Let's build a turntable...by cnw1961
I need a turntable for my next layout (HO). I want to scratch build the ATSF roundhouse at Redondo
( <!-- m --><a class="postlink" href="http://atsf.railfan.net/structures/rhredondo4.jpg">http://atsf.railfan.net/structures/rhredondo4.jpg</a><!-- m --> ). Even though the turntable at Redondo is 120' and my turntable must not exceed 90 scale feet, I want to build it the same style. To make construction easy and to have a perfectly rounded pit, I ordered this MDF wood ring at an online store for car hifi products.

pennsyrrfan found a source for these rings in the US: Able Audio. Thank you, Paul.
The online-store in Germany: CHP car hifi produkte Online Shop


The inner diameter is 11 1/2" and it is 3/4" thick. That makes a shallow pit of 81 1/2'. It will be just big enough for my Mikado.

I thought of using a phone jack as the center shaft, but I don’t want to turn the bridge with my fingers. I need some sort of mechanism to turn the bridge from underneath. I haven’t decided yet, if I want to use a motor or a handle, but this rules out the phone jack as the center shaft. I will use this .240 brass tube as the center shaft and these gears, I found at a hobby shop. The gear ratio is 1:40. I hope, they will do the trick.


At first, I want to build the bridge. To get reliable operation, I think it is essential to have a sturdy bridge, that does not wobble or flex when a loco is standing on it. So I use two layers of .060 styrene to build the deck. I already marked the center of the bridge – it won’t be so easy to do when the bridge is assembled.


The braces at the bottom of the bridge and the girders are made of .060 styrene too.



In the last pic you can see the braces on the inside of the girders. Here is another view.


Now it is time to add some detail to the bridge. The braces on the outside of the girders are made from .013 and .020 styrene. The strips at the bottom and top of the girders are .020.



To be able to fix the center shaft to the bridge (I’ll do that later), I glued this piece of plywood to the bridge. I drilled the hole before I glued the plywood to the bridge. If the hole is not perfectly at a right angle, it is easier to take another piece of plywood and try it again!


After I finished the fundamental assembly of the bridge, I turned to the power arch. I used my computer to do drawings of these delicate parts, printed the drawings and glued them to .020 styrene using re-positionable adhesive spray. Now it was easy to cut the parts for the arch precisely (the zig-zag line is .040").


The next two pics show how I assembled the power arch. With these delicate parts it is very important to allow the glue to dry completely, before the next parts are added.



After it dried completely, I fixed the arch to the bridge.


On the front of the girder you can see the trusses for the walkway.

The next pic shows the power arch after I applied all details.


I started gluing the ladders to the arch. Then I cut a piece of .040 styrene for the platform.


I drilled holes for the stanchions before I glued the platform to the arch. The handrail and stanchions are .020 brass wire. I formed little rings on one end of the stanchions to fix them to the handrail.


Then I soldered the joints. It took some fiddling and cursing until the wire had the right shape and I could glue it to the platform.


The last step was to attach the box on top of the arch. That was quite easy, as you can imagine.

After I finished the power arch, I turned to the walkway at the side of the bridge. I used .200 x .040 stripwood for the walkway. I did not fix it to the bridge, the bridge has to be painted first. Then I installed the handrails (made by Central Valley).


The next two pictures with the engine on the bridge give you an impression of the size of the bridge (this Stewart F3 is another modeling project waiting on my workbench).



The control cabin is only a mock-up to find out the right size. I can do better than that.

After I finished the construction of the bridge (I’ll do the control cab in the end), it is getting a little tricky now. At first I have to adjust the height of the bridge. That’s still quite easy. I cut two washers from .060 styrene and glued one of them to the bridge. The other one will be glued to the bottom of the pit. Besides adjusting the height, these styrene washers will make the bridge turn easily without any grease.


I think I tell you no secret, when I say that I made the ring rail from a piece of flextrack. I cut it on the inside of one rail, the I put into my pit to determine the length. I made sure that the side of the ties I did not cut was on the outside and that the rail fits tightly into the pit. After cutting the rail, I closed the ring with a rail joiner.


Now I had to determine the position of the trucks on the bridge. First I measured the height of the truck when it sits on a piece of track. Then I had to determine the distance from the middle of the truck when it runs on the ring rail to the middle of the turntable. Now you can see why I haven’t fixed the bottom of the turntable to the wall yet. I placed the wooden ring on the drawing of the turntable that I did before I started. Then I put a truck on the ring rail and a small piece of track and marked the middle with a pencil (more accurate than in this pic). If you can think of a better way, please let me know.


