Adding Detail to the Trusses
It took me two weeks to review my design of the Third Avenue swing bridge span and to create the vector graphics files for the additional details. And cutting the files on their 60W laser wasn’t a top priority of my laser cutting service during Covid-19 times. But when I received the shipment from Trevor Hinze from CapitalCustoms I knew it was worth the wait. He got the redesigned MDF parts for the operators’ house and the turntable perfectly cut. The same for the additional layers for the gusset plates on the trusses and for my first version of the pedestrian walkway.
To get more depth on the trusses, I added several more layers of lazerboard. The outside of each truss got a layer with the gusset plates mounted to the top and bottom chord. The inside of each truss got only a simple cover layer. The outermost trusses also got one final layer of thinner 0.011″ lazerboard. This would emulate the top cover visible on the upper chord of the bridge. I also glued tiny rectangular pieces of lazerboard as gusset plates over the point where web members cross. Finally, I added a 6.5 mm wide band of lazerboard along the curved outlines. With the small overhang of the band, the resulting width would translate to a prototypical 1 meter. Strong enough for my model and almost a bit too wide in reality. But the three segments added together made the massive bridge looking convincing, especially after I had painted them.
Some Thoughts on Rivets
How much riveting would I be required and willing to apply on the bridge was a question I was struggling with from the beginning. The bridge construction is full of rivets, visible on many of the archive photos even at smaller magnification. Adding rivets on water slide decals would be a challenge. Moreover, it wasn’t even clear to me if they were to be visible to the naked eye. If I started adding them on some exposed and well visible parts, I’d have to apply them consistently across the entire swing bridge. The task would be daunting and the result doubtful. In the end I decided against them. The only place where I added a set was on the girders of the turntable.
Bridge Flooring
What about the Third Avenue Bridge’s flooring? Let’s have a look at it sister bridge further southeast, the Willis Avenue Bridge. This one had an open grid steel deck when New York City replaced it in 2010. And as anyone remembers who’s ever run the New York City Marathon over the deck of the old bridge, that open grid was “unfilled” in bridge engineering terms (photo below and at the bottom). According to another source, the “original deck on the river spans was timber block pavement over concrete, supported on steel buckle plates”. I could not locate any source that would provide any details about the Third Avenue Bridge deck. Did it have a similar decking as the Willis Avenue bridge? Did it change after its reconfiguration in the mid-1950s? I must leave this question open.
With that much uncertainty about the prototypical deck, I decided for a simplistic approach. I’d assume that by the early to mid-1950s, an asphalt or concrete deck would have been a likely flooring. I chose 1 mm Styrene sheet over the MDF structured base plate for the decks of the three segments. Since I already laid a pair of tracks in the center of the access ramp and girder bridge for the Third Avenue (TARS) trolley, I also included the southbound track in the middle segment. The northbound TARS trolleys had gone long ago by the mid-1950s so I didn’t bother about a second track. I built the track by soldering code 40 MicroEngineering rail sideways on PCB ties. This gave me a grooved rail in a thin deck layer of no more than 1 mm. The web of the code 40 rail is deep enough and not too wide for N scale flanges. To continue the design of the access ramp, I embedded the track in MonsterModelWorks cobblestone sheets.
Building the Operators’ House
With the trusses and the decks pretty much completed, I was finally able to go ahead with the operators’ house in the center of the bridge. There’s fairly good photographic material at least of the outside of the structure. This allowed me to design the house easily recognizable from the side. High windows, a door and a walkway around the house. The two trusses of the middle segment make it impossible to build it in one entire piece, so I had to design three separate sections. Tabs in between the sections would allow them to interlock so that the three parts would appear as one unit. I designed them robust enough so they could become the backbone of the bridge segments.
The house is built of three layers. I made the core of the same 1/8″ MDF as the truss frames. Next, a layer of lazerboard provides for the windows with its sashes and (0.55 mm wide) mullions and for the door. On top of that layer, I’d glue .0208″ thick and .0416″ wide weathered scale lumber. The windows and the door would get a proper frame and sills or thresholds. For windows glazing I’d use 0.3mm clear Plastruct sheet. I weathered the lumber with a black ink wash and some dry brushing with gray paint. Compared to the prototype, the resulting lumber wall shows a slightly more weathered texture.
Each section of the house connects with its adjoining trusses through small mortise and tenon joints. The three segments and the sections of the operators’ house tightly hold together without glue. The resulting bridge looks almost complete, even though it still lacks a few pieces. To complete the bridge, I will add the walkways around the operators’ house, its roof as well as the pedestrian walkways, and finally the portal struts and bracings.
Below, the author (center) on the Willis Avenue Bridge deck on November 2, 2008 during the New York City Marathon. The mats laid on the open grid somewhat reduced the impact on the sharp edges of the steel grating. Since that bridge was replaced in 2010, runners have enjoyed a much smoother run over the Harlem River.
