3D printing large surfboard fins

General Discussion
281

It shoud be noted my hybrid construction fin which broke, Did not snap off just above finbox because of lateral stress/fatigue, but broke the fin base within the box when the back of the fin impacted bottom after i lost the board.  I was lucky to find the fin on the bottom nearby when I bodysurfed upto the board.

 

The core of the fin, to from base to tip coud have been pushed back in the box, there was just no way to keep it in there. The front fin tab snapped off cleanly and was pushed deeper into the box, an the back broke off further away from tab and was pulled partly out of the box.

 

But I was expecting this fin to break off at fin base as your stress testing revealed it would with enough pressure.  Figured it was a matter of time before I snapped it there, and it was, but it did not snap off like I thought it would, just above the base. 

 

It will be shortened,  a few carbon rods added, and be made to fit my probox center fin for my 6’11".

 

It was my third favorite GW fin.  The first being the red self destructo i reinforced with carbon roving and a layer of cloth, the second being the 12mm hollow silpoxy filled one which snapped off clean above the base the first session on it.  That one was feeling magic upto that point.

 

The red one did stiffen up rotationally after reinforcement and is still more rotationally flexy than the 12mm Silpoxy one was.

 

The  broken Hybrid 11mm  seemed  to be the least rotationally flexy, and I like(d) the red one more, but red has the 21mm flanged base tapering to a narrower tip.

 

The 10mm silpoxy and 11mm silpoxy filled versions remain unused, as the 12mm magic silpoxy snapped off fairly easily when kicking out  up and over a close out on my backhand.

 

I still wonder ihow much stronger a hollow chopped fiberglass/epoxy  fin would be compared to the Silk saturated epoxy stuffed fin.  I think that might be worthy of trying, with a carbon rod or 5 of course too :) 

 

There was something special about that 12mm Silpoxy GW fin.  It really felt like magic up until the point it snapped off,  Like could do no wrong an the board was an extension of my mind.  The red GW fin is great, but that silpoxy was the supermodel Nympho that gave me a short lived taste pure goodness before leaving me all to early.  Sad,  riled up, and wanting more.

 

 

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That was the first experiment with a thicker foil, efforts got derailed because of the snapping off issues.

Once I have a reliable build method, fine tuning of thickness can start again.

I need to look up how I made that fin and reconsider.

An idea just hit me, for how I can replicate that fin while solving a bunch of problems all at once. Faster, easier, maybe cheaper, but stronger.

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I wouldn’t say it was too weak because it prevented damage to the board which I really appreciate. 

I messed up the drop in, flipped it and landed on the fin with my shins. Hurt quite a lot but no bruise. (The wave was really annoying because the cleanup sets are steep for the take off for just a second which you need… But then immediately go mushy for take off and also break across faster. My ability sucks though, no excuse.)

I prefer the WG2 over the gulwhale but the harftub over both of them. It’s basically due to poor waves and slightly also ability though so a bit more testing and I might agree to like the gulwhale. I do put the fins forward in the box to balance things out though. 

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284

In my boards i find that Mr Mik’s fins work best if the trailing edge is lined up with where my regular raked fin’s trailing edge would be, within a half inch or so. If I move them farther forward they are too pivotal and loose and the sweet spot becomes less sweet and more broad. Too far back and it is obvious the board is taking a bit too long to come  around and I tend to get stuck on my backfoot and have to limit the power I put into my turns, or fall.

 

The harftub7s13 is my favorite harftub. Though there are several  others I have yet to try. The harftub9.5’s are also very good, and a bit looser, and  a fair percentage more forgiving.  The 6.5 seems  a smidge quicker and has some more grip/resistance and matches my longboard better.  If one wants  a fin with looser and more forgiving nature and is willing to give up a small amount of quickness, and perhaps top end speed too, the harftub9.5 would be my recommendation.  My testbeds have soft rails in the tail and a good amount of tail rocker and are limited in top speed, not by a fin or the wave, but the hull itself.  I’ve yet to try them with more modern railed boards, as I am on a traditional single fin  longboard, or what I consider my shortboard.  Nothing in between, but my Semiguns, soon to be for sale.

