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I’ve been quiet on this front of late, but not idle. When we last left off, I had nearly finished gluing the cross-sections into place. Once finished, my concern about the main profile board proved well-founded, with the board making a gentle but noticeable arc from front to back. This meant the centerline of the entire helmet would be incorrect once finished. However, I noticed that I could manhandle it into correct alignment. I hatched a scheme to create a platform for the helmet into which I would drill regular holes for dowels that would enforce the spacing between each profile. After doing just the center two and two toward the rear (around cross-section 8), I realized that the dowels just weren’t rigid enough for the idea to work. They bent too easily, meaning the heavy mass of cardboard was better at shifting their alignment than they were at keeping it aligned. I ultimately went with a simpler approach and tried to fix each of the cross-sections in place by anchoring them to other cross-sections with masking tape. It mostly worked.
Next came the insulation foam.
I knew going into the process that the foam would push the cross-section boards around, hence all of the fiddling around with dowels and tape, but I also thought that the pressure of foam expansion on each side of a given cross-section would more-or-less balance out, leaving it roughly where it was supposed to go. After my first pass, I realized this hope wasn’t going to pan out.
Still, given where this distortion occurred–the relatively undetailed middle section, I decided to continue with the front half.
Last night, I started out with a handsaw, cutting away large chunks of foam that had expanded well outside of the cross-section gaps. Once I had gotten closer to the cross-section cardboard, I switched to using a palm sander.
As you can see here, the cardboard warping was far worse than just the middle section. The entire curvature of the helmet is basically ruined, especially considering the goal of using these precision-cut1 cross-sections was to maintain as accurate a shape as possible. However, it also proved to my satisfaction that the method itself works. I just need to use more robust materials and do a bit more work to ensure those materials stay where they’re supposed to go.
So! This particular attempt is a bust, but it’s given me a bunch of excellent data with which to proceed. I’m going to try the same approach again, but using wood rather than cardboard. I’m also going to rearrange the layout of the cross-sections. The density felt too low in the front and back, but too high in the middle, which ultimately meant I did a lot of work for little gain in that mid-section. Instead, I think I’ll rely on thicker pieces of wood for the cross-sections there, and more numerous, but thinner pieces of wood for the face and back. It gives me an excuse to get a jigsaw,2 the lack of which many of my mini-projects involving carpentry have really felt. With wood, I can also drill alignment holes through each cross-section and insert dowels to ensure that everything lines up properly. This may further aid in keeping the correct spacing between each cross-section once the foam goes in.
Rather than feeling disheartened, I’m actually delighted with the results. The plan worked; the idea is sound. The materials didn’t hold up in execution, but that’s easy enough to remedy and with better materials and the experience gained from the first attempt, I am certain that the revised approach will be that much better.