Early followers of this blog may be familiar with several projects to 3D print kiteboard and stand up paddle (SUP) board fins, including some fins you can freely download if you’re into kitesurfing. It’s been a little while between posts on this topic, however, I have been busy in the background producing a system to help people with no CAD experience design and customise their own fins ready for 3D printing. The full details have just been published in the Computer-Aided Design and Applications Journal.
Quite a few people have used 3D printing to produce surf fins – after all, it’s very cheap and means you can produce just about any geometry you like. Researchers have looked at the strength of different materials and 3D printing technologies for this application, as well as the performance (fluid dynamics) of different geometries. However, if you are not a relatively advanced CAD user, it is unlikely you will be able to design the fin of your dreams, no matter how awesome the research suggests 3D printing can be! This is what I was interested in solving.
Using Rhinoceros and Grasshopper, the complexity of a fin was condensed down to a series of limited controls that allowed for freeform experimentation. The above image is the interface that allows surfers to customise a fin design in real-time. It is based on a handful of common fin properties such as the fin system, fin position on the board, cant, fin depth, sweep, base length, base foil profile, tip sharpness and tip thickness, all of which can be modified using some simple sliders or dropdown menus. Feedback is also provided in the form of overall dimensions and volume. From the image at the top of the page, you can get a sense for the wide variation in designs possible from this simple interface.
Once you’re happy with the design it can be exported ready for 3D printing. I’ve 3D printed a couple of different designs for testing on my SUP board, the smaller white fin in the image above being 3D printed using FDM, while the larger fin was 3D printed using selective laser sintering (SLS). Both worked well in flat water paddling, although I’m sure some carbon fibre would give me a bit more confidence heading into the surf.
Hopefully some more to come soon as spring and summer approach.
– Posted by James Novak
edditive blog 
Great article thanks James. I’d be interested in using this (I surf, SUP and kite and have a FDM printer (new at this)). Any chance you will make the system publicly available?
A couple of points to consider, especially with FDM:
1) For optimum strength you would need to get it to print the shell primarily with head laying down the material top to bottom (I’m not sure if/how this is possible)
2) also I am not sure what percentage of infill would give you adequate strength. Certainly, for FCS, the connector tabs and the surrounding area would need to be 100% (I think). Not sure how possible it is to make parts of a model have different infill settings.
Cheers
Tim
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Hi Tim,
thanks for your interest in this project. In terms of the system, at this stage I won’t be posting the files as it is something I continue to develop and may lead to some future projects/partnerships for my job. However, I have detailed the entire process in the paper, so if you have any experience with Rhino/Grasshopper you could definitely re-create the system, or even just the parts you’re most interested in.
In terms of the print orientation for FDM, I always print them laying down on the bed as shown in my previous kitesurfing post https://edditiveblog.wordpress.com/2014/11/07/fin-printing-success/ . It’s not great with the support material, but does create the strongest fin with the layer orientation. More painful with larger surf fins!
As for the idea of different infill settings, yes! There are a lot of hacks and settings you can try to achieve this, for example check out https://3dprinting.stackexchange.com/questions/6522/different-infill-in-the-same-part . There are also some interesting YouTube videos around on this topic. Definitely worth trying to increase strength in certain areas like you suggest. The other option is to just increase the number of perimeter walls until the FCS connection area becomes solid, and the larger interior uses infill. A bit of mucking around with your slicer settings and you should be able to achieve what you want.
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Thanks for your reply.
Yep, another option, re the FCS tabs, would be to simply make them out of plywood (tapered up into the fin), and have holes in the fin to slot (glue) them in. Or, instead of wood – model some inserts and print them with 100% infill while printing the rest of the fin at 20% or what ever you find works (would imagine you would need at least 2 shells, possibly 4 depending on material used).
I’ve used your kite fin – works great. But I printed it standing up (upside down) to avoid the hassle of removing support material.
I have tried to model surf fins but struggled to get the right shape (mid you that was years ago) – both the foil and outline shape. Can you offer any tips on how to approach this? ie do you loft the foil along a path??
Thanks again.
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Yes definitely a lot of experimentation to optimise the print settings and even try combinations of materials! Lots of fun 🙂
Without knowing your background I’d suggest looking at published research on the strength of different infills and densities – there is a ton if you look at Google Scholar! e.g this is just one example https://content.sciendo.com/view/journals/aucts/69/1/article-p23.xml . If you’re not an engineer it might get a bit technical, but you should be able to get some value out of the graphs.
As for modeling surf fins, yes I just use a loft. Sketch the side profile of the fin you want, create a couple of cross-sections through the profile, and connect it all together. Maybe I should post a tutorial on here one day…
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