Make your helmet more aerodynamic while revealing your inner artist! This instructable will introduce you to composite manufacturing and get you closer to being Lance Armstrong.
Step 1: Sketch the shape. Dream big!
Drawing inspiration from both the fish and a nearby airfoil, I put a piece of butcher paper underneath the helmet so I could sketch a few ideas and see how they looked. Here's a parts list for this project:
-Fiberglass cloth, epoxy resin, slow cure catalyst (can buy at Home Depot; ask for fiberglass boat supplies)
-Foam sheets you can cut with a hotwire (plus a hotwire cutter; or make your own)
-String, masking tape, hot glue, 5 minute epoxy, string, masonite scraps (see step 2)
-spackle (same kind used for drywall is fine) and spackling/putty knife
-metal bonding compound (should be sandable)
-Sandpaper (80-100 grit), razor blade/scissors for cutting fiberglass cloth
-latex gloves, safety glasses, respirator with organic vapor/HEPA filters
-a BIKE HELMET you're ready to convert into a MASTERPIECE!!!
Step 2: Cut out the desired cross-section.
Scissor out your desired cross-section from the butcher paper and trace it onto a piece of 3/16"-thick masonite. I used a bandsaw to cut the masonite (with safety glasses, of course). Use a file to smooth out the edges of your masonite cutout.
Step 3: Fit the cutout to the back of the helmet.
I prototyped the shape using paper again.
Step 4: Add a sheet of foam on either side of the cutout.
Sandwich the masonite in between two sheets of foam. Using a hotwire, shape the foam so that it matches the contours of the helmet. Gaps of 1-2 cm are ok.
Step 5: Make two more cross-sections.
Dust off your imagination and use it to envision a cross-section that's one foam sheet away from the original one. I chose to cut this piece to match one of the vents in the back of my helmet (see photo) so that I would have an easier time with assembly. After you've decided on the shape, cut out a second identical version to go on the outside of the other sheet (e.g., in the picture we can see the cutout that goes on the right side of the helmet; a copy of this cutout will be attached to the opposite foam face).