Apr10 Written by:Tom Farin
4/10/2008 7:09 PM
It's been quite a week. First of all, I took delivery on a Howe Truss bredge kit from Pond Smith Junction on Wednesday. I assembled it that night. What a great kit. You'll find my review and construction step by step in the Track, Trestle and Roadbed Forum at:
http://www.mylargescale.com/forum/topic.asp?TOPIC_ID=48302
Here's a photo of the completed bridge.
Most of this holiday weekend has been devoted to developing the trackage for San Anselmo. I'll post a setp by step a little latger today. But the concrete roadbed for most of San Anselmo is complete.
The following is a log of the construction step by step for this bridge. It was posted between August 29 and 30 2007
My NPC garden RR needs two bridges in the community currently under construction, San Anselmo California. My modeling era is the gay 90s. I've been unable to locate any photos of the two bridges from that time. Howe Truss bridges are cool. But I tried scratch building one a few years ago. Lots of precision required. Not a good first bridge scratch build project.
Then I came across a MLS post talking about the building kits being sold by Smith Pond Junction.
http://www.spjrr.com/
In perusing their site I came across the announcement that they had recently released a Howe Truss Bridge kit. The base kit for a 24" bridge is $80. But it is designed so it can be expanded in 12" ($42)or 24" ($76) sections to whatever length you need.
If you've visited my builders log on the NPC you know I have lots of projects going on.
http://www.mylargescale.com/forum/topic.asp?TOPIC_ID=47789
And there's a golden spike celebration looming a month out. I don't have time to scratch build bridges right now. And I need at least one bridge quickly.
So Monday I ordered the base kit. It arrived today (Wednesday) by express mail. Wow, now that's service! Here's what the kit looked like when I took it out of the box.
And here's what I had when I took the package apart.
The wood is all precut to size. I didn't touch a razor saw in assembling the kit. All the holes are predrilled. I didn't need a drill. In fact the only tool I needed to assemble the kit was a nut driver and a hammer. The only materials I used that were not in the kit were some brass brads, some Titebond II glue, and some clear Thompson's water sealer. Oh, did I mention that all the brass rods were precut and prethreaded?
The instructions are printed in type large enough for an old fart to read. And that roll of paper at the top of the photo is a set of full size CAD drawings that when unrolled are nearly 8 feet long.
The wood is gorgeous - precision cut, no burrs. It was so good I decided to skip sanding prior to assembly. I'll touch up edges that show once the bridge is assembled.
On to assembly.
Side Truss Assembly
The first step is to assemble the side trusses. Do you remember erector sets? This is billed as a craftsman kit. But if you could build stuff with erector sets -- this kit is an erector set executed in brass and wood.
Assembling a truss half is easy. Match the parts to their drawings on the CAD drawing. Lay the parts on the full size cad drawing. Then put it together step by step. It's like assembling a dagwood sandwich. First some bread. Then a layer of cheese. Then another layer of bread. Then a layer of meat. Then another layer of bread.
In this step the first horizontal sticks are laid on the CAD. The second layer is the vertical truss elements that lean to the right. The brass rods with washers and nuts on the unseen ends keep everything in alignment.
The third layer is another pair of horizontal sticks. They are a size shorter than the first layer. You'll see why in a second.
The fourth layer is the vertical truss elements that lean to the left.
The fifth layer is the last set of horizontal sticks, even shorter than those in layers one and three. You'll notice these horizontal elements end half way across a brass rod. Put nuts on the other side of the brass rods and you have half of a vertical truss.
Now repeat the previous steps and build a second truss half.
When finished you will have two truss halves that when laid side by side pointing in opposite directions look like this. Note that in flipping the right truss half over, the longest horizontal pieces are on top. In the left truss half they are on the bottom.
Hmmm. That's not how the side trusses are supposed to look! OK, so remove the four rods in the middle that have been holding the parts in alignment. Then slide the two truss halves all the way together. The long pieces on the right side will match up to the short pieces on the left side and vice versa. Study this for a while. While layers 1,3, and 5 are each made up of two pieces butted (tops and bottoms), the fact they are staggered prevents these butted pieces from weakening the structure. While I didn't have the drawings and parts for the expansion kits, when you observe how the left and right truss halves are put together, you can see how an expansion kit could easily be placed in between without weakening the structure.
