Aerodynamic bike helmet!

Step 6 Preserve the alignment of the cross sections (drill alignment holes)

In the previous step, I was just holding the pieces together with my hand (although in retrospect a clamp might have been useful). Still holding them tightly, I placed the foam-masonite-foam-masonite stack onto the table and carefully removed the upper layer of foam so that I could maintain the orientation of the smaller masonite piece with respect to the larger, central piece. I then traced the small piece's outline onto the big piece. What we're going for here is a way to preserve the alignment of the pieces so that the overall piece will be symmetrical (in other words, I want the whole helmet to be symmetric about the plane that the two bike wheels are in, if the helmeted rider is facing forward). After tracing the little piece's profile onto the big piece, I drilled two holes in the little piece, lined it up with its outline again and then traced the holes onto the big piece. What's pictured here is all three pieces (two small identical, one big) stacked up; each piece has holes in the right place. There's a *related instructable* about how to drill a hole called "Drill a Hole" where you can read more about the details I left out: Drill A Hole