More distinguished visitors

Real ones this time! We had the honor and pleasure of hosting two visitors recently, Dr. Gerard Fitzgerald and Dr. Gabriella Petrick. Both are both history professors. Gerard is teaching a course this year on the history of technology at UVa. He is actually going to make his students read Herman Haupt's book on military bridging. Gabriella specializes in the history of food at NYU.

Here Gabriella and I are discussing the optimum height for a valance. We concluded that there is no such thing because people come in different heights.

Gerard remarked that his students at the first class were dismayed to learn that the history they were going to learn will start before the invention of the internet. To put things in perspective, the students in college today have no memory of Ronald Reagan and Mikhail Gorbachev as political leaders. Steam power? Industrial revolution? That's ancient history, buddy where's the nearest WiFi? Since I had several reject sections of the lattice truss left over from the bridge project, I gave them to Gerard to use in his class. I also donated the prototype HO model of Crozet tunnel to the cause. Hopefully it will help his students better understand the evolution of technology.

Gerard is a HO modeler building a layout of a freelanced branch of the C&O near Richmond. He is associate editor of the Seaboard-Coast Line Modeler at http://s-clmodeler.aclsal.org/index.htm He has written for the LDSIG Journal and lectured at numerous NMRA shows. They have a home in Delaware, where the layout resides.

The O Scale Figure Dilemma

One of the problems I am encountering in this project relates to the "O" scale civil war era figures. While there is a pretty good selection of 40mm civil war era figures available, such as from the Sash and Saber, and the Honorable Lead and Boiler Suit (HLBS) company, they are intended for wargaming. Thus they are built robustly to take abuse from handling during games. Hence the overscale swords, and other weapons. They also tend to have "war-like" poses, charging, shooting etc. I expect that I will be converting many of them for use on the more sedate operation of running the railroad. For example, I'll probably have to grind off the swords, weapons and adjust the poses. I'll also have to remove the cast on bases and introduce pins so they can be installed on the layout.

I find that I am ordering artillery men, and officers more for use on the layout. Most of the infantry figures have weapons and battle rattle (canteens, packs, mussette bags, cartridges boxes etc.) inappropriate for figures that would be hanging around the RR. However, I do plan to use some of them for at least one scene where a long line of troops are marching off to their camp.

There are a few manufactures that make civilians appropriate for this era and I have a bunch on order, mostly from the UK. Woodland scenics makes a line of O figures that are good, especially their railroad crew. But, they will need to be converted to 1860's attire. The Sash and Saber figures have separate heads, so swaping heads with the Woodland Scenics figures will be easy. (They are shown at the lower right of the photo). Since I am modeling winter, adding frock coats will not be hard. The Woodland Scenics figures need to be repainted, as their existing paint jobs are too cartoonish.

Another problem I encountered is that what constitutes an O scale figure varies from manufacturer to manufacturer. Compare the figures in the prototype photo of the locomotive Haupt to the model figures. For reference, the locomotive has 60 inch drivers.

The 28mm wargame figures are in general too small, but will work in background scenes, especially the Old Glory figures. Most 28mm figures are notorious for being over-scale to allow the sculptor more room to model detail. However, the over-scale size helps in my application. They are also more affordable, especially the mounted troops.

The Tamiya 1:48th scale figure tends to be a good 25 percent smaller than the Woodland Scenics guys. The Woodland Scenics are about the same size as the Sash and Sabre. I purchased some 1:43 figures from the UK and these are slightly smaller than the Woodland Scenics, which should go the other way if one believe the nominal scale. Dave Emery painted the 1/43rd Stadden figure.

As can be expected, the Tamiya figures are probably closest to scale. This Tamiya figure is a German soldier from their WWII line. They do not currently offer a ACW era figure. Being styrene, it should be easy to modify.

The trick is to mix and match the figures while remaining aware of the size differences. I enjoy figure modeling, so this will just add more play/build value to the layout.

A Distinguished Visitor

Mr. D. Emery, a noted New England RR executive, visited the USMRR A&F today. Here Mr. Emery is discussing installation of a new switch stand with General Haupt. Mr. Emery is a British 1/48th scale figure based on Mr. George Stevenson, the developer of the first practical steam locomotive, the Rocket. He was painted by Dave Emery and given to me as a Christmas present. He used a combination of acrylic and oils. It is well done. Thanks Dave.

