3D printing large surfboard fins

I think I better start a new thread with a more appropriate title, because I have clearly moved on from my attempts to cast ‘hybrid laminated fins’.
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3D printing fins from PLA has turned out to be possible after much experimenting, although only longer term real world surf testing will conclusively show if the mechanical strength of the 3D printed PLA fins is sufficient. And the fins would likely deform if left in a hot car in Summer.
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See http://www.swaylocks.com/forums/casting-hybrid-lamination-fins for the lead-up to this 3D fin printing adventure.
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Also see: https://shop.prusa3d.com/forum/print-tips-slic3r-settings-kisslicer-model-repair--f12/printing-a-large-surfboard-fin-t2675.html and http://www.swaylocks.com/forums/discussing-wavegrinder-scientific-fin-design and http://www.swaylocks.com/forums/finfoil-v11-released for more details.
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The 3D printed fins are getting more consistent and also more colourful, because I’m using up the small amounts of PLA filament left on spools that don’t have enough on them to print an entire fin. This leads to the nice side effect that it is possible to make fins that are identical in shape and properties, yet every single fin can be unique due to practically unlimited colour combinations.
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The fins shown are high aspect ratio fins with leading edge tubercles and an Eppler 168 foil.
The fins are printed solidly from PLA on an Original Prusa I3 MK2 3D Printer, built from a kit. The newer version is the MK2s: http://www.prusa3d.com/
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The idea to use a high aspect ratio fin came from the ‘Wavegrinder fin’ http://finsciences.com/surfboard-fin-science/, whose maker got the idea from multiple examples of high aspect ration foils that are in use almost everywhere where high lift and minimal drag is required, and where a scientific approach is used to optimise the lift to drag ratio.
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I got the idea to use tubercles on the leading edge of fins from Roy Stewart, who was to my knowledge the first person to 3D- print tubercled surfboard fins. RoyStuart.biz: How do whalebumps work on fins?
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A quick internet search will show you that a lot of research into tubercles has been done in the last 10-20 years, initially spawned by interest in why humpback whales have tubercles on their flippers. Leading edge tubercles are being used or investigated for use in many applications, from rudders to keels to fans, propellers and wind turbine blades. A good overview can be found in this thesis by Kristy Lee Hansen: Redirect Notice
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The idea to use a snap-in fin base came from using a snap-in McCoy Gullwing fin with ‘Effect System’, which is unfortunately no longer being manufactured. After I accidentally lost the fin in the surf, I found out that I could not buy a new one, so I decided to make my own snap-in fin system.
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The UTFB (Universal Tough Fin Base) is my own concoction and incorporates several features that are unique as far as I know. It can be used as purely snap-in fin, with no pin or screw holding it in the fin box. This should make the fin safer, because it allows the fin to be released from the box in a collision or if the surfer falls onto it in a wipe-out. The UTFB can also be used with a pin inserted at the forward end, which reduces the risk of the fin falling out of the box, but then it causes much more damage if a collision occurs, like the Effect System fins or standard screw in fins.
And, the fin can also be used as a ‘traditional’ screw-in fin, by inserting a pin at the aft end and using a standard screw and plate. A small part of the UTFB needs to be cut off for this purpose and the cut-off location is marked in the 3D print.
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The software used to design the fins themselves is finFoil http://www.finfoil.io/ Without finFoil, you would have to invent finFoil to make fins like this. It is an extremely useful program and amazingly easy to use.
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The UTFB was designed using OpenScad, and the 3D printing .gcode files were created using Slic3r Prusa edition.

The basics of how to 3D print large fins have been covered in the threads linked to above.
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Remaining tasks are to use the quick turnaround time between design and rideable fin, and the reproducibility of the fins to fine-tune various fin designs.
The UTFB snap-in system allows fast and easy swapping of fins between boards in the surf, so that more objective testing in very similar conditions becomes possible. However, when printed solidly, they sink. Once a very good design is available, I will again put some effort into making these fins light enough so that they might float in water. So far, ride reports have been positive and my own experiences surfing these fins have been positive, too.
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However, there may be better ways to arrange tubercles on high aspect ratio fins than the pattern I made for the initial version shown above, and that’s what I want to investigate in this thread.
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Screenshots show a few examples of the UTFB with fins as seen in OpenScad:


Now I’m printing this fin:
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The idea is to make ‘fractal’ tubercles by combining small amplitude, high frequency tubercles into larger, lower frequency tubercles.
I hope it minimises the slight increase in drag, while keeping the increased lift and softer stall characteristics of the tubercles.

