Building the front of the Coroplast tailbox.
Now you make the front piece of the tailbox. This is where you’ll start attaching one piece to another. Careful alignment now will pay dividends with the finished product.
Technique 2: Attaching one piece to another with zip ties requires that enough Coroplast remain between the hole that the zip tie goes through and the edge. This distance is about 3/4", enough to keep a taut zip tie from pulling through.
Technique 3: Making smooth curves across the grain can be difficult. When attaching pieces along an arc, work systematically from one edge to the other.
This piece fits between the tire and the rear of the seat. If your bike is like mine, there's very little space to play with here. Careful eyeballing of the various surfaces before all the zip ties are tightened will prevent egregious errors.
Cut a piece of Coroplast 17" x 23" with the flutes or grain running parallel to the short side. Cut a 6" wide x 7" deep notch centered on one of the short sides. This forms "horns" which will be at the top of this piece while the opposite edge will get attached to bottom-front edge of the interior piece.
Stuff this piece between the seat and the first piece of Coroplast. This will take some tweaking, and you'll probably end up creasing piece #2 a bit. Don't worry, it'll smooth out.
With the tapered reamer, poke three holes in each bottom tab of piece #1, spaced about 2" apart and 3/4" from the front edge. Poke corresponding holes in the bottom edge in the bottom edge of piece #2. These holes should be lined up so that outside corners meet each other.
Cut two pieces of PVC pipe 5 1/2" long. These will be the braces for the right-angle joint formed by pieces #1 and #2.
Insert the zip ties from the front, down through the bottom and attach them loosely. Put the pieces of PVC in the corner formed by the Coroplast pieces, inside the loops formed by zip ties. Pull the zip ties tight so the "zip" end is underneath the bottom. It should look something like this: Trim off the excess zip ties.
With duct tape, temporarily bend down this piece so it ends up pointing its "horns" rearward. The next step is to stitch the two pieces together in a "tee" joint. You can do this with the pieces on the bike (which improves accuracy) or off the bike (which eases access). Probably the best method is to do the first two or three zip ties on the bike, take the pieces off the bike, and finish stitching.
Here's how it goes: with the reamer, poke two holes through piece #2 about 2" from the bottom, lined up so there's one on each side of the vertical panel of piece #1. Poke a corresponding hole in the vertical panel about 3/4" from the edge. Thread the zip tie through the vertical panel, forward through the first hole in piece #2, and back through the second hole. Pull this taut so the pieces form a tight "Tee", like this: Repeat for the other side, always threading the zip ties from between the two vertical panels. (I'm not doing that to be difficult- after the zip ties are trimmed off they have pretty sharp ends. Doing it this way keeps the sharp points hidden.) Working from the bottom, continue stitching the two pieces together until you reach the top. There should be a rectangular gap between the top of piece #1 and piece #2. This is where the seat supports go.
Once all of the stitching is done, crease and bend the "horns" of piece #2 up so they are in the same plane as "tab" of piece #1. Cut off the tops of the "horns" or the "tab" so their top edges line up.
The pattern (click to enlarge):
Piece #2, partially done. Note that the front is temporarily attached to the interior by duct tape and that there's a big crease just above the bottom. This smoothes out once the zip ties are installed and tightened (click to enlarge):