I am about to rebox a few of my unused slalom fins into weedys. I have built a jig that allows me to hold the fin upright (as it would sit in the board) and pour epoxy/polyurethane into a split mold from the top. I've read many of the related posts on here and am considering r5 epoxy or polurethane. Can anyone suggest a polyurethane product that they have used or an alternate epoxy?

I use R180 epoxy from FGI, I cut up a heap of old carbon first and fill the box around the fin then pour in the resin. Carbon cuts up nice and fine and adds a lot of strength to the box area. Use glass if you dont have any carbon, I'd avoid using just resing alone

Here are a couple of pics of the jig.

That's a pretty comprehensive looking jig.

OK, one word of advice, if you put the fin across your knee, and pull each end with your hands, as hard as you can, it shouldn't flex more than 1 or 2mm, any more than that it won't make a good weedy. You can put a layer or 2 of carbon over it to stiffen it up before reboxing, then it's got a chance of working. You also have to consider the change in thickness to width ratio, from upright to 45deg is an increase in flow length of about 20%, so the fin in effect becomes 20% thinner. So a 10% upright fin becomes 8% at 45deg. That is fine, well within the margins of usability, but if you start of with an 8% foil, it's going to be a little over 6% when you rebox it. Might be OK downwind, but could tend to spin out upwind.

I use epoxy with micro fibers added, that both thickens and toughens the resin.
Polyester is a bit brittle, tends to crack under load, but with some fiberglass in the mix may be OK.

Most of the molds I've seen are the other way up, sealed at the base and poured from the fin end. That way you can use it with any fin. Looks like yours will have to have a different sealing arrangement for every fin, although it will be easier to pour.

Yeah the jig is probably overkill for a few fins but I engineered it to prevent the errors I usually make by rushing jobs.
I think I have it set so I can be assured of proper alignment with an easy pour but the cost is the lower seal needing to be fit to each fin.

Be interested to hear how it goes, cause the other way round can be a bugger to pour.

I use HPR5 from Adhesive Technologies [ATL],
It's a rubber toughened epoxy and needs no reinforcement.
Machines very well.
Negative is that it is a bit of a bitch to work with.
At room temperature the resin has the consistency of thick honey, so I keep
the container warmed on an electric blanket to make it runny. if you mix it
cold it traps a lot of air in it.
Done loads of fins with this, no failures and never chips. Great stuff.

Hi Decrepit, I can report back that the effort to seal around the fin was too much time for the convenience of pouring resin from the top. I have re-jigged the jig to the conventional approach of the fin being inserted into the mold from the top and pouring around it. By the way how much microfibfe do you add to your resin? I like the sound of the r5 but already have the west system resin and microfibre.

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Te Hau said..

I use HPR5 from Adhesive Technologies [ATL],
It's a rubber toughened epoxy and needs no reinforcement.
Machines very well.
Negative is that it is a bit of a bitch to work with.
At room temperature the resin has the consistency of thick honey, so I keep
the container warmed on an electric blanket to make it runny. if you mix it
cold it traps a lot of air in it.
Done loads of fins with this, no failures and never chips. Great stuff.

I've seen Te Hau's fins. They're awesome!

Boogie said he used to use a rubberised resin on his first Custom Carbon Composite fins. Must be a NZ thing. Certainly the base of my X2 was nice. Te Hau your "room temperature" might be a bit different from our Aussie summer room temperatures...

Hey Yoyo, I had the same thought about room temperatures as well. I reckon its been about 40c in the shed most days this last week or so.

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TerryF said..

Hi Decrepit, I can report back that the effort to seal around the fin was too much time for the convenience of pouring resin from the top. I have re-jigged the jig to the conventional approach of the fin being inserted into the mold from the top and pouring around it. By the way how much microfibfe do you add to your resin? I like the sound of the r5 but already have the west system resin and microfibre.

Doesn't want to be too much, or it gets too hard to pour. There's mainly compressive loads on the base so it doesn't need heaps of strengthening, the biggest load is probably at the rear bolt. In the past, I've added some cloth in this area, but again it can interfere with the pour. I can't give you an exact ratio, but just keep adding it, until it gets to a thickness that's still pourable, but anymore would stiffen it too much.

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decrepit said..

TerryF said..

Hi Decrepit, I can report back that the effort to seal around the fin was too much time for the convenience of pouring resin from the top. I have re-jigged the jig to the conventional approach of the fin being inserted into the mold from the top and pouring around it. By the way how much microfibfe do you add to your resin? I like the sound of the r5 but already have the west system resin and microfibre.

Doesn't want to be too much, or it gets too hard to pour. There's mainly compressive loads on the base so it doesn't need heaps of strengthening, the biggest load is probably at the rear bolt. In the past, I've added some cloth in this area, but again it can interfere with the pour. I can't give you an exact ratio, but just keep adding it, until it gets to a thickness that's still pourable, but anymore would stiffen it too much.

