Friday, September 19, 2014

Big Thunder Creek: Part II ~ The Bridges

Click here for part I

Three bridges now span the rocky chasm of Big Thunder Creek. It looks like a clear, sunny morning in Thunder Mesa country but a storm could boil up in the afternoon and send a flash flood cascading through that dry creek bed.  Time will tell...

This past week saw a lot of progress on the layout with the completion of three railroad bridges across Big Thunder Creek. Up on the Calico High Line, a small stone arch crosses the creek where it's narrow at the source, while farther down, a rustic 20' king post truss does the job on the mill spur. Near the front of the layout, a 48' wooden trestle on the main line spans the wide, clear pools below.

Follow along with the photos to see how each of these bridges was constructed and installed.

The Stone Arch

The stone arch bridge is little more than a fancy culvert, carved from a block of 1" thick Balsa Foam. The arch was shaped with some medium sandpaper wrapped around a small plastic bottle and the stones were scribed in with the point of a hard 5B pencil. HO cork roadbed was glued to the top to bring it flush with the track.

Here's the stone arch painted and blended into the surrounding rock-work. The Balsa Foam carvings are painted in shades to match the surrounding scenery using artist's acrylics. An undercoat of Buff Titanium (a very light tan) is brushed on to seal the carving and represent mortar. A stiffer brush is then used to dry-brush Raw Sienna, Burnt Sienna and Burnt Umber on to the faces of the stones. Finally, a very thin wash of Carbon Black was brushed over all to darken and blend everything together.

The King Post Truss

The deck, trusses and abutments for this bridge were assembled separately at the workbench before everything was put together directly beneath the existing rails on the layout. This photo shows the simple foamcore jigs that were used to assemble the deck and trusses.  Kappler 10' suger pine bridge ties were used above 12 scale inch (1/4") diameter dowels to build the deck. All wood was scribed with a razor saw to simulate age and grain before being stained with a mixture of Kiwi black shoe dye thinned with 70% isopropyl alcohol. My method for creating this stain is to simply empty nearly all of the dye out of the Kiwi bottle and then refill it with alcohol, replace the foam applicator top, shake well and it's good to go. 

One of the truss assemblies under construction. A king post truss is about the simplest truss one can make. It was a popular design in the 19th century for crossing spans of about 20' or less (any longer would require something stronger like a queen post truss).  The beams of this truss are a scale 8" in diameter and notched at the joints.

The completed deck installed beneath the rails. A few dabs of thick ACC were applied to the bottoms of the rails and the deck was slid into place. Blocks of foam were used to support the deck from below while spikes were driven into pre-drilled holes. A tiny dab of ACC on each spike guarantees they won't work back out.

Next it was a simple matter to cement the trusses into place and add a little colored chalk weathering. The iron plate supporting the king post came from a set of Grandt Line narrow gauge boxcar details. A few strategically placed nut/bolt/washer castings complete the bridge.

Overhead view of the 20' king post truss. This bridge is about as narrow as a narrow gauge bridge can be. The caboose just visible at right was used to check clearances and my widest rolling stock just squeaks through with only a scale inch or two to spare.

A pair of wooden retaining wall bridge abutments were also built at the workbench, again using Kappler ties, NBWs and 1/4" diameter dowels.

Installing the abutments beneath the bridge was a little harder than I thought it might be. But after a little cutting, fitting, re-sculpting and cussing, both abutments were cemented into place and the scenery blended in around them. 

The 48' Trestle

The Big Thunder Creek trestle started life as a Hermosa Creek Truss kit from Goldline Products and for quite a long time I had intended to build it as designed. In fact, there are many photos of the bridge in various stages of completion in older posts on this site. However, once the real planning for scenes around Big Thunder Creek began it became apparent that the bridge as built would be a little too overpowering. My solution was to remove the trusses and modify the bridge deck into a low slung trestle.

The first step was was to remove the bridge from the layout and then cut down the ties with a razor saw, shortening them from 16' to a more trestle appropriate 10'. The masking tape marked ties not to be cut so they could be used to support fire-barrel vestibules. 

Once again a simple foamcore jig was made to aid construction of the 10' high trestle bents. Scale 12"x12" lumber was used for the posts and beams, and 6"x8" stock for the sway braces. The wood was distressed with a razor saw and stained with Minwax Dark Walnut pens prior to assembly.

Since this trestle sits in water, stone footings were carved from Balsa Foam. Here a hard 5H pencil is used to carve the mortar lines between stones.

The carved Balsa Foam footings and abutments were first painted with a sealing coat of Buff Titanium acrylic paint. Here a stone retaining wall is also being painted.

Once the base coat was dry, Raw Sienna was dry-brushed on to the faces of the stones.

Individual stones were then picked out with earthy, contrasting colors like grey, Burnt Umber and Burnt Sienna.

A completed trestle bent ready for installation. Each bent was detailed with 24 nut/but/washer castings and weathered with colored chalks.

Oops! It turned out that one of the trestle bents would stand right on top of a large boulder already sculpted into the creek bed. A portion of the scenery was cut away so that the bent's stone footing could be blended into the rock work.

Here's a nifty trick I learned for mixing up small batches of plaster or, in this case, Sculptamold. Pour some into a ziplock bag, add a little water, seal, then squish vigorously until well mixed.

When ready, snip off one small corner and squeeze out like a pastry tube. This works great for hard to reach spots where you don't want to mess up existing scenery or details.

Here both bents have been installed and fresh Sculptamold worked in and blended around the left abutment. The deck is not attached at this point, just floating on the bents so that it can be removed for detailing of the creek bed.

The big boulder has been repainted to match and blend with the existing scenery and real rocks and dirt added to the creek bed.

The creek bed stones were collected from real creek beds in Sedona, AZ and near Silverton, CO. The rocks and dirt were cemented in place with matte medium and white glue diluted 1:1 with water. The fire barrels are painted castings from Rusty Rails.

Here's a view from below Big Thunder trestle. From here I'll continue to detail the creek bed, adding more rocks, junk and some plants before pouring the Envirotex resin "water."

More to Come

Looking at our plan shows there's still much to be done before this area of the layout is finished.

That should just about wrap it up for this week. I hope everyone is enjoying this build and that my explanations are clear. As always, any questions or comments are most welcome! If all goes according to plan, the next week or two should see the addition of cascading waterfalls and crystal clear pools to this scene. Thanks for coming along. Adios for now!

Click here for part III

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