Casting hybrid lamination fins

[MrMik]

Cheers Surffoils, I’m on the Gold Coast. As long as I have at least one (even if imaginary!) reader, it’s worth trying to explain and document. ‘See one, do one, teach one’ is only partially depending on the actual presence of a student. What really counts is the effort to explain something. You cannot explain it if you have not understood it, and in the process of trying to explain it, you gain better understanding.

Sorry, I’m starting to waffle…

I’ve come to a conclusion about Pop: It’s great stuff, but compared to more modern silicone moulding agents, it sucks in many respects. I will try to use Pop for situations in which I only want to make one cast (or one mould) from the Pop model, or when I want to shape the cast product by hand, after it has been cast.

In situations when I have put in significant time and effort to make something like the wood pattern for a snap-in fin box, then the expense for silicone moulding material becomes small by comparison.

Today I was pondering my recent messed up casting attempt while commuting, then came up with a plan and took a stop at the hardware shop on the way home, then put in a couple of hours cleaning up the mess and tinkering with the latest idea of how to do it better.

I still think I’m on the right track and that I will succeed.  See pictures and try to guess how this is going to proceed…

 

[MrMik]

Patience, patience, patience…

For completenes’ and honesty’s sake (spell it how you like it best): The epoxy cast was much more resilient once another 12 hours had passed after I snapped it during my attempts to remove it from the mould. I thought the epoxy would be more flexible when not fully set, but it seems that it is rather more brittle in that state. Keep in mind I’ve been using out of date epoxy for this ‘prototype.’ It might be different with fresh stuff.

If I had waited longer, I would have had a cast DFT that would have been serviceable with some sanding effort, but the Pop mould was doomed no matter what.

Silicone, here I come…

[MrMik]

Wacker M4503 looking good.

Sometimes it becomes obvious that mathematics really is your friend.

I had only a fairly small amount of this silicone resin, which I bought as a left over half-full bucket. I measured and calculated the volume I had available and found that I’ll have around 250ml left over once I have poured two half-moulds of 8.8mm thickness each. I measured out 700ml of component 1 with a 100ml syringe, then weighed the total amount and added 5% by weight of component 2. Those about 40ml of component 2 were my safety margin to compensate for what remains stuck inside the mixing bucket and on tools. 

Bucket practically empty, mould form filled to just were I wanted it to go, bingo!

What the photos show is the Dummy Fin Base suspended on stacks of brass washers so that it is level. The glass plate it all sits on is also level. A bit of weight on top of the wooden pattern to ensure it will not start to float in the silicone.

From underneath through the glass, it looks like the silicone has flowed nicely into all the right places.

I think the silicone layer is much thinner than what most would recommend, but that stuff is expensive and I hope I’ll get away with it, because I use the 10mm glass plates to provide dimensional stability and support to the silicone mould.

[jrandy]

MM- another ‘watcher’ here. 

Did the second-to-last part you casted (first dummy) have any fiber or was it just resin? 

Epoxy likes to find any hole or crack it can and grab and make the parts hard to de-mold.

I 've noticed that epoxy is able to absorb some of the homebrew release agents like petroleum jelly, car wax, vegatable oil…I have destroyed a few plywood molds that way. Have you tried Partall Coverall  PVA mold release and their green Paste Wax #2?

I have 2 HDPE ‘cutting board’ molds that naturally release epoxy but still the parts can hang up in the mold since the molds are not super smooth, radiused in the corners, or drafted on the side walls.

They are for 1/4" x 3" tabbed fins. I want to try installing pusher rods on the tabs to initiate the de-mold so I don’t have to pry with a screwdriver.

[MrMik]

Thanks jrandy! It’s baffling how unexpectedly tight bonds can occur, and at other times things split along a plane that you did not know existed…an interesting lesarning curve for certain.

The first attempt to pour a Dummy Fin Base was made with out-of-date epoxy resin, no glass or additives. Once I saw that much more than expected was running out through the gap between the Pop split-moulds, I mixed up a bit more and added some Q-cell powder. Maybe I should have added Q-cells from the start.

I have not tried any other mould release substances except vaseline, yet.

 

[MrMik]

Wacker M4503 sticks very well to glass. ‘Tick’ for next lesson learned…

I did not expect that.