 

The Gullwhale is not as forgiving as the Harftubs, but it has a certain precision and a fluidity, and once used to it can really be pushed hard and the rewards for doing so have been a bit shocking, and confidence inspiring.  late sideways takeoffs paddling in at a hard angle… I find that waves i would previously let go as impossible to make are now game, and I’ve gotten more than one comment about how they could not believe i swung on ‘that one’, and made it.

 

I do not find the WG2 to be all that forgiving due to the tracking when one has the opportunity to sink the rail and push, but the fin says hold on a sec MFer.  That delay waiting for the Wg2 fin and rail of my board to work together is kind of irritating to me, forcing me out onto the shoulder more, whereas the harftubs and gullwhale are like :'turn here? Hell yeah, lets do it!"

 

When locked into a turn after that delay, the WG2, accellerates back into the pocket on a downturn like no other, but it does not seem to want to end that arc.  getting back onto the other rail to bottom turn and continue the wave withthe Wg2 is my issue with it, other than the weird unloading at the end of harder frontside bottom turns which unsets my  rail.

 

The Winglet angle of the Wg2 makes huge differences.  The Wg2 fin fits badly into my worn stretched fin boxes and I stuff zip ties under it, and can angle the winglet to dig more or less by the Zip ties I stuff under it, then tighten the screw.  The more it ‘digs’ the better faster and more responsive it feels with tail up higher in the wave, the less it digs and the thing is a rocket in the trough but more tracky when up high in the wave.

 

MrMik sent me a WG2 clone, that is a bit stiffer, and I broke the winglet, and made one out of a hardwood  glassed it on, deliberately lessening that winglet angle, and its speed.accelleration in the trough is second to none, but the arcs it allows and the tracking are still there.

 

Something about those turbucles yield a happy go lucky forgivng nature with few penalties.  Even when it rakes some seaweed and kelp, it has to be a considerable amount before it feels as listless and dull as my regular raked fin, though kelp is much worse than grass in this regard.  If the kelp still has its big leaves it just breaks, but if the leaves have broke off and one drags the stem, then about a 30 inch length of that  stuck on a turbucle  nearer the tip, makes it feel like my regular raked fin in trim speed and through turns.  Draggy and slow.

 

Learning to avoid paddling through kelp or large patches of grass and clearing the fin once one gets outside, becomes second nature after a while. No way am I going back, not unless I surf somewhere where the kelp is still attached  to the bottom, and prolific.

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Thanks for the clarification, much appreciated!

So there you go, the upside of fins not being extremely strong. That looks like a near ideal breaking strength, not quite breaking the board, not breaking your bones.

I think the hybrid fin’s toughness is in the right ballpark after all. Maybe my crude destructive testing method is ignoring the surfboard as the weakest link a bit too much.

How strong is the glass on the slightly damaged board? Is it as strong as McCoy boards, 6oz glass on the bottom, or more of a HP lightweight glassed board?

286

When I clamp this fin in the vice, it can carry my full weight, although the screw plate ends are broken.

Carbon rods in the fin make it so.

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This was actually an elleciel board. Perhaps David will chime in as to the bottom cloth weight? I’d send an email to ask but the workshop is closed for summer at the moment. ( Wow, he’s in the Ments at the moment at $200/day for nearly a month… and a shaper? What’s the secret? Must have found a system for getting there cheaper by boat! Congrats! ) I think it’s 2oz + fabric inlay + 2oz but I’m not sure. 

The fin does have carbon rods in so maybe the records are wrong? You can see one of the rods in the photo I think? I can certainly see black dots where they run through the plastic. 

IMHO the strength of that fin was perfect! It broke off just before breaking the board as can be seen from the stress line in the glass.

288

Does that fin above have 5 or 6 rods?  Same thickness as the ones in my red selfdestructo filament GW fin that i keep having nightmares about breaking?

 

Is it fairly safe to say there is not much risk of me breaking the red GW  while turning, and my nightmares about losing it and being GW finless can end?

289

It has 5 rods, but in a different configuration and orientation than the newer fin.

Have a look at the transparent fin picture: https://www.swaylocks.com/comment/544855#comment-544855

I checked my files, and it turns out that the red self-destructo fin did not have the solidified ellipse around the rods activated when I rendered it. That means that the area where the transparent fin shows the solid ellipse is interrupted by areas of 25% infill in the self destructo fin. That’s why you found some hollow spaces when it cracked.

The total cross-section of carbon in your self-destructo fin is 93% of the total in the newer version, so no nightmares are required I think!

