So.... whose built fins before?
I'm keen. Thinking of just laying up some glass on a flat surface then cutting, drilling, tapping, shaping manually.
should i make a mould? not sure i can be bothered.
ps i'm going to build thruster style fins for my mutant.
You can buy a wife as well...
I didn't make one yet, I would make a Plaster of paris mold:) Easy to reproduce this way...
Back in the day, as a kid, I used to make my own surfboard fins.
Consider what type of resin you use. Laminating resin has a high wax content and is difficult to sand when shaping the fin. Go for filler resin. Or there might be some more modern solutions I don't know about.
of course i can buy fins. but thats not the point. i can also make them aswell. ]
i'll think about a mould. but i'm thinking i'll want to try various shapes and sizes. so a have shape might be the go until i have dialed the shape i want.
scroll down on this thread.....
www.seabreeze.com.au/forums/Kitesurfing/General/DIY-Board-and-Design-Spreadsheet/
Enjoy! 
Look forward to seeing the results
polycarbonate.... might be worth considering. but i do have excess resin/glass lurking so glassed fins will cost me $0 extra . Think i'll try my hand with some glassed units first than move on to polycarb later if i'm successful.
I made a set for a board I built- I just sprayed a spare fin with cooking oil and pushed it into a ball of plastacine to make a mold. Then filled the mold with epoxy and some fiberglass fibres. Then I got the screws I intended on using, covered them in vasaline and sat them into the epoxy where I wanted the screw holes to be and allowed the epoxy to set. I set the screw in the epoxy because a previous set that I tried to make all cracked/ broke when I tried to tap screw holes for them. 2 years on and the fins are still fine and I didnt have to pay the ridiculus prices for fins.
That's it. First try...Used 2 packages, each $2.4, very, very soft.
Curing over night, and 72hrs to fully cure. Than will use fast epoxy...Used beeswax & Vaseline as release agent.
After applied wax, noticed that ALL (8 of them) fins are cracked near holes, some more, some less:(
The typical fin. 28 layers of 6oz cloth laminated makes 7mm thick board. From there sanding is helped due to the contours shown as layers are sanded back. Laminating resin is not recommended because it has NO wax in it. The 7mm thickness is intended for a slot box. TT fins are made from G10 laminate which is an ordinary E glass but compressed in manufacture to a very high glass content,(no excess resin) so is very strong. The problem with screwing into the edge of ordinary glass is the fibres are running the wrong way and the layers are likely to separate and fail at the screw. Of course the load depends on the depth of the fin, but I've found mutant size fins pretty lacking as far as drive goes. But good luck.
Col
i have made dozens of fins and some of them have been used now for over 6 years with no sign of damage . 10mm lexen ( bullet proof glass) shape it , drill it , tread it and use it 
but dont paint ....
ok so glass fins tend to crack at the screws,. polycarbonate are successfull...
hmmm.... i have never worked with polycarb. any tricks? doesn it tend to crack like perspex? do i need to do anything special to cut a thread in there?
ebay uk maybe not as much fun as making your own but cheaper than what you can buy the materials, they arnt big brand names but will do the job, ive been doing a bit of research for a skim board im making
Yep, sure it's easy. Was waiting one month to get it off e b a y + postage...
The easiest way is to visit some shop and buy used fins...
With 500g resin A and 100g fast resin B, expense is about $40. How many you can make with half a liter? Many.
Damo suggested using normal kitchen cutting board for the fins. Easy to cut and sand out. Would that be the polycarbonate? duno.
Hey cauncy send the info to me too iam looking at this tread very seriously . Thanks
or put the info up here iam sure there are others out there with same intrest
While I'm waiting for the mold to cure, made a fin for my Shinai (Darkside has 1" symmetric fins).
Got a kitchen board from Coles, cut it with a jig saw, sanded it with a belt sander, made a hole with 4m tap tool. All in about 1 hr.
I can say you'll definitely need precise drilling tool. I'm using this for boards as well. It's not easy to drill on curved fin, hence a few clamps...
Reproducing a fin, using a mould, with hand laid mat / resin will result in a very weak product. (unless making something very small so flex is irrelevant, but even then screws / inserts will not be as strong)
The fins you buy are either glass/resin laminated under heaps of pressure to make a sheet and then CNC machined, or they are resin and chopped strand forced into a mould under great pressure.
You will not reproduce that at home.
So your only options are
(1) buy G10 sheet which is what windsurf fins are made from. I can give you a a link but you'll be buying a LOT of it so for just having a go it may not be ideal
(2) make up a mould with ally plate (like 10mm plate with bolt on sides), spend a week cutting out glass squares to fit, wet it all out and layup (another hour) and then set under pressure in a mechanic's bearing press so it is under about 2 or 3 tonnes.
I'd choose option #1 BTW.
Then you spend hours shaping it with flap wheel in an angle grinder and getting itchy-as-buggery, covered in nasty respiratory disease causing fibres, so extraction fans and full overalls etc is the go (yet uncomfortable). Then a few more hours doing wet sanding, getting a wet pasty crotch and bloody sore hands.
If you are really accurate and careful you can make something as good as factory.
Enjoy.
(dbabicwa - to avoid trying to drill something curved and get it straight, why not drill the flat object before shaping, then index all your measurements for shaping off the bore axis of the holes?)
Excellent advice! Will do that, cheers
Now, I was always wondering, why there are no Stainless steel fins ? SS might be even lighter than G10, thinner, flex the same, environmentally friendly more than G10, etc...Injuries from it the same, I guess.
db. drill and tap your threads before you shape your fin. then you will have a good clamping surface.
Chopping board is the go. Don't get the $4 variety, spend $2 more. They are a bit thicker (no drilling issues). Use a router or file the edges. Got 10 Cab fins out of a chopping board, took me an hour. In one year 1 chopping board fin has broken, 2 originals have broken. Look for a white glossy board, almost no flex..last spotted at Target, Harris Scarfe and Spotlight. The cheapy boards are too thin and flexible. Should be strong enough for mutant fins.
wisha. Thanks some detailed choppingboard reporting!.
amusingly i have offcuts of choppingboard so chopping board fin will be built today.
Mark australia,
that sounds like a challenge to me. I will build some fins from glass that will work without a multi ton press.
Better off buying an inflatable one......more chance of her goin down on you 