This is the only part of the Vertical Truss assembly that is fiddley. An extra hand or two would come in handy. But once the two truss halves are fully pushed together and in alignment, you'll reinsert two of the four brass rods. The completed truss will look like this.
Add nuts and washers to the tops of the brass rods and tighten the nuts, making sure the threaded rod ends sticking out both sides of the truss are approximately the same length. Don't tighten too tight. You are working with Western Red Cedar, a beautiful but soft wood.
Before moving on to the second vertical truss, read my next post.
The Second Vertical Truss
The instructions for the bridge have you build the second truss in exactly the same way as the first. If you do, when you put the two truss halves side by side, the will look like this.
If you look closely, you will see these two trusses are identical. In the left truss, the first vertical truss element leaning away from us in the photo is in the second layer from the left in our Truss sandwich. It is also in the second layer from the left in the right truss. If this doesn't bother you, follow the instructions in the manual and skip the rest of this post. The changes I'm suggesting in this post will complicate assembly, which I assume is why the instructions read the way they do.
On the other hand, I felt the right truss element should have been a mirror of the left, rather than identical. In other words, I think it should look like this.
Note that the first vertical truss member (leaning away from us in this photo) is in the fourth channel from the left in the Left truss, while in the second channel from the left in the right truss.
Unfortunately I didn't discover the little nuance two photos ago until both trusses were fully assembled. I stared at the two trusses. I told myself nobody else would notice. But I know every time I look at the bridge I'm going to notice. I figured my alternatives were to take 15 minutes to fix the problem now, or have it nag at me forever.
So how did I fix what was bugging me? No, rotating the truss 180 degrees horozintally doesn't change anything at all. I know, I tried. I could have solved that small problem by rotating the truss 180 degrees vertically, and created a much bigger problem - a bridge where the long side of the truss is on top on one side and on the bottom on the other.
No, what I really needed to do is take one of the two trusses back apart a layer at a time. When I got to the vertical truss members in layers two and four, the layer that leaned right was changed to lean left and vice versa. 15 minutes later the reassembled truss was a mirror rather than an exact copy of the first (second photo).
Of course if you are going to add an extension section, you'll also need to do the mirror thing with one of the two vertical truss extensions.
On to the deck assembly.
Assembling the Deck
I was really worried about this section. I figured I'd need to get out my square to make sure the longitudinal and cross pieces were at a right angle and my ruler to make sure the cross pieces were exactly four inches apart. Duuuuh! I had a full scale CAD drawing.
I laid the longitudinal pieces on the CAD drawing. I put a dab of Titebond II where the drawing showed the cross pieces would cross over. Then I laid the cross pieces on their place on the drawing. Then piles of books on top while the glue set.
It went so fast, I forgot to take pictures of the steps. After the books applied pressure for 1/2 hour, I removed the books and used a hobby knife to scrape off excess glue. When I finished, the deck looked like this.
When I reached the next step in the manual I rebelled. All along I've been pretending I'm one of the Carter Brothers under contract with the NPC to build two Howe Truss bridges in San Anselmo. To this point we've faithfully reproduced the wood used in construction (cedar, not redwood) and the truss rods used to hold the bridge together (brass, not steel). i can deal with these slight differences in materials.
But I'm sure either of Carter Brothers would have thrown a temper tantrum had you asked them to use an air tool to drive brads into the deck to hold the longitudingal and cross pieces together. Air Gun? It's the 1890s for Pete's sake. No way!!!
I actually logged onto the Microfasteners Web site to see if they had either 3/4" or 7/8" long miniature hex head lag screws. No joy. So I went down to my basement where I had tucked away some 3/4" brass brads. And I nailed them in the way the Carters would have, with a hammer !!!!
If someone peeks under my bridge, they aren't going to see air hammer dents.
On to final assembly.
Final Assembly
Here's where parts become a bridge. First I put a washer and nut on one end of the long truss rods and inserted them through the holes in the cross pieces of the deck.
Then I laid my vertical trusses between the truss rods, dropped the top cross pieces over the rods and added washers and nuts. By the way there were extra nuts and washers in the kit. That's real handy for clumsy folks like me handling small parts that when dropped run for cover. In this photo, all the pieces in place but they are not aligned and the truss rods have not been tensioned.
