The current prototype trestle was built in 1932 when an adjacent tunnel collapsed and the entrance slid 30 feet down the side of the mountain. The need to keep trains running required a quick solution until the tunnel was rebuilt. The answer was this large wood trestle. It worked so well that the tunnel was never rebuilt. The trestle is still standing, and will be used again once the collapsed tunnels on other parts of the line are repaired.
Here are some of my photos of the actual trestle:
I will eventually have photos and drawings of the trestle model. It is four feet long (scale 633 ft) and 14 inches high (scale 185 ft), and took me a year and a half to construct (We needed the kitchen table back). There are 417 actual feet - 66,785 linear feet of scale lumber (not board feet) in the model. I spent over 380 hours on it, and had to invent methods of construction on the fly (I built it upside down!) Before I put the scale 2x4 handrails on it the trestle supported two bricks and an anvil.
Mounted on over 135 individual cast footings, this all scratch built N scale structure was incorporated into the Pacific Desert Lines Exhibit of the San Diego Society of N Scale at the San Diego Model Railroad Museum in Balboa Park in time to be running for Christmas of 1991.
The trestle bents were started by former SDSoNS member Nick Neff, but he badly hurt his back and couldn't continue, so he sent the club what he had started. I volunteered to complete the trestle, not realizing that it would dominate my life and various parts of my house for almost two years. Many of my friends had tried to find the trestle out in the desert and never quite got there. A mystique grew around these attempts that must have infected me. I also remember seeing the trestle model built in HO size in the Balboa Park House of Charm, up on the wall in its glass case. This model now has a home in the San Diego Model Railroad Club exhibit.
Mr. Neff was working from sketchy information, mostly small SD & A drawings and SP standards, and created fairly generic bents. I had more complete information from photos in Robert Hanfts' book San Diego and Arizona, the Impossible Railroad, and drawings of repairs made at the bottom of the trestle where storm damage had washed out some of the footings. I removed and reworked the cross bracing from the lower 2/3 of the bents and added more bracing to match the actual trestle. After all bents were completed, I worked from photos to trim the bottoms to match the existing terrain, which is very irregular.
The diagonal cross bracing for this particular trestle is different than other wooden trestles I have seen. The major diagonals were long single timbers that ran from top to bottom. To be able to insert these into the structure, I decided to assemble the bents and diagonals first, upside down.
I used my Macintosh computer and a CAD program to create a top view of the deck, which follows the prototype with a straight section, a spiral curve section, and a constant 14 degree curved section (30" radius in N scale). The bents occur at two intervals, 15 feet apart at the ends and 20 feet apart in the middle. The bent locations and the tie locations and lengths were added to the view and then printed in reverse, making an underside view of the deck. I taped this to a work table and ran a strip of double sided tape down the centerline of the deck. This gave me a way to keep the bents in place while I added the diagonals.
All of the wood used is scale lumber, stained with a diluted india ink mixture. I worked from one end to the other, adding the diagonals and keeping everything plumb with architects triangles as I went. Old dead batteries of all sizes were used as weights to keep the completed sections in place. The diagonals were held in place by first lashing them on with string loops and then gluing them in place. A test section I had made with water based wood glue melted as I was spraying on some weathering, so I decided to use Cyanoacrylate (CA) to glue the joints. As the joints dried, much of the CA went into the wood, making very clean connections.
When all the bents and diagonals were in place, I removed this assembly and started on the deck itself. The double sided tape held all of the ties in place, and I added the horizontal bracing under the deck, using Epoxy for added strength. I then flipped the deck over and added the rails and guard rails. The SDSoNS uses PC ties to solder the code 40 rail in place, so I used the same method, but doubled the number of PC ties. This way I could solder the guard rails to alternating ties and not de-solder the running rails. Wires were added to each rail section for track power, and hidden between the deck braces. Finally, the deck and bents were glued together with Epoxy.
The next part of construction was the hardest. I made a scale footing out of styrene to match the concrete footings of the original. From this master I made a rubber mold and cast the 135 footings needed from Hydro cal plaster. When these were ready, I had to get them into position on the bottom of the bents, but they needed support. I built a 2 foot by 4 foot base out of foam-core, and roughed in the terrain contour under the trestle with styrene blocks. I mounted the trestle, using vertical 1 x 4s for support at the ends. By cutting, wedging, and fiddling, I got the footings under the bents, and glued them in place with 5 minute Epoxy.
From maps and photographs, I roughed in the surrounding contours with plaster, and started adding more detailed texture under the trestle while I still had access. Once on the layout it would be hard to get under and around the bents. The last things I added were the fireboxes, barrel refuges, handrails, and the barrels with sand and shovels.
The area on the layout to receive the trestle was redesigned to match the contours of the Goat Canyon area, with a modelers adjustment. The background was flipped to allow the SDSoNS to add four smaller trestles in the background that are actually East of the Trestle (the 'dots' referred to in the photos above) and still connect to the other areas of the layout. I laid out all of the contours on paper, and even built a scale model (1in = 1ft) of the area to show how it will look when finished. Earlier track work was removed, and new bracing, spine support, roadbed, track, and wiring was added by the club.
Work is now in progress to finish the rest of the scenery and build the other four trestles, following photographs of the site. The finished area will include more site details, what little vegetation there is out there, the fire car that sits on the siding to the right of the trestle, the water tank up the hill, and access steps.
The trestle model is constructed from actual drawings, engineering data, fire plumbing data, bent repair drawings, photos I took and photos by Richard Steinheimer in the book: San Diego and Arizona, the Impossible Railroad, by Robert Hanft.
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Thursday, 08 September 2011
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