Step 1: Materials
One messenger bag (re-purpose an old bag!).
3/4" Stainless steel machine screws (#10) - 2 $1.50 ea
#10 Stainless steel hex nut and washer- 2 - $0.50 ea
3/16" rope clips - 2 $0.88 ea
Grommet size "0" - 6 $3 dozen
Grommet size "2" - 2 included with grommet tool
Blue Hawk 3/4" Chain Quick Snap - 2 $7.00 ea
One bungee cord (24" length) - $1
One key ring (about 1") - $0.20
1/4" Plywood - 13.5" x 17" (may be smaller for some bags) - $5
Saw (handsaw, jigsaw or bandsaw)
Hand drill and bits
Total cost: $29
Obviously this would be cheaper if you already have some unused bolts or plywood in your garage. You could also save some $ by using a carabiner.
Step 2: Measure Your Bag
2. Grab your plywood and use a straightedge to cut a piece that approximately matches the footprint of the back of your bag. You don't have to be very precise here. Your cuts don't even have to be pretty. This is going to be on the inside of the bag. A semi-famous man once said, "don't make your project into an anal retentive neurotic nightmare". I try to keep this in mind when I am designing my projects.
3. Round the corners and test the fit. This piece just needs to sit inside the bag to keep the back stiff when hanging on your bike rack.
Step 3: Prepare Your Bungee
2. Use a lighter to melt the ends so that they don't fray. Be smart about fire. This worked really well for my bungee which I think has some sort of nylon housing. If you have a cotton-housed bungee, don't try to melt the end!
3. Measure the diameter of the bungee and make sure you pick a grommet that fits over it.
4. Tie a knot in one end and make it tight.
Step 4: Drill Holes in Your Wood Like So.
2. Drill two holes for your bungee to pass through (mine were 1/2"). Check that your bungee can fit through these holes. The holes will be located about halfway down the length of your board.
3. Drill holes near the bottom two corners for your machine screws. Make sure the screws easily pass through your drilled holes.
Step 5: Trace Little Holes and Cut
2. Make small cuts in the fabric at these spots. This is where you will place your grommets. Cut the holes just big enough to slide in the grommets.
3. Insert your grommets and set them in place using your grommet tool. There are many grommet variations. The easiest for this project is the hammer-in type of grommet.
Step 6: Assemble Your New Pannier!
2. Insert screws and rope clips with "Chain Quick Snaps" in place. Tighten on the inside of the bag.
3. You are done! Now snap it on and go get some groceries! (and look cool doing it!)