Looking back (and this thread is very helpful for this!), I have not actually poured silicone onto glass before. With the first (the transparent) silicone mould shown on page 1 above, I poured the silicone onto a vaseline covered surface, with the underlying surface having been cured Pop, modeling clay and polycarbonate. The second part of my first split silicone mould was poured onto a vaseline covered silicone and polycarbonate (and modelling clay) surface. But never before have i poured it onto glass.

I vaguely remember reading comments like “the silicone sticks to nothing except silicone” on the net, but now I know that that is incorrect.

Some (maybe all?) RTV silicone casting compounds bond very well to glass, and Wacker M4503 is one of them. It might not be stuck as firmly as some silicone sealants would be stuck. I mean the ones designed to stick to glass, like aquarium sealant, but it is not far off from it. It’s stuck alright.

The next photo shows how well the silicone flows into small spaces. In other words, it has made a very good and uniform bond with the glass plate…Note how far it got under the aluminium sides, and under one of the brass washer stacks. If there was a gap in the hot glue surounding it, it would probably have continued to flow out slowly until it stiffened, or until the form would have been near empty.

The solution for this latest setback is obvious (as solutions usually are, once someone found them): I’ll simply leave the glass on the bottom of the mould. It was only ever going to be useable with the glass plate under it, anyway, because at 8.8mm thin, the silicone layer would not hold it’s shape unless perfectly supported.

The silicone did not stick permanently to the aluminium, the wood or the PVC ‘key’ pipes. Although it sticks initially, it can be pushed to release and then it releases very cleanly. So overall, still my most successfull mould pour so far. It’s level, it’s at the half-way line.

The third photo shows vaseline applied before pouring the second half of the split mould today. The silicone absorbs the vaseline over time, so we (I had a helper) continued to rub it in while mixing the 790g + 39.5g Wacker M4503, before wiping it fairly clean just before the pour, but after the shown photo.

[MrMik]

An epic stuff-up…

While waiting for the silicone split mould to cure, I thought I’d quickly try casting an epoxy fin in the clear silicone mould that I made a couple of weeks ago. I wanted to mix in enough q-cells so the fin would float, and find out if it would be an easy way to quickly make fins that are strong and light enough, even if they will not be as strong and as light as the carbon/kevlar laminated versions.

Well lets just say I learned a lot…

The resin got to almost 150degC before I managed to get a fraction of the stuff into the mould. See pics.

Next time I need to cool the ingredients, prepare them better, and have a larger hole and a funnel to pour the resin in, and a second hole to let the air out of the mould.

Here is a question I have asked before, but IIRC there was no answer forthcoming: Can Q-cells be mixed into the epoxy resin before adding the catalyst? That would save a lot of pot time, I found it difficult to mix the Q-cells with the resin and spent 9 minutes on mixing the Q-cells into the resin.

[MrMik]

Well, that fin turned out a bit small, but in most respects it was a success.

The mould is still 100% OK.

The small part of the cast that was actually filled with resin reproduced more than enough detail for a fin.

Practically NO resin leaked into the virtual space between the two split silicone mould layers. Very different from the Pop mould, but remember I was using straight epoxy resin in the Pop mould, while this is the "I learned something’ version, with plenty of q-cel added to make it thicker.

[MrMik]

I think I turned defeat into triumph, but I’m taking a risk here calling it early…the mould is still full of runny stuff and time will tell if it sets.

However, I reckon I nailed it this time.

Much bigger holes.

Hot melt glue baffles.

Mixing Q-cel and resin part 1 first, keeping it cool in the fridge (and tipping the container out into the fridge, using up all of the additional 10% of everything I added to the mix just to be sure to be sure…)

BINGO! Big mess in the fridge, but all cleaned up without much timing stress, then added part 2 to the mix, stiurred it for 10 minutes or so, with plenty of pot life left, then poured it into the mould through those big new holes. 

A couple of scary moments watching the events through the transparent silicone, good to see those big bubbles rise and disappear…

Then I used a chop stick to work in left over carbon / kevlar chopped strands into the tab and down into the fin area as fas as I reckon is required for spreading the load of lateral forces.

Now it’s all good again, except for that "patience, patience, patience " part…

[MrMik]

It’s in the oven for some accelerated curing at 60degC. Interesting how soft epoxy gets when it’s hot, it gives you an understanding why your epoxy board will start to ‘flow’ when you leave it in a hot car.

The fin can take the heating because it is again in it’s mould and on a level glass plate. Otherwise it would deform.

