Structure - "Uncovered" bridge

One of the MMR: Structures certificate requirements was to build a bridge. It could be any type of bridge: a wooden railroad trestle crossing a gorge, a modern concrete highway overpass for cars, or a wooden foot walkway over a creek. The requirements are loose so that you can build what you want. And what I wanted was something special. Living in the northeast, I considered the trademark wooden covered bridge but while researching different things came across an "Uncovered Bridge." Huh?

It was featured in an article in the August 1993 Model Railroader magazine (portion of scanned page below) by William Rooke and was based on a Boston & Maine Railroad prototype. The deck had lots of interconnected braces and girders which looked interesting. It had vertically planked sides, which were capped with shingles! And it was small enough to be manageable. I was sold.

It was all stripwood except for some steel wire trussrods and the shingles, so I had to order more wood. This time, I went with Kaplan Mill & Lumber Company because the article specified their products in the purchase list. Like my last wood project, I colored in the drawing and laminated it, and that helped me visualize where all the different sizes of lumber went.

As I discussed on an earlier post, the first thing I did was color the wood. The bridge's foundation was to be a weathered, faded dark black, and the sides were to be more aged gray. I used acrylic paint washes (brown, black and gray) to first color the bridge's girders and braces and later stained them several times with alcohol and ink washes.

The bridge has a lot of cross-braces, including two extra long ones. I built up a styrene fixture to hold them perfectly parallel and spaced properly. It is a shame that it is a one-time use thing.

The cross-braces were added, and then the parallel girders on each side of the bridge were glued on.

Two more full size girders, and two thinner girders which support the railroad tie ends were attached next. I gently lifted it out of the fixture.

A truss rod runs through the bridge in the very center, so I drilled it out with a small drill and then ran some 0.025" steel piano wire in the hole. The girders are actually supposed to be notched for it, and for the inner girders I did just that with a small file.

Next, there are a pair of diagonal braces. The girders are supposed to be notched to let the smaller diagonal brace boards through, but that looked clumsy and required a level of precision I didn't have. So, I instead made them from lots of smaller sections of wood. I started by drawing out the location of the braces in red on some graph paper, then set the bridge on top of it.

Then, piece by piece the diagonal braces were added. Care was required to keep them all aligned so it didn't look stupid. But, much will be hidden by the track ties anyway.

The bridge with the finished diagonal braces. Twenty two pieces total. It was these types of architectural details that drew me to modeling this bridge.

The railroad ties are longer on the bridge than regular ties, so I cut them 4 at a time from strip wood. They were then heavily stained.

Some bridges have ties spaced more closely together than on regular track, but the picture in the article didn't show that so I used a styrene tie jig I had previously made for handlaying HO scale track ties. It was sized for 7"x9" scale lumber. The bridge used 8"x10" and the ties in some spots were a tight fit. As a result, I could only use portions of the jig and had to pull the ties in batches. The ends look longer in the strip in the jig, but they were cleaned up to size. 

Then, tiny dots of glue were added to the underside of the ties and they were applied to the bridge and weighed down until the glue set.

I took some Micro Engineering flextrack and laid it on the bridge, and then cut away all the ties that would interfere with the bridge. I left the ties on the ends, which helped hold the gauge on the bridge. Then, the rails were spiked down.

Spiking the rails down wasn't fun. The small Micro Engineering spikes I had on hand were too long and I had to grind them shorter so they wouldn't poke out the bottom of the girders. But they were also still too large and split the ties even with pre-drilling the holes. And, they weren't consistently sized and the heads on some were out of scale. Worse, they had a tendency to break some of the fragile glue joints of the ties. This all combined for a big problem. (Edit: I later learned that ME makes much smaller spikes and I should have used them)

So, I switched to some very small Life Like track spikes. They were also too long but easy to shorten, and their heads whilst round were at least consistently sized. And, they didn't require pre-drilling. I spiked here and there, jumping around to keep up my interest. I used short needlenose pliers to insert and push the spikes into position. There were only 112 total spikes (28 ties x 4 spikes per tie). Thank goodness there weren't any guardrails on the bridge or that would have required more spiking!

I hate oversize spike heads on handlaid track, at least for HO (it isn't noticeable on the larger scales) but here I thought it better to add them rather then leave the rails unsecured. I painted them brown to match the rails and hopefully that will help minimize their bulk.

Then, I painted the rails brown. Finally, the excess plastic ties at the ends of the track were cut away and it was set aside to dry.

After that, some thin wooden stringers were attached to the ends of the ties on top. What their purpose was I could not say, as they don't seem like they could hold a derailed train on the bridge (nor would they need to, with the sides and all) and they are too narrow to walk on as a walkway. But they made the bridge look more presentable. 

The sides of the bridge were framed with 12"x24" lumber, and the tops were pitched at an angle and shingled on the top. The sides were sheathed in 1"x6" lumber... lots of it. To get started, I cut the 12x24 lumber and then framed up each side into a box. For ease I put the top connecting piece below the edge of the angle. Otherwise, if I attached it at an angle part would have needed to be sanded down along the length where it stood proud of the sides. 

For the top surface, I used a very thin piece of wood and glued that on. It was flimsy, though, and I wanted to strengthen it. Though it will be a display model, applying the shingles might cause it to bow otherwise so it needed some rigidity.

