roller pick-up assemblies were obtained online at $1.50 each from Lantz’s Hobby Shop, Horseheads, New York.
The following photo shows the bridge mounted in the final pit configuration. The track, wood decking and Scenic Express hand rails are attached to the bridge. The wood deck is stained a dark brown, and the hand rails were painted to replicate steel, prior to being attached to the decking.
A second .25" X 2.5" X 30" piece of oak was glued to the top of the one piece oak base. This was done for both cosmetic reasons, and to strengthen the bridge and its epoxied center shaft. This second piece of oak can be seen across the top of the bridge in the following photo.
In the future the control cab will be lighted whenever power is applied to the bridge track.
The turntable is now complete and operational. The bridge will be removed from the drive mechanism and pit so that the pit can be mounted into Module Two on the California side of the layout.
Click You Tube to see a video of our turntable in action after installation into Module 2.
To see more photos of the installed turntable, go to Building the B&P Part 2, B&P 2.
With the turntable installed and operational in Module Two of the California side of the layout, we now use a small HO (DC) Transformer to power the turntable's two DC motors. To make it easier to control direction and duration of power being applied, we have installed a DPDT / (On) - Off - (On) Momentary Toggle Switch between the transformer and the two motors. We have found two transformer power settings that work very well. One is approximately 80% power for higher speed rotation. The second is 20% power which allows for very slight adjustments and final track alignment.
By avoiding our trial and error, we believe that any experienced modeler can build a similar turntable with very good results for approximately $350.00 in parts and materials. The finished product will rival commercially available turntables costing four to five times as much.
Our parts and materials list (not including paint, glue and stain) and what we paid follows.
Rev-A-Shelf 6012, 28" two shelf, dependent system - $75.00
Plywood/Red Oak pieces - $30.00
PVC Boards 12" X 18" X 1/8" - $19.00
Bridge Track/Pit Rail - $32.00
Roller Bearings (Conveyor Belt), eBay - $8.00
Vacuum Cleaner Brushes, eBay - $6.00
Roller Pick-Up Assembly (4 @ 1.50) - $6.00
O Scale Girder Bridge Plates, ScenicExpress.com - $34.00
Turntable Arch/Control Cab, Diamond Scale Products - $50.00
Bridge Deck Handrails, ScenicExpress.com - $15.60
DC Motors, Geared to 15 RPM, VirtualVillage.com - $35.00
Total materials and parts, excluding glue, paint etc., $310.60 (2011 $$$)
If you have any comments or questions, please contact us at firstname.lastname@example.org
Good luck, and Happy Model Railroading!
After the glue thoroughly dried, approximately three days later, the rail was removed. The tops of the now secured ties were sanded smooth in an effort to provide a better surface on which to install the pit rail. The pit step surfaces between the ties were hand painted with gray acrylic paint. Where needed the ties were painted with brown acrylic paint, following photo.
The completed bogies, two Lionel Roller Pickup Assemblies, and 14 gauge wiring were mounted at each end of the bridge, following photo.
To reduce friction between the moving parts, an inexpensive “fiber washer” was placed on the center shaft, between the shelf collar and center shaft collar assembly, above photo.
The final portion of creating the drive mechanism is adapting some type of electric motor to actually rotate the turntable bridge. Bob’s drive mechanism concept is based on reviewing how both commercially available and scratch-built turntables have been powered.
The turntable drive concept involves using the second 28" Rev-A-Shelf, mounted on the center shaft below the plywood base, within the drive mechanism platform. This 28" round shelf will be referred to as the center shaft drive wheel.
With the drive wheel locked in place on the center shaft, rotational torque can be applied to the outer edge of the wheel with the shaft of a small electric motor. Controlling the speed of the motor and the ability to precisely stop at various track locations is essential.
Bob’s first effort involved using a DC motor from an old hand-held garden trimmer. On opening the trimmer case, we found parts that could be adapted to our drive mechanism concept. The only problem with this motor was controlling the speed at which its shaft would turn.
In its original grass trimmer configuration, it did have some gear reduction. However, this motor did not have a rotating shaft that could be used to apply torque to the drive wheel.
Bob found that the motor’s large black final gear had a socket that perfectly fit a .5" bolt. In Photo 46 the grass trimmer motor is to the right. Bob has already epoxied a .5" X 4" galvanized bolt into the final gear socket. In the following two photos you see all of the parts necessary to configure the motor for the drive wheel.
A 36" X 36" piece of plywood was cut with a 25" diameter hole in the middle. This size hole is necessary to accommodate the Rev-A-Shelf’s under side reinforcement ribs. This piece of plywood will serve as a base for the pit floor, and will provide a structure to which the turntable drive assembly will be attached, following photo.
The turntable bridge detailing will include a lengthwise wood deck with hand rails on each side of the deck, a center turntable arch structure and turntable control cab. The O Scale turntable arch and control cab were obtained from Diamond Scale Products, Alliance, Ohio, for less than $50, following photo.
