My original plan was to use a 90' Walthers Cornerstone HO kit and modify it for narrow gauge O scale. That would give me a 49.6' turntable which is just barely long enough for my 2-8-0 locomotive. When I started to assemble the kit I realized how cheesy the quality is and quickly cancelled that idea. I could buy one of several other O scale turntable kits that are available but the cost or the looks or the dimensions are not what I wanted. My only reasonable solution was to build my own. I spent some time cruising the net looking at old photos to get an idea of what I wanted. I found a scale drawing of a turntable used by the East Broadtop RR and used that for inspiration. I drew up a full size (1/4" = 1') drawing of my own to work out the dimensions. The photo above shows my design above the Walthers turntable. I expanded the bridge to be 13.5", or 55 scale feet, which looked better with the 2-8-0. It's also wider to allow a walkway on each side of a locomotive and tender. The pit is 2" deep and I added a ladder on each side of the bridge for access into the pit. Diamond Scale (click here) makes excellent turntables in almost every scale. The quality is very high and the prices are in line with that. Out of my league. Luckily for me they also sell individual parts. I'll be using their O scale wheel dollies along with several other parts they make for the center shaft. I contacted Diamond Scale and they offered to send me a scale drawing of the wheel dollies so I could incorporate them into my drawing. When it arrived I found that all I needed to do was notch the ends of my girders to make things fit.
I ordered the plastic parts I needed from Plastruct (click here) for the girders and wood parts (8" X 8" sugar pine ties, 2" X 10" decking planks) from Kappler (click here). While I wait for delivery I'll get done what I can with what I have in my shop. I cut out a wood buck from a full scale piece of 2" X 2" to form up the base of the bridge. It will be clad with the girders and topped with the decking so you won't be able to see it but it'll add some needed rigidity for the center shaft and the wheel dollies.
I made the hand rails while I was waiting for other parts. Actually, I made them several times. The first time around I used heavy copper solid core wire and soldered on stanchions from the same material. The result was a handrail that looked like it was 100 years old and severely beaten. Since my railroad will still be in it's infancy in the 1920's and my foreman is meticulous with maintenance this just wouldn't do. A friend suggested I try brass rod. I found some 3/64" rod that measured out to 0.045". My 2" railing in O scale would be 0.042" so this is plenty close enough. I wanted to show pipe joints where the stanchions meet the handrail but couldn't find anything that looked right. I ended up using heavy blobs of solder at the joints, filing them down to a good shape and then using three coats of brushed on enamel paint to build up the joint uniformly. In reality the final result probably can't be seen from 3' away but I'm happy with the results.The stanchion supports are made from 0.010 thick styrene super glued into place. A resistance soldering station would have allowed me to use brass for this and the final results would have been much better. Note to self......
Referring to the book "Bridges & Trestles" from Model Railroader magazine I was able to closely match the prototype for girder construction. Closely but not exactly. The prototype used 3/4" steel plate and angles but I felt that in O scale the equivalent was just too wimpy looking. Instead of 0.020" I used 0.030" which looked better to my eye. It only shows on the edges of the flange and bracing angles. The girder web plates are cut from 0.030" sheet styrene and the angles are 1/8" (6" x 6") and 3/64" (4' x 4") ABS. I used ABS instead of styrene because the styrene angles inside web is angled while the ABS is flatter which would make a difference when trying to mate them up. I used 0.030" x 0.100" strip styrene for backing, or filler, for the bracing angles. I also cut my own 0.030" x 0.280" cover plates for the top surface of the girders. Where my girders change angles or are notched for the wheel dollies I doubled up the bracing angles and placed them back-to-back as if the girder was made up in sections and then riveted together.
I will be adding rivet detail to the angles and ordered some 3D resin rivet decals from Archer (click here). The prototype spacing for bridge rivets was generally 3" (0.063" in O scale). I drew this out in scale on paper and it looked way too bunched up. At least to me. The O scale bridge rivets from Archer are spaced at 0.195" (about 9.25") and these looked too far apart. I found the S scale bridge rivets spaced at 0.146" (6.9") looked pretty good so I'll be using those.
