Hey Mds, there are several ways to do it. Really just depends on what tools, skills, and expectations you have (other than it fitting snugly into the box). That being said, here's a thread I posted some fin-base casting tips and pics on that might be useful http://www2.swaylocks.com/forums/yet-another-fin-thread . I know there is also another pretty good one by Bert Burger (I think) for FU box bases.
Also, if the fin isn't shaped yet, you should leave as much wood on the base as possible for strength.
A quick way I've found to make really tough/glass-heavy bases and tabs for singles is to laminate a small fiberglass panel of about 20 layers of 6oz glass. Cut two rectangular strips out of it as wide and long as the entire fin base will be. Route out an area on both pieces where your existing fin base can fit into and sandwich it between, laminating the two panels together using the same resin you built them with. Finish shape, drill your holes and you're done.
Oh yeah - you want to do this after you've glassed your fin, but before glossing.
Hi mds. I've done a few timber fins for fin box's. But they have a glass core and are about 3/4" thick. But you could use the same process to make a 10mm thick fin.
I lay up a panel about 6mm thick. Then cut it out to the shape of the desired fin including the part that fits the box.
Next you need to build up the base to fit into the box and at the same time make a flange to land the timber on. So you need to clamp some timber with tape on it so it will release, to the fin so it forms a right angle to the base. The bottom of this flange will need to be close to the top of the finished fin box when finished. So you will need to work out how far up the panel you will need to clamp the timber. When you lay up the base and the flange, the bottom of the flange moves down.
Hope this is making sence so far.
Fit the base to the box. Some tweeking is needed here. When you are happy bond your timber to the fin. Foil the fin. What you should have is a fin with a glass leading and trailing edge and a glass edge around the base where the timber sits on the flange. Seal the whole thing with a couple of layers of glass and finish.
The one thing you need to do is drop the fin straight down into the box. So you need a box long enough to do this. You can not drop the fin in at an angle as the flange will stop you from doing this.
I have some photos somewhere. I'll dig them out and post them. platty.
I had a wood fin years ago that was constructed much the same way as the ones in platty’s pics. Solid glass core made up to the thickness needed to fit the box, and wood panels applied to the outside and glassed over. It came with an Overlin I bought in '74. So, it may have been a Rainbow fin or FU.
These are the only photos I have that show the fin. It was broken and discarded years ago. The light colored line that’s visible is the edge of the wood. The glass had an amber tint that looked pretty good in combination with the plywood that was used.
I lay up about 10 or 15 sheets of cloth on a glass pane. Cut to outline, add wood, foil, build up base, cap wood, hot coat and smooth it all out before glossing.
A couple of things maybe worth mentioning... the wood must be sealed. I've seen wood composite fins with the lower edge leaking. A glass halo around the wood is a good idea. Some wood fins take the tiniest hit and start leaking. The pivot pin and screw tabs should not be through the wood... more places to leak.
One thing I recently found out (the hard way) with thick foils is that Surftech installs their boxes a bit different from normal glass boards. Ever notice how the paint goes right to the edge of the slot? Look closely near the top of the inside of the slot and see the Bondo build up over the box. I've made fins that fit one board but depending on the amount of Bondo, might not fit another. Don't expect it to fit another board.
The latest fin I made would fit a Yater Surftech, a Takayama Surftech, but absolutely would NOT fit a Wingnut ll Model, which is the board it was actually made for. Check the pics at the layer of white stuff above the box on the red board. On the particular Wingnut model in question it is so thick the foil would not clear the top.
The problem with putting the vaneer in the middle of the panel is it will be exposed all the way around the outline of the fin. You will need to seal it in some way after foiling. Also putting the vaneer in the middle you will need to make sure your panel is nice and clear other wise the timber will not show up all that well. platty.
