Instructables

Model Train Bridge

Using Google Sketchup, I designed this HO scale model railroad bridge. It's based on the C&O bridge that spans the Ohio River here in Cincinnati. I downloaded a full scale train model from the library and then scaled it down to HO size. This bridge is approximately 7' long which would span approximately 500' if scaled up.

The challenge with this project is finding the right materials to construct it. The larger supports are 1/2" square, the smaller 1/4". Unfortunately, at that size, wood tends to warp over large lengths. Aluminium or perhaps plastic pieces 3D printed would be ideal.
Or you could buy scale bridge parts from micro engineering. Don't reinvent the wheel. Model railroaders have been building bridges like this since the '40s
meeko2 years ago
Love it! Voting for you!
caitlinsdad2 years ago
Even at 7 feet, you are replicating the engineered trusses of the bridge so the wood segments shouldn't really warp or sag. Still, you might want to consider using hollow aluminum or plastic square stock. Architectural models can be built for indoor or outdoor use and the choice of materials and finish would need to be considered.
skeplin (author)  caitlinsdad2 years ago
I looked into using aluminium "U" channel for the long sections, but I couldn't figure out a way to attach the cross-braces. Up to this point, I've only worked in wood.

There is one other minor issue --- the train must curve onto the bridge. If you look at my other Instructable (Ledge Train), you can see what I'm talking about. I thought about building the bridge superstructure on top of the board that I have up now, but it wouldn't look as authentic.

Thanks for the recommendations!
You could try mini-pop rivets or make out of wood and glued plastic and paint to look like metal gray, weathered rust.  Or cover metal rods with wood and paint.  Most overhead installations use a layer of plexiglass as the roadbed support so you can see the train go overhead.

skeplin (author)  caitlinsdad2 years ago
How I envy you, Gomez.
I have used this stuff called "Alumaloy". It is an aluminum welding product that uses the heat from a MAPP Gas or Propane torch. It's pretty spendy, cut you don't need that much for this project. I've used it myself for patching holes in an aluminum boat and it works well. Just don't overheat the aluminum or it will turn to liquid. For this application I would suggest the Propane as the MAPP gas reaches higher temps.

http://www.alumaloy.org/

On another note, if you use copper square rod, or copper square tube you could solder it together like a Tiffany lamp minus the glass shards. Copper is pretty flexible, but I think the truss work might add the rigidity you need. Just a thought.
skeplin (author)  CementTruck2 years ago
Copper would look very nice, but would be heavy and expensive. Thanks for the tip on the "alumaloy" -- I'll check it out.
Kiteman2 years ago
I'm sure that careful construction could overcome the warping issues.

Are you going to try?
skeplin (author)  Kiteman2 years ago
I would like to. I don't have a planer so I can't mill my own stock. The 1/2" square pieces of poplar at Home Depot or Lowes aren't straight in any sense of the word. Walnut or oak would be ideal.
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