In the final assembly step, parts need to be aligned and the truss rod nuts tightened. I worked on one vertical truss at a time, from one end of the truss to the other. At each truss rod, I first aligned the bottom of the vertical truss. This is a little fiddley but the key is that the small horizontal truss rod should be exactly between the two vertical truss rods. Once the bottom is aligned align the top the same way. Then tighten both nuts and move onto the next pair of vertical truss rods.
If you assembled the deck properly if the first horizontal rod is aligned properly with the pair of verticle rods, all the bottoms should be in alignment. So the key is to bring the top into alignment and tighten the next pair. I finished up one vertical truss and moved to the other and repeated the process.
Be careful about overtightening the truss rod nuts. Keep an eye on the angled vertical elements in your vertical trusses. If they begin to bow, your nuts are too tight. Back off a bit.
When you are finished you will be rewarded with a gorgeous bridge.
Thoughts on the Kit
I had a riot building this kit. The enjoyment alone was worth the $80. But in addition, I have this great bridge. It was very rewarding to begin a project and end a project the same day. Total elapsed time came to around four hours. I still need to add some touch up sanding and give my bridge a Thompson's bath.
The folks at Smith Pond Junction claim a 1 hour build time. If I knew exactly what I was doing, had no false steps, didn't decide to change the build process, and I approached this purely as a production job, I might be able to build one of these in an hour.
As it was, I hadn't worked from a drawing in a while and it took a while to figure out how to proceed. There was one early false step and then there was my decision that the vertical trusses should mirror each other.
But I also took the time to smell the roses along the way. I really did think about the Carter Brothers and the shop they had in Sausalito, and the role they played in the development of the NPC. The fantasy is a big part of the fun.
My criticisms of this kit are piddley. When I ordered the kit I spent some time looking at the photos at the Smith Pond Junction Web site. I never noticed the vertical trusses were identical rather than mirrored. It was only when I looked at MY bridge that I noticed the difference and decided to modify the design.
As for my commentary about air guns and the Carter brothers, well that was just for fun and not a criticism at all. The manual clearly points out that you can drive brads with a hammer if you lack air equipment (or are not inclined to use it). By the way, I do have the equipment to use air to shoot brads when I am so inclined.
This kit has great quality and is delivered by very nice and conscientious people who are obviously very customer service oriented. I highly recommend this kit.
Note for Scratchbuilders and Kitbashers
When I ordered this kit I was considering building a second bridge from scratch. With the kit I have a reusable CAD drawing, and parts to be used as templates in scratch building parts.
After reviewing the quality of materials, I'm going to build my second (identical) bridge from a kit. Yes, I might be able to save $30-$40 building from scratch ... although I'd need to visit a building supply store to get the cedar. And I'm never successful getting out of Home Depot at a cost of less than $100.
But if you read the post in the NPC log, there is a 10' Howe Truss Bridge in the plans that will traverse a corner of my pond. Ideally its design will be closer to the Howe Truss Bridge that once crossed the Russian River at Duncan Mills. That bridge is a potential project for this winter.
I feel I have learned enough from the wonderful design of this kit bridge to successfully scratch build a 10' Howe Truss Bridge based on the Duncan Mills Prototype.
On the other hand, I could take this Smith Pond Junction kit bridge and add four 24" sections and have a 10' bridge (200' at scale) for around $400. Given the tradeoffs between money and time, and the quality of this kit, that's not a bad fallback position.
Additional Thoughts for Scratch Builders and Kit Bashers
As I indicated in my previous post, when I'm ready to build a second copy of this bridge, I'll just order another kit. Even if I was able to save $30-$40 by scratch building, I'd have to cut the lumber, drill all the holes, and cut and thread all the 3/32 brass rod. I have a hard time justifying the additional effort for cost savings I may or may not realize.
