Ive been asked by a few people to make a thread on fin molding.
this is my first attempt making fins. I just applied some knowlege of making other fiberglass parts to come up with a method to make a set of fins. I dont have the kinks worked out, but the second fin is coming out better than the first so Im doing something right. This process only works on side fins because one side is flat.
Thanks to my buddy Gabe for the mold making idea. Gabe made some cool bandana pattern fins last month.
Mold making process:
Step One: make a sealed box that is slightly larger than the fin and 1/2" deep. I made mine from balsa. It is glued together with medium CA glue (superglue). Note the shim in the top of the box. This gives the 3 degree offset for the fin. see pic surf24
Step 2: coat entire fin with mold release wax. Librealy coat the entire fin and top box in resin. Spread a sheet of waxpaper on the inside of the top box. smear out all air. Screw the fin to the inside of the top box. Make sure the fin mount lines up with your shim. see pic surf24
Step 3: Dump about 10 oz of resin into the box. Smear as much resin as possible on the fin. bring the box and the cover together at an angle while trying to squeeze out any air. Put lots of weight on top. See pic surf28
Step 4: Make sure the resin has hardened as much as possible before taking the mold apart. First remove the screw in the top. You may need a screwdriver to wedge the halves apart. Try not to damage the mold with the screwdriver. Take a X-acto knife and trim all the loose resin overhangs in the mold. Pop all air bubbles. See pic surf 25 and surf 32
Step 5: Make a mixture 50 50 mixture of resin and microballoons by volume. Fill in all the bubbles. Make sure to periodily check the mold because The microbaloon filler may sag over any steep edges. Sand when dry. Final wet sand with at least 400 grit. see pic surf26 and surf41
first of all cheers for being so generous with your info, its great to have somone sharing all this great info…
I’ve been trying to make sense of your molding process from the start, and i think that the key line is :
"This process only works on side fins because one side is flat. "
I didn’t click they were side fins, thinking maybe you were dipping/molding one half of a centre fin and then the other half and somehow getting em together
I’m sure this process can be applied to FCS fins as well…
The two questions I have is, whats a shim? and the 3 degrees you mention, is that the cant of the fin?
When I first popped the fin out, It was much more flexible than the original plastic fin. After 2 days, it is about 3-4 times stiffer than the plastic fin
pic surf27 just shows the wood and carbon stacked in the mold to show the shape of the fin. This is not an actual step in the process. I will cover this in more detail when I actually make the fin.
There is only one strip of carbon. It shows through on both sides. There is nothing inbetween but resin. I just lay each piece in the mold. Coat some resin on it, then lay in the next and so on… Then I squeeze them all together.
First I fill the mold with water and pour it into my mixing cup. I draw a line at the water level so I know that I need at least that much resin. pic surf49
Then I dry the mold and coat the entire inside with wax. pic surf50
Then I brushed some resin into the mold. pic surf51
This is what It looks like after the fin pops out of the mold. The next pic shows the fins after sanding. Next steps: filling in any air bubbles, final sanding, and clear coat
