Casting hybrid lamination fins

[MrMik]

I’m testing some old epoxy resin on the back of the silicone mould, with and without Q-cell, and with and without petroleum jelly, to see how hard it would be to de-mould.

I figure I might as well use the old resin to make a fin, rather than mixing it before tossing it out.

I measured the volume of the Gullwing fin today: 246ml. So hopefully I’ll have just the right amount of resin to fill it. I think I’ll ad some pigment for UV resistance, Q-cell powder for strength and styrofoam balls for weight reduction.

I plan to fill the mould from the fin tab side with a first small batch of resin, then rotate it to cover all sides with resin. Then continue to rotate until gelled, then add the next batch with styrofoam balls. That way, there will be no styrofoam directly at the surface. I figure the styrofoam will float to the top, so I want to fill the fin to about 25mm above the fin tab with the resin / Q-cell / styrofoam mixture, then fill the rest (the tab mainly) with resin / Q-cell mix, close the inlet with hot glue and turn the fin around so that the tab is down. That way the tab will hopefully end up with the strongest and heaviest resin in it, while the styrofoam floats towards the tip of the fin.

[Surffoils]

So I’ve got a sacrificial cardboard collar around the Mold. The Mold is thoroughly waxed and the fin too. 

Mix up a slightly thin batch and carefully pour it over the fin ensuring the mix fills and touches every part of the fin. Mix a slightly thicker mix and almost fill the cardboard collar.

Then as a last touch a thinner mix that will flow and form a level base when it sets.

 

[Surffoils]

And several hours later the two halves open up leaving you to start the creative part of making your own fins.

Now what are you going to make your fins of…

Glass, veneer, carbon or maybe some exotic space age material just to experiment ?

Patterned colour fabric inlay ? Staggered layers of complimentary materials ?

Glassing off cuts, recycle those old board shorts, or something really different ?

[MrMik]

Thanks for that, very informative!

What do you use to wax the mould and fin? I have used vaseline (petroleum jelly) and ‘mould soap’ so far. I think wax might be better

My experiment with bits of epoxy on the silicone mould went well, the vaseline made no difference and it seems to disappear into the silicone. There is just not a trace left of it after some hours. That cannot be good for the mould, the volume of the vaseline must  going somewhere, i.e. the mould is expanding ever so slightly with each vaseline application. The good news is that resin with or without Q-cell came off easily, and the resin with Q-cell added floats in water! I want the fin to float and it seems to be achievable even when casting in epoxy resin.

I obtained 20kg of Pop today, and a tight sealing bucket to keep it in, and more containers and buckets and stirrers to make the process easier. When making moulds of much larger fins it becomes quite hard to even mix the required material thoroughly in time. Getting the 1.5kg Pop for the last mould through the flour sifter was an effort, hands getting weak and starting to cramp up after 8 minutes of as fast as I could sifting. That was with a helper to ladle the Pop into the sifter while I was operating it at full tilt. I’ll use a different method next time.

[MrMik]

The snap in parts (link somewhere earlier in the thread) look a lot more suitable than the previous lot. Slightly different from the ones used in the Bodyglove fin, very different from the ones in the FCS fin.

Both the FCS ball spring plungers and the Bodyglove ball spring plungers have more powerful springs than the ones I bought. I reckon’ I can compensate for that by using more of them, but the devil may be in the detail.

[MrMik]

Here is the more appropriate container to make gullwing / whale fins:

It’s big enough to make a cast of my marine ply / carbon /kevlar lamination, which has a convenient thin centre line marked by the middle layer of carbon/kevlar mesh.

That laminate is my first attempt at making a fin, and the one that convinced me that sanding it back is a bad idea, and it’s big enough to accommodate either the straight tip gullwing fin, or the standard gullwing fin, or the gull-whale fin. It’s not big enough for making an extended tip gullwing fin.

I’m meditating on how to make an oversized Pop cast of the fin, but one that already has a perfect fin tab on it. And a sturdy fin tab, one that I can clamp in a vise, so I can file and sand the plaster fin. I think it might be the perfect job for that suspect, out of date epoxy resin.

So what I want to make next is a cast of a perfect fin tab (including markers for the snap-in thingies), so that it has a thin core for the fin sticking out, with multiple perforations (like the plastic paddle-pop sticks in re-useable ice cream making moulds). I imagine that I can then place this into a mould for an oversized fin, pour Pop (with additives if needed) onto it, then use the sturdy tab to hold the fin ‘dummy-blank’ while shaping the soft Pop until perfect.

