Because he can
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 1123589 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 1123589 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 1123589 times
This is the result: a nice negative form of your fin.
- DSC08688.jpg (40.34 KiB) Viewed 1123589 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 1123589 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 1123589 times
- DSC08319.jpg (40.79 KiB) Viewed 1123589 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 1123588 times
Good tinkering!
cheers, tungsten