What is the best way to cut a slot in a blank for a standard 10" (or smaller) fin box? Also, how do I fill a poorly placed fin box hole in a blank I am recycling?, ex. turning a twin fin into a single fin.
I just replaced a botched fin job - over catalyzed my FCS plugs and weakened the surrounding foam. I took a Dremel tool and cut a big rectangle (~ 3 x 5 in), peeled back the glass, and routed out the foam with a Dremel router bit and the router attachment. This was a side fin, so I didn’t have to deal with stringer, but I don’t think it would be a problem. I grabbed a spare piece of foam, did some rough measuring and cutting (on the bigger side of course) then sanded and checked, sanded and checked, until it fit in the hole snuggly. Leave the piece too tall, so you have a handle to pull it out with after you get the fit right (so you can put the resin in). I used pure lam resin, no cabosil, and locked it in. The next day I took out my saw and cut it almost flush, then sanded it down a little past the glass – then glass away. It was a good repair experience, and came out very well, you can hardly even notice it, if you sand it snug. Of course, if you have a router, that’s a better tool, but I avidly support Dremel – 101 uses and counting. Cheers,
To set a 10" center fin box: Make a template out of a decent piece of plywood. 1/2" baltic birch works good. Cut the overall size about the same size and shape as the tail of the board you will work on.(approx.16" long and 6" wide at the bottom, 12" wide at the top. Then cut a slot in the center of the template EXACTLY the size and shape you want the hole for the fin box to be. I recommend 1 1/8"x 10 1/8". That size will allow for some resin sqeeze-out and adjustment. It's very important to make the slot exact, with smooth sides, because you will transfer that shape to the board when you cut it. Clamp the template (lightly: just enough to hold it) in place. To cut the slot, use a plunge router with a pattern bit. A pattern bit is a straight cutting bit with a bearing ON TOP of the bit. The bearing is the same diameter as the cutter, and runs inside the template. As you plunge the bit down and run it around the inside of the template it cuts the exact shape of the pattern you've made. The slot should end up a hair over 1" deep. Be careful that the template doesn't slip during the cut, and don't rush it. Some rubber or foam on the bottom of the template will help. Good Luck! Doug Schuch
At 3" from the the tail, I have very little to work with for installing a 10" fin box. Whats the recommended foam depth for installing a fin box. Im worried im going to weaken the board if I don't leave enough foam between the deck and the box. Any suggestion. It seems at 4" I'll have a 1/4 inch to spare. One more question: On the 10" box I have, the box has a 1/4 " vertical lip on the perimeter of the box. Should this be grinded down or should I be submerging the lip as well. I haven't see a fin box lately, but I'd like to make it thinner so I can install it closer to the tail, but grinding may be a a pain....no? I hope that made sence. Thanks, Kevin
I was a little afraid of my thickness, and ground the top of the box off a bit also. It was really simple, sureform did the job fine.
Rick, I have a correction on the size of the cutout for a 10" center finbox. The length should be 10 5/8", or 1/16" bigger than the box all the way around.
jeff. thanks for the input. I think im gonna definately shave it down some. Right now its 1 1/4". I think if I can get it down to an inch I'd be in good shape. K
where should i buy future twin fin boxes and what size do i need for twin fins