Wednesday, March 19, 2014

Bridges for the Ntrak lines - Part 1

On the Hot Springs Junction Ntrak module, the three main Ntrak lines known as Red, Yellow, and Blue have to cross a stream.  I wanted to keep the the riverbed scene as visible as possible so I needed to be careful what types of bridges to use.  I was also concerned that the track would be accessible for cleaning and as the tracks were only about 15 to 20 scale feet above the river there was not much clearance underneath.

What I decided on was to use three single track concrete trestles with a ballasted deck.  I got inspiration from some parts I found in Green Max kit # 47-5.  There was a set of trestle bents with 3 posts that were vertical.

Seeing this I knew I could make something similar but with the outer legs angled outward like they are in some of the prototype  photos I've seen.

In this photo notice I mention the use of 4 penny finishing nails.  Holes are drilled through horizontal beam and the nails provide additional strength to the posts and beam connection.

To have some additional variety, I made another similar set using the same styrene material for the horizontal beam on the top but then used .100 square tube.

Instead of using nails on this one I used brass rod to strengthen the connection between the posts and beam connection.

The bridges themselves are rather simple.  To give them extra strength I built them around a piece of .100 inch acrylic sheet.

The best way to explain the construction of these bridge structures is with a drawing of the end view.  All of the styrene pieces go the full length except for the quarter rounds which are only in the middle.

Each bridge is a slightly different length and were test fitted along with the bents before painting.  This photo shows all three along with their tracks at this stage.

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