Recently some good info has come up on fin boxes. But I still have one last question. Does it do any good to put a glass patch in the area where you will route the slot for the box (under the bottom lamination, not in the routed area)? If so is an oval shape better than a rectangle? In the past I have done both (with patch and with out ) and have not really noticed a big difference in durability. But then again it is not like I have done a lot of them (maybe 20 overall). I am doing a 6’3" double wing pin single fin. I am going to put in a 10.5" fins unlimited box. I am trying to avoid those all too common stress cracks that pop up at the top of the box over time. I know about using mill fiberglass and all that, but what about a patch under the bottom layer of glass? Just curious as to what the more experienced do about this? Is the one of the keys to avoiding these stress cracks, a slow kicking batch of resin to set the box? thanks.
i use milled fibers and lam. resin. why do some people use cabosil?
cabosil is great stuff. I very much prefer cabosil, but I’ve used it at work for years so I know it. try it.
Mike - Someone posted the idea of using a pencil and poking a couple of holes from the front of the routered box slot into the foam on either side of the stringer before inserting the box. Bruce Jones routes a couple of slots on either side of the box and inserts “mini stringers” to bridge that weak area at the front of the box. Greg Liddle (and others) applies an oval shaped patch or two OVER the box after it is inserted - check his website and you’ll see areas around the boxes where the volan reinforcements are visible. Double stringer configurations allowing enough space for a box is another idea. The goal is to reinforce that notoriously weak area right at the front of the box where you’ve essentially removed all but a tiny sliver of the stringer to insert your box. Any impact on the fin is transmitted directly to the front of the box where it eventually cracks, leaks or even breaks the board. A couple patches of cloth inside the box slot will reinforce the installation against side stress. A patch under the main bottom lamination before routing the box slot may add some strength but not where you need it most.
about Bruce Jones’s idea…do you mean just deeper passes in the routed slot. example…say i route the box at 1 1/16". then i route out a few “channels” at 1 3/16." would these channels be the bridges??
I just looked at Greg Liddle’s site and he talks about putting 2 layers of 6 over the fin boxes. Do you think he installs his fin boxes before glassing? Otherwise he’s got a bit of a bump to deal with. How about cutting out the glass from inside the box slot? Any explainations? Mike - Someone posted the idea of using a pencil and poking a couple of > holes from the front of the routered box slot into the foam on either side > of the stringer before inserting the box. Bruce Jones routes a couple of > slots on either side of the box and inserts “mini stringers” to > bridge that weak area at the front of the box. Greg Liddle (and others) > applies an oval shaped patch or two OVER the box after it is inserted - > check his website and you’ll see areas around the boxes where the volan > reinforcements are visible. Double stringer configurations allowing enough > space for a box is another idea. The goal is to reinforce that notoriously > weak area right at the front of the box where you’ve essentially removed > all but a tiny sliver of the stringer to insert your box. Any impact on > the fin is transmitted directly to the front of the box where it > eventually cracks, leaks or even breaks the board. A couple patches of > cloth inside the box slot will reinforce the installation against side > stress. A patch under the main bottom lamination before routing the box > slot may add some strength but not where you need it most.
Bruce Jones’ idea has been pictured in some of the longboard magazines - I checked his website and didn’t see any examples. He routes out a couple of parallel 1/4" channels on either side of (and extending past the ends of) the box and glasses in some wood strips. I believe Greg Liddle inserts the box with glass patches lining the routed slot, then laminates patches over the box. It looks like he tapes off the box slot as close to the edge of the slot as possible - just enough tape to keep resin out of the slot. When trimming the patches, leave as much cloth as you can right up to the edge of the tape. This allows for a couple of layers to cover the seam at the edge of the box. I have an old (3/2/78)Liddle board that was done this way… I know the fin has taken some pretty solid hits and the box is perfect to this day - NO cracks(!) I think if you hot coat the bottom before inserting the box, you can scuff around the box area and after the patches are applied over the box with sanding resin, they can be sanded flush leaving little, if any, bump. The Liddle board I have has a sanded finish and it appears as if that’s how he did it. I know that’s how I do mine.
Mike D. When I am laminating the bottom I use some of the offcut glass to put under the bottom lam.I use 10" boxes so I cut one rectangle about 2" wide and 12" long to go down first then on top of this I put a larger rectangle 4" wide by 15" long then I wet these out and roll out the bottom lam over the top. I have never had any problem with boxes cracking at the front. I don’t put any glass inside the routed hole unless the board is styro and epoxy or it’s an ultra thin performance longboard where the box will go right to the deck glass. I don’t glass over the boxes unless it is requested by the customer. I’ve found that under cover carparks are a fin boxes worst enemy…
I’m not an expert on this so bare with me, but I was thinking that you could peg the box into the stringer. If, before you put the fin box in you drilled a single hole in each end of the box, say just for example an eighth of an inch in diameter, central in the end faces. You could then set the box with a very shallow set mix just to tack it in place, and get the box straight and level. Once set, you could drill through the holes into the stringer end, I guess you wouldn’t need to go too far in. Then you could use some glass fibre rod/sparring, perhaps 1" 1.5" long (like the use on those power kites etc) or even some carbon fibre to peg the box into the stringer, with some resin or even some epoxy glue? to keep it strong and water tight. It would then be a case of finishing of the pour around the box, with which ever mix you like. It would distribute more of any potential loading into the stringer area, rather than the foam. Don’t know whether it works, but I might give it a try next time. Peaman
I have some good ideas now. Thanks.
Recently some good info has come up on fin boxes. But I still have one > last question. Does it do any good to put a glass patch in the area where > you will route the slot for the box (under the bottom lamination, not in > the routed area)? If so is an oval shape better than a rectangle?>>> In the past I have done both (with patch and with out ) and have not > really noticed a big difference in durability. But then again it is not > like I have done a lot of them (maybe 20 overall). I am doing a 6’3" > double wing pin single fin. I am going to put in a 10.5" fins > unlimited box. I am trying to avoid those all too common stress cracks > that pop up at the top of the box over time. I know about using mill > fiberglass and all that, but what about a patch under the bottom layer of > glass? Just curious as to what the more experienced do about this?>>> Is the one of the keys to avoiding these stress cracks, a slow kicking > batch of resin to set the box?>>> thanks. I’m a little late getting into this thread but here goes. I reinforce the box area with a 2 1/2" by 13" piece of 6 oz glass on top of bottom lay up, I also put a piece in the bottom of the routered hole. I find that glass wrapped around the box does not stop the glass cracking in front of the box hole. Bruce Jones idea works really good but you can also order blanks with foam/wood T-band stringer with the foam part the width of a box. Rout the hole and your wood reinforcers are already in place. Aloha, Kokua