Now I could measure the distance without any problems.


I use some Atlas freight car trucks with metal wheels. To make them suitable for my turntable, I replaced the inner wheels by nails (I had this idea when I read how doctorwayne built his turntable Turntable – thank you). Then I attached the trucks to the bridge.


I took a deep breath before I placed the bridge on the ring rail in the pit, but to my relief there was nothing wrong with my calculations. The bridge fits perfectly.



BTW, greetings from my wife to Big Blue. She said, I should tell you it’s her fault that you have to endure all this. It was her idea to start model railroading a few years ago. But she could not know at that time, how much I would like it.

Today I started to build the pit. The bottom of the pit is a piece of 1/2" MDF . It has a nice smooth surface, which is easy to paint. I glued it to the pit wall (my wood ring) and secured it with eight small screws.


After I determined the center of the pit, I drilled the hole for the center shaft. I made it .020" wider than the shaft to give the shaft enough clearance to move freely. Then I mounted the bridge on to the shaft. The bridge turned easily and I think, I could have operated the turntable without any problems. But on the ends of the bridge I could feel additional movements caused by the clearance of the shaft. And the bridge could be moved sideways a little bit. I remembered that I had some small ball bearings somewhere. After some rummaging in our basement (I am not the guy who keeps everything neatly lined up on shelves), I eventually found them.


The use of bearings causes another problem. The clearance of the shaft helps to make up for inaccuracies of the position or angle of the center hole. If you eliminate the clearance of the shaft, the bearings have to be aligned and centered perfectly.

I widened the hole for the shaft and glued a ball bearing to each end of the hole. I had to remove and adjust the lower bearing before I managed to get it right (in the pic you can see the small strips of styrene that I used to keep the bearing in the right position).


Now the bridge can turn only into the desired direction, no more additional movement.


Here’s the bottom of the pit with one of the gears in place.


I installed the gears to drive the bridge and to my great relief, it works absolutely fabulous. I attached my electrical screwdriver (how do you call this thing?) to the shaft that comes from the gears and when I switched it on, the bridge turned just as I hoped it would. Tomorrow I’ll try to find a small motor for my turntable.


Now I only have to find a way to attach a phono jack to the lower end of the center shaft.

I got the ultimate motor for my turntable today . It is a 12 V/DC motor that has a small gearbox attached to reduce the speed of the shaft. When the motor is running at full speed, the shaft does only 85 rpm. The bridge of the turntable makes one full turn in 30 seconds when the motor is running at full speed. And it is no problem to let the bridge crawl until it is hardly visible. Even then, the revs of the motor are still high. I will plug the motor to an old DC power pack and I will get the perfect control of my turntable. I think it is as good as it gets without an indexing system. But the guys who operated turntables in the real world did not have indexing systems as well.


And I painted the bridge today. Now it needs some weathering.


Did not have much time to work on my turntable today. Only weathered the girders. After having painted the bridge, it deserves a painted engine now .



BTW, now that I know of these 12 V/DC motors with gearboxes, I would change the design of the transmission, if I had to do it again. I am happy with the performance of my turntable, but it is always better to keep things simple. With the new design, I would only need 2 gears instead of 4. That’s how I would do it:


As you can see, I enjoy working with styrene. You can easily cut, glue sand or file it and you get good results in no time. In this picture you see nearly all the tools I use for working with styrene (sometimes I need a longer ruler as a straight edge or a bigger file).


A straight edge and a knife is all you need to cut styrene. Scribe the styrene and then bend it to snap it off. Thin styrene (.013" or .020") can easily be cut, just like paper. (BTW, I use a piece of .300" window pane to protect my workbench when I cut styrene.)
I use this knife with snap blades most of the time. The tip of the knife has to be sharp to get good results. For very thin styrene or delicate parts, I use the surgeon’s knife.
I use this triangle as a straight edge. I think most people prefer to use a metal ruler, because it takes some practice not to cut the triangle and damage it. The big advantage is, that I don’t have to draw any lines on the styrene to see where to cut – saves a lot of time. With all these parallel and rectangular lines, I can use the triangle to measure and cut in just one step. With this triangle I can cut strips of .020" (.013 styrene).

To glue styrene is even easier. I recommend liquid glues like this Revell glue that I use, because they are applied and spread easily. These glues melt styrene and after a few minutes the glued parts are firmly fixed. To glue parts, apply glue to one of them, hold them in place for a few seconds and then don’t touch them for a few minutes, that’s it.
Here’s how you apply the glue. It comes with a needle applicator.