But what if I wanted to use this kit as a base to build something a little different? First of all, there are only two lumber sizes in the entire kit, 12"x12" (1/2" x 1/2" at 1:24), and 4"x12" (1/6" x 1/2" at 1:24). So if you want to cut your own lumber and have the right equipment, there are not a lot of setups to change. On the other hand, Smith Pond Junction sells scale lumber in these dimensions. So if you need wood parts to complete your kit bash or scratch build project, you can order from them and skip cutting the dimension lumber. The 1:24 scale isn't a problem for those modeling in 1:20.3, 1:29 or 1:32. Side trusses are sufficiently high to clear any rolling stock or engines you are likely to run. We all run on the same width track. Unless you open your mouth, none of your scale fanatic friends are likely to know this is a 1:24 scale bridge.
The rod is 3/32" brass and is threaded for a 3-48 nut. Add #3 flat washers and that's the entire list of raw materials in this kit. The brass rod is available from a variety of sources and with an appropriate die, a vice, and cutting oil, you can thread your own rod. Nuts and washers can be ordered from a source like
http://www.microfasteners.com
Once you have a kit (Smith Pond Junction doesn't sell plans for this kit separately), you could use individual parts and the CAD drawings to create drilling and cutting templates from 1/2" wide brass bar stock for the eight different lumber parts in the kit.
That opens lots of kit bash opportunities.
Kitbashing a Double Track Howe Truss Bridge
For example, if you want a double track bridge, you can order the kit and however many extensions needed to span your river or gorge. You'll need to replace the cross pieces on the deck and at the top with longer 12x12s. You'll need to drill holes in these pieces for the vertical truss rods. You'll need additional longitudinal 12x12s to build a wider deck. With a copier, a scissors, and tape, you could even modify the CAD drawings so you can glue up your wider deck on top of the CADs. You can cut the 12x12s needed for the longitudinal deck pieces and longer cross pieces from cedar, or order the lumber from Smith Pond Junction.
Scratch Building a Prototype Bridge
What if you want to more closely replicate a prototype like the Howe Truss Bridge that crossed the Russian River at Duncan Mills? The sandwich approach used in the kit to build up the vertical trusses could be modified. The Duncan Mills bridge has two vertical truss components leaning one way with one sandwiched in between leaning the other. I could use the three middle layers of the kit vertical truss sandwich to replicate this feature.
Of course that would weaken the bridge because of the butt joints in the design as there would only be two horizontal components, layers 1 and 5. But the butt joints in the horizontal truss components are there to allow the trusses to be assembled as half trusses and to allow for addition of expansion sections. If I was cutting my own lumber, I'd cut full length horizontal pieces, eliminating the butt joints. Or I could order these full length pieces custom cut from Smith Pond Junction. If I wanted to upgrade strength, I could upgrade the 4"x12" horizontal components to 6"x12".
The Duncan Mills bridge has more vertical truss bars. I could replicate them with addiitonal cross timbers on the deck and at the top and more threaded rod.
The bottom line is if you have lacked the confidence to take on a Howe Truss bridge project, then I recommend you buy the kit. Put one together. If you don't need the bridge for your layout, use it as a display piece or give it to a friend. But keep the drawings and make cutting and drilling templates for the more complicated components out of brass bar stock. Then when you get ready to build your prototype bridge, you'll have a tested design, cutting and drilling templates, a CAD drawing, and experience building a bridge. You'll be ready like I am.
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Wayne Jacobson post.
You may have already seen this, but here are plans for a so-called "cheap and dirty" Howe truss: http://www.girr.org/girr/tips/tips2/howe_truss.html
I built one of these (a photo of it and several others are on the above link). I cut my own threads on the brass rods, which was very time consuming. The SPJ kit sounds like a good value.
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Wayne,
I hadn't seen the George Schreyer instructions you linked to. The first prototype photo on his page is a very similar design to the Duncan Mills NPC bridge, only much shorter. It has the left leaning vertical element sandwiched between two right leaning vertical elements. It also has the boxed off ends that also existed on the Duncan Mills bridge.
Schreyer's construction plans are very similar to the Smith Pond bridge. The Smith pond bridge is 4" (rather than 4.5") on center, has a slightly different deck construction, and slightly different timber dimensions. It is taller providing a bit more clearance. It uses the same sized brass rod and the same size nuts and washers.
It is also interesting to see the variety of bridges that have been adapted from Schreyer's basic design.
Of course all of the bridges on the Schreyer page were scratch built. But all offer potential for being bashed from the Smith Pond kit.
Interesting. Thanks for the follow up post.
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