Bob Sorenson - myLargescale.com

Scratch Built: Howe Truss Deck Bridges
BY
Bob Sorenson
Las Vegas, Nevada
USA
(Model Making/Topic: Howe Truss Deck Bridge -- Progress and Updates)
Couple of weeks ago I did a series on cutting scale lumber on a band saw.
Cutting Scale Lumber on the Band Saw
To prove the band saw techniques, I built a pair of “Howe” truss deck bridges. The bridges are
an average of examples in “Model Railroad Bridges and Trusses”, Kalmbach Publishing Co,
1992, ISBN 0-89024-128-7 and sources on the Internet.
There are two purposes for the project. First is to build a nice, complex looking bridge using
only a band saw, drill press, a hand drill, commonly available materials and simple construction
techniques. No tricky steps, special tools or materials needed. Secondly, these will end up on a
portable live steam layout I’ve been planning to do for years. Or something out in the garden.
Another “roundtoit” project.

The bridges generally follow real practice. The truss rods are functional and under considerable
tension. Very little glue is used. Lots if nails and #2-56 nut, bolt, washers. To start on the
project, draw a full-scale truss panel section. Draw it out carefully so you can take
measurements from it during construction.
Truss Panel Plan
The panel drawing is in 1:1 dimensions. This bridge project is
scaled 1:20.3. That will make a very stout narrow gauge bridge 69
feet in length. It will look just right for a light bridge in 1:13.7 scale,
spanning 47 feet.
It is helpful to have a table of standardized scale lumber dimensions.
This table rounds dimensional lumber to 1:20.3 scale to the nearest
1/32”. Well within the accuracy of the band saw.

The project proceeds in 4 phases:
1. First is the deck section.
2. Second the truss assemblies.
3. Third the end bents.
4. Lastly, final assembly.
Start first with the deck stringers. The stringers
are 2 sets of 3 timbers 8" x 18" ganged
together. Between the stringer timbers, insert
2” lengths of 1/16” thick plywood or leftover
strip wood as spacers. Use 5 spacers over the
stringer length.
Add some detail to the stringer sets using 18
gauge nails to simulate bolts for mending or
splicing plates. Use a 2” length of angle as a
template to drill pilot holes for the nails.
Glue the stringers and spacers.

Hold the jig in place by hand and drill pilot
holes for the nails. 18 gauge nails are 0.047”
diameter, so use a #57 or #57 drill.
Install the 12 x 18 floor beams to the bottom
of the stringer sets. This is done using short
lengths of 3/16” diameter wooden dowel pin
and glue. The stringers and floor beams go
together with a drop of glue, “tinker toy” style.
Drive in the nails. Makes a nice looking detail.
That’s it for today, next time we will finish the
bridge deck.
Drilling for the dowel pins requires a little
precision. Mark out the hole locations on the
stringers and floor beam. Clamp a length of
straight edge on the drill press table so the drill
center is on the center of the stringer. Align the
drill by eye with your mark. Set the drill press
stop for consistent depth.

Drill the holes along the length of the stringer. Flip it end for end to drill the other side of the
stringer. Re-adjust the straight end to drill the center stringer member. This is a very quick and
consistent method to drill holes along the edge of a board.
Use the same technique to drill the floor
beams. The floor beans need additional holes
to receive the truss hanger rods during final
assembly. Drill them now while the pieces are
easy to handle.
Now install the 8 x 8 ties using 18 gauge nails,
1 inch long. Make an “L” shaped drilling jig
from some scrap material.
Cut lengths of the wooden dowel and slightly
chamfer the ends. Glue them into the floor
beams first. And then assemble with the
stringers. A light tap with a soft mallet and
they go right in.

Mark one tie with the hole locations, use it as a
master to set the drilling jig. Clamp the jig to
the drill press table aligned with the marking
on the tie. Set a tie in the jig and drill.
As before turn the ties end for end and drill.
Since the ties are centered on the stringers, one
jig setting will drill two holes. This is a very
fast drill method. I drilled 6 holes in 100 ties in
less then an hour.
Nail down the ties starting from the center of
the stringers and moving towards the ends.
Apply a little glue to the tie. Center on the
stringer with a ruler; square it with a square;
space it with another tie. Holding by hand, use
a hand drill to drill pilot holes into the
stringers. Use a #57 or #58 drill so the nails go
in just a bit tight. Drive in the nails. Repeat a
bunch of times.
The process of nailing ties looks tedious, but it’s not. After 2 or 3 you get the hang of it and it
goes quickly.
Next is the guardrail or guard cap. It is a 6 x 8
cap nailed on the end of the ties. Drill #60
pilot holes thru the guard cap using the straight
edge fence on the drill press table. Use glue
and tiny 20 gauge nails to spike it down. No
pilot holes are need in the ties.

