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| | North Pacific Coast Garden Railroad
Howe Truss Bridges
Prototype Bridges
The 1900 track plan shows two bridges crossing San Anselmo Creek. No
photos have surfaced that indicate the types of bridges used at these crossings.
NPC Garden RR Bridges
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As no physical evidence indicates types of bridges used, I'm going
to use a Howe Truss bridge in both crossings. This will give me an
opportunity to use a commercial kit from
Smith Pond Junction. It will also give me an opportunity to
use the kit parts and plan as templates for an identical second
structure. Should photos surface later, one or both bridges may be
moved elsewhere on the layout as it expands. |
Construction
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The kit
arrived two days after I ordered
by express mail. Wow, now that's service! Here's what the kit looked
like when I took it out of the box.
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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. |
Assembly - Side Trusses
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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.
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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.
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The fourth layer is the vertical
truss elements that lean to the left.
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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.
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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! |
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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.
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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.
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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.
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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
horizontally doesn't change anything at all. I know, I tried. 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). |
Assembly - 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.
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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.
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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!!!
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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 !!! |
Final Assembly
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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. |
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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.
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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 I finished I was 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. 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.
There is a 10' Howe Truss Bridge in the plans that will traverse a corner of my
pond scheduled for the summer of 2008. 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.
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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