In the meantime, work continues on the roadbed. My brother Marco took a crack at it, but was having trouble getting the spline to flow evenly without kinks. I was able to get some nice flowing splines using my 30 inch radius track template. The trick is to let the splines take their natural curve. He was trying to force easements and was having trouble with cracking and kinks.

Note the holes in the wall to allow the track to arc through the closet before returning to main room. The track will be hidden under a hill side as it traverses toward the harbor in the workshop.

The fascia here needs to be replaced as it needs to be higher at the back to allow for a sloped hill. The hill will help hide the view of Falmouth when standing in the aisle near Brooke, hopefully making the layout seem larger.

The plywood table is a remnant of an earlier N Scale layout. The radius of the inside curve is too tight for the O Scale track plan so I will need to pull it out.

The bottom photo shows the roadbed on the north side of Potomac Creek. The bridge is not yet done, so I won't be able to lay the track here until it is.

All Quiet on the Potomac...

Merry Christmas

from the superintendent and crew of the

USMRR Aquia & Fredericksburg Line.

Basic scenery for Potomac Creek

The Potomac Creek bridge is almost done, so it was time to prepare the scenery under the bridge. Once the bridge is installed I won't be able to reach very far behind the bridge.

First I cut the 1x2 temporary bridge piece. Then I cut away some of the rock outcroppings to make room for the bridge abutments. The selective compression is affecting the natrual look of the abutments, but i think it will end up OK.

I installed the rubber rocks mold to the base scenery using hot glue. I cut it into sections to better fit the curved slope. Then I used a mixture of Durhams Water Putty, sifted dirt, acrylic paint and water to make a clay colored scenery base. I applied it with a spatula and paint brush to blend in the rock carvings and stream bed. Next I need to touch up the paint on the backdrop, especially where the creek meets the backdrop. Then the rocks must get final paint and dry brushing, ground cover, stream bed detailing, etc.

Here is the nearly finished bridge place temporarily in position. The stringers and ties will bring the rail height to the proper level. Then I will adjust the abutments underneath. This is reverse on how an actual bridge is built, but should work out here.

More good news for O Scale Civil War Modelers

SMR Trains announced some new models this week. Get your orders in before they are all gone. Got to love that paint job on the McCallum's tender.

This locomotive was named after General McCallum, the general manager of the USMRR.

A confederate version for the Richmond and Danville will also be available.

Potomac Creek Bridge Progress

The holidays have slowed progress on the layout, but I have been able to get some work done on the Potomac Creek Bridge. Here the bridge is resting on the 1x2 lumber temporary roadbed. Once the bridge is ready, that road bed piece will be taken out and the bridge will drop down to take its place. Note the holes cut in the embankments for the abutments.

There are a lot of parts in this thing. It's over 1,000 so far and it's not done. The bridge still needs the upper story supports from arch to upper chord, rail stringers, ties, the lateral Howe Truss along the bottom and NBW's. Then the piers and abutments must be made. Whew, this is becoming the bridge that ate Sheboygan!

New Wooden Truck Design

I spent the weekend working on a new design for wooden rigid beam trucks for my freight cars.

The first wooden truck I developed just didn't look right to me. They were a tad chunky using 1/8th inch wood and the design actually caused the freight cars to ride too high. The photo at the left shows the new design on the left and the old design on the right.

The new design is based on a NY&H RR truck. The wheelbase is the same, but the parts are made using 3/32nd basswood. By omitting the delrin bearings, I was able to make the truck narrower.

It is difficult to model these cars to prototype dimensions because a standard gauge O scale wheel set has gauge that is .062 inches too wide, and has wheel tread and flange height that are bigger than scale. Once you modify one dimesion to accommodate the over scale wheels, the dimensions of the rest of the truck design must be adjusted to maintain clearance. It took seven iterations of design, laser cut, build and test before I settled on the final design.

I also modified the journals. The new design does not use a delrin bearing. The metal axle point rides in an appropriate hole in the journal. With a touch of Wahl Clipper oil, the wheels roll very freely. So just like real railroad trucks, these journals need to be oiled. I made the journals on one side of the truck as separate pieces, so the truck is easier to assemble. Now you first assemble the frame, then install the axles without having to force the axle into the frame.

I did not add working brakes to this car. I am thinking about etching parts for the brakes. Each truck has 32 NBWs!

This new flat car is also sporting the new photo etched link and pin couplers. They are a fold-up design using etched stainless steel. They are quite sturdy and will show shiny metal when the facing surfaces wear.

I also tried making white lettering decals on my laser. They actually worked out. They look great as there is no clear film associated with each letter.