Honey, not toothpaste.

Although not recommended for your toast or brushing your teeth

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yoyo said..

Boogie said he used to use a rubberised resin on his first Custom Carbon Composite fins. Must be a NZ thing. Certainly the base of my X2 was nice. Te Hau your "room temperature" might be a bit different from our Aussie summer room temperatures...

On the plus (??) side we do get to go windsurfing and skiing on the same day.

You can do a quick mould if you have 3 spare tuttle fins. Use two heads to space apart two sections of waxed aluminium. Then you make a rough profile of the fin head out of plywood and drop it in between the two bits of aluminium. Use a bit of modelling clay to roughly fill in the rough inside corners of your makeshift mould, and then get the third tuttle fin to press it into shape. The box aluminium gives a nice reference to make sure your fin is upright when you pour in the epoxy resin. (I've proven in the past that even a 17 degree cant is quite sailable so don't worry if it's not upright by a single degree.)

You should then get away with only a little filing, you're going to get the thickness right first go after all!

I don't think you need put reinforcement in the resin. I nailed a thick rope anchoring a buoy in Tuesday's noreaster, a full on stop and and over the handlebars. The fin held.

looks the goods Ian a demountable easy way to wax and clean the mold up aswell, one of the downfalls about using a finbox as a mold,

if your going to use a fin box don't fill the holes with blue tac , if your going to use a plastic release agent make sure its totally dry at the bottom

if your going to use the fat chunky barrel nuts you will need to fit them further into the base and definitely use some reinforcement, some fins are a tight fit and cracking the base with the screws can be a problem

As mentioned previously I've adjusted the jig so that the mold is up the other way. The mold is a chinook fin box cut down so it is split into 2 pieces and also has the base removed. I'm going to seal inside the mold with packing tape and have the open base sitting tight on a silicone sheet. The join in the 2 mold pieces are also separated by small silicone gaskets. The pics probably make more sense this explanation.

I have also set up the jig so the fin is gripped between 2 lengths of sail track which will be screwed to the piece of mdf behind the fin. This piece of mdf holds the fin vertical and the horizontal angle is adjusted by tilting the fin to the desired spot before screwing the sail track to the mdf. Then I can slide the mdf piece down to the place the fin at the correct depth in the mold.

I hope its not to late to chime in .
I use a product Called Barnes 808, its a fast set, easy pour plastic urethane . Sets within minutes but at 20-30 minutes is rock hard to shore D 80 +- 2.(Rock hard). really easy to use and easy to machine/sand unlike epoxy's can be.
There is a slow version Tc 891, alot slower and longer demould time.
I has had best results Using a SIKA primer 210 on the fin (especially G10 ) as it promotes adhesion.
If your in Perth Simon at Kirkside products is your contact.
You can also get pigments, but it comes in white if your happy with that.
For approx 100$ you can have enough to 10-12 fins.

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fuges said..

I hope its not to late to chime in .
I use a product Called Barnes 808, its a fast set, easy pour plastic urethane . Sets within minutes but at 20-30 minutes is rock hard to shore D 80 +- 2.(Rock hard). really easy to use and easy to machine/sand unlike epoxy's can be.
There is a slow version Tc 891, alot slower and longer demould time.
I has had best results Using a SIKA primer 210 on the fin (especially G10 ) as it promotes adhesion.
If your in Perth Simon at Kirkside products is your contact.
You can also get pigments, but it comes in white if your happy with that.
For approx 100$ you can have enough to 10-12 fins.

^ Slowboat's fins?

Sure look nice whatever they are!!

Hi Fuges, no not too late at all. Trying to finish the jig before I sort out the product to use. Great to hear of a urethane option that has been tested. The fins pictured look fantastic. Do you have any issues with air bubbles in the mix (e.g.that need degassing by vacuum) or is it easy to mix without getting too much air trapped?

The urethane I used last century, made gas as soon as it was mixed, it was necessary to let it sit for a few minutes until it stopped fizzing.

PM me for more info if you want , the technique i use is nothing special . im happy to share with any one.
I only have ever had issues with 808 "gassing/bubbles" when contaminants enter the mix somehow, Swet seems to be my biggest issue in this heat at the moment.It hates water!!! so your molds need to be really well sealed and everything your mixing with dry and clean.

Thanks for the offer I will pm for more details on the urethane. In the mean time I did a test run using the West System and milled glass fibres I already had in the shed. Here is the end result (still need to drill for barrel nuts).

Hi. I'm coming from Holland and reading seabreeze for a couple of years. Wanted to let see how I'm reboxing.










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Great pictures of how you do it with the fin sitting the right way up Thanks.