My solution was to flip them over and fill the gaps on the inside with round toothpick scraps and wood glue. I flooded it in, knowing it would seep into the gaps and then shrink beneath the surface level.

Once dry, it was nice and strong and would later be hidden by the outer sheathing boards.

I then lightly sprayed them with gray paint and attached them to the bridge. I also stained the wood after this shot was taken with my ink/alcohol stain to give it some color. Naturally, though, most of it is hidden.

I needed lots of 1x6 boards for the sides, and I wanted them more of a grayish color than the black I had used on the bridge framework. Soaking the wood in my paint solution didn't seem to work very quickly (even with my oven drying) or effectively, so instead I decided to brush them with watered down paint. But holding each piece of stripwood to do it would likely take just as long, and drive me nuts. So, I taped them to some surplus laminated pages I had lying around. 

For color variation I painted them in three batches. The top had medium gray paint mixed with black ink and alcohol solution. The middle group had black paint mixed with the black ink solution. The bottom had light gray paint mixed with plain rubbing alcohol. I then went over the top and middle groups lightly with light gray paint and plain alcohol solution. I cut them to size and mixed them up for a variegated appearance.

I quickly noticed that I would need every spare inch of wood, so I removed the tape and colored the portions underneath. I had purchased the four packages required but it looked like I would need more. Then, I used my NWSL chopper to cut them to length. Thankfully, the prototype bridge had boards that didn't perfectly line up at the top or the bottom, so that gave me some flexibility when installing them. 

I didn't shoot for perfect, but I did try to have everything pretty close. The top edges of the boards were hidden by a trim strip anyway so no perfection there was required. Each side contains 85 vertical boards, including two per slot where the diagonal braces come out of the sides. Each board was glued on in three spots underneath, and after each board was laid in place any squeeze-out was removed. There wasn't much. I discovered early on that another horizontal brace was needed to support the middle of the delicate boards.

Where the diagonal braces come out from the sides I added vertical boards on top and below. I added braces behind to support them. They give the bridge a distinct appearance. I liked the variegated appearance of the boards and am glad I weathered them in different colors and patterns. 

Because some of the lumber bent away from the sides while gluing, and a couple of boards aren't perpendicular to the sides, it developed a rustic, "worn" feeling. I didn't try for it, and intentionally didn't break boards or add other signs of age, but it ended up looking like a used bridge.

It was at this point that I realized I was short 1x6 lumber. I had ordered the exact amount the article called for but only had enough to do the sides' outer walls and the end walls. I still had to do the inside walls, so I essentially needed double the lumber required. The author of the article had cut his own scale lumber, so he probably guessed as to quantities needed. And he was wrong. So, another order for scale lumber was placed. This time, I went with Northeastern Scale Lumber which delivered quickly. But, the wood was much more fuzzy than the Kaplan stuff. Including the ends, there are 354 individual boards! 

While waiting for the second batch of lumber to arrive, I started adding Grandt Line #127 nut/bolt/washer castings along the ends of the tie stringers. After they were glued in I painted them a rusty, red color to make them pop and distinguish them from the rusty brown color of the rails and spikes.

The underside also received some Grandt Line #5096 nut/bolt/washer castings. Since the underside of the bridge is visible from certain angles I added them all along the edges. They too were painted a rusty red color.

The base is a piece of 1"x4" lumber that I cut to length, and then used my belt sander to add a bevel to the edges. It was stained and polyurethaned. To build up the trackbed high enough to (sort of) justify a bridge, I used a piece of 2"x4" lumber and some more green florist foam scraps.  

Then, everything was covered in ground goop, real dirt, and ground foam.

Simple "concrete" bridge piers were fabricated from styrene, painted gray, and weathered with chalks. Then, they were glued to the base and scenery was applied around them. Some commercial Mt. Albert Scale Lumber ties that I had on hand were weathered and applied to the roadbed.

The bridge set in place and the rails were spiked on either end. The bridge itself wasn't glued on, and the rails alone hold it in position.

The spike heads were painted brown, and the track was ballasted with Woodland Scenics ballast.

One detail on the plans was a truss rod running up through the extended crossbeam and then along the diagonal side brace. I added this feature with steel piano wire, and a nut/bolt/washer casting. Note how the wood looks very yellow in this picture, and gray in other pictures. 

The shingles for the top of the bridge started out as index cards that I spray painted gray, then added mottled random blotches of three concentrations of India ink and alcohol solution. 

I let them dry, cut them into strips, and notched them with a knife to match the commercial shingles I had used on my church. Even for such a small bridge, it was tedious work. 

They were glued on in rows, and along the top another wooden strip was attached to act as a cap. I didn't strive for perfection but also didn't want it to look like the roof needed to be replaced either. 

And with that, my bridge was finished. I contemplated modeling water underneath the bridge but in the end decided to stick with how it looked. I do wish I had made the base was wider, though, as the sides of the bridge crossbraces stick out farther than the edges of the base.

But I am happy with my "uncovered" bridge. I liked working with wood, and really can appreciate now the amount of effort invested by those who build structures board by board. It took over 4 hours to do just the sides, and though I enjoyed it I don't think I will build a large barn or mill using individual pieces of wood. It is just too time consuming. And making my own shingles was okay on such a small scale, but in the future I am sticking with commercial products. What to build next?