Namaste Fin Fondlers and welcome to this instalment of making surfboard fins using epoxy casting resin. You may have noticed that things have been a bit on the quiet side on my blog. The rumours have been flying around and it has absolutely nothing to do with my lack of activity on the surfboard building front or my new interest in gerbil farming. I have been busily beavering away in the Ashram working on some new and exciting fin creations, in wood and also resin. I have also been researching into the amazing hydrodynamic properties of elliptical fins and applying this new found knowledge to fin design. I've managed to create an elliptical 9" long board fin using CNC machined marine ply and the results have been fantastic. But more of that in a future post. In the meantime, put on the kettle, make yourself a nice hot cuppa char, sit back and enjoy.
The first step involves designing the fin in CAD (Computer Aided Design) software. I've been using FreeCAD which is a free open source package. It's taken a bit of time to learn the ins and outs of the software but I've managed to teach myself everything I need to know to put together a fin design. This particular fin design uses an elliptical plan shape (think Spitfire aircraft wing) and a NACA0012 symmetrical foil which is a high lift, low drag, and low stall foil. Perfect for a surfboard fin. Once the fin is designed I super-impose it over a mould block to form the mould blank.
The mould design is then imported in CAM (Computer Aided Manufacture) software. This is where the tool paths are created. These tool paths are a set of numbered coordinates that the CNC machine will use to cut the mould out of a timber block.
Now the fun bit. Letting the machine do its thing. Cutting the mould blank out of high quality (Furniture grade) pine. This takes about 3 - 4 hours. It's high precision stuff accurate to 0.001 mm. A mould block is machined for each side of the fin.
The completed mould block sanded with 600 grit sand paper, and finished with a polyurethane varnish.
Some timber sides are screwed in place to hold in the silicon rubber.
The silicon rubber poured and waiting to cure. This is done for both sides of the fin.
The completed silicon moulds ready to be clamped together.
Ready for the casting resin.
Mixing up the casting resin with a little translucent black colour. This is a fit for purpose epoxy casting resin with excellent mechanical properties and a low viscosity for easy pouring.
Pouring the resin.
I leave the resin to cure overnight.
Splitting the mould.
And presto! As my old Dad would say "It's just like a bought one."
Ready for some light sanding around the edges.
I made a set of three fins (thruster prototype) for my mate Paul who is in the process of testing them for me. I'll keep you posted and provide a ride report.