#44 - Reality Check

Leaf-Inspired Trunk Pt. 6

Previous Parts in This Series: Part 1: Intro, Part 2: Mold Unknowns, Part 3: Mold Attempt #1, Part 4: Mold Attempt #2, Part 5: Theoretical Understanding

(Step 2 isn’t done yet, but I skipped ahead to 3 for now)

There comes a time in every idea’s life when it must go from its cozy life in the imagination, where hopes carry more weight than truths, to the rough realm of reality, where the roads are paved with crushed dreams.

That time had come for my leaf-inspired stiffener. I had theoretically shown that a panel with discrete stiffeners in a veined pattern would be stiffer than a traditional cored panel at the same weight, but how would they compare in real life?

Before I could compare the panels, I had to make them. (Sometimes I wonder if I spoil my readers with too much incisive, visionary thinking.) Both panels used the same two base components: composite and core.

For the composite, I used fiberglass and epoxy rather than linen and casein glue because I wanted to keep everything but the design as standard as possible. For the core, I looked at nomex honeycomb and balsa wood, but ended up choosing a PVC foam. I only have a pocket knife and a knock-off Dremel, so I bought the foam core because it would be easier to shape. By “shape”, I mean ramp / chamfer the core down to create a smooth transition between the cored and uncored areas. Composites don’t really like sharp steps.

I cut the core down to size by scoring and snapping it along the score line. Then, to create the ramp, I scored the foam again to give me a target, cut away material between the scored line and the edge, and finally, I sanded down to the final shape.

I did that a few more times to get a section of a vein pattern.

The core for the other panel was just a rectangle.

I utilized the weight I saved from using less core in the veined panel by adding unidirectional fiberglass on top of the veins. (I forgot to take a picture, but unidirectional just means that all the fibers are aligned along the vein).

Both panels got two plies of fabric below the core and two above. Here’s them after a quick trim.

I checked that they weighed the same and they were close enough.

On to the test. I clamped both panels to a table.

You’ll notice that I drilled a hole in the same spot on each panel and made a loop of fiberglass. To that loop, I hooked a fish scale to measure how much force I was applying to the panel. From the fish scale, was a ratchet strap to a kettle bell. By ratcheting up the tension, I could apply up to 35 lbs. Pretty clever, I thought.

Here’s the panel bending under load.

So what was the result? It appears that the vein concept is the winner. It came out stiffer than the cored panel -- my test showed 50% less deflection. I don’t really care about the exact number since that wasn’t my aim. The test was supposed to be a sanity check to make sure that the leaf-based idea could survive a rub with reality. And it did.

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Drawing exercise #33. If you missed it, here’s why I’m learning to draw.

That’s plate four done.