Updated Track Plan

I did some work refining the modified track plan. Here it is. You can find a higher resolution version by clicking here.

The turn back curve will be 30 inch radius. I made a mock up of the curve with cardboard and decided that punching through the wall into the HVAC closet will create the best scene.

I also updated this drawing with the as-built configuration of track and bridges. The big bridge at Potomac Creek is about 50 percent complete.

I like the fact that I can model a town in this design. In this case, the town will be Brooke. In actuality there was just a church and perhaps a store there. But I plan to add a mill, tavern and a couple houses.

I will depict the town as largely abandoned and now occupied by the Union Army. The blacksmith will be a Union operation for repair of wagon, horse shoes, etc.

The first photo illustrates the mill scene. Since it will be toward the rear of the scene, I may try some selective compression on the structure.

I can't remember where this mill was actually located, but I believe it was someplace in eastern Virginia.

The foreground items shown in the plan at Aquia Landing are piles of supplies such as lumber, barrels, artillery pieces and military stuff. I also read that Haupt had prepared several prefabricated truss bridges for use in the planned drive on Richmond. So I will need to have several of those laying about ready for action.

The Aquia Landing area will be considerably reduced. Fortunately, there should be room for a nice harbor scene. Most of the structures on land will end up being flats. The second photo is about what I hope the building flats at Aquia Landing will look like. Note the track buried in the dirt. A high resolution copy of this photo is available from the Library of Congress. I love to study the details in all the various uniforms and dress of the men depicted in the photo.

The current church at Brooke looks like this, but I am not sure it was there during the 1860s.

Big Design Change Coming

Two nights ago my brother Marco was working on extending the roadbed from Potomac Creek to Aquia Landing. We discussed several possibilities for adding the wye to Burnside's Wharf at the south end of Aquia, none of them satisfactory. See here for the original plan.

After he left I began to look at the layout, then I started squinting. Since a wye was not going to work, I dropped the idea. That freed up some possibilities.

I did some measurements, and decided that Aquia Landing would fit on the shelf in my workshop adjacent to the main layout room. I had planned to use this layout footprint in my previous N scale layout. I think it will work here.

The advantages are several: a longer run, room for a long siding at Brooke, the possibilities to model a small town where the harbor would have been, room for more structures and scenery.

The main disadvantage is that the harbor area won't have as much room for ship models and structures, but the track arrangement would stay about the same.

There would also need to be a non-prototypical tunnel to let the track loop back around the HVAC room to the work shop. I'll make it look like Crozet

Tunnel, since I have the laser artwork for that tunnel done and the actual tunnel predated the ACW.

I still need to work out the details, but it looks promising. Note that for the sections of the layout already completed, there are slight changes from this plan. At some point I will update the complete drawing with the as-built design.

Interesting Backdrop Painting

The conventional wisdom on backdrop painting is to keep it indistinct and neutral. But when a good artist is able to paint a backdrop the effect can be spectacular. The best backdrops I have ever seen in person were Mike Danneman's and Ed Louiseaux's. Ed hired a professional artist to do his, while Mike, a professional artist, did his own. Mike's backdrop and layout lighting is so skillfully done, that a visitor has a hard time discerning where the layout ends and the backdrop starts.

I happened to see recently Troels Kirk's blog that is documenting the construction of his layout. Troels is a Danish professional artist living in Sweden. His backdrop is stunning. Click the link to see more. He models the 1930's along the Maine coast in On30. (Photos by Troels Kirk)








Dare I tried something similar over my harbor scene? This is a Photoshop file I did as a test for a backdrop. The ships are composites from photos I took of contemporary ships with editing to backdate them, such as removing radars and antennas, and some artwork from a book on civil war ships. Brian Kammerer volunteered the artwork for the car ferry after he saw my original, unsatisfactory attempt. The water and distant tree line is from an actual photograph of the Potomac River taken last March.

I need to practice my painting techniques if I hope to capture this scene. I could try a large computer print as before, but I am concerned about how to blend it with the rest of the backdrop. Maybe a combination of cutouts and hand painting will work.

Etched Switch Stands arrive

The test etches arrived for the new switch stands today. We tried two thicknesses of stainless steel, .010 and 0.008 inches.

I had trouble soldering the first 0.010 inch sample using the paste flux I had on hand. But, when I switched to liquid flux the job went a lot easier. Of course being liquid in a bottle and all, I spilled the flux all over the work bench. Drat!

It looks like the design is good. I may make a few tweaks to improve it. But overall I am pleased. The stainless steel is quite strong, but I may switch to phosphor bronze to make soldering easier.

