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Gluing
the Gusset Plates
To glue the
bottom and top chords to the bottom and top gusset plates, we start by
laying down our pieces of wood on paper towels (instead of newspaper)
in order to keep them clean. We will glue the heavier chords to
the heavier gusset plates and use these pieces for the top of the
bridge. We will glue the lighter chords to the lighter gusset
plates and use these pieces for the bottom of the bridge. If the
wood being used for the chords is slightly warped, it is best to point
the warped sections "up" so that the warped wood acts like little arch
bridges. We use "Gorilla Glue" to glue these pieces together.
Gorilla Glue "foams up" when it comes in contact with water.
This foaming action lets it penetrate every pore of the wood and is
one of the reasons it is so strong. We apply the glue directly
to the gusset plates. Make sure you don't put on to much,
otherwise you will have to scrape off the hardened foam later.
Slightly moisten the chords with a sponge filled with water.
Then press them together and put another layer of paper towels on top
of them, followed by a layer of phone books and weights. This
process is a little easier to understand when you see it "live" and is
shown in more detail in the video.
Removing
the excess glue
Most likely,
glue will have seeped out just where you want to put down the
"Vertical Hips" and "End Posts". Use a saw to cut out this
excess glue. Make sure to keep the saw flat when cutting and do
this job gently, or you will cut too deep.
Assembling the sides
Mark a dot 9
inches from each end of the "Bottom Chord", and use the "T" square to
align the "Vertical Hips" on the "Bottom Chord".
Lay in the
"End Post", and cut off 1/4" of its top tip to make room for a lateral
strut later. (see below)
Apply the Gorilla Glue, water,
paper towels, phone books and weights as before. Notice that the
"Top Chord" is glued "off center". That is because we will use
the pieces we trim off as portal struts.
Creating the Portal Struts
Once the glue has dried, trim
off the pieces of wood that lie outside of the end posts. We
will use the big piece of trim to make "Portal Struts". Cut
both pieces of trim
trim into two 5 1/4" lengths (four struts altogether). Then cut out a 1/4" notch from
each end, so that it fits in at the intersection of the "Vertical Hip"
and "End Post" as shown below.
You may want to weigh the sides
and "Portal Struts" at this point to see if the bridge is still within
the weight limit. If it isn't, then trim off some of the portal
gusset plate.
Gluing the Bridge together
Apply "Carpenter's Wood Glue" to
the points on the "Portal Strut" that come in contact with the sides
of the bridge. You will clamp the "Portal Struts" in place from
two different directions. First, you will put rubber bands
around the outside of the bridge right along the "Vertical Hip".
Second, hold a flat piece of wood against the lateral "Gusset Plates"
using a rubber band and a pencil. Both clamping approaches are
shown below.
Putting in the Last Pieces
To keep the "End Posts" from
buckling, we place a piece of 1/2" x 1/4" wood between them. To
keep the bottom chord from crumpling at the corners, we place small
1/2" x 1/4" pieces there (This makes the corners 1/2" wide). To
keep the corners from bowing outward, we place in a 1/4 " x 1/8" piece
between the corners. Finally, if we have enough weight budget
left we put in cross braces on the lateral gussets. This is
shown below with the individual pieces to the left and the pieces in
place on the right.
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