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Make your own fins - #1 THE COPYCAT

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Make your own fins - #1 THE COPYCAT

Postby tungsten » Tue Oct 30, 2012 7:41 am

Why would anybody in his right mind make his own fins?

Because he can 8)

So you decided you want to make your own fins. You've got this brilliant set of fins, and you want a copy - they are hard to get by, you might lose yours, because you need them on another board, or you start using boards with a different box system your fav fins are not made for. Many good reasons.

Get started with making a mold - side fins

There is a bazillion ways to make molds. Any of the methods (molding silicone, plaster, plastilin, deep drawing ...) have their advantages and disadvantages: price, availability of the material, rigidity of the mold, heat resistance, necessary machinery ... I tried some and ended up with a method called "deep drawing", which consists in thermo forming a plastic sheet around the sample in order to get a negative mold. There are lots of useful youtube clips about it, so I won't explain every little detail. Here we go.

1. Start with building a vacuum box. It's a closed air tight box with lots of holes on the top and a big hole in front. This is for the hose of the shop vacuum cleaner.

DSC08693a.jpg (41.44 KiB) Viewed 285117 times

2. Beautiful box. Now we need the material our mold is going to be made of. I found sheets of clear 0,7mm PET in a hardware store for cheap, 5€ per m2. PET is a kind of polyester. This is the stuff coke bottles are made of, although coke bottles are thinner. PET is easy to work with and if you fark one sheet up, it won't blow your budget.

There are other materials like PP, PE used for deep drawing. You can try those as well if you get sheets of 0,7mm to 1mm thick.

A pic of the trimmed PET sheets I use:

DSC08691a.jpg (29.47 KiB) Viewed 285117 times

3. Prepare the box and sample. I stick a rubber lip (window insulation) on top of the box so that the PET sheet will sit air tight on top of it. The sample (your fin) fits nicely in the free space. Close all the holes around the rubber lip with tape. Only the holes inside the rubber lip are open.

4. Form the mold
-Heat up the sample fin in boiling water. This is important. Otherwise the PET sheet will cool out once it touches the fin.
-Now place the fin on the vac box, and place one sheet of 0,7mm PET on top.
-Heat the PET sheet a couple minutes with a hair dryer until it gets soft.
-Activate the shop vac (or any household vacuum cleaner for that matter). The vacuum will suck the sheet down on the sample fin. Keep heating the sheet until it lays smug and snug on the fin. Pay attention to edges and corners.
-When you're happy with the result, keep the vac running for another minute cooling down the sheet with cold air (if you hairdryer doesn't do cold air, use a wet rag or think of something else).

DSC08694a.jpg (41.35 KiB) Viewed 285117 times

This is the result: a nice negative form of your fin.

DSC08688.jpg (40.34 KiB) Viewed 285117 times

5. Cast your fins
-Wax down your mold with car wax or a proper release agent
-fix it to some wooden frame. Why use a frame? Epoxy gets hot when curing. You want something stable around the mold when it comes to casting.
-fill the mold with fibreglass left overs. Make sure there are lots of layers on the top part where the fin connects with the fin box. This is critical. -Alternatively, you make an insert out of G10 and put in the mold in the right place before pouring the resin. That's what I did. Inserts:

DSC08686a.jpg (43.46 KiB) Viewed 285117 times

-Pour the resin. Some practical tips:
-use universal tints for poured epoxy. They contain emulsifier, which guarantees the epoxy to mix well; also looks better.
-don't cast more than 7-8mm thick layers at a time; epoxy will become too hot and form bubbles. If your fin is thicker, pour a first layer, wait until it gels (half an hour or so, depending on temperature), and pour a second layer.

DSC08317.jpg (52.28 KiB) Viewed 285117 times

DSC08319.jpg (40.79 KiB) Viewed 285117 times

After the epoxy is cured, I put the mold as is in the oven at 50ºC for 20 minutes. Take out of the oven and cool rapidly (cold water or fridge). This helps disconnect the new fin from the mold

Take out your new fin and finish it (cutting of leftovers, sanding). When it's ready, you will want to harden it. Put the fin in boiling water for 30 minutes. Why? Epoxy cures under heat. THe complete curing process take 1 week. The hotter, the better (up to 100ºC that is).

Another thing: When epoxy is hot (over 80ºC, called the glass point), it gets soft and you can form it, bend it, whatever you want. It stays in that position after cooling down. So if you want to build a cant into your fin, just heat it up after making it, bend it, cool with cold water for a minute, and you're set.

And this is the result (before sanding and finishing). Those copies are true to the original to 1/10 of a millimeter. That is quite acceptable.

DSC08685.jpg (149.85 KiB) Viewed 285116 times

Good tinkering!

cheers, tungsten
Last edited by tungsten on Wed Oct 31, 2012 6:14 am, edited 6 times in total.
Posts: 243
Joined: Wed Mar 11, 2009 4:24 am
Location: Malaga, Tarifa, Spain
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Re: Make your own fins - #1 THE COPYCAT

Postby tungsten » Tue Oct 30, 2012 8:39 am

Make a mold - center fin, which is symmetric

In order to make the molds for the center fin, you need a support to carry your fin, covering exacly half of it. I cut and sanded my support out of 5mm ply. It works both ways (for both sides of the fin). This is what it looks like:

DSC08697.jpg (26.39 KiB) Viewed 285116 times

Place the fin on top, place the whole on top of the vacuum box, and make your two halves of the mold.

DSC08698.jpg (21.83 KiB) Viewed 285116 times

Now you're ready to cast your fin.
-drill a hole for a straw like in the picture
-fill the two halves with pieces of fibre glass - in the pic there's no glass inside the mold, it's just for the photo.
-put the insert in its place
-stick tape around he border of the two halves. Otherwise the resin will drop out
-clamp halves together. More clamps than in the pic
-put the mold in a position so that the straw hole is at the highest point. NOT LIKE ON THIS FOTO
-insert resin with a syringe through the straw. it's important to fill the mold slowly from bottom to top. Otherwise air can't escape.

DSC08702.jpg (43.83 KiB) Viewed 285116 times

That's roughly it. You'll have to play around in order to get good results. As I said: who's stupid enough to make their own fins?

cheers, tungsten
Posts: 243
Joined: Wed Mar 11, 2009 4:24 am
Location: Malaga, Tarifa, Spain
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