I suppose there is an increased risk of snapping above the rods, because of the 25% infill compared to 100% infill in the newer fin. But there is still one rod reaching much higher.

290

Finally, another lot of fins is ready for shipping to wrcsixeight.

One AlbatrossWhale fin made from red PLA, carbon rods, ‘Peace Silk’ and epoxy;

one AlbatrossWhale fin ‘El Twistolero’ made from Polyamide, cabon, ‘Peace Silk’ and epoxy (black);

one GullWhale ‘El Twistolero’, unfinished (not shown in photos);

and 6 broken fins.

One of the broken fins is an AlbatrossWhale fin (purple), but is has a strong and undamaged core. It’s base was filled with peace silk and polyurethane, which turned out to be too flexible so that the screw plate protrusions tear off. If the undamaged (red) AlbatrossWhale fin turns out to be better than a GullWhale fin, then it would be worth the effort to repair the screw plate ends of the purple fin. If  the undamaged (red) AlbatrossWhale fin does not surf well, then you can shorten the purple fin and try it in your shortboard.

The other 5 fin fragments were not quite strong enough as single fins, but might make good center fins for a shortboard.

The ‘El Twistolero’ fins are a special case…their rotational flex changes drastically with moisture content, ranging roughly from stiffer than the other fins to double as flexible. And it all happens during one surf session! This property should allow to evaluate where the sweet spot for rotational flex is for these fins. The lateral flex does not change much when the moisture content changes.

The El Twistolero fins may not be very practical for regular use, except if it turns out that very pronounced rotational flex is desirable. It’s easy to keep these fins ‘hydrated’, but quite an effort to dehydrate them and then keep them dry.



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Awesome, I’m Always a bit giddy when a new fin package is on the way.  

 

The last hybrid pla Epoxy GW fin that I broke, and was able to retrieve from the bottom, is now cut down to fit into my Center Probox for my 6’11" double wing round pin hybrid/ speed egg that I consider to be my shortboard.

 

Very much looking forward to getting the broken ones above to fit into the rail boxes and see how they go. Am considering setting them using the insertess proboxes as a mold.

 

The Cedar toe side rail fin is also ready for the next chest high+  swell.  11.86mm thick with flat inner side.   Should have tremedous lift.  It is 5 7/8" deep and very high aspect ratio.

 

 

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I have a question for those of you who are more adept with OpenScad than I am.

Hopefully, trying to formulate the question clearly will lead to the answer, if not, then you’ll get to read this post…

I want to make fins with and without flanges at the base. There have been some previous debates about the usefulness and hydrodynamic effect of using flanged fin bases or ‘skillets’ when glassing fins into a board. 

The flanged bases that are possible with 3D printing cannot easily be made using traditional methods of fin production, so fins with a big flange are usually glassed in, which makes experimenting a bit difficult.

Anyway, the question is this:

How can I difference an object from the fin, adjacent to the fin box, so that the resulting surface is not flat?

Or: What object do I need to difference?

Or: How do I make such an object to be differenced?

An ellipse or a cylinder come to mind, but how do I put a straight edge on those?

The side of the object that starts at the box needs to be dead straight, but the surface area between the box and the ‘non-differenced’ fin surface should be rounded, because flat spots on fins are generally bad.

The screenshots show what happens when a 45deg cube is differenced from the fin on each side. I have also experimented with other angles, but the basic problem of having a flat surface remains of course unaffected by the angle.

The fin is a GullWing 7 F with 200% increased thickness to make the issue easier to see.


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Hi MrMik.

Although I am not a user, from my understanding of OpenScad what you are asking is not a simple thing to do. In other propriety CAD systems (CATIA, Unigraphics, etc) you would apply a varying fillet to the sharp edge you have created after the “subtraction” you have made. Or you could “loft” a smooth tangential surface between  two developed curves on your existing surfaces and “cut” your solid with that surface to remove the sharp edge.

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Thanks, RDM, most helpful!

The magic of Google applied to “loft openscad” returned this link: This-To-That - Loft from one shape to another in OpenSCAD by ezra_reynolds - Thingiverse

Now if I can figure out what it all means an how to use it…that’s another question! But I think it is exactly what I’m looking for, and you are right, it’s not simple.

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I think this approach is not going to be fully sufficient, because it uses two 2D objects to ‘tween’.

