dancam wrote:Would you mind trying one more puncture test for us? Could you take a bathroom scale, zero it to the weight of the screwdriver and sample piece, then stick the screwdriver pointing up in the middle of the scale and push down onto the screwdriver tip with the sample piece. Watch how far the scale moves and you should be able to feel when the screwdriver punctures the sample piece and that will give a better rating. Another person watching to tell you exactly when it punctures may help.
That makes a lot of sense! Would be nice to have a real number. Unfortunately I only have a digital scale that won't read unless the weight is stable.
I did some playing around with denting. Just turned the screwdriver around and used the rounded handle and put my weight on it. I could dent the single layer of PMF fairly easily, but could not detect any obvious dent on the 3 layer sample. The luan would make crackling noises but no visible denting. A layer of fiberglass over the luan nearly eliminated crackling, but not quite. The 3 layers of fiberglass crackled a lot, and I could see cracking in it. But oddly this did not compromise the structure when I tried the penetration test. At least not enough that I was able to get through it.
I now have a bunch of other fiberglass samples. 18oz roving + 10oz cloth, 10oz cloth x2, 10oz cloth x2 with 2mm bulking matt, 17oz biax, 17oz biax + 10oz cloth, 17oz biax x2. I was surprised that I could poke a hole in the first two. Maybe the epoxy is less strong than what I used before, or I need to let it cure longer. All of them crackled when subjected to the blunt end of the screw driver, though the one with 2mm bulking matt did the least. I didn't know what to expect from the bulking matt. It makes the fiberglass layer much thicker but it takes a lot of resin (~.2 lb/sq ft), so I don't know if it would make sense for this "lightweight" application.