Milan Branch of the Iowa Interstate RR

Category: Scenery (page 1 of 2)

Rock River bridge girder spans

I just received my two Rock River girder spans from my friend, Clark C. They came in a very well designed protective wood enclosure because of all the delicate parts. The spans look fantastic and I’m excited to get to work on prepping them for placement.

Both spans need to be reinforced with metals strips along each inside length to make them more rigid to support the weight of the trains. After that, I will prime and paint them in a dark rusty brown color, add the ties and rail and then move on to scenery construction for the piers and river scene.

Clark provided the spans so that I can get the track work up and running across the river. The lattice trusses will come later and will be attached via the side beams. Both spans measure roughly 16 inches in length.

Here is an overall view of the two spans.

This closeup shows some of the detail. There are rivets lasered into the acrylic, but it is hard to see in the photo.

Lattice girder development

Work is progressing with the lattice  truss bridges. My friend, Clark C., who’s helping me with the bridge design and fabrication is doing a fantastic job. I really appreciate his talent.

We decided the best approach would be to design and laser the girder structures for the two spans first so that I can put them in place to get the track operating. Clark has designed the bridge so that the side trusses can be fabricated separately and then attached to the girders at a later time.

Of course, once one of the trusses is complete to our satisfaction, the other three will be easy to create.

I’m very excited about these bridges because they will be my signature scene on the layout. Lattice truss bridges are not modeled very often, so they will be a truly unique feature.

Lattice truss bridge spans

Below is a picture of two scale cardboard mockups showing the lattice truss bridges which will span the Rock River.

Lattice truss bridges are not modeled very often, even though there are many examples of that type of bridge throughout the country.

The photo also shows the location of a speaker which will be embedded into a small river island and will play moving water and bird sounds. Attached is a small snippet of the sound which will loop once installed.

 

A friend, Clark C., is helping me create the custom bridge spans with his expertise using lasers. He first mocked up a schematic for each of the different lattice configurations based on an Illustrator file I sent him (below). The spans have several distinct horizontal lattice designs which include angle iron and I-beams in two different crisscrossing reinforcing lattice patterns. In addition, those designs alternate between the inside and outside of the main truss. This creates a very interesting and somewhat complex fabrication challenge.

We will be developing the depth of each side span in “layers” similar to 3D printing. This will allow the unique open areas (see image below) between the main lattice members to be rendered accurately. At least, that’s the idea. 🙂

Clark mocked up a test section to see how the laser would render a portion of the truss and supporting lattice.

Below is what the computer rendering looks like. Each tone represents a different depth of cut, and the laser can be sped up (more intense ablation) or slowed down (multiple passes for better detail) to achieve different quality levels.

By their design nature, turn-of-the-century lattice truss bridges are delicate looking which makes them unique but also challenging to construct. We’re hopeful that the “layered” approach will allow those delicate cross members to be modeled faithfully without the potential for bending or warping along their length.

Clark discovered that the laser cuts did warp the material as shown below. But by applying oven heat to slightly ease the material and then applying weights as it cooled resulted in flat, uniform pieces.

Below you can see some of the cross members attached to the main truss and weathered for effect.

Clark will be creating some additional cuts to see if the material can be thinned down even more. So far, it looks very promising for these unique spans. Stay tuned!

 

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