The transition from square to heart is the one most similar to my fin flange problem, maybe I can create a 2D object by intersecting the fin with an infinitely thin rectangle, instead of differencing the rectangle from the fin to create the flat cutoff.

Need to mull that over for a while.

Meanwhile, I have re-visited finFoil to try to address the problem by designing the fin better in the first place, but I came to the conclusion that the thickness distributions which used for the ‘S= straight’ and ‘F=flanged’ fin versions are already optimised for the purpose.

In other words, I don’t think I can solve this issue by using finFoil.

The best solution so far is to hand-sand the edge of the flat part after 3D printing, it results in a reasonably rounded surface.

 

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Reworking by hand is your best bet at this point I think.

If you need it done in CAD eventually I can probably help you if you were able to supply me a DXF file from Openscad that I can import into CATIA and modify.

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The Yellow cut down version of the Gullwhale fin has been in use the last 3 days in the rather significant south swell hitting Southern California, as has the cedar fin.  All Lefts, so that toe side cedar rail fin did not get engaged all that much, but the first day I started with a different center fin.

 

A few waves revealed that first day center fin to be a bit squirrelly with the swell’s power, and while in the lineup I pulled it out and put in the Yellow cut Down Gullwhale turbucle fin, which I call the 0.45GW.

 

I put it all the way back in the probox and only caught a few more waves afterwards, but the board felt much more solid and predictable before I got out.

 

Next day Swell was bigger, more powerful and consistent, and I moved 0.45GW fin to center of probox.  Board felt wonderful.  It was easily the most powerful surf I had taken this board out in.  Only one wave allowed me to do a hard top turn and the new cedar rail fin and 0.45GW fin felt incredible on that backside top turn, and I had an Awesome all around surf.

 

Today, the surf did not drop nearly as much as forecast. I moved the 0.45GW fin almost all the way forward in the probox and got many of the most memorable rides I’ve had in a long time.  There is no Weirdness with the 0.45 GW fin, the outside rail cedar fin does not appear to be too large at 5 7/8" deep, and its almost complete lack of rake seemed to have no Downside, but granted I was rarely on that rail.

  The 0.45GW almost all the way up in the center box had the board feeling especially wonderful once I got my back foot over the rail fins.  My heelside rail fin is a fcs1 TC carbon redline fin.

 

I’ll of course need to get it in waves where I need to generate speed from mush, as opposed to  powerful surf where the speed is required and there for the taking. 

My leash did get stuck on turbucles twice when sitting on my board but was only a factor at that time, never up and riding.  Kelp and grass were a rare site and if I dragged any grass I remained unaware of it.

 

I think perhaps I could cut a different GW fin down another turbucle for smaller less powerful waves, and I need to get it on some rights befire I really give it a thumbs up.  What I can say is that it did nothing weird or unexpected, and my board felt wonderful underfoot in the powerful consistent uncrowded conditions, and I had a freaking blast and have been buzzing ever since.

 

I snapped these photo’s yesterday, 30 minutes after getting out.

 

There were some sets a bit larger than the first shot and the seldom set considerably larger.

 

The third photo, the  guy on his 6’2" dissappeared from the next frame.

 

 

 

 

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I finally managed to try the Gulwhale 7s 11mm out in indo with decent waves (only waist to shoulder high though) . Although crowding limited what I could do I’ve never felt more in control on the bottom turn especially with this fin! It feels amazing. Just a lot of feeling of control.

I think it has stretched my fin box though as the WG2 now wobbles inside and doesn’t feel as good as it used to. It felt wrong even before I realised what had happened. I use bluetak to keep it in place but there’s still some movement. I’ll have to find a harder shim. 

The Gulwhale also snapped off at the pin. I was just trying to knock it back a bit in the fin box - bad idea. Being slightly thicker than the harftub it didn’t move and just the pressure of my hand was enough. 

What I’ll do now is try to make a tether with some fishing line. 

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@jago25-98: Sorry to hear the second fin also snapped, what a shame. 

But glad to hear you like the way it surfed! Both your fins were made from PLA-Epoxy hybrid material, without any reinforcements in the fin or in the base. 

I have good news, just an hour old: My latest fin making technique resulted in a fin that fit’s into three different boards on first attempt, anywhere in the box; is strong enough to not snap off laterally and strong enough to not snap off easily at the fore or aft screw plate ends. 

