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Make your own fins - #2 THE FIN SHAPER

PostPosted: Tue Oct 30, 2012 10:54 am
by tungsten
So there you are, you want to make your own fins, but you think it's a bit of a joke to just copy some fin out there. You have your own design for your fins. How to start?

1. You have access to CAD software and a CNC mill. Then you are there already. You don't need advice. You probably only read this to chuckle about the amateurs.

2. You have a proper duplex grinder with big wheels and some stock of G10. Put on the protective suit, mask and respirator and get going. With a bit of practise you will be able to make brilliant fins.

3. You only have access to basic tools and some cans of beer, but you have a pretty good idea what you want to try in terms of fins. This is where we are now. :D


A good material for that is ply wood, of the lighter, less dense sort. Not marine grade. Having plies, it's easier to work your model symmetrically and equal on left and right side. Less dense means you work faster and with less effort. Choose your profiles, calculate the fin, print them out and start shaping.

The outcome might be something like this (the red ones were semi-destroyed in the process of making the mold):

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From here, you go ahead to make a mold for your fins. Many ways to do it. This time I chose to cast a mold with epoxy resin.
-Treat the fin model with a release agent,
-put in a box with some plasticine on the bottom, and
-pour resin over it.

When the resin is set, clean away the plasticine, put the mold plus fin model the other way round in the box, clean it thoroughly, treat with release agent, and pour resin over it to make the other half.

When the other half has cured, take both halves and the model out of the box, and drill holes through both halves, near the corners. Thus you have a guide to put the mold together correctly.

That's your mold!

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Next step is preparing the mold for casting your fin.
-drill a hole on top to insert a straw
-treat both halves of the mold with a release agent
-fill one side with pieces of fibre glass. make sure there are many layers on top where the fin sits in the fin box.
-put in the straw
-cover the straw with many layers of fibre glass

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-put on the other half of the mold and screw them close
-tape the gap between the two molds, so that no resin can drip out when you fill it
-clamp mold parts together all around the rim

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-inject resin through the straw with a syringe

What you get is something like this:

Before cleaning and finishing

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Finished fin:

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cheers, tungsten

Re: Make your own fins - #2 THE FIN SHAPER

PostPosted: Wed Jul 10, 2013 3:42 am
by Alon
nice information...:)

Re: Make your own fins - #2 THE FIN SHAPER

PostPosted: Tue May 17, 2022 10:36 am
by monimorklea
How I wish I read this years ago so that I am the one who makes my DIY fins :) outdoor living spaces