I’m wanting to start making fins for Fins Unlimited box. I’ll be using poly and 4oz. cloth (better flex, lighter).
Seen all types of ideas in the archives. Instead messing with the whole fin mold deal and pouring resin with chopped cloth, why not just cut the base and the fin out together as one? Tape off the base, foil the fin, drill the whole, throw it in the box. Seems it would be alot stronger (and quicker).
Am i missing something here?
You need to insert the crossbar also, there is someplace online you can get them, perhaps someone can post up the size/method for inserting them.
You are right there is no need to mold a box for rectangular section glass fins. You need to mold boxes for unusual shape flanges, like Lokbox, or if you need cant in the fin tab, like Futures rail fins.
I guess it would be pretty difficult to line a hole up the right way, without destroying the base. So I’ll put the crossbar between the two layers of cloth…but how do i pop the bar out when it comes time to put the screw in?
Howzit blakestah, You can buy the stainlesss steel pins from Bahne. That's where I got a bunch (50) when I was making fins a few years back. Think they were about 25 cents apiece. As for the positioning of the pins just get the measurement from another fin. The drilling of the screw hole is the tricky part since the fiberglass wants to split, so go slow when drilling the hole.Aloha,Kokua
Use a drill press for drilling fins, no exceptions. Sure, you might get 'er done with a handheld, but you’re just as likely to ruin the fin you spent so much time laying up, cutting, and foiling. If you don’t have a drill press, ask around. School workshops, neighbors, car mechanics, they’re pretty common.
Stainless Steel “roll pins” are available at most ACE hardward stores in the little pull-out bins. 5/32" is a good size to match the slot in a finbox. It should be 5/8" long, so it sticks out 1/8" on each side. My ACE only sells them in 1", but just clamp it in a vice with 3/8" sticking out and you can run your hacksaw blade right along the side of the vice for a straight cut.
Center the hole 1/4" up from the bottom of the fin’s base (which should be 7/8" tall x 3/8" thick) and 5/16" in from the end. Drill the hole at the same 5/32" as the pin, no need for a tight fit. Put a dab of 5 minute epoxy in the hole right before you tap in the pin and it will stay.
For the screw hole in the tab, the danger is in splitting the glass panel as you drill. The bond between layers is much weaker than you think, when you’ve got a drill bit burrowing in. The path of least resistance is not to remove material, but to just crack open and then you’ve basically made yourself a glass on.
I take 2 blocks of hardwood, at least 2" square and exactly 7/8" thick. I clamp the tab tight between the 2 blocks. The blocks being the same thickness as the fin base means that I’ve now got a 4 3/8" wide base sitting in my drill press, not a wobbly fin. This ensures that the hole will be plumb (90*). Even more important, the wood blocks won’t let the glass tab crack open, which means the drill bit actually will remove material like you want it to. I also clamp the whole thing (blocks, fin, and horizontal clamp) down to the drill press base, so the work doesn’t lift up along the bit as it turns. Take your time, do it right.
Edit: I always make fins with the screw tab on the front. Lots of reasons: (1) I can actually drill them out as described above; (2) I can slide the fin all the way to the back of the box, which I seem to want to do way more often than I want to slide it all the way to the front; (3) If you hit a rock, the tab or the screw plate (especially the black plastic ones with an insert) will likely fail and your box / board will be preserved; (4) if you want to, you can tighten up the fit of your fin with some clear fingernail polish and skip the front screw altogether. This makes the fin adjustable out in the water, and definitely protects your box if you’re surfing over shallow rocks and are likely to hit stuff (not recommended in heavy kelp). If you hit something, you don’t lose the fin since the roll pin holds it in the back of the box. I do this all the time…
I dont have an actual drill press, I use head of an old in my plunge router but basically it does the same job.
For the cross bar I’ve cut an old box in half and drilled a pilot hole lined up with the channel.
Ff you can’t get hold of the split pins just cutt up a 2" stainless steel nail.
For the (vertical) hole, for the plate and bolt I use a special bit for putting holes in glass and mirrors. Unlike a normal bit they have a pointed paddle instead of the thread. drill thin piolet hgole first.
Clamp up either side like benny says before drilling.