Wondering if someone can check me on a FU installation.
~goes on after the hotcoat
~route outline/template (no wider than a 1/8 gap)
~optional: rough box with 36ish grit/wipe with acetone
~set the box with small amount of lam resin while the fin is in the box (taped off at box).
~hold fin straight with tape or modeling clay until cured
~mix lam resin with cabosil, milled fibers, pigment, or combination
~optional: line box with cloth - layer on bottom or a fully line the box
~once set, totally fill box with resin mixture
~grind everything flush
~optional: cap with cloth
Last, do the little tabs on the box, sit on top of the glass (see pic, r04-0566 box)? Also is there a front and back of the box (doesn’t seem like it would, but inside the box, the pin guide angles in a slanted direction making me question)?
ALWAYS wipe down the box with acetone. I also rough sand with 60 grit.
the little tabs that you see are always trimmed flush.
There is no front or back.
Route to a close toloerance for the box, say maybe leaving a 1/16" border, lay a couple of layers of 6oz on the bottom. Line the routed slot with a mix of lam resin and either milled fiberglass, or cabosill. Waht you want to do is have enough of the resin mix in the slot so as to allow for only a little seeping out after you push the box down into the slot. Do this correctly and you will not need to fill in the gaps as they will already be filled with the resin mix.
Some say cap, some say it is a waste of time…you decide.
Spend the time to make a good, close tollerance, jig. Then when you lay a couple layers of glass in the hole, which you should do, the box will fit very snuggly. So when you add your lam resin/milled fibre/cabosil/white pigment mix (I stay clear of the cabosil if my box is tight, less small bubbles and you don’t need the thickness) the fin is pretty much held perfectly upright. Plus you use a lot less resin, so if you kick it too hot your not going to mess things up - as much. So long as your box is tight in the hole, I would skip doing the ‘add a little resin in the bottom and let it dry’ trick.
there are (as always) different ways to do it. I don’t trim the tabs off first, although I suppose you could. But, you can also use the tabs to set the box square in the board without using a fin and tape to ensure it’s perpendicular. Just tape over the slot in the fin box, fill your routed slot with resin/pigment/filler/catalyst (not UV resin, and not too much catalyst, keep the heat down or you’ll warp the box), then push the fin box down till the tabs are square on the glass, and put a weight on it so it doesn’t float. Then grind/sand away. (If you watch the Master Glasser DVD by mr cleanlines, I believe thats how he does it.)
I clean the box with acetone. And use the black ones, they are stronger than the white ones.
One advantage I’ve found to setting the box with resin on the bottom only, then pouring in resin after it is set, is this: You can see the slot you’ve cut in the surfboard and can therefore center the box as you straighten the fin. If you do it the other way, colored resin squeezes out and the finbox can shift a little without you being able to see it. Then when you sand it flush, it may look out of whack: nice finbox with an uneven white border around it. Everyone usually finds a way that works best for them, but I like the former method. Doug
Doug, I like the idea of tacking the box into place first. Tell me, assuming the hole is routed with no more than 1/16-inch clearance, how do you fill around it with a thickened resin mixture?
Another question on the same subject: has anyone ever figured out an optimal ratio of resin to milled fiber for setting fin boxes? Let’s say I’m going to mix 4 ounces of resin, for example. How much milled fiber should I use? Is there any benefit to using cabosil? If so, how much?
Any tips on cutting the hole (pretty precisely) without a router? I have a jigsaw, dremel, drill, and a really big hammer, haha… I was thinking that I could use the dremel with a cutting bit & drywall guide - then gently clamping a straight edge as a guide to follow for cuts?
Or, do I just need to break down for a router and make a template? This board is getting really expensive.
Any tips on cutting the hole (pretty precisely) without a router? I have a jigsaw, dremel, drill, and a really big hammer, haha… I was thinking that I could use the dremel with a cutting bit & drywall guide - then gently clamping a straight edge as a guide to follow for cuts?
Or, do I just need to break down for a router and make a template? This board is getting really expensive.