I made the upper bracing that goes between the girders using the same bracing angles as I did for the girders and added gusset plates made from 0.030" styrene. When I laid it on top of the wood buck I realized there needed to be some spacing. I ran the buck through the table saw and recessed the top surface about 3/8" in between the girders. When the wood gets painted black it should "disappear". The reality here is that the top bracing probably won't even show beneath the 8" x 8" bridge ties and the 2' x 10" decking but if something does show through then it'll have some depth to it.
Update: I got the rivets from Archer and spent a good two days getting them in place. Tedious work. Before I did that I sprayed the bridge in primer grey so I'd be able to see the rivets better. When I got the rivet packages opened I found more detailed information than had been provided on the website. I ended up using scale 3/4" rivets spaced 3.25" apart and it came out looking just right. In the center section I added five rows of vertical rivets and a small sheet of .030" styrene to simulate the pivot bearing mounts. I also added additional rivets in the area where the frame is notched for the wheel dollies. This is to indicate the addition of splice plates. It adds some extra detail and I'm explaining it with the story that the turntable was lengthened when the railroad added the 2-8-0 to it's roster. I made up some end plates for the bridge using the same basic construction as the main girders and added 0.030" x 3/16" cover plates to finish up the ends of the girders. Once again......this area probably won't show when the model is finished but I know the detail is there.
Another Update (1-9-18): I airbrushed the bridge in engine black and right away realized the rivets had disappeared. I mean they were still there but just didn't show up. I used Bragdon weathering powders to give it some age and they did return if you looked real close. I think they don't stick up far enough to really show. My opinion at this point is that they weren't worth all the hours of work it took to get them in place. I'm still waiting on an order from Diamond Scale for the bridge trucks and center shaft. Also waiting on an order from Kapler for scale lumber that will be used for the bridge deck and ties. Slow building process at this time of year.
Update (1-31-18): I've spent most of the last two weeks working on the control system and have covered that in Part 3. I wanted to mention here how the drive system is mounted. The turntable shaft extends through the pit floor and is held in place by a bearing and retainer. Mounted to the shaft is a 60 tooth GT2 pulley which is a metric size with 2mm between each tooth. This pulley is driven by a stepper motor with a 40 tooth pulley mounted to its output shaft. The pulleys are connected by a 400 tooth (800mm) belt. In the picture above you can see there is an idler pulley mounted behind the turntable shaft. I chose this location to prevent side loading on the shaft. The belt still has enough contact on the shaft pulley to provide good drive. Both the idler pulley and the stepper motor mount are adjustable to provide the proper belt tension.
I also finally received the wood strips for the bridge decking. I spent a day cutting everything to length and scribing wood grain on all surfaces. I then sanded everything lightly with 220 grit paper to remove sharp edges and fluff sticking out from the scribing. When all that was done I threw all the pieces into a one gallon zip lock bag and poured in my weathered wood concoction. I let this sit for 12 hours, turning the pieces over and sloshing the liquid around every now and then. The next day I poured the stain back into its container and laid the pieces out to dry for two days. The next step is to assemble the deck. For information on the weathering check out Rusty Stumps Weathering Parts 1 and 2 (click here) and (here).
Update (2-5-18): Made some progress on the bridge. It's almost complete now. I'm still waiting on parts for the dolly trucks from Diamond Scale. When they come in I'll get them painted and mounted to the bridge. After that I'll just have the pit and control panel to do to finish up this project.
Update (2-13-18): I finally got the rest of the dolly truck parts in from Diamond Scale. The truck frames are cast white metal and the wheels are small diameter bearings with brass bushings. I filed down the castings to clean up the flashing but they are very nice pieces to start with and didn't require a lot of work. Diamond Scale uses these trucks on much larger turntables than what I'm building here. Mine is only 55' and I think some of theirs are as big as 130'. The cast frames hold the wheels at an angle to match the ring rail and because of this I had to modify them. My ring rail is just over 12" in diameter so the angle for the wheels has to be pretty tight. I had to cut the dolly frames down the center and file in a 10 degree angle. I then glued them back together and then glued in a flat panel across the top to add some rigidity. Once the glue was set I primed and painted the frames and then added some age using Bragdon weathering powders.
The picture here shows the top dolly is modified and the other stock. Sitting on the ring rail it becomes obvious that the modified one follows the curvature better.
Now that the bridge is finished I have the final dimensions I needed to complete the pit. Woohoo!
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