The extra cost for the transparent silicone was so very much worth it. Nothing beats being able to see what is going on inside of your mould. I think I paid about AU$160.- just for that silicone; non-transparent would have cost maybe $120.- .

De-moulding was very easy and clean for the silicone part, but not so for the hot melt glue and epoxy against the glass plates. I need to fine-tune that part a bit better, maybe a bit of vaseline onto the glass before mixing the resin. And I need to reduce the amount of hot glue needed. Use some other barrier, like a piece of plastic and fix it with a tiny amount of hot glue, rather than building up the hot glue.

**Mixing the Q-cel with the part 1 of the resin before mixing in part 2 has not had any obvious adverse effect so far, and I will use this method until I find a problem or until someone actually explains why they think it should be done any other way. **It is in my opinion far superior to the time critical mess if you do it the other way around. I found a nice way to measure the Q-cel: Suck it into a syringe, dunk it under the resin level, then eject it. Sometimes it comes out explosively and puffs of dust get out, but most of the time you get very little dust. I used the syringe as the stirrer. Eventually it cloggs up, but it can be made to work again, and with no time pressure it is easy. I used my asbesthos rated vacuum cleaner to suck any Q-cel dust away from me while mixing, that is way superior to wearing a mask. Wearing a mask just allows you to work messy, then the dust sits everywhere in your workshop and you (and everyone else) inhale it some time later when you move things and you are not wearing a mask.

The fin looks great (if I say so myself) and feels light enough to float in water (not tested yet). I think it will look like a dorsal fin sticking out of the water once the heavy stainless steel spring ball plungers are installed in the tab. Very little sanding will be required, except for the large remnants at the tab from pouring it in. Once the fin has cured for a few hours in the oven, I’ll saw that off somehow.

Shame I have to paint it, because the epoxy is not resilient to UV light

 

[MrMik]

Check mate I reckon.

Unless this construction method turns out fins that are too weak and keep snapping, it beats the ’ laminating first and foiling later’ by a mile.

Cutting off the excess parts from the casting process and filing the front end of the fin tab took about 20 minutes. Removing the grates around the leading and trailing edge took less than a minute. Literally, a bit of a rub with an old sock was enough, no real sanding required. And once I have the process refined for making my own fin(s), not much work will be required to touch up the fin tab, either.

I’m happy  (the understatement of the week!) to announce that I finally have a fin ready to stick into my favourite board and go surfing. “23 days ago” is when I started this project, now I’m ready to go surfing with my first self made fin (plagiarised admittedly, but I tried to buy another one but I could not). And now I can surf with this fin and not worry about losing it if it snaps off. Unlike the printed polycarbonate fins, this fin will continue to float even if it snaps off (but I don’t think it will snap).

It is a few grams heavier than the polycarbonate fin, due to the larger fin tab.

Around 30g of materials wasted to make a 180g fin means about 6% material wastage. That’s very low compared to the mess I would have made if I had continued to doggedly sand down that plywood laminate, instead of venturing into this process.

I now am convinced (pending months of testing in the surf of course) that I will be able to reproduce a fin as often as I like, so it will be worth my while to shape that (first) one perfect fin…

This fin snaps in and out both ways, I’ll let you know how this pans out in the line up.

[MrMik]

Back to making a (reproducable) fin from scratch…

I repeated the cardinal mistake and made the hole to let resin in (and air out) too small. 

At least I used a lot less hot melt glue this time, and I greased the glass with vaseline, so the clean-up should be easier than last time.

I think I got away with it, but only at significant extra time cost while casting the DFT. I had to resort to all sorts of tricks to get the resin to go in, and the air to come out. Not much point going into details. An hour or more of dedicated fiddling.

As a minimum improvent for the next time, I need to cut out the inlet channel from both parts of the split mould, not just one side.

Again, mixing Q-cel and West epoxy part one, then adding West epoxy part 2 a bit later worked very well as far as I can see. It’s still in the mould, but it’s looking good.

[MrMik]

About those photos above:

80ml is the measured internal volume of the DFT.

West epoxy needs 5:1 mixing ratio.

I figured adding 100% by volume of Q-cel increases volume by 30%, but it looks like that’s incorrect, depending on how you measure.

Measuring Q-cel volume is tricky to say the least. And they are not all the same. The ‘fluffed-up’ density of Q-cel is much lower than it’s "settled-down’ density. Almost a factor of 2 involved there.