If I stuff it up. I’ll smash the Pop and pour another cast onto the epoxy tab. If it comes out the way I like it, then I can make a new mould of my creation, with a perfect fin tab already on it. And then I can re-create that shape in a variety of materials, over and over.

I hope this makes sense…

 

[MrMik]

I think I’ve got it!

In order to make my own fin design, I have to rethink the entire approach and design it with my own fin tab.

What I have come up with is going to solve multiple problems of current fin design, especially the problem of predetermined breaking points (to protect the fin box and board) and to reduce the injury risk to the surfer and other people in the water.

The fin tab does not need to have a fixed pin (at either end) to hold it in the box. This is only required if the fin would be lost if it falls out after being bumped. It is not so much an issue if the fin floats on the water surface after coming out. It could even be tethered to the fin box with a bit of fishing line if frequent fin loss turns out to be a real problem. 

If the fin comes out when it is being hit hard from front or aft, then neither the fin nor the box would break in many (maybe in most) surf accident scenarios.

In order to fully retain the placement options of the fin in the box (i.e. the new fin with snap-in tab can be put as far aft or forward as a standard fin), the fin tab should be symmetrical and as long as the previous tab from tip to end. But there will be no thinner part (where the screw usually goes) at either end. Multiple ball spring plungers all along the tab length will do all the holding (combined with a tight fit in the box to start with).

I’ll make a prototype fin tab from laminated marine ply and carbon/kevlar mesh and epoxy, with a rudimentary fin on top, and then insert the ball spring plungers. Once this laminated tab works well, I will make a mould of it in Pop, and then cast a couple of sturdy tab / fin holder tools, which have the purpose of having softer material cast onto their top (the actual fin area) later on (the re-usable ice cream maker paddle-pop approach).

Once I have these dummy fin bases (DFBs), I’ll make a fresh Pop mould of them, which is large enough to contain the entire fin that I want to shape. After removing the DFB from the fresh Pop mould, I’ll scape out a rough shape of the fin, a bit thicker and larger than the planned fin.

I will then place the DFB into the mould and cast Pop (maybe with some additives) into the mould.

What comes out will be an over-sized fin on a perfectly shaped fin base, with markers for the correct locations for the ball spring plungers. The tab will be sturdy enough to be put in a vise, and the fin top soft enough to easily shape it by hand. Once it has cured fully, wet sanding should be an option, so that this method can be used inside the house with little mess.

Once the Pop fin is shaped on top of the DFB, a final mould will be made of it and then the actual fin making can begin.

Because I now know that I can make a very good and light fin if I have a good mould of it, it is worth the effort to shape my own fins.

[Surffoils]

I’ve got my two Mold halves finished now but you’re making great leaps forward.

[MrMik]

DFB = Dummy Fin Base.

I’m trying to work out how many Spring Ball Plungers (SBPs) I can fit on the DFB.

I have some fin boxes with ‘serrations’ every 6mm along the upper edge of the rail inside the fin. So I figure I need to space the SBP’s in multiples of 6mm apart.

12 mm apart is too close, I think, because that only leaves 4mm of actual resin between SBP’s (they are 8mm wide).

If the SBPs are 18mm apart, that leaves 18 - 8 = 10mm wide spaces of fin substance between SBPs. I think that will do, because the SBPs are 17mm down inside the fin box and the forces are greatly reduced, when compared to the maximum stress point just outside of the fin box.

I assume that all the other fin boxes without serrations on the inside will be more forgiving wrt. the exact SBP placement. I may well be wrong about that.

In order to allow for variations between different boxes, I’m going to make the pattern fit the widest fin box that I have found (not a thorough search at all!), which is the 12’’ centre box I had retro-fitted into a 6’6’’ XF TSA Nugget. If it fits into that board’s box, then a bit of sanding will make it fit most of the other’s.

The other measurements shown in the diagram are a bit too big, too. Instead of 10mm, the real distance between bottom of fin base to centre of SBP should be 9mm; and the height of the fin tab should be 25mm instead of the 27mm in the drawing. Those differences between the pattern and the intended actual fin are intended to allow a margin of error that I can sand off until it’s perfect.