The springs were purchased at Home Depot and are attached using small metal key rings.
With nine volts DC applied to the motor, this configuration results in the turntable bridge smoothly rotating 360 degrees in three minutes. This is possibly a little slower than expected, but very realistic and easy to precisely stop at desired positions.
Final Turntable Drive Mechanism
After careful adjustment of the Turntable Bridge boogies and drive shaft, the bridge rotates very smoothly, with no drag, and no tilting.
To insure adequate rotational torque to move the bridge and provide greater holding power when the bridge is stopped, Bob decided to use two geared 15 RPM DC motors in the drive mechanism. Both of these motors were purchased from Virtual Village.com for less than $35.00, including shipping.
The same 3/8" aluminum fittings previously shown on the Micro-Mark motor were used on the new motors' output shafts. Short pieces of 3/8" rubber hose finish the shafts and increase the traction/friction on the drive wheel. The Micro-Mark motor will be put to use on the layout at a later time.
With 9.7 volts applied, the bridge rotates 360 degrees in three minutes. With 12 volts applied the same rotation takes two minutes.
With 15 lbs. sitting atop the bridge, its rotation is smooth and precise. The following three photos depict the final drive mechanism configuration.
The clamps weighted with other clamps hanging around the upper pit wall edge, seen in the above photo, were placed where they were to help maintain as true a circle as possible until the glue thoroughly dried, three to four days later.
The shelf’s bottom edge was wrapped with a single set of 10mm X 10mm PVC strips. This was to compensate for the fact that the side edge of the shelf is angled in at the top, following photo.
The turntable bridge was trimmed and sanded until it freely rotated within the pit wall. We then placed a small aluminum self-standing carpenter’s square atop and extending out from one end of the bridge. Slowly turning the bridge with the square in place helped determine anomalies in the pit wall’s height.
The pit wall height was planed and sanded until the bridge, with the square atop could freely move around the entire wall. The completed pit was then painted with Rust-Oleum “Stone” spray paint. This is a textured paint that comes in a variety of colors. We used Gray Stone to simulate concrete, following photo.
Once both the top and bottom PVC strips were securely attached, the pit step and outer circumference were rough sanded. Imperfections in what would become the pit step were filled with auto body spotting putty, following photo.
Using the second Rev-A-Shelf 28" shelf as a form, a new pit rail was fabricated using three sections of Atlas Nickel Silver rail. The process of achieving the final size was the same as previously noted, except that the final circle of rail was adjusted in size until, bottom-side up, it snugly fit atop the Rev-A-Shelf form, following photo.
The above and following photos are the finished product. We actually had to spend $311 for various items, but we believe that what we have achieved rivals commercial turntables selling for four to five times as much. Read on to see how we did it.
Click You Tube to see a video of our turntable in action.
As previously mentioned, continuous AC track current, for the bridge track’s outside and center rails, has to be provided to the moveable bridge.
The center rail current is transmitted through the Rev-A-Shelf center shaft and collar. Inspired by the work of other modelers, Bob wanted to use carbon electric motor brushes to accomplish this. A “Rube Goldberg” plumbing assembly was made to hold two carbon brushes from a vacuum cleaner motor in place against the rotating center shaft, following three photos.
The two most difficult steps of building the turntable pit were the creation of the round pit wall, and fabricating and attaching the pit step’s rail and ties. Before you can fabricate the pit wall, you have to determine its height. The pit wall height is determined by the height at which the turntable bridge will operate in the pit.
In the upper left of the above photo, the red oak base of the turntable bridge has been completed. A more detailed description of the bridge’s construction is provided later. To determine the height of the pit wall, the rough bridge was mated with a portion of the Rev-A-Shelf center shaft and inserted through the pit floor’s center collar, following photo.
This rail was left on the Rev-A-Shelf form for several days in an effort to reduce distortion of the circle upon removal.
The following photo shows the completed turntable with the Control Cab and railroad worker inside. Track power and TMCC have been tested while the bridge was rotated 360 degrees. The results have been perfect.
The eight screws and the pit rail were removed.
We took several Atlas ties and sanded their tops to remove any remnants of the molded plastic spikes and tie plates. Using the smoothed ties, the pit rail was reinstalled using the previously drilled eight holes on the outside of the rail. An additional eight screws were then mounted inside the circle of rail evenly spaced between the eight outside screws. The placement of the eight inside screws was adjusted as necessary to achieve as perfect a circle of track as possible, following photo.
The wider than normal gaps between the ties, seen in the above photo, are for the rail joiners and rail wiring. To the extent possible, additional ties and partial ties will be added to address cosmetic issues.
The pit rail was reinstalled atop the ties, and secured in place with several, strategically placed No. 4 stainless steel screws located on both sides of the rail. Additional cosmetic ties and paint were added, following photo.
This wire will be attached to the bridge track’s center rail.
