Designing a Surfboard Fin

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mario52
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Re: Designing a Surfboard Fin

Post by mario52 »

hi
woodbuddha wrote:Hi Florian,
Yes I get the same thing happening to the TE of my foils as well. How did you resolver the problem?
TK
this is a normal situation reason to the connection points (BSpline) between points that form a right angle
to remedy you need to closed=False and connect the last and the first point manually
Looktree wrote: - I'm using the Macro: AIRFOIL IMPORT & SCALE v2.
- I changed line 51 to: Draft.makeBSpline(points, closed=False)
see the topic here Fin Design and Macro Airfoil and Scale
mario
Maybe you need a special feature, go into Macros_recipes and Code_snippets, Topological_data_scripting.
My macros on Gist.github here complete macros Wiki and forum.
westcoastguy
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Re: Designing a Surfboard Fin

Post by westcoastguy »

woodbuddha wrote:
fintest1.png
I managed to do a typical raked fin. This was a little harder. I had to loft it in two sections to get the curves right.

TK
@woodbuddha:

I am trying to accomplish almost exactly the same thing (but for a hydrofoil, not exactly a fin), but as I am new to FreeCAD, I am struggling with how to do it. May I ask you please to explain the steps you took to create the raked fin model?

I am guessing it is something like:
* create cross sections by importing wing profile .dat file
* loft along a path (several paths) using the cross sections

Some of the problems I am seeing are:
I am trying to use an imported wing profile .dat file, but when I try to convert it to Bspline it gets deformed at the trailing edge.
How can both the shape of the leading edge and trailing edge be controlled in the loft process?

P.S. I have a 3D printer so if you have models that would need printing I might be able to help.

Thanks
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quick61
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Re: Designing a Surfboard Fