I’v had no strength issues with FCS plugs, in Western red cedar, which is more dense than either Agave or balsa. I was going to use them again on my latest build when i was steered toward Probox by members here. Thank you.
Probox have all sorts of tips for strengthening their inherently strong fin system, like a glass sock which fits in the routed hole cleanly , and wrapping the box itself twice with woven roving strands. Also, one can, at the bottom of the routed/ drilled hole, undercut the sides at the bottom, so the resin forms a wider base. One can also drill angled holes into the sides, so the resin form ;tentacles’ which branch out and spread the load over a larger portion of the foam/ Wood. Milled glass fibers help the strength of those tentacles.
With Agave being so porous, I would first soak the holes until they absorbed as much warmed thin epoxy as they want, and once thet gets a bit thicker then set the plugs, tape the cant and toe in, then fill in around the sides, perhaps in two stages if your epoxy is fast.
If you try to simply fill the hole aroung the plug, it will turn in into a bubbly mess, and that is if it does not exotherm too badly.
I used a very slow epoxy to set my Proboxes in cedar. 70 minute pot life at 77f IIRC. I also heated the receptacles and hull with a blow drier, and the entire tail with a heating pad set to 106f max when I poured in the very slowly mixed( for no bubbles) unpigemented warmed epoxy.
I was not worried about exotherm, I was worried about the cedar blowing bubbles. With the heated board cooling down, and filling to nearly the top of the resin dam, before walking away, I found post jig removal and sanding flush, that I still had to add some more resin to level it off. But a bubbly mess was avoided and I with a strong light can see to the nase of the probox and the wood down there.
There are a few bubbles despite these precautions, but no where near as bad as previous FCS nstalls where I Simply poured the epoxy in in two stages.
I’d highly recommend heating the board and the epoxy so they are cooling while the epoxy is first poured in to the receptacles.
While The probox has a much bigger footprint, my boards are hollow. The receptacles for the pro boxes, I might have gone a bit overboard with.
Despite layered glassed wood, I still cut a groove around the base of each receptacle to widen the footprint and help prevent pull out on impact. This was done after the photo below was taken.
With fin strength, I tend to want the fin tip, or whatever I hit with the fin, to be the weak link. rather than the fin’s base or the fin box itself, or the board.
