Deck for the Circular Bridge

The finished bridge deck

With the Station at Poppyfield Flats and the Observation Shelter at Inspiration Point finished the only structure left to tackle was the Circular Bridge, er, well, in this case, the Circular Arc Bridge. Of the three, I consider this one the most challenging to build.

Styrene strips were cut and laid out over the plan

I should say that this bridge is mostly freelanced although it is inspired by the Circular Bridge on the Mt. Lowe railway. Those familiar with real bridge engineering may want to avert your eyes.

When I laid out the track above the valley where the circular bridge resides I was primarily concerned with making sure the curve wasn't too tight and the grade wasn't too steep for the trolley. Getting those things right was done by trial-and-error. I didn't have plans I built to.

The plan came later. I took a piece of tracing paper, laid it over the rails, and then using a soft pencil traced the curve of the rails and marked the span of the ties. I then did a little guesstimating on how wide the bridge's deck should be and finished by penciling in those guesses - which I didn't get right and had to correct later as I'll show further down.

The plan was placed over a scrap of foam board so the deck pieces could be pinned down during construction.

The deck is built up from pieces of 0.080" x 0.188" styrene strip that I had bought late last year for this project. Yeah, four months or so between stock purchase and use :-)

I guess in retrospect there's nothing all that difficult about this project. It's essentially  just cutting the pieces according to the plan, applying glue to them, and then sticking the pieces in place and holding them firm with pins while the joints set up. I spent some pleasant afternoons gluing pieces and listening to episodes of 'Round Midnight.

The thin inside stringer pieces are cut from 0.060" x 0.188" styrene strip.

Here's the finished deck. The styrene glue doesn't stick to the tracing paper, so the deck peels easily away once the pins are removed. Some sanding on both sides was required to smooth out the surfaces. Later I painted the deck with some acrylic flat white paint.

As a first test I laid the deck over the track.

And then I cut out the track's temporary foam board support over the valley and slid in the new deck. The fit was good, but it confirmed my suspicion that the deck needed to be widened a little to give the impression that the ties and rails were actually being supported by the deck's stringers. After some inspection I decided to add another layer of pieces to the inside of the outer stringer and to the outside of the inner stringer. Got that ? :-)

So, literally, back to the drawing board.

The inner and outer stringers are thicker, and a second inner stringer has been added.

Skipping the cutting and gluing part and jumping to the result, up there is the enhanced bridge deck. You can see both the outer and inner stringers are thicker, and a second interior stringer has been added to retain a symmetrical look to the thing.

Here's the deck slipped into place to test the look. To me the ties now look as if they are supported. At this point I've also begun to paint the ties on the bridge track white. This is artistic license on my part. I wanted to eliminate the strong contrast between the ties and the rest of the bridge's structure so the track doesn't visually stick out as much and call too much attention to itself. As well, I wanted the bridge to look like a single, unified structure.

Next I'm going to do some terrain modification in the valley so there's room for the bridge's vertical supports, and to frame the scene a little better.