So the plan is to laminte ply wood (4mm x 1layer +2.8mm x 2 layers = 9.6mm). Then sand off a tiny bit on each side to make the tab fit perfectly into the fin box, and leave the 4mm plywood at the core to stick out to serve as the tab for the eventual fin.

Then drill holes for the SBPs and fit them in the DFB, and test if the DFB actually clicks well into a fin box…

 

 

[MrMik]

Much harder than I thought to cut to specs with a jigsaw, particularly in the dark…

So I made the DFB a few mm larger than initially planned and will sand it back until it’s just right.

[MrMik]

The DFB now fits tightly into most of my single fin boxes (so tight it amost does not need any spring ball plungers to hold it in).

And the first 4 SBP’s are installed and work quite well. This part of the DFB with the first 4 SBPs will be cut off soon, I just wanted a couple of trials before starting installation of the 8 semi=permanent SBPs in the middle of the DFB.

I think that if I did install all 12 SBPs, then it would be hard to get the DFB back out of the box without breaking the tab off. With a proper fin it would not be a problem to get it back out. 

Using an 8mm drill bit and vise-grip pliers achieves a very nice fit for the DFBs. In the eventual end product real fin, I’ll add some glue or resin before pressing them in, but they need to be taken out of the DFB again for the next stage in the process.

[MrMik]

My first pattern finished. Not perfect, but good enough.

12 SBPs is probably overkill, but I’ll make the first mould from the complete pattern anyway, in case I want to make a really large fin later on. I need more practice making Pop moulds anyway.

I sanded it through the grades to P800 and then covered it in furniture polish for 10min, then wiped it off. Feels very smooth and slippery, the Pop should come off easily.

I sharpened the edges of the ‘blade’ thingy and drilled shallow holes in both of it’s sides, taking care not to drill through, because that would make mould release difficult. The sharp edges might help to get the depth of insertion into the Pop just right, and the shallow holes should help bond the Pop to the DFB so it does not strt to come loose while a fin is being shaped.

[MrMik]

The first half of the split mould for the Dummy Fin Base has been poured. I’ve used 1 part Pop and 0.8 parts of water without additives this time. I poured about 1/2 of the Pop into the container, then soaked and squished the hessian layers inside the runny plaster, then treated them similarly to squeegy-ing fibreglass and resin to get more bubbles out, then poured the second half of the pop into the container.

I had plenty of time left to clean up before the Pop was starting to set. The main improvement ewas from using a much larger sieve. Although this was the most Pop I have mixed at once so far, I got it into the water without stirring it initially within 3 minutes. Much superior to that small mechanical flour sifter I used the last time. A big floppy rubbery tub also helps to mix and then pour without splashing.

All the hessian was prepared and laid out in the order of planned addition to the Pop.

The DFB pattern had the SBPs removed and the holes slightly under-filled with moulding clay, and some imperfections filled with clay.

I used an electric blower to help blow the surface bubbles towards one side of the container, then mop them up with some tissue. Eventually the surface looked very nice, then it started to form a very thin layer of water (<1mm), at which time I inserted the pattern and tried to sink it in to the halfway line. The sharp edge was helpful, but it was again impossible to get a pefect insertion for the main body of the object. I think this is mainly due to the displacement of runny Pop, which then bulges up next to the inserted object. I might try to insert it earlier next time, before the watery surface layer appears. All the water was eventually re-absorbed into the Pop.

[MrMik]

24 minutes at about 21degC ambient temp from start to insertion of the object. 

I got a helper to take notes:

[MrMik]

Next is drying at 60degc for about 24hrs. Perfect fit for a standard home oven.

The bits of Pop that came off during de-moulding were hopefully not important. Time will tell when it’s dry enough for sanding.

I think I’ll try a different version of my "make it flat and level’ approach, rather than surffoils sloping edges. I cannot explain it clearly yet and I might well be wrong, but it seems to me that the sloping edges are less suitable for larger fins / objects.

I wonder what caused the multiple small bubbles in the ‘blade’ area, while there are none anywhere else.

Note the bubbles of air that cause a double crater in those dimples drilled into the ‘blade’. I think they will make the adhesion stronger, and the exact shape of the ‘blade’ is inconsequential in any case.

Another (for the current project) inconsequential problem that I noticed is this: The moulding clay absorbs water, and consequently expands. In this case it probably just helped to lift the object out of the mould and caused no problems, but for projects with tighter tolerances it could not be used with watery Pop.

