fangy said..
This is meth for me and now causing the list of jobs given to me by the Minister of Household Affairs to blow out to several pages.

maybe you should do some aerodynamic tests to establish a better understanding of the tip vortices, and see if you're getting somewhere. Be sure to keep the Ministers list close, you know, somewhere close to the air flow so the Minister can rest assured that you're getting to it soon.

I've heard those industrial sized tree shredders like the councils use create a decent amount of air flow.

I guess the point I am trying to make is that the bell shaped lift distribution comes partly by having a symmetrical section at the tip but also by having washout, If you add washout to a fin it is no longer symmetrical, it works better on one tack than the other. Therefore you cant actually make a symmetrical fin with a true bell shaped lift distribution as you can never have zero lift at the tip on a symmetrical fin (unless the fin is running at (zero AOA, which it doesn't)..... I have played with it on foil wings and it works...but they are not symmetrical foils.
Enough of my hijacking......

Flex2 said..

Mr Milk said..
Are the fins stiff?

You can control the stiffness of the fin by adjusting the infill density, the type of epoxy, the amount of carbon rods and additives like cotton flock or milled glass fibre. (Probably can use more exotic filaments to make stiffer but hasn't seemed necessary so I haven't tried yet even though I've bought the filaments) To answer your question:- Yes, you can make them as stiff (or as flexy) as you want. Photo below shows a 3D printed fin and a quality G10 fin (Tribal WS 31) both loaded at 18cm from the board with a 20Kg bag of salt. I couldn't measure any difference in deflection angle using Fusion 360. I have been playing around with all this and working on anther video. Trouble is both lack of wind for testing and me being slow at editing videos means I can make fins much faster than videos.

Have you considered using a donor fin as a base and printing a new exterior "sock" to your specific tolerances? Seems to me a super stiff 3d printed skin with those awsome looking flanged bases potted over a donor core using something as hard as spa bond may be a great solution. That way the head that engages is already to spec, fitted with inserts and presumably set at 90 degrees to the box, ground down to fit inside and then you add on your super duper new shape and voila! Just an idea! Maybe a new use for those thousands of dud fins being traded on sea breeze every day!! Your thoughts?

peterowensbabs said..

Flex2 said..

Mr Milk said..
Are the fins stiff?

You can control the stiffness of the fin by adjusting the infill density, the type of epoxy, the amount of carbon rods and additives like cotton flock or milled glass fibre. (Probably can use more exotic filaments to make stiffer but hasn't seemed necessary so I haven't tried yet even though I've bought the filaments) To answer your question:- Yes, you can make them as stiff (or as flexy) as you want. Photo below shows a 3D printed fin and a quality G10 fin (Tribal WS 31) both loaded at 18cm from the board with a 20Kg bag of salt. I couldn't measure any difference in deflection angle using Fusion 360. I have been playing around with all this and working on anther video. Trouble is both lack of wind for testing and me being slow at editing videos means I can make fins much faster than videos.

Have you considered using a donor fin as a base and printing a new exterior "sock" to your specific tolerances? Seems to me a super stiff 3d printed skin with those awsome looking flanged bases potted over a donor core using something as hard as spa bond may be a great solution. That way the head that engages is already to spec, fitted with inserts and presumably set at 90 degrees to the box, ground down to fit inside and then you add on your super duper new shape and voila! Just an idea! Maybe a new use for those thousands of dud fins being traded on sea breeze every day!! Your thoughts?

Thats a great idea.
With a template, you could cut a simple standard triangle shape to insert. Also, different thickness of donor fin, different flex.
Also , if you smash the plastic bit off, you still have a tiny bit of fin to get you home.

peterowensbabs said.

Have you considered using a donor fin as a base and printing a new exterior "sock" to your specific tolerances? Seems to me a super stiff 3d printed skin with those awsome looking flanged bases potted over a donor core using something as hard as spa bond may be a great solution. That way the head that engages is already to spec, fitted with inserts and presumably set at 90 degrees to the box, ground down to fit inside and then you add on your super duper new shape and voila! Just an idea! Maybe a new use for those thousands of dud fins being traded on sea breeze every day!! Your thoughts?

Yep. Way, way back the initial plan was to CNC an aluminium or titanium universal base and tenon arrangement and simply slip different skins over the top held in place by a grub screw. The quotes I got to do it this way were eye watering to say the least, not to mention the minimum order requirements. I like the idea of reskinning old fins, and certainly the recycling side of it. I think the process might be do able on thicker foils: for example on a foil that is 16mm wide (width of the box) and say *4mm for each skin thickness, that leaves only 8mm thick 'tenon' to slide the shell over. IDK, but wonder if the remaining tenon base would be thick enough to be strong enough?? Bonding the skin and the underlying tenon will obviously be helpful, plus shedding load onto the fillet. Of course this will require a different base for every foil rather than being interchangeable, but as you say the fin bases are already out there doing nothing, so no big deal on that score. Certainly printing the epoxy filled skins with a predetermined recess for the tenon is do able.
If you want to do the experiment I can send you 3D file of a fin for you to print, fill, and bond. If you are really patient (lots of stuff on my drawing board waiting to be printed), I could do a finished skin and mail it to you to bond to your own base to try out.
*I would defer to whatever Prof Flexafario says is the minimum thickness we can go as he has much greater experience than I do in this area.

