fin box filler...

Hey, I was wondering if anyone knew if instead of using cab-o-sil or Q-cell as your filler for your fin box hole, that you could use maybe just resin and some choped up fiberglass? or maybe even suncure? I dont know if this would work, or if its even possible? any suggestions of knowledge?

resin + chopped up fiberglass = GOOD Suncure Resin = BAD

Yeah, you want some glass in there, either wrap the box in cloth and drop it in with laminating resin, or lam resin + chopped glass. Grind it smooth on top. Better yet, route the hole in the blank, glue it in the blank with chopped glass and resin, and glass a margin around the top of the box at the glassing step. Assume the glass will be about 1/16" thick, grind it smooth when you’re done.

I doubt suncure would work since there’s no sun down in the hole, so forget suncure for this application. What/whether you use as filler on a fin box install depends partly on how close tolerance your router jig is. If the routed hole is a very close fit, I’d not use any filler (Qcell, chopped fiber, whatever). If the hole is not a close fit than when using straight resin there will be a visible “line” around the box, partly depending on what color the box is, and what color the board is. As kokua noted in a post several weeks back, Qcell does not add strength to resin; chopped fibers add a little. Enough to matter, in either case? Maybe so maybe no, but we’d like to err on the side of caution, so suggest add some chopped fibers. I just scissor cut some scrap 6 ounce, diagonally with respect to the weave, so the fibers may be up to 1/2 inch long. I used to put three layers of glass on the sides and bottoms of all boxes, but this is overkill and unnecessary. Now I use a closer tolerance router jig and straight resin is all that’s needed.

I feel that it is better to “cap” the box with fiberglass cloth AFTER insall. Here is what I do to all fin boxes: 1 route box after hotcoat (normal) 2 set fin with chopped fiberglass+ pigment 3 grind 4 use two layers of 4 or 6 glass overlapping box by 2"…don’t tape in the hole-the resin will not drip into the box…trust me. 5 sand around lap edge and use a cheater to fill 6 finish coat/or hot 7 sand/polish whole board 8 route 1/8" deep with a 1/2" bit going about 1/8th outside the inside of the box slot. Just clamp a straigh edge to one side of the box so that the base of the router rides agaist it 9 cut tab bridge 10 use a de-burring tool to take down the sharp edges This sounds like more work than it is.a I feel that the extra work makes for the best fin set. This is the way I do it and have never had a box pull up fore or aft. Maybe not a production method… Dave This tip came from Sparky in Hawaii from a friend who used to work for him…

My question stems for the original, so i put in a bane box and the resin seem to have seperated from the box in the form of a thing gap along the back quarter of the box. My method was such, no jig, just traced and cut with a router. Then the filler was just sanding resin and q-cell. I lined up the center of the box with the center of the stringer on both sides so its more or less straight. But the resin does not seem to take, the box was sanded with 220. To finish the box was just ground down and sanded tolarable with320. Should i have then put a hotcoat or another sanding coat over the bugger to seal it and sand again. Or is this why you wrap the box with couple of layers of clothe? Thanks

Use laminating resin instead of sanding resin. Sand the sides of the box with 50 grit before pouring resin. Chopped glass or a layer of glass would help, too. A glass cap over the top will help, too. Don’t forget that sanding resin is for outside finish work - other resin layers do not stick to it. http://www.blakestah.com/surf/