This is a fun project that I get to blend artistic creativity with science and fun! I am currently working on designing a process for building surfboard fins, kiteboard fins, and skim fins (think wake or kite skimming) out of fiberglass plate.
The process begins by making a fin plate, this is a fiberglass plate that is laminated from multiple layers of fiberglass fabric to get to the correct thickness. The fin plate can be colored, clear, or have graphics added to it, like the holographic fabric in the keel fins below which is super trippy because you don’t see it until the light hits it just right, or the fabric in the plate at the top of the page.
Once we have our plate we need a computer file of the fin or fins to cut out. This file can be generated in a number of ways sometimes I’ll do them from scratch, using a NACA foil generator to develop the foil profile for the fin and sometimes I’ll jump over to finfoil.io and use their generator to develop the fin file. With the fin file in hand I’ll add any details like the base or trailing edge thickness to it and then develop the cut file. The cut file is simply a string of code and coordinates that tells the machine where to go.
The tricky bits are to get the plate flat and squared and then to make sure that on the flip that the cutter height is correct. Get that all right and the fins come out perfect! The steps are to flatten the fin plate to a uniform thickness, then square the perimeter, this is important because I use the perimeter of the fin plate to line up the plate when I flip it to mill the other side, if my flip is off then the fins won’t be correct. Once the plate is flattened and squared I then do the 3D milling on the first side. I use Fusion 360 to program the cut and use a scallop cut to mill the foil in starting in the middle and working out, this way the tool can clear itself and no other operations are required for clearing. Once the first side is foiled I flip the plate and foil the second side. Finally I use a contour cut to cut out the bases from the plate leaving tabs to hold the fin in place.
On this cut I’m using a 1/4” ball nose PCD (diamond tipped) end mill, running at 300ipm with a .6mm stepover. The diamond holds up well to the abrasive fiberglass and the small stepover leaves almost no milling marks making the sand out easier and faster. For planing the sheet flat I use a shear hog bit and for the final cutout of the fin I am running an 1/8” burr bit with diamond coating (Ultra-tool 222) at full depth and 100ipm.
There are some other steps to finishing, including sand, paint, and adding any hardware or holes that are necessary for the fin to work with the box system it is designed for and maybe I’ll go into that more in another post but for now if you are interested in having some fins made please contact me. Thanks!