The control fin to compare it to will be this one:
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Same number and size of tubercles, but all arranged in a linear fashion.
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And both of them need to be compared to the version with 9 tubercles of reducing size shown in the previous post.

Very nice work Mr Mik to advance beyond the initial thread yet leave a trail for others to back track the intellectual progress…
Some of your new work is just amazing.

Thanks for all your great work and advanced usage of finfoil!

These kind of thread give me energy to continue working on it.
It’s really hard to find some free time for me last years, but some github followers might have noticed a slight progress:
https://github.com/hrobeers/finFoil/milestones

Great work, I’m following closely!
Very interested in the outcomes of your experiments.

Thank you, Surffoils and Hans!
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So far it looks like the resolution may be high enough to reproduce the high frequency bumps, I expect they will need careful sanding by hand anyway. Maybe if it turns out to be a very effective tubercle pattern, I might spend more time on trying to tweak it further in finFoil.
It did not cause any problems in OpenScad or Slic3r. Next time you could try an even higher resolution (if it does not require inordinate amounts of computing time), but that’s fine tuning for later when it is more clear what tubercle configurations work well.
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The print is progressing nicely. I hope it will take about 12hrs, that’s the print time for the 9-tubercle version with 0.3mm layer height.
Note how the undulations continue almost to the trailing edge.

The alignment is definitively not perfect, but neither are whale flippers or bird wings.
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I’m convinced that eventually a formula for optimal placement of tubercles will be developed and then they will be computer-generated to an exact pattern for optimum performance characteristics, customised for the intended purpose.
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But for now, it’s tedious small adjustments and judgements ‘by eye’, or using a more technical term: Pi times rule of thumb, to make these shapes.

@MrMik

Currently the placing of the horizontal slices in finFoil 3D renders is determined by the outline control points, which most often results in high resolution at the tip and lower resolution at the base.

I could update the algorithm in later versions to produce a more even resolution.

For simple fins I actually like current behavior because it gives quite smooth results even at low resolutions.

Any feedback about this is welcome.

@ Hans: An even resolution across the span would make it easier for multi-tubercled fins, for sure.

The first HARFTUB fin has been 3D printed!
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Definitely a good idea to use the UTFB without pins and screws for this one, it would hurt to run someone over with it…
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Let me know if you have any suggestions for a better name for these fins, please.
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HARFTUB stands for High Aspect Ratio Fractally Tubercled Fin.
This particular one is HARFTUB-E168-143.
Print time 12h52min, total PLA weight including support system (which will be removed manually) is 216g.


After sanding for about an hour with various files and 240grit sandpaper:
Total weight of PLA plastic now 202g.
This means about 6.5% of the material needed to make this fin is being wasted on support structures for printing. Not too bad considering that PLA is made from renewable resources and is potentially bio-degradeable (but only in a nice hot compost heap, it’s not going to rot while surfing!).


I am now using different ball spring plungers (BSPs).
These ones have a plastic (?or nylon?) ball instead of a stainless steel ball.
They are a little bit more expensive than the full SS variant, but almost 1g lighter for each BSP.
That weight difference might be what it takes to make these fins float, eventually.

These photos show how the UTFB is secured to the fin box, so it can release in a frontal as well as in a rear impact scenario.


One of the difficulties of 3D printing a large surfboard fin, even when using PLA, is warping.
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3D printing these fins using multiple colours increases the warping risk, because the enclosure needs to be opened, or left open for the whole print. The cool drafts or sudden temperature changes tip it over the edge.
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The first attempt to 3D print this HARFTUB101 fin ended with the fin tearing itself apart in the orange part.