Anywhoo, by applying rule of Pi x thumb : As much Q-cel (tapped down a bit by plonking the cup on the bench a few times) as resin part 1 makes a good enough mix, and the fin will float in water. That’s for a 5:1 ratio like the West epoxy system. For a system using a 3:1 mix ratio, I would try to mix a bit more than equal volumes Q-cel into the resin, before adding the second part.

[jrandy]

Nicely done Mr. Mik! Looking forward to your ride report.

I really like the effect of the added fiber, visually and structure-wise.

How rigid is the silicone mold? Would it be possible to ‘load’ the half molds separately, flat on the table, and then add a long piece of fiberglass cloth with a bit more resin in the middle,  and then bring them together to finish curing?

This might be a way to add more structural materials from base to tip without having to smash it through the sprue holes.

[MrMik]

Thanks, jrandy!

The correct answer would be “40 Shore A” , but if that means as little to you as it does to me, then this picture might give you a better idea. This half of the split mould weighs just over 1kg. It is held in one spot by a clamp.

 

[MrMik]

You can load the split halves and then put them together. That allows to put the cloth close to the outside, where it adds maximum strength. As a centre layer, cloth of any kind would not strengthen the fin anywhere near as much as the same cloth located close to the outside of the fin.

 

[jrandy]

Thanks for showing us the flexibility of the molds.

Yes, that makes perfect sense: a cloth skin is stronger than a cloth band in the middle.

 

[MrMik]

The maiden surf with the new fin has landed me in ED!
Some beginner dropped in on me and her longboard somehow slid over the top of my board, in the process giving me 2 lacerations to my heel. Lucky it did not get deep enough to damage my achilles tendon. I’m not certain what cut me, but I assume it was a fin of the opposing surfboard. It was a mad tangle of 2 bodies and 2 boards. The fin performed very well, but the waves were only 1.5m faces max and I did not catch many due to the crowd factor. Not much power in the waves and no powerful turns performed, so strength of the fin is not really tested yet. It did not move, wobble or fall out, even when the leg rope got stuck on it once in a wipe out.

[MrMik]

The first cast of the DFT is out of the mould!

It is very hard to get the glass of this Wacker silicone. (I mean a glass plate that was placed on top of the cured silicone split mould to hold the two halves together while casting the first DFT).

This silicone is a lot softer and stickier than the clear silicone used in my first mould. The glass had ‘vacuumed’ itself to the silicone and it took about 10 minutes to get it of, with slow and steady separating pressure between the glass plates. I jammed paddle-pop sticks in between the glass plates to keep up the pressure, it really is quite hard to do. I have since then worked out how to use clamps to do it for me: Push the handles of the clamp together, then stick fingers in to hold it open, then put the handles between the glass plates to steadily push them apart. Then do something useful while the glass is slowly, slowly lifted off the silicone by the clamp handles.

The first part of the mould being stuck to the glass plate caused more problems than I anticipated. Also, the brass washers had made contact with the epoxy, and they really liked each other quite a lot.

Removing the cast was scary, because I snapped the last one. But, with great care and small steps, and finally by inserting a scraper in multiple places under the cast, and lifting it just enough to lift off that area without bending the whole cast, eventually I made it happen.

This problem is only a problem because one half of the silicone split mould is deprived of it’s floppyness by being stuck to the glass plate. Therefore I reconsidered if I really want to leave it on there, and then used a very sharp chisel to separate the silicone from the glass plate while pulling the silicone away from the glass. I have done similar things before, and so it worked quite well.

[MrMik]

I fixed up two two small imperfections (caused by bubbles in the resin), sanded the bumps until they felt more pleasing to the touch, and then covered the fin in a layer of Zerovoc epoxy resin. All shiny now.

Then I cleaned up the white silicone mould for the DFT and covered it in a bit of talc powder. That makes it much more user friendly, because it stops sticking to everything once it has been covered in talc powder. Until then, it is almost impossible to lay it down flat on a piece of glass without some distortion to it’s shape. 

Then I poured a layer of ‘dental plaster’ onto the silicone mould with the DFT in it. (I’ll have to do this agin to make the other side of the split mould for the ‘Dummy Fin’.)

One of the photos shows the Dummy Fin Tab inside the split mould, so that the Dummy Fin blank can be cast onto the DFT.

I’m shaping this fin without any stencilling or use of existing fins for copying.