Go ahead and spike down some rail to the ties.
It is easier to do it now rather after final
assembly. This is code 250 aluminum rail, but
use whatever you have.
With that, the deck assembly phase is done.
Next time we will work on the truss
assemblies.
The braces are assembled to the angle blocks
by a 1/8” diameter wooden dowel pin. Here is
how that works.
To start on the trusses, here’s an assembled
truss with some nomenclature for the parts.
Now that we know the answer, let’s work thru
the steps. First making the angle blocks. A
strip of angle block material is cut from the
edge of a 3/4" board. Tip the band saw table to
45 degrees and clamp on a fence in the same
manner as a regular rip cut.

Run the board thru the saw taking a diagonal
cut. One cut is all. Use the sliding table and
cross cut stop to cut off individual blank angle
blocks.
Next step is to drill the angle blocks for the
1/8” pins in the braces. Tip the drill press table
to 45 degrees and clamp on the drilling jig you
used to drill the ties.
The angle blocks have different hole arrangements. Some have three holes on one side and one
on the other. Some are two and two; some are two and one. Carefully inventory the plan so you
drill them correctly. You don’t want an unused hole or come up short.
Next glue the angle block to the chords.

Now it’s time to drill the braces. Turn the drill
press table to 90 degrees. Clamp on some
straight edges for guides and stops. Drill both
ends of the brace.
Add some cleats on the top side of the bottom
chord and shoes to the bottom.
Get ready to assemble the trusses. Cut short
lengths of 1/8” dowel and glue them in the
braces. The brace ends that go in the angle
blocks are dry. DO NOT try to glue the braces
into the angle blocks. Insert braces into the
angle block on the bottom chord. Insert braces
into the top chord starting at one end and
working to the other. This is real fiddle work,
need about 59 hands for this. Eventually they
go together. Tap down with your hand to seat
all the braces.

Let’s have a look at the progress. Looking
nice. Next time we’ll work on the end bents.
Next get the bent posts and bottom beam cut
and drilled for 3/16” dowels. Measure the
lengths of the bents from the actual project,
not the plan. By now errors have crept in and
the plan is only guidance. That’s about it for
fabrication of the bents. The rest of the bents
go together during final assembly.
Cleats and shoes go on with nails and glue.
The cleats are very important. The outboard
angle block on the bottom chord has no
support other then some glue. It will snap off
when the truss rods are tightened. Makes sure
the cleats are tight against the angle block,
well glued and nailed.
Let’s get on the end bents, final assembly and
wrap this project up. The end bent assemblies
are straightforward. They are made up using
the glue and dowel pin technique as on the
deck assembly. The first thing to do is attach
the top beam to the stringers.

Now it’s time to start final assembly. First cut
the 12 x 12 bottom stunts that go under the
trusses. Drill them for truss rods to match the
floor beams above. The bottom struts need a
short length of 1/8” dowel to secure them to
the trusses.
Those 1/8” dowels holding the bottom struts in place are important. They assist in getting the
bridge together. They also prevent the bottom struts from getting knocked out of place if the
bridge gets bumped by accident.
Now for the truss rods. There are 3 options. First is to use solid rod and run a threading die over
the end. The second is to use “all thread” rod. The third is to use bicycle spokes.
The most realistic option is solid rod. However it requires a die to cut the threads, which is a
specialized tool. Solid rod is somewhat difficult to die unless you have a way to align the die to
the rod. Eye balling it is kind of difficult. For this project I wanted to avoid special tools and
methods.
Bicycle spokes come in various lengths and are threaded on one end. I have not tried them, but
I am sure they work fine.
I went with #2 x 56 “all thread” rod for this project. All thread in this size is available in 6-foot
lengths from McMaster Carr. #2 x 56 is a bit larger then M2. Use M2 or M2.5 if that’s
available.
To assemble, set the trusses on the bottom
struts and place the deck on top. Have an extra
set of hands available. Cut lengths of all
thread. Put a nut and washer on one end. Drop
it down thru the holes and put another nut and
washer at the bottom. Tighten each rod a little
at the time until all the braces pull down tight
on the angle blocks.

Use two washers against each nut. One washer is a regular, the other an extra wide fender
washer. Fender washers distribute pressure better and won’t dent the wood. Regular sized #2 x
56 nuts will work fine, but don’t look right. Use “small pattern” nuts or model hex nuts.
McMaster Carr has small pattern nuts.
Position the bents plumb and square. Place a
clamp across the truss to hold the bents in
place.
Next, install the end bents. Turn the bridge up
side down and drop in the bents.
Drill a 3/16” whole thru the truss shoes into
the bottom bent beam. Glue in a length of
3/16” dowel.

Install 6 x 12 cross bracing on the truss ends.
And finally, install 6 x 12 cross bracing on the
end bents. I forgot to mention drilling all the
holes for cross bracing and stretcher rods
ahead of time. Carefully come up with a
drilling plan so you all that before everything
is assembled.
Install #2 x 56 stretcher rods between the
bottom chords. Use nuts and washers on both
sides of the bottom chords.
Well, that’s it. Ready to install on the pike.
While they look complicated, they are not
difficult to do. Every dimension cut was taken
on the band saw. A drill press and a hand drill
were the only other power tools. There were
no tricky or hidden steps. All hardware and
materials easily available.
Thanks to everyone for their kind word and stopping by for a look.