Heh… much to the confusion of most my friends and roomates: getting into making surfboards is not about trying to save a buck. If you’re doing it for money… I did my first fin box (10.5") with the Dremel and router attachment. It took forever, burned out a router bit, and probably wasn’t good for the Dremel itself… but it can be done. Make a jig, do some math, you can get it ultra close tollerance. To save some life on your Dremel and bit, I’d use a utility blade to try to remove the glass - if you haven’t laminated yet use some tape to stop the resin from soaking in to the foam where the box is placed. The resin soaked foam isn’t a big deal, but the resin soaked stringer is… for the little Dremel. Take small cuts. I just did another single fin and broke down and bought a plunge router… it took more time to make a flimsy little jig. With the jig made, it can be done in under 5 minutes.
Let me put in my 2 cents here about the milled fiber thing… Fiber doesn’t add strength in this application. Think: the box needs to stick to the foam. The box is far stronger than the foam. What are you going to put in there that will increase the strength? Nothing. Therefore, no fiber.
The hole for the box should have the smallest clearance to the box as your tooling, router template and skills can make it. Then just fill with only enough resin to make the bond. If it’s a tight fit, there won’t be resin all over the place.
When I set a box, I do it through the bottom lam. I tape off the bottom lam, and clean off most of the excess resin that gets squeezed out, lest it run all over.
When I set a box in a oversize routed hole, I put an old fin (actually use a 11" monster windsurf fin) in the box and tape the top of the box to keep resin from getting in. Then you have something to eyeball for verticality, and can tape from the tip of the fin to the rail and keep things nice and straight. Wait till the resin is fully cured before removing that fin, 'specially if it’s in there tight.
First box I ever did, the resin went too fast, melted the box and partially collapsed it. Good thing the fin was in there already!
after laming I trace the outline and free rout the hole. I use the “o’fishal” boxes. they are sealed with a raised “cap” that sticks up abuve the level that you sand to. makes it realy easy. any way…right on with tight tolerance holes.
I usualy find that no glass in the hole works best but mix sanding resin with a little cheloidal silica to make my “glue”. it does not colour the resin. sometimes I do add colour but it does obscure the alignment. so far I’v been lucky. sanding the box never hurts however the plastic that these things are made from is chemicaly designed to degrade a bit and bond with poly resin any way. any way…before gluing mask the area to just out side the hole and pour the “glue” in till it fills about 1/2 way then press the box into it untill it “seats”. tape in place if nesessary. after it sets sand the “cap” of the box off along with any exess resin. the tape gives a good guide and comes off easyly when sanded down to. sand down to the level of the glass or just abuve(1/32 or less).
then after the box has been sanded open and the tape is off …mask the opening of the box with a couple of layers of tape, trimming the tape to very close to the opening and hot coat. when the hot coat is still in a “jelly” stage(semi firm) razor around to the tape line and just peel the tape up.
then sand as usual. this leaves the level of the box just below or at the level of the sanded hot coat.
The guys at Fins Unlimited told me that the black boxes are made from a different material than the white ones, which bonds better with the resin. As far as using the little tabs to align the box vertically, I don’t trust them. You can use an old worn out fin or a piece of material (plywood, masonite, whatever, cut to size and stuck in the box). Whatever you use should fit just snugly enough that there’s no slop between it and the fin box, but not so tight that it pushes the walls of the box outward. This allows room for resin shrinkage without the risk of the box pulling away from the cured resin when the fin is removed. This advice is all from the manufacturer, which I used to install my first box about a month ago. Can’t wait to do it again.
Howzit Honolulu, I agree with you about not using fiberglass around the box. What I’ve found works the best is use a mixture of resin, milled fibers and some pigment if you want color. Since using this process I don’t see any stress cracks at the front of the box, which seems to happen to a lot of them. Also I punch a hole in the foam on both sides of the stringer at the front and back of the routed hole with the small end of a wooden chop stick. Aloha, Kokua
