I needed a real-world 3-inch track extension over a creek to make the spur long enough to hold an engine and a 40-foot car. I decided on a simple wooden trestle bridge as a perfect scratch-building project. I followed a design found in the book "Model Railroad Trestles and Bridges", page 125. After studying the design and making a materials list, I ordered the strip wood needed for the project from Kappler Mill & Lumber Co. It took about two weeks for the parts the arrive. The first step was to start working on the abutment. There are two round poles that hold the 3"x12" scale bulkhead planks in place. These are necessary to hold back the soil. The first step was actually the hardest, because I wanted to make sure the structure was straight and square. I measured the required height of the abutment given the structure's location on my layout. It will be mounted against the edge of one of the modules that makes up my layout. The height comes in at about 14 scale feet. I cut two scale 13" diameter dowels to that length, and then set about cutting the bulkhead boards out of scale 3"x12" strip wood. Each board is one foot longer than the one above it. The design diagram in the book indicates that they should be 2 feet longer than the one above, but that would make the overall structure too wide for my application, so I cut the length difference down to one foot. This first photo shows the first bulkhead plank being glued to the two poles. What made this difficult is the fact that the two poles needed to be square while the first board was being attached. I used all sorts of tools to make sure that this was the case, and then carefully left the parts alone to allow the glue to dry.
Once the glue dried, it was a simple matter of gluing the remaining planks to the poles. I was careful not to use too much glue to avoid having it ooze out between the planks. When they were all attached, I used some metal weights to hold them down while the glue set, as seen in the photo below. I eye-balled the planks' position so that they were centered across the poles.
The next photo shows the front (creek-facing) side of the abutment. The bottom plank will be trimmed to the right height to match the length of the poles.
I decided to build this trestle bridge in-place. That way I could make sure that the track section is level with the track in the other module. Like I said above, the abutment was to be installed against the edge of the module. I glued it to the inside edge of the module using wood glue. The metal weights hold it in place while the glue sets.
The next step was to assemble the stringers (top, vertical boards) and the post caps (bottom, horizontal boards) that form the top of the structure. I cut the parts, and then started to glue the stringers and caps together. Like with the poles and the first bulkhead plank, I needed to make sure that everything was square. The next photo shows the first two stringers being glued to a cap. The cap near the bottom of the photo is just to hold the stringers up. The caps are made out of 12"x16" scale wood, and the stringers are 10"x18" scale.
In the next photo I am installing a small "table" that bridges the gap between the module on the left and the abutment installed on the module on the right. The top of the "table" represents the "ground" level where the track's ties are to go. The "table" will eventually be completely hidden in scenery. In the background you can see the two caps glued to the four stringers.
I am building this trestle bridge extension in reverse order, because I want to make sure that the poles that go under the caps are an exact fit for the installation. I glued the cap/stringer assembly to the abutment using wood glue, and a couple of lightweight plastic clothespins. The level on the stringers was used to make sure that the assembly was at the same horizonal angle as the track on the other module. It wasn't perfectly level, but it is more important that the rails eventually line up.
I wanted to have slightly angled poles under the bridge. I tried making them one at a time but they came out at different angles, and at the incorrect lengths. After pondering the situation, I decided to make a simple jig. Since I only need two bends, I wanted to keep the jig as simple as possible. The jig became nothing but a piece of 1/4-inch plywood with the critical lines drawn on it. The outside poles are at a 12-degree angle, and other inner poles are at a 6-degree angle. The center pole is straight.
I cut five poles a little over the needed lengths, placed them on a jig's lines, and glued a scale 4"x10" board diagonally across them. The next photo shows a metal weight holding the board down while the glue is drying.
When the glue was dry, I glued another board on the other side on the opposite diagonal. This makes for a very sturdy model. I then cut the poles to length. This was quite challenging. I tried different handsaws, but eventually settled on using the Dremel tool with a cut-off disc. By keeping my hand steady and as parallel to the poles as possible, I was able to cut them to length. Some final sanding made the bend assembly fit under the caps already in place. I repeated the same process for the other one (the one in the back), which doesn't need the two 12-degree outside legs. I then glued them under the pole caps.
Next, I added some diagonal sway boards. For the model they are not necessary, but it makes the structure look stronger, easily able to support the weight of a switcher engine! I cut and installed the ties, which are at a closer spacing than normal ties.
I used Minwax "Red Oak" stain to stain the wood of the structure. The ties received my standard Minwax "Special Walnut" stain. Further weathering and integration into the surrounding scenery will be done later.