The switch stand kit includes parts to allow use in either a normal two way switch or a three way switch using a different guide plate . These switch stands are very close to scale size. Combined with the bridles, these turnouts will be as close to scale as I can get. Hopefully they will be a product for Alkem Scale Models.

While I was soldering Paul Dolkos and his son Todd stopped by to help out (they were actually escaping ladies' book club night back at Paul's house.) Paul spiked about 12 inches of rail, while Todd supervised my initial feeble attempts at soldering the switch stands. They didn't stick around to see my more successful effort.

Adding Arches to Potomac Creek Bridge

Work continues on the bridge. I finished making the arches and swaybacks. I started adding them to the bridge trusses. Each span gets four. With 3 spans I need twelve arches.

Both trusses are complete. I also prepared the floor beams and made a trip to Pearl Arts and Crafts to pick up some long sticks for the stringers. I could have cut them on the laser, but decided to use some scale lumber. They are supposed to be 5" by 10" by 32 feet. I couldn't find that exact set of dimensions, so I went with 1/8 by 1/4".

The bridge will be about 2 inches lower than in this bottom photo. I have not yet cut away the ground where the abutments will be, so the bridge is riding a bit high.

When I installed the arch cover plates I noticed that the bottom pieces that cover the sway backs are too short. They should extend to the below the bottom chord and abut the adjacent arch. I can cut new ones and install them separately, so it's not a big deal.

Third Time is the Charm! Or was it the fourth time?

After several nights of work building a total of 16 linear feet of truss in tests of different dimensions I have coalesced on a final design in the third version (actually the forth if we count the first short section of truss using 50 percent reduction.) The drawing below shows the actual Potomac Creek bridge compared to the design of the selectively compressed version I am building. 

The actual bridge had 3 arched sections at 120 feet each, with a short length of truss at each end for an overall length of about 400 feet. The overall dimensions of my bridge are 192 feet long in three arched sections of 64 feet. The actual truss is 20 feet tall, the model is 13 feet. As such, the model truss could not be used as a through truss, as there is insufficient clearance.

Another key change in version three is that I used 3 inch treenails as pins, just as in the

prototype, instead of using the commercial dowels I bought. A 3 inch treenail scales out to 0.0625 inches. The model hobby industry does not sell dowels that small. The nominal 1/16th inch dowel actually measures about 0.085 to 0.090 inches. This meant the holes in the braces and chords to accommodate this size were too large, weakening the braces and looking clunky.

Ship modelers have long faced the problem in needing various sized dowels for masts. Actually they have an even bigger challenge as they frequently need to taper their dowels.

They use a draw plate to reduce the diameter of the dowels. I made my own draw plate by drilling a series of ever decreasing sized holes in a used hack saw blade with 1/16th being the smallest. It worked very well. I laser cut strips at 0.070 wide in 1/16th inch thick basswood. These passed easily through my homemade draw plate to make the 0.062 inch dowels I needed for the treenails.

I have one truss of the third design done. It takes several hours to assemble this truss as there are hundreds of parts, though many of them are the same. I'll post photos later.

Just for kicks, we placed some of my HO scale ACW freight cars on the bridge section. They looked really cool. If I was modeling in HO scale, I could have modeled Potomac Creek full size with no compression! Such are the trade-offs in modeling in a larger scale.

Haupt's encounter with Hooker about the rebuilt Potomac Creek bridge

Here is an excerpt from Haupt's autobiography about the rebuilding of the Potomac Creek bridge. He didn't describe the actual process, but I now believe they built it over the existing trestle as I described in an earlier post. Haupt's reply to Hooker gives some insight into his personality. I find it somewhat condescending and possibly disrespectful way to talk to a superior, but he got away with it. Hooker died in 1879 and did not write a memoir, so we have no record of his version of the story.

After leaving General Hooker I determined at once to build a new bridge across the Potomac run. One of the Corps commanders had, very unwisely, as I thought, cut down all the timber in the valley above the bridge, which, in case of a freshet, would be carried against the bridge and sweep away the trestle-work. I therefore gave orders to E. C. Smeed to proceed at once to erect a new military truss-bridge in spans of 120 feet resting on the stone piers, and remove the old bridge.

As soon as the work was commenced I was summoned again by General Hooker, who wished to see me immediately.

I reported at Headquarters, when he said rather excitedly: "I understand you are going to take down that large bridge at Potomac Creek and build another."

"Yes, sir."

