The crossing of Los Gatos Creek at Wrights was always an odd scene. I really loved how the scenes on either side had turned out; the area around the Wrights station had the right look of California hills and trees hanging over the tracks. The area around the summit tunnel also gave the right look of diving into a dark redwood forest.
But the bridge scene - well, it just looked like mediocre work. The bridge didn’t look prototypical; it neither looked like the actual SP bridges along the route, and to be honest didn’t look particularly realistic for any railroad. The stream scene had never been completely landscaped and still showed bare spots and unrealistic slopes. It was also missing water in the stream bed, details on the bridge and in the surrounding area.
Now, some of this could be fixed; I’d done decent scenery elsewhere, and had my methods figured out. I’d use a gray-brown paint for the dirt color, sprinkle over sifted and sanitized dirt from our garden (“downstream from Los Gatos canyon, so really prototypical!”). I used yellow ground foam and static grass for the grassy areas, and a mix of Woodland scenics foliage and Supertrees for the larger trees. For water, I’d use the remainder of a jar of the Woodland Scenics decoupage stuff. Details also weren’t hard - just a matter of looking at photos and figuring out some debris to put here and there.
I’d have a harder time matching the prototype details. Prototype photos of the actual bridge, as well as other bridges through Los Gatos Canyon, always had a very specific Southern Pacific look. The piers were cast concrete, with rounded edges and gently angled sides. Bridges often had walkways hanging off each side with outriggers and cross-bracing from dumping pedestrians into the creek if they leaned too hard against the railings. Bridges often had very obvious concrete abutments.
None of these details were things I could buy - the standard SP look just didn’t match the store bought pieces. I could buy piers, but they’re not going to exactly match the SP shape. The handrails on the bridge are not available for love or money, and would need to be scratchbuilt. The bridge abutments? At least those would be easy to scratchbuild from some styrene with a bit of work.
3d printing to the rescue
The 3d printer sitting there in the corner seemed like the perfect item to solve some of these problems; the piers, abutments, and bridge details all came out of the 3d printer.
Drawing the pier using SketchUp's "Follow Me" tool. I drew the oval base and a single cross-section of the pier, then dragged the cross-section around the oval.
I started off with the piers because the SP’s booklet on the bridge showed the exact plans. The cast piers were 15’ 2” wide at the top and 5’ thick. There was a 4” lip at the top of the pier. A 1 in 24 slope on all faces made the pier 16’ 3” wide and 6’ 9” thick at the bottom. The pier’s curve on each side had a 2’ 10” radius, with 8’ 6” spacing between the two half-circles.
With all these measurements, making a 3d model of the pier took only around 30 minutes. Sketchup has a feature called “Follow Me” where you can select a cross section, and move that cross section along a line in another plane. Sketchup automatically creates a shape using that profile. For the pier, I drew the oval (for the top of the model), then drew a cross section of the base - hollow to use less material with printing. With “Follow Me”, I had a rough pier done. The pier printed from the top to the bottom. I tweaked the design to get the wall thickness right, but soon had two piers ready to paint and install.
I could have added form impressions on the design, but decided against it - I assumed I could fake some with paint when the model was done.
The abutments came next. I needed the abutment to serve two purposes: they needed to mark the limits of the roadbed, but they also needed depressions to hold the 4x12 beams that sat atop the trestle bents on either end of the bridge. I could have done these in styrene sheet, layering multiple pieces to get the shape I needed, but once I had the 3d printer running, sketching out a quick design and sending it to the printer was quick.
The Wrights bridge has wooden trestle bents leading to the steel truss bridge in the center. I made these from scale 12 x 12 wood; I’d done this kind of work before, and didn’t mind switching to stripwood and white glue for the project. My big surprise was that getting these short trestle bents right was a bit of a challenge.
In the past, I’d sort of eyeballed how quickly the trestle bents spread out; this time, with the drawings from the “Southern Pacific Lines Common Standard Plans” (published by Steam Age Equipment Company a few years back), I knew the precise arrangement - piles on 2’ 4” centers, 12x12 cap, and three 8x18 stringers under each rail. I also knew the piles sloped out at 1 in 12 and 3 in 12.
My first couple attempts to do these by hand failed miserably -I couldn’t get the slopes quite right, and the short pieces were hard to cut and fit. I finally 3d printed a template to help me cut the pieces to length and hold them in place while gluing, and ended up with decent parts.
Finally, I moved on to the walkways. The bridge itself was a Micro Engineering plastic model; Micro Engineering’s bridge track had appropriately long ties for the trestle and girder sections of the bridge. Getting those handrails and walkways on the bridge, though, didn’t have an obvious solution. The ties weren’t long enough to hold a walkway at the correct length. The individual posts, with cross-bracing sticking out from the bridge and in both directions along the bridge, were complex and tiny shapes that would have been tough to scratchbuild, especially because they had bits sticking in all directions - they weren’t just something that could be assembled flat on the workbench. Because these parts stuck out from the ties, there also wasn’t any good way to glue them onto the plastic ties. Worst of all, building the handrails out of stripwood seemed awfully fragile for an operating layout; I didn’t want to do hours of handwork only to have me break them off while track cleaning.
The 3d printer again called out to be used. For the problems of attaching the walkways and handrail, I realized a 3d part could both stick between the ties, and have a gluing surface to attach to the outside of the ties. The 3d printer could handle the multiple supports (as long as I oriented the parts right.) I could add the walkways and handrails as separate pieces, and add notches for the stripwood to align with the part.
Again, an hour of sketching gave me a simple part that worked. I printed a couple dozen of the supports, then sanded each to fit between the ties, superglued them in place, and the next day attached the walkway boards and handrails. Apart from some fiddling to get the supports attached (because of different tie spacing), assembly went quick and easily.
The Conclusions Rebuilding the bridge at Wrights started off as a straightforward process - redo some scenery based on some new facts I'd learned as part of research. Although I've used 3d printing for many projects, I was surprised how going to the 3d printer was my first choice for the piers, walkways, abutments, and pier template. If I'd been sending my parts out for manufacturing at Shapeways, I can't imagine asking for so many parts. But with the 3d printer already on my desk, the 3d printer becomes the tool of choice.