No need to clean anything if you don’t leave it without the cap for more than a few minutes. And even then, a small wire is all it takes.It might be necessary to fix big parts with adhesive tape sometimes, but this rarely happens. After the glue has dried, you can shape your parts with sanding paper or a file.

I think that’s all you need to know. Get some styrene and glue and just start doing it, you’ll see it is very easy – as you can see from the pics, even I can do it.

Only a short update. I cannot finish the deck of the bridge and the electrics until next week. I need a piece of Atlas code 83 track and I have only Peco code 75 at hand. I have to go to the LHS next week. Today I painted the pit. At first I applied a clear primer with a paintbrush to seal the MDF board and sanded it afterwards. Then I spray painted it with white paint. After the paint had dried, I used a piece of cloth to apply several thin layers of acrylic paint. Don’t look at the rim of the pit too closely, I only painted it to hide the white paint that I applied first. Once the turntable will be installed on the layout, the rim will not be visible.


Next step: paint the ring rail and glue it to the pit.

I found out that the right speed of the bridge for me is 1 min 15 sec for one revolution – I don’t know about the prototype, but it looks good at this speed and I don’t fall asleep. The motor is running at 40 % (1700 rpm) of its maximum speed (4250 rpm). I am glad that can keep it at this relatively low speed, because above 2000 rpm it gets noisy. The noise of a motor at high revs is an important point that one should think of when calculating the speed of the bridge, rpm and gears.

I painted and installed the ring rail, "detailed" the pit and finished the walkway.


Earlier on this thread I posted a picture that shows the mock-up of the control cabin. I claimed that I could do better than that – I’ll try to prove it now.

When I scratch build a structure, I simply glue the plastic sheets for the window panes to the backsides of the walls. This little control cabin has windows on all sides and I want to build it without a door. To make it look good I have to think of a better way to attach the window panes.

Instead of using .040" styrene for the walls, I take two halves of .020 styrene for the wall sections (except the front wall with the door opening). The openings for the windows are .040" bigger on the inner halves. This allows me to insert the window panes into the wall. I did the cutting templates on the computer.


After I cut the parts, I glued the halves together and inserted the window panes. Then I scribed the front sides of the wall sections with the tip of a knife to make them look like wood panels.


After that, I assembled the cabin.


To hide the seams between the wall sections, I added strips of .013" styrene as trim to the corners.


Now the cabin still needs to be sanded and painted, and not to forget – a roof.




In reply to several queries, here is a little additional information.
To determine the size of the turntable was very easy. The biggest turntable I can use is 90'. It has to be as small as possible, but still big enough for my longest engine.Then I found the wood ring and that settled it. From looking at prototype photos of the Redondo turntable I knew that I wanted a shallow pit, but I needed at least .700" for the ring rail, the trucks and the deck of the bridge. The wood ring is .750" – couldn’t be any better.

When I plan to scratch build a structure, I look at as many pictures as I can find. From known objects in the pics (engines, cars, track etc.) I deduce the size of the unknown objects. But if you don’t want to count rivets, you should always bear in mind that your model does not have to be right, it has to look right. Take the power arch of my turntable as an example. I was lucky to find some pics that show a 4-8-4 on the bridge. Knowing the length of the loco, it was easy to determine the length of the bridge and the height of the arch. But when I built the arch to the right height, it did not look right on my bridge. If you take a close look at the first pic of my bridge with the power arch in place, you will see that the arch is higher than in the pics I took later.

To ensure reliable operation, it is important to have a sturdy bridge. I decided to use the thickest styrene I had at hand: .060". That was easy. To decide which thickness to use for braces and other details, I take a look at the prototype photos and try to choose the styrene that just looks right. But sometimes I am determined by what I can do. I think the right thickness (or the closest match) for the power arch had been 0.013". But I knew that it would make the arch too delicate. That’s why I decided to use .020". BTW, the zig-zag bracing is much to big to match the prototype, but I think no one will notice if I don’t tell about it. I hope you will keep this secret.

Now, on to wiring the turntable. I power my layout with a DCC system and will use an auto reverser to power the bridge track of the turntable. It makes wiring a lot easier.
I thought of using a phono plug and jack to connect the bridge track just as proposed earlier on this thread. But then I realized that I could only make it work with great constructional effort. To prevent the bridge from slipping on the center shaft, I have to glue it to the shaft. If anything is attached permanently to the shaft under the bottom of the pit, I can’t remove the bridge. To make this work with a phono jack is too much effort. Instead of the jack I thought of using the simple method I found on a Heljan turntable (I think Walther’s TT without indexing is the same in this aspect): two metal rings on the center shaft and two metal strips.


