N Scale Bascule Lift Bridge: Assembly

Part 1: http://www.trainsanddioramas.com/ultimate-scrap-building-bascule-bridge-introduction/

Part 2: http://www.trainsanddioramas.com/scratch-building-a-lift-bridge-in-n-scale-design/

Part 3: http://www.trainsanddioramas.com/bascule-lift-bridge-the-concept-of-scrap-building/

Part 4: http://www.trainsanddioramas.com/scratch-building-a-bascule-lift-bridge-the-rocking-truss/

Part 5: http://www.trainsanddioramas.com/scratchbuilding-a-bascule-lift-bridge-the-tower/

Till Part 5 I’ve covered how I’ve built the 3 main components of the Bascule Lift Bridge – the leaf (or the deck), the tower and the rocking truss. The below photo shows the progress made so far.

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Photo 41: All 3 completed components before painting, detailing and final assembly.

Finishing and Final Assembly

Finishing and assembly consists of the following four steps:

  1. Establishing the links and making the basic operational mechanism, additional detailing (like retaining plates and rivets) and complete painting
  2. Installing Track
  3. Final Assembly and making the concrete counterweight
  4. Finishing and weathering

Establish the links, Operational Mechanism, Detailing and Painting

As illustrated in Photo 42 and 43, the first task is to create the “trunnion”, and link the leaf and tower together. Since I was working with wood in this small scale, I did not take the risk of replicating the true trunnion mechanism for this model; rather, I created a sturdy wooden link attached to the leaf that can withstand repetitive movement over long-term use.

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Photo 42: The “trunnion” for this bridge is a relatively large block of the wood strip cut, aligned and fixed appropriately to the leaf (deck).
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Photo 43: Testing the trunnion and leaf movement. Notice that the leaf is actually joined to the slanted end post of the tower.

There are a couple of things to notice here:

  1. The white retaining plates. These are thin cardboard pieces perfectly cut and aligned with the profile of the truss beam joints.
  2. Notice the green, slightly extruded cylindrical pieces. This is another very important piece in our assembly.  These are small pieces of standard 16-gauge electric wire insulation with the wire removed. What you cannot see is a paper pin that is connecting the end post of the leaf and the small wood pieces, inserted from the other side. I will show in detail how this is done, and how easily you can create moving links with these very simple and easily obtainable components. The way you see it in Photos 42 and 43, the paper pin/wire insulator combo was not used to create pivots, but was used to strengthen the joint.
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Photo 44: Paper pins and small pieces (3 mm/0.12”) of 16 gauge electric wire insulator with the wire removed.
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Photo 45: Final mock-up with all the established links and pivots. The paper pins will tell you exactly where the pivots (trunnions) are in the link system.

In Photo 45, you see the complete assembly along with the established links and pivots. This is a mock-up (you can see the paper pins protruding from the tiny holes). At this time, build the counterweight link as shown in the drawing specifications and glue all retaining plates in place. This is a good time to check everything, one last time. The basic structural elements, weak links, mandatory detailing, and most importantly, the alignment and movement of the bridge must be correct. You must have a moving parallelogram, and the top surface of the leaf and the tower base must align perfectly.

Once you are satisfied with the final assembly mock-up, and have done the fine-tuning as required, it is time to create the basic mechanism to lift the bridge. I decided to go for an under-the-table lever that can be connected to a servo.  To create this lever, there are two steps.  The first step is to create the pivot housing on the underside of the leaf, toward the tower. As you see in Photo 46, I used a 10 mm (0.4”) long, 2.5 mm (0.1”) styrene tube, housed in a casing made of wood and 3 mm (0.12”) thick cardboard (you can use wood as well). It is fixed at the center of the retaining cross support beam at the bottom of the base.  In Photo 47, you see how the lever arm is joined to the leaf. The lever rod is essentially a strong ladder type structure with 11 mm (0.43”) spacing between the two long sides, secured by three separators at equal intervals. Holes are drilled on the top, and a paper pin is inserted through one side of the drilled hole of the lever arm, through the styrene tube and then it comes out through the hole on the other lever arm. It is cut with a wire cutter and then secured with a small wire insulator piece. You can see the whole assembly in some of the later photos as well.

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Photo 46: The pivot housing for the under the table lever arm.
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Photo 47: The under the table lever arm linked to the pivot housing.

The next step is to apply the first coat of paint. In photo 48 you see all of the components as they look upon assembly.

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Photo 48: Bridge components in mock-up assembly (the links are not joined in this photo)

The next step was to add an important detail, the rivets in the retaining plates. Mouli took a thin styrene rod (0.5 mm/0.02” dia) dipped one end in the metallic grey mixture, and simply dabbed the paint in equal intervals around the edges of the retaining plates.  As you can see in Photo 49, there is an instant and dramatic change in the overall appearance of the bridge and it looks much more realistic and prototypical with the rivets.

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Photo 49: Rivets on the retaining plates.

It’s time to install tracks and finally have some trains running! But that’s for the next post. Please feel free to subscribe through email so that the future posts get delivered to you directly in your inbox – pretty convenient isn’t it?

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