Have you considered using a donor fin as a base and printing a new exterior "sock" to your specific tolerances? Seems to me a super stiff 3d printed skin with those awsome looking flanged bases potted over a donor core using something as hard as spa bond may be a great solution. That way the head that engages is already to spec, fitted with inserts and presumably set at 90 degrees to the box, ground down to fit inside and then you add on your super duper new shape and voila! Just an idea! Maybe a new use for those thousands of dud fins being traded on sea breeze every day!! Your thoughts?

Hadn't considered this before but is actually a really good idea to refresh old fins or for more conventional pointers that have had their day. I literally just purchased my first 3D scanner today (a Creality CR-Scan Ferret Pro which is currently going here in Oz at good price with 0.1mm accuracy at $549AUD..this is roughly same accuracy as better 3D printers). I got it to scan my boards in and clone them as a certain someone who promised to send me a good board design hasn't delivered after 2 weeks of promises...he will deliver but kinda like Musk, might take some time. I'm impatient so thus the 3D scanner.

In theory the process would go like this: You scan your old fin to 0.1mm accuracy, it should scan all the imperfections. Import to Fusion 360 (or your CAD program of choice). Convert the Mesh to a body. Design your new fin. Subtract the scanned old fin from the designed fin. Use the push pull command to give a 0.4mm or desired tolerance. Print the fin sock(vertically) in as many parts as required with whatever exotic or plain filament you want. Wall thickness can be as low as 0.4mm (or 0.2mm if you go the smaller nozzle) Mix up a little bit of epoxy, coat the old fin with this and stuff it in the 3D printed "sock". Sand the new fin to your spec and job done. Probably cost $1. My scanner should arrive within a week and I have an old pointer lying around and will do exactly that and update progress here.

Flex2 said..

mr love said..
I would have to question how relevant bell shaped lift distribution is to a symmetrical shallow water weed fin.

Who said my fin is symmetrical?

Well thats a good point!!!

This printed fin sock concept sounds awesome
I don't have CAD design software or a printer,but I do have a neighbour with one who is happy to print stuff if I can find it on Thingiverse. I recently had an Axis foil shim printed which works a treat.
Jim, I think this wasn't intended to be a fin only discussion, so I have one request: can someone please design a clew pulley molding like the Chinook ones, that can then have the pulleys and bolts attached

Stretchy said..
This printed fin sock concept sounds awesome
I don't have CAD design software or a printer,but I do have a neighbour with one who is happy to print stuff if I can find it on Thingiverse. I recently had an Axis foil shim printed which works a treat.
Jim, I think this wasn't intended to be a fin only discussion, so I have one request: can someone please design a clew pulley molding like the Chinook ones, that can then have the pulleys and bolts attached

ya Stetchy, the intention of this thread was not 3D printed fins but how 3D printing can solve/evolve/reduce cost of many things associated with any vaguely wind related sports that is accessible to anyone. I for one cannot hope to keep up with the many endless possibilities but hope others with share here their ideas/wishes here. My near term bucket list is the high $ stuff in descending order: Board, sail, Fin (sorted), harness line, other (like outhaul pulley etc)As far as the outhaul pulley goes the Severne one you can get for $25 at 2nd Wind (call ahead) is way better than Chinook as you can leave them installed on your many sails. (I got 6 to instal on upper and lower clew hole for my 3 fav sails) However, thats yet another example where 3D printing can save big bucks as really should only cost $2 for the stainless bits.

mr love said..
I would have to question how relevant bell shaped lift distribution is to a symmetrical shallow water weed fin.

Is the Prandtl wing by its nature not asymmetrical anyway? And 2nd the wing needs to be more than 20% longer than with an elliptical wing... scholarworks.calstate.edu/downloads/q811km846

The tensile strength of you print is very surprising.
Is it relying on the bond strength between filaments, or is it printed the other way?

SchobiHH said..

Is the Prandtl wing by its nature not asymmetrical anyway? And 2nd the wing needs to be more than 20% longer than with an elliptical wing... scholarworks.calstate.edu/downloads/q811km846

Yep, Agree with Q1 one, and agree with part two IF I was aiming for the full Prandtl bag of tricks. For me (not speaking for Flex) I simply wanted to play around with tip vortex mitigation strategies.

My surface layup has 2 layers of glass at about 30deg in opposite directions.
I'm wondering, if you can do something similar, can you overprint a second layer with the fin the other way?

decrepit said..
My surface layup has 2 layers of glass at about 30deg in opposite directions.
I'm wondering, if you can do something similar, can you overprint a second layer with the fin the other way?

that one is tricky...at least with current level of easily available current tech. There is new class of 3d printers that allow printing on different planes that the nerds are working on but this is currently out of reach of most...however only a matter of time before this becomes consumer level (search 4 and 5 axis 3D printing to see more):- example here:

Awesome work Jim. Thanks