I have started to build a model of the Montezuma Bridge that was on the North East Dundas, narrow gauge line in South West Tasmania. I am modelling in On30 (1/48 scale). First a picture of the bridge.
Plans of the bridge are from The Light Railway Society. The plans give all the dimensions as well as timber sizes. I am cutting my own timber to scale for the whole bridge. The timber I am using is Huon Pine, a fine grain Tasmanian timber. The Huon pine will be weathered with Isopropyl Alcohol and soft artist chalks. Huon pine does not take an ink very well due to its oils.
I drew a contour Map of the bridge area from the plans and photos. The contour interval indicate the difference in land hight in relation to the bridge structure. The numbers relate to the bridge trestle (leg) numbers on the plan, 4, 5 & 6 being the the tallest centre section of the bridge.
The structure for the module is on an Aluminium frame that is braced with plywood (4mm) and built up with expanded foam. The below photo shows 12mm marine ply used to give strength to the overhang, and the plate to join to other modules.
The build continues and is very strong, it also has a Plywood and Foam spine underneath to add to the strength. All the contour layers are in place, but need more foam to give the land profile. The lower level (just below the green foam) is where the three middle trestle legs are supported, 51 feet below the track (326mm in O scale).
The glue used for the expanded foam, Plywood and the Aluminium frame is a Polyurethane. This has proved to be a great choice, only wear gloves and have good ventilation. It foams up as it sets so clamping or weights are required, 2 to 4 hours to dry. I am a fan of Titebond wood glues (Right) and used Titebond Polyurethane (Centre) and then a Polyurethane glue (Left) that was easier to get locally.
The build continues, more on the landform and timber for the bridge next.