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-mode... and http://www.swaylocks.com/forums/discussing-wavegrinder-scientific-fin-de... 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. http://www.roystuart.biz/2015/07/how-do-whalebumps-work-on-fins.html
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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: https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=r...
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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.
Thu, 2017-08-10 12:02
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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:
Screenshot from 2017-07-23 10-32-51.png
Screenshot from 2017-08-10 22-34-25.png
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.
Screenshot from 2017-08-10 22-28-46.png
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.
Screenshot from 2017-08-10 22-27-41.png
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.
https://www.change.org/p/stop-beating-our-children-in-school?recruiter=849630455&utm_source=share_petition&utm_medium=copylink&utm_campaign=share_petition
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.
finFoil: free fin designing software
http://www.finfoil.io
https://twitter.com/finfoil
http://www.swaylocks.com/forums/finfoil-v11-released
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.
Screenshot from 2017-08-11 00-01-20.png
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.
Screenshot from 2017-08-11 00-34-09.png
@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.
finFoil: free fin designing software
http://www.finfoil.io
https://twitter.com/finfoil
http://www.swaylocks.com/forums/finfoil-v11-released
@ 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.
HARFTUB-E168-143-transilluminated.jpg
HARFTUB-E168-143_tangential.jpg
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