[MrMik]

A major problem is if the Dummy Fin Tab (DFB) is not perfectly level in the mould.

Once the rough fin shape gets carved into the mould, it will be very much level, and any inaccuracy in the DFT placement will cause the eventual fin to have cant or toe-in, or both.

While yesterdays mould is still drying, I poured another one trying to get it level this time.

I used a slightly thicker Pop / water ratio for simplicity’s sake: 3kg Pop + 2.25kg water (1 part Pop to 0.75 parts water).

I tried to fractionate the Pop mix by sifting the Pop into the water , stirring it very briefly only, then poured about half of it into the container with the hessian. I kept working and mixing the part in the mould container for 20 minutes, working out bubbles from the hessian and trying to trigger a faster curing compared to the second half left in the mixing bucket. Then I let it stand for another 5min until it had turned to jelly consistency. 

It turned out the part left in the mixing bucket was also like jelly, but it became runny enough again with a brief thorough mixing. It did not spontaneously level itself when poured on top of the first half, but a bit of rattling the box flattened it out nicely (I hope).

Then I placed the pattern on top of the runny Pop and pushed it in, using a spirit level as guide to get it close to perfect. The glass plate under the mould container is also level.

The difference in setting speed between the two portions of the Pop pour was not large enough for my liking. Next time, I’ll try to ‘seed’ the first part of the mix by sprinkling ground up dihydrated Pop dust onto the hessian. That will hopefully provide multiple cristallisation nuclei to get it going much faster than the part left in the mixing bucket.

[MrMik]

First split mould is done.

It has a few small imperfections, but nothing that cannot be patched up with moulding clay.

I had to scrape out an area around the tab, because the Pop level was too uneven against the tab, and there would have been several thin areas in the second mould that would surely break off. The way to fix it is to cut out boldly and with right angles. 

I hot glued a spirit level to an extra wide sanding pad and blasted it clean every 20 sec with a water hose. It clogs up completely in no time when ‘sanding’ fresh Pop.

First time I used shellac, fabulous stuff. Dries within seconds, even on a fresh, wet Pop cast, and immediately seals the surface. That means that mould release agents, like vaseline or green / mould soap, will stay at the surface where they are needed, instead of getting sucked into the plaster core.

For the second half of the split mould, I mixed two lots of Pop 20min apart, so the first one would be firm enough to hold the hessian cloth away from the core, but soft enough to bond well with the next pour.

I used a few crumbs of still moist, set Pop from the pour of the first half of the split mould, and mixed it into the second lot. This shortened the curing time by 6 minutes or so.

I had to add a bit of moulding clay, hope that works to keep the resin in once I get around to pour my first DFB with this mould.

[MrMik]

See pics if you’re interested. I’m happy to answer questions if there are any.

Scrape a channel for the resin, then seal with shellac.

Cover all surfaces with vaseline and wipe most of it off again.

Pour in a bit more than the internal volume of the cavity in epoxy resin, then watch the levels drop in despair, then see the resin drops appear at the lower edge of the mould (they show really well in UV light).

I added a second pour with a bit of Q-cell added, next time Q-cell will be added much earlier to thicken the resin and reduce the amount that leaks out between the split mould halfs. Another possible fix for this problem will be to delay the pour until towards the end of the pot life of whatever will be poured into the mould.

While the resin was leaking out of the mould, I used the rest of it to vacuum-in some resin into three spots along the trailing edge of that fin I made a few weeks back. First I heated the fin to 60degC, then took it out of the oven and immediately coated the training edge with the left over epoxy resin, so the resin would get sucked into the fin’s hollow spaces while the fin cools down again and the air inside it contracts. Tomorrow I’ll know how well (or not) that worked.

While I had gloves on, and runny resin available in more places than I wanted it in, I decided to cover the entire fin with another very thin layer of epoxy.

Having a very light weight fin makes curing such a coat of resin much easier. Vise grip pliers are heavy enough to cantilever it off the edge of a table. Noice!

[MrMik]

That did not go so well…

[Surffoils]

Hi MM, don’t worry that no one is replying, they’re watching.

You and I revel in the process but a lot are waiting for the result.

I dig your successes and ‘learning moments’.  Good work !

Are you in Sydney ?