Thursday, December 29, 2016

Wrights Bridge 2: 3d Printing All The Details

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.

The Piers

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

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.

Handrails installed

The Walkways

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.

Handrail part. Large projection fits between ties in bridge tie flex track.

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.

Wednesday, December 14, 2016

Movie Night XXV: Wrights Bridge

While we're talking about the new bridge at Wrights, let's check out some video of trains rolling through the new scene!

Tuesday, December 6, 2016

Replacing the Wrights Bridge: Part I

Sixth Crossing, Los Gatos Creek

I love research because it convinces me to throw away perfectly serviceable parts of my layout.

Wrights, located at the top of Los Gatos Canyon, is a key scene for my model railroad. It has a photogenic location at the top of Los Gatos Canyon, with the tracks suddenly jumping across the canyon to dive into a tunnel. Photogenic structures - the old general store, tiny station, and abandoned warehouses - fill the scene. A siding, originally intended to go to the Sunset Park picnic grounds in the 1890’s, provides a way to hide a reverse loop at the top of the layout.

Original scene

The Wrights scene is also one of the earliest bits of scenery on my layout. During the first nine months of building, I focused on getting track laid all the way to my upper level so I could confirm that I knew how to build my two-level benchwork. Once the track was in, I decided I ought to do the messy scenery on the top level first; I’d hate to dump plaster on a good-looking scene below.

The resulting scenery was a mix of good and bad. I matched the rough terrain of the location deep in the canyon, and captured the look of both the redwood-covered hills above the tunnel and the creek deep in the canyon. I reproduced the wooden trestle from narrow-gauge era photos. I also made the model a bit "more interesting" with trestle bents that weren’t perpendicular to the rails, and a split-level concrete foundation matching an odd trestle bent I’d seen on Jack Burgess’s Yosemite Valley railroad. I also rushed construction of supports for the road bridge just upstream of the railroad trestle, plopping down plaster onto the hillside and shaping it to look like a massive concrete block supporting each bridge end.

Of course, then I started reading more about the actual location. Later photos showed a different bridge - a wooden truss bridge - in place of the trestle across the creek. I found some maps hinting that the road from the new Wrights station, on the other side of the creek, dipped under the bridge to make it to the road bridge and the road up-canyon to farms in Austrian Gulch and beyond. Adding that road was one of the few improvements to the scenes since 2006.

Then, last year, while searching up at the California State Railroad Museum, I found a little stapled set of blueprints, set up like Powerpoint slides. (I wrote a bit about those blueprints and maps I found back in August.) I’ve been claiming (without proof) that the booklet must have been the work of some summer intern in the engineering department. That intern had remarkably good lettering skills...

That booklet showed pictures and drawings of the actual bridge… which didn’t look anything like the actual bridge I’d made. Now, that’s not uncommon; I’ve found plenty of scenes on my model railroad that turned out not to match reality. In some cases, I ignore the mistake. Perhaps I needed to swap two scenes to fit my garage, or perhaps I believed the difference wasn’t noticeable. In other cases, I'm annoyed by the difference - but not so annoyed by the mistake that I’d do something about it.

And in some cases, I get annoyed enough to rip out completed, decent scenery, just to match details that the summer intern sketched out a hundred years ago, and stapled in a cool little booklet.

The Prototype

For the railroad, the bridge at Wrights was the “sixth crossing of Los Gatos Creek”. Los Gatos Canyon was an awfully narrow place to survey a railroad, and the railroad reached the headwaters by bouncing from bank to bank to keep grading costs low. Two of the bridges were just above downtown Los Gatos in the narrows at Lexington Reservoir. The third was near Alma. The fourth was near Aldercroft Heights. The final two crossings - just below Wrights, and just above Wrights - were the fifth and sixth crossings.

The South Pacific Coast Railroad laid all that track back in the 1870’s in their attempt to break the SP monopoly and get access to the lumber traffic from the Santa Cruz mountains. The SPC was narrow gauge - smaller trains and bridges kept the fledgling railroad’s costs low. Their original bridges met their “cheap” image, with most bridges being trestles with piles driven into the unstable soil holding them up.

The sixth crossing of Los Gatos creek, up by Wrights, was originally a trestle built on pilings by the South Pacific Coast. The tracks, on the east side of the canyon, suddenly made a right turn, cut across the creek and rolled across a filled-in gulch before diving into the mile-long summit tunnel. Photos from the 1880’s and 1890’s show a trestle that looks like it would have caught ever bit of debris rolling down the creek in the winter storms.

The SP leased the line in 1887, planning to make the line into a solid, first class railroad… eventually. When the plans to standard gauge the line started in earnest in the early 20th century, the SP widened the route and put in some slightly more solid bridges. SP finished dual-gauging the tracks to Wrights by 1903. The Wrights bridge, according to the intern’s slide deck, was replaced in the same year with a straining truss wooden bridge, built just as the tracks up to Wrights were being standard gauged. The intern described it as:

Old Structure. 80 ft. Straining Beam Deck Span on frame piers, with concrete footings with trestle approaches. Designed for narrow gauge track and equipment. Constructed 1903.
The plans to complete the standard-gauging of the line from Los Gatos to Santa Cruz got interrupted on April 18, 1906 as the Great San Francisco Earthquake hit the region. Landslides buried the track on both sides of the mountain, and the summit tunnel at Wrights was cut in the middle.

After the earthquake, the Southern Pacific spent three frantic years rebuilding the Santa Cruz branch. In Wrights, the railroad cleared and widened the summit tunnel, moved the station across the creek, and standard gauged the line. They didn’t replace the bridge, though, leaving the 1903 improved crossing in place.

And then we come to the project described by the intern. In 1915, the SP finally got around to improving both the 5th and 6th crossings of Los Gatos Creek. It wasn’t quite a new bridge; the intern noted that the new bridge was “Second Hand 50 ft Deck Plate Girder from the Santa Clara River (Montalvo Bridge). (Our 1915-vintage Sixth Crossing bridge was very lucky to get replaced and yanked out of Southern California. The bridge that superseded it was washed out to sea when the St. Francis Dam burst in 1928. Cue obligatory music.) The old wooden piers disappeared, replaced by a pair of concrete piers placed on the existing concrete foundations. Even if the bridge wasn’t local, the concrete was; gravel for the new piers came from Campbell, and the cement came from Davenport.

Road crossing under the bridge

The SP spent $6,556.98 on that new bridge: $3500 in labor and the rest on material, spreading the work over fourteen months from November 1914 to February 1916. The intern even broke down the costs - $1500 for the piers, $600 for the pilings for the trestle approaches, $700 to install the new steel bridge, $700 for the trestle approaches themselves, and $200 for ties and guardrails for the bridge. They also accounted for the corporate expenses - $500 for falsework, $300 for use of the work train, $600 for rental of equipment, and $180 to haul the materials up to Wrights.

Now, I just needed to figure out how to build that bridge to match the intern's drawings.

Coming up next time, I'll talk a bit about how I built the scene, and how many of the key parts of the scene were actually 3d printed.

Excerpts from blueprints were taken from "Sixth crossing of Los Gatos Creek Near Wrights", a booklet created by the Southern Pacific Coast Division engineering department to describe the project. Original in the California State Railroad Museum library, Sacramento.