The photo shows the AlbatrossWhale -S-118% fin, made from a 3D printed shell stuffed with carbon parts and soaked with epoxy resin. I have not bothered trying to snap it off in the ‘vice test’, it has more carbon reinforcements against that than the fins previously tested as good enough in that respect. What is new is that the base is also packed with carbon parts.

I hit the fin with my hand from fore and aft quite firmly a few times, and eventually the 3D-printed screw plates let the nut rip through the printed material of the screw plate. So neither the fin nor the board get damaged when the fin hits an obstacle. When falling directly sideways onto the fin, I expect that the box would get damaged or the fin would snap. 

So basically the 3D printed screw plates turned out to be a safety release mechanism. It’s use is optional, if the surfer thinks that it’s better to have the fin installed so firmly that something (more substantial than the printed screw plate) must break in an accident, then s/he can use a standard screw plate and hot-glue the nut to it. The stainless steel screws and nuts I use for the 3D printed fins and screw plates are the perfect size for this purpose. 



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I am glad to hear someone else likes the GullWhale  fin as much as I do.

 

I have had several sessions on the Albatross whale fin on two different boards, one stiff fin, and one super flexible, and am having difficulties connecting with its feel, especially super the flexy one.

 

There are times when these AW fins during a turn feel unreal, and other times when it seems way too pivotal and loose, whereas the GW fin just feels so natural to my positioning desires.  There have been some instances where in trim that it feels like the first step or two in the airport getting on a moving walkway, and other times like I am stepping off of one, and more so with the super flexy one.

 

I cannot quite put it into words, the AW fin is by no means a dud, but it does not have the same predictable and fluid feel of the GW fin.  With more sessions I bet I could learn this fin’s peculiar characteristics well, but while the GW fin allows thoughtless mindsurfing, the AW fin requires one expect something unexpected and that hard turns can unintentionally be way too sharp and send one flying off the board.  On a couple of kickouts where I was expecting and intending only a 90 degree turn, I would up spinning past 180, and this is on a ~25LB 9’7" board.  A few bottom turns Where it was fall on the board or lose the board, and with the rather insane water temps and the amount of tourons in the water inside the surf zone, I do not want to risk taking one of them out

 

The wavegrinder WG2 fins wobbled like mad in all my boards, even one without a worn and stretched finbox. and I was using Zip ties with many layers of clear scotch tape to firm it up somewhat, and this was fairly temporary as the tape would get chewed up and spit out.

Larry Bertyllman might have liked a wobbly fin, but I very much dislike the fin moving at all in the box, and think it leads to a delayed response and a duller feel.  Since my finbox is more stretched and worn in the middle it is hard to get a fin to not have any lateral movement, and When i do achieve a really good fit, then the fin cannot easily be slide fore or aft.

 

I do like the printed screw plates and thinner diameter screws as well. 

The standard  10-32 SS screw is way overkill for fin retention, and these fins in my experience must be seated to full depth, then the screw plate slid in place and the screw threaded.  There is to be no leveraging the fin into the board with the screw  and plate as one can do with an all fiberglass fin.  Relocation of the fin, I have tried backing out the screws as far as they would go then allowing it to slide out of the box the ~8mm or so, but sliding fore or aft proved impossible so i wind up removing the fin completely resetting it and relocating the plates.  The printed plates have a guide so that they self center on the screw, which is a nice feature.

 

Last night I drilled 3/16" holes into the untried 10 and 11mm  Silpoxy GW fins for the insertion of carbon rods from base to as deep as 6 inches into the fin.  The unreinforced 12mm GW Silpoxy fin snapped off the first session but was feeling magical upto that point, which I surmise was due to its  particular flex pattern compared to my other GW fin.

 

MrMik sent me some GW fins which he broke in stress testing in the vice, which I have cut down to fit my proboxes on my Shortboard, though I have not yet tried them as rail  fins.  The GW center fin did nothing weird on big days.  It felt solid, but the sessions were mostly point and shoot down the line racing.

 

I’ve added carbon rods to the cut down GW fins to reinforce the probox bases, but they are homemade rods, which are nowhere near as stiff as the Pultruded carbon rods MrMik has been employing in the fins.  They are very stiff in the boardroatationally and laterally, and look kinda funny to someone who has gotten used to funny looking fins.

 

 

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