"Well! I cannot permit it. I am now loading my wagons, and cannot allow any interruption to the trains."

I rejoined: "I do not propose to interrupt the trains."

"Why, how can you take down that bridge and build another without stopping transportation for some days at least ?"

I said: "General, it is your place to indicate to me what you wish to have done, and mine to carry out your wishes in such manner as will best secure the results desired. If you wish a detailed explanation, I will make it; but I say to you now that the bridge will, before you are ready to move, be replaced by a more safe and substantial structure, and not a single train will be detained for a single hour."

"Well!" replied the General, "if you say so, go ahead; but I don't see how you can do it." His chief of staff, General Butterfield, echoed: "And I don't see how you can do it either."

The new bridge was erected and was in use for some weeks before the forward movement commenced, and no train was delayed during its construction. I cannot find the report of the time required in its erection, but my impression is that it did not exceed three or four days.

Note that Haupt describes the spans at 120 feet. That contradicts other reports that list the bridge at 400 feet total.

Selective Compression of the Potomac Creek Bridge

I spent the weekend getting the dimensions of the Potomac Creek Bridge to my liking. A problem you sometimes encounter in building model railroads structures when you can't build a full sized replica is, how do you scale it down to make it fit and still look like a believable structure. Model railroaders call this process selective compression.

This drawing is from Haupt's book on military bridges. It is a good drawing of the arch-truss bridge similar to Potomac Creek, though there are some differences.

No scale is given for this bridge, but using the track spacing at 4' 8.5" yields a total span of about 160 feet. In O Scale this bridge should be about 40 inches long. This is actually longer than the arch spans at the bridge at Potomac Creek. But it does show the general construction details. It is also a through truss while the Potomac Creek Bridge is a deck truss (i.e. the tracks ride on top of the bridge instead of inside the truss "tube.") It's hard to believe that wood trusses can be so long and still carry the weight of a train.

So how big should I make both the overall bridge and the individual members? As I mentioned in an earlier post the direct scale down by 50 percent resulted in a bridge that was too spindly (though it would work for HO Scale). To resolve this dilemma I built two more versions of the truss.

Using the guidance from Haupt's book, I built a 48 inch long truss using chords and braces at 0.064 by 0.25 inches as this works out to 3 by 12 lumber in scale. That ended up looking like a grade school Popsicile bridge. This shot shows the laser-cut 0.25 inch pieces being assembled on the workbench. The pins help hold it place while the glue dries. I tried making pins from brass rod, homemade brass washers and solder, but that was a lot of extra work that is not needed for strength. I'll just use NBWs on the final model.

I rechecked Haupt's book and sure enough, he says the braces should be 2 by 10 and not 3 by 12 lumber. Thus the braces should be slightly more slender than the chords. I redrew the model bridge and decided that even that was a bit too wide in my reduced to fit span.

So the compromise I ended up with is selectively compressed in a couple different ways. The chords remain at 0.064 by 0.25 inches (3 by 12), but the braces are reduced in width to 0.186 inches which works out to about 3 by 9-by lumber. I also changed the number of stations in the bridge. Instead of 16 as in the prototype, I now have 10. In this case "stations" is used in the civil engineering sense where each vertical brace is a station. This shot shows all three trusses next to each other. The middle one is the one I am going with.

The bottom photo shows the final dimensions in the intended location, though it stills needs to be fitted to the scene.

One of the disconcerting things I noticed in reading the Googlebooks version of Haupt's Military Bridges book is that the plates cited in the text do not match the plates in the appendix. The scanned Googlebook also has some plates missing. For example, Plate 3 is in the paper copy of the book, but not in the Google scan.

Also, I noticed one other perplexing trait of this book. In the text, plates are cited with Roman Numerals, but in the appendix the plates are listed with Hindu-Arabic numbers. I noticed that Official Military Atlas to the Civil War does something similar but opposite. In that period book of maps, the plates are listed with Roman Numerals while the index is hindu-arabic. In any case, I find it weird at best and confusing at worst.

Arched Truss at Potomac Creek

I have reaffirmed my decision to build the arched truss. I got some interesting feedback from several folks about how a spindly trestle might look cool. It's true that most of the USMRR building projects were by necessity expedient. But in the case of the Aquia and Fredericksburg line, the Union Army was encamped for several months. That whole time the highly industrious USMRR construction crew under the command of W.W. Wright and Herman Haupt were hard at work.