It’s very easy to do, but I heard of complaints that it does not work consistently. The metal strips are the weak spot. Then I thought, why not use motor brushes instead of metal strips. If motor brushes are good enough for motors that do several thousand rpm, they should be good enough for a turntable. So I got me a pair of brushes and two springs.


To make the housing for the brushes was quite easy. I made it of .060 styrene. In this pic it is still without the cover to see how the brushes and springs are installed.


I glued the cover to the housing and installed it to the bottom of the pit.


I think that should work without any problems. Now I have to find a way to attach the wires from the bridge track to the metal rings.


I found an easy way to attach the wires from the bridge track to the metal rings. I drilled small holes into the styrene shaft for the wires. Then I put the wires into the holes and removed the isolation at the end of each wire. Then I applied some super glue to the shaft and pushed the metal rings on the ends of the wires. Sorry, I can’t explain it any better, this picture might help. The right ring is already in place, the left is still to be done.


I feared that the glue might have negative effects on the contact of the wires and the rings, but as the next picture shows, everything is fine.


Before I glued the plastic shaft to the center shaft, I cut the wires to the right length and soldered the ends to be able to solder them to the track without anything getting too hot.
If I apply some solder to the track before I put it on to the bridge, it will only take a short touch of the soldering iron to connect wire and track.



I am close to the finish line now. Only the bridge track and the wood planks for the deck are still to be done.

A fellow member of our forum sent me a PM to warn me that electrical contact between the wires and the brass rings (see my last post) may fail due to oxidation on the inside of the rings. Even though I checked oxidized brass with my multimeter before I decided to use brass rings, he is absolutely right to suggest that I should change the method to connect the wires. No need to take any risk.

As a first attempt I soldered the wires to the sides of the rings. After I filed the soldered parts to make them fit through my bearings, there was so little solder left, that it didn’t look very reliable to me. That’s why I decided to solder the wires to the inside of the rings. First I flattened the ends of the wires and applied a little solder.


Then I applied some solder to the inside of the rings and filed it until only a thin layer was left. Then I soldered the wires to the rings.


I carefully filed away some solder and some plastic of the styrene tubing until I could slip the rings on to the plastic tube. I secured the rings with super glue.


Didn’t get much done yesterday (sometimes life disturbs the modeling). I got my Atlas code 83 track and now I can finish the deck of the bridge. I cut the track for the bridge .040" shorter than the diameter of the pit. Before I glued the track to the bridge. I applied some solder to the spots on the outside of the rails where I wanted to attach the wires. After the track was in place I bent the wires to the right position for soldering and secured them by adding some glue to the insulation of the wires. I used cardboard strips to protect the girders against accidental contact with the soldering iron. Now it only needed a short touch of the soldering iron to fix the wires.


After I glued the track to the bridge, I painted the rails and the space between the ties. Then I cut .180" x .040 strips of wood for the deck of the bridge. I made little cuts each 1 1/4" to make it look like single planks.


Then I glued the strips together to form the three parts that make the deck.


Before I fixed them to the bridge, I wanted to paint them. It is easier to make changes if I didn’t like the color after the paint dried if the parts were not glued to the bridge.

I didn’t like the clean look of the stripwood. To give it a more weathered look, I painted it dark grey and after the paint had dried, I used a knife to scrape it off again. Then I sanded the parts and applied some greyish brown paint.


In this pic you can see that the deck is well above the rim of the pit.


This is something special with the design of my turntable. At the Redondo roundhouse (the prototype I try to model) all tracks that lead to the turntable are built as street trackage, with the tarmac lying on top of the concrete pit wall. This extra height gives me the chance to model the crumbling edge of the tarmac.


For a more common design, I would glue a strip of styrene (I love that stuff) to the wood ring to match the height of the ties. This strip makes the narrow concrete rim of the pit, that you see on most turntables.


Or just build a lower bridge to get a turntable with a broad concrete rim.





This excellent tutorial was recreated for The NEW Academy thanks to Kurt (cnw1961) and doctorwayne.

This thread was moved to The NEW Academy on August 12, 2009 and is now closed to further comments. Some posts may have been removed or edited for the sake of clarity. If you have any feedback on this topic, please create a suitably titled post (e.g. Question about TOPIC in the Academy) in the Upper Berth.

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