Our first anti-tilting bridge bogie design used a single roller mounted longitudinally at each end of the bridge. This proved to be unsatisfactory. Coming up with a workable solution involved many weeks and a lot of trial and error.
Bob’s final bridge bogie design involves using four 1/2" round roller bearings, originally used on conveyor belts, a piece of L-shaped aluminum from Home Depot, and four 1/4" locking nuts, following photo.
Center shaft alignment tolerances within the pit floor collar can be affected by using the Rev-A-Shelf locking screw. The shelf locking screw is provided to fix the shelf’s position on the center shaft. However, if the shelf locking screw is tightened and fixed in a position just short of locking the shelf’s position, while still allowing the shaft to freely move, the tolerances of the shelf collar can be improved. The shelf locking screw can be seen on the right side of the shelf collar in the following photo.
With the addition of its track, the turntable bridge is functionally complete. To add to its realism, and make the bridge in fact look like a steel bridge, we added one 26.5" long O Scale Girder Bridge Plates from ScenicExpress.com ($17 each) to each side of the oak base. These are molded plastic pieces that arrive gray on color. After painting them with Rust-Oleum Textured Aged Iron, we screwed and glued them to the recessed sides of the oak bridge base, following twp photos.
As noted above, we thought we were on track to having the turntable completed in two or three months. However, we encountered a couple of technical issues (pit rail and bridgebogies) that took several months of trial and error to resolve.
Building our O Gauge turntable consisted of three modeling projects, the: (1) concrete turntable pit; (2) turntable bridge; and, (3) under layout turntable drive mechanism. While we discuss each of these three topics separately, they were actually undertaken in parallel. Completion of the three projects is interdependent on information gained from the completion of the other. For example, you cannot complete the turntable pit wall without knowing the height of the turntable bridge. And, you cannot finish the length of the turntable bridge without knowing the inside diameter of the pit wall, etc.
Bob decided on building an approximate 30" turntable, for two reasons. First, he found existing products that would facilitate the modeling of the concrete turntable pit. Second, O Scale girder bridge plates that would facilitate the modeling of a turntable bridge of approximately 30" in length were commercially available from ScenicExpress.com.
For the turntable pit, Bob first looked at 30" aluminum and plastic “water heater” pans available at building supply stores, e.g., Home Depot, etc. Then, after doing much of his research on how others constructed turntables, he started to think about the “Lazy Susan” concept. From this, Bob stumbled on revolving shelves found in many kitchen corner cabinets.
Focusing on the Rev-A-Shelf 6000 Series Full Circle System, Bob envisioned pieces that would: (1) facilitate the construction of a turntable pit; (2) provide a precision center shaft to support and drive the turntable bridge; and, (3) provide a precision round drive wheel for the turntable’s drive mechanism, following photo.
Second pieces of aluminum were cut to fit the top of each bogie frame, and laminated to each with super glue, following photo.
Current travels up the wire connected to the galvanized pipe, to the spring-loaded carbon brushes, to the steel center shaft, to the shaft collar locking the turntable bridge to the center shaft, to a wire traveling through the bridge, following photo.
We thought this completed the turntable pit. However, when the turntable bridge was installed with its first anti-tilt bogie design, we found that there was a slight variation in the height of the pit rail over approximately 90 degrees of its 360-degree circle, following photo.
The above photo also shows the initial work we have done on building a wood deck for the turntable bridge. The deck hand rails were purchased from Scenic Express for $15.60.
Turntable Drive Mechanism
As previously noted, to provide a stable platform for the rotating turntable bridge, the Rev-A-Shelf center shaft and collar are attached to the oak bridge’s epoxied 4" upper shaft assembly. The center shaft is placed vertically down through the pit floor’s metal collar. The center shaft extends far enough below the turntable’s plywood base to allow installation of the second 28" round shelf. This entire assembly aligns with the Rev-A-Shelf bottom pivot which is mounted on what Bob refers to as the drive mechanism platform. The drive mechanism platform was built using better quality .75" plywood and is attached to the underside of the plywood base using deck screws and glue, following two photos
Each bogie will have two rollers. Four roller bearings were bought on eBay for a total of $8.
Two 4" lengths of the L-shaped aluminum were fabricated as shown, following photo.
To complete the Turntable Pit, the pit rail will be removed, 14 gauge wires will be soldered to opposing sides of the circle, pit rail ties will be added, and the rail reinstalled.
The Turntable Bridge
The turntable bridge started as a single piece of Red Oak, .75" X 4" X 36" cut to approximately 31" in length. As close as possible to its center, a 1.25" hole was cored.
The cored piece of oak was laid flat on a “level” surface covered with aluminum foil. The top portion of the Rev-A-Shelf upper shaft assembly (with nylon bushing) was cut to approximately 4" in length.
The 4" section of the Rev-A-Shelf upper shaft assembly was centered, leveled with a small square, and secured to the oak with a two-part epoxy glue. After allowing the epoxy to thoroughly cure, the top of the bridge was sanded, following photo.