I’ll send off some more fins for testing by wrxsixeight later today.
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They are only roughly cleaned up after printing and need to be sanded before use. They have surface rough spots and need a bit of wet sanding all around, which takes about an hour or so. It works very nicely under water, zero dust.
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I’ll include 6 BSPs with plastic balls, this brings it right up to the 500g airmail limit which seems to be the most economical option to send them.
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Wrcsixeight had a good idea for how to try smaller fin versions: Cut off a tubercle from the tip of the fin and sand it round again. So he’ll probably try that with this HARF9TUB fin.
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The other fin is a Wanderfalke 2 fin, or a Gull-whale fin, based on the McCoy Gullwing fin. I’m not certain this one is quite optimal, because I made up an unusual foil for it.
Surffoils has one of them (but with hollow tip area, and this one is solid). The foil is an exaggerated Eppler 168 like foil, with concave areas in front of the trailing edge. I have surfed an identically shaped fin just once (but printed hollow and then filled with carbon rods and epoxy resin) and the waves were poor and crowded, and the board brand new, so I’m not certain how it compares to other fins. I thought it felt extremely loose, and now I think this might have been very high lift generation at low surfing speeds. Or the loose feeling was just due to the new 8’4’’ McCoy Nugget. The fin could have issues like cavitation at higher speeds, it only had a little bit of testing so far, but Surffoils likes it.
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Thanks to Hans I now have high resolution finFoil files of the Wanderfalke 2 fins to 3D print them (with and without tubercles) with unmodified Eppler 168 foil. I have not printed them yet, just one printer is not enough for the intensity with which I am working on this at the moment. Long print queue…
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However, my general plan is to send one Wanderfalke2 fin together with a HARFTUB fin to wrcsixeight at a time, because it adds up to the most economical postage weight that way. Next time I might have a smooth fin with the same foil in the pack, or a tubercled version with the Eppler 168 foil.

Here it is, after 12h44min printing time:
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This fins purpose is to establish a baseline to evaluate how they work with low amplitude, high frequency tubercles.
This can then later be compared to fractally arranged tubercles of same frequency and number on the fin, like in the purple + blue HARFFTUB143 shown above.
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I figure if fractally arranging the tubercles has a beneficial effect, then the effect would show in many of the possible versions. That would then be sufficient cause to try to find the optimal fractal arrangement. There may of course be several, for different purposes.



I was cheering too soon…A closer feel and look at the green HARFFTUB101 reveals that it has warped.
What happened is this: The warping forces got too strong and the distal (tip end) support pad came off the print bed. See photo, it shows a concavity that is not just limited to the centre as usual, but it has breached the outer perimeter where the pad lifted off the print bed.
The fin did not split like the last one, but the problem occurred in the same general area in the upper half of the fin. It can be felt, the fin is foiled properly at the base, but towards the tip there is a twist / step in it in the forward part.
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I will do three things to hopefully prevent this failure:

  1. Scrub the PEI print bed sheet with 0000grade steel wool and acetone, then wipe clean with acetone and paper towel.
  2. Increase the print bed temperature from 65/55degC to 80 / 70degC (first layer temp / all other layers temp).
  3. And close the printer with the top half of the box at some time early in the print, and leave it closed until at least the fin is finished. This allows to have different colours for 3D printing the trailing edge of the fin, and the fore part of the fin tab (so as to 3D print every fin in a unique colour combination).


Looking forward to trying the Fins you sent and will be eagerly checking the mail.

This one has pictures included, full PDF download for free.
Looks interesting!
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Mimicking the humpback whale: An aerodynamic perspective
Abstract
This comprehensive review aims to provide a critical overview of the work on tubercles in the past decade. The humpback whale is of interest to aerodynamic/hydrodynamic researchers, as it performs manoeuvres that baffle the imagination. Researchers have attributed these capabilities to the presence of lumps, known as tubercles, on the leading edge of the flipper. Tubercles generate a unique flow control mechanism, offering the humpback exceptional manoeuverability. Experimental and numerical studies have shown that the flow pattern over the tubercle wing is quite different from conventional wings. Research on the Tubercle Leading Edge (TLE) concept has helped to clarify aerodynamic issues such as flow separation, tonal noise and dynamic stall. TLE shows increased lift by delaying and restricting spanwise separation. A summary of studies on different airfoils and reported improvement in performance is outlined. The major contributions and limitations of previous work are also reported.

Mimicking the humpback whale: An aerodynamic perspective (PDF Download Available). Available from: https://www.researchgate.net/publication/304512350_Mimicking_the_humpback_whale_An_aerodynamic_perspective [accessed Aug 13, 2017].