If you look at the pictures on this blog you'll see a RR that for the most part is built to a high standard. The first trestle, the “bean pole” one, was built quickly and it captured Lincoln's imagination. But it was gone by the time I am modeling. Over that winter the new trestle was substantially better built using sawn lumber as opposed to local logs. In early spring Haupt replaced that trestle with the truss to avoid washouts that he worried could take out the trestle. It utilized the existing stone piers and abutments.

Also consider that the USMRR Aquia and Fredericksburg line used the existing roadbed of the RF&P. It was built before the war with good drainage, stone abutments and a level right of way. The roadbed did suffer damage when the confederate cavalry churned it up during their retreat, but the USMRR construction crews quickly re-graded it, albeit using compacted soil and not gravel ballast.

So having a sturdy bridge, as opposed to a flimsy bridge, better suits the image of a railroad serving a powerful army with nearly unlimited logistic might behind it.

I did a quick spreadsheet calculation to see what the truss will involve. Each section of arched truss will require about 438 individually cut wood parts and over 600 pieces of hardware including about 256 NBWs. Multiply by three for three sections. That's a lot of pieces. Thank goodness for the laser.

Wood Part			No. per panel	Number of panels	Total per section
Diagonal Braces and Uprights			48	2	96
Top & Bottom Chord			4	2	8
Arch Laminations			3	2	6
Vertical Hanger			10	2	20
Horz sway braces			32	1	32
Lateral Hanger			16	1	16
Sway Braces			32	1	32
Main Stringers			2	1	2
Bridge Deck			64	1	64
Rail Stringer			2	1	2
Bridge Ties			64	1	64
Arch Spacers			16	2	32
Chord spacers			16	4	64
				Total wood parts	438
Metal parts & Hardware
Spikes			256	1	256
Vertical Rods			10	2	20
NBW			128	2	256
0.015 Pins			48	2	96

I built the first panel of truss last night. My approach was to scale down the bridge by 50 percent, both in

overall layout and individual members. This keeps the overall look correct, but I am concerned that the truss members are too small for an O scale bridge. For example, the prototype chord is a lamination of 3x12 beams, 4 on each side of the truss members for a thickness of 24 inches of wood across the chord. That works out to 8 pieces at 0.062" thick and 0.25" inches tall. I used 0.062" by 0.125". The overall proportions are good, but the individual members look too flimsy.

I consulted Haupt’s book (I was able to borrow a copy of the original print run from 1864 – reading 145 year old source material is cool) and determined that even for shorter spans the chords should be 12-by lumber. That means I need to rework the drawings with thicker chords. I also now better understand the means of fabricating the chords, so I should be better able to replicate it.

As to proportions, Haupt says that trusses, be they deck or through, should be 16’ - tall enough to clear a locomotive. This allows the use of standardized parts in either type of design. That works out to a truss depth of 4 inches in O Scale. I think that won’t look right in my application. I need to do some more mock-ups to check it out.

Potomac Creek Bridge Mock-Up

I was in the mood for some CAD time tonight, so I started the drawings for Potomac Creek Bridge. This mock-up is to help me decide which type of bridge to build. I currently think the truss will be the best bet, but the bean pole and corn stalk trestle has a strong historical appeal- any bridge that amazed Abe Lincoln has got to be cool.

What do you think, truss or bean pole trestle? To refresh your memory, the bean pole is similar to the picture in the blog header image.

This mock up is essentially a half scale version of the actual bridge. The dimensions of the truss are 2.5 inches tall and 48 inches long in three arched sections. The parts will be all laser cut with precise drilled holes for the pins, so it will assemble fairly easily. The arch will be cut from 1/8th inch plywood and then laminated together to get the proper thickness and spacing for the vertical members. Not all parts are shown in the mock-up.

The piers will also be laser cut plywood and then faced with plasticard stone.

I had a Eureka moment last night. As I studied the bridge photos and started drawing the bridge parts it occurred to me how they built the truss bridge. I now believe that they built the truss over the existing trestle. The truss uses mostly identical parts that could be lowered in place with a light crane, possibly mounted on a flat car so it could be moved. These would be nailed or bolted together piece-by-piece while the existing bridge hosted traffic. The lower story of the trestle would have supported the chords as they built them out. Essentially the trestle would act as scaffolding for the truss as they erected it. Once the two walls of the truss were completed and able to bear weight, they would have removed the trestle sticks, if any, that were in the way to allow the diagonal sway braces to be installed.

Now, how about this as a scene, showing the bridge in a state of construction? The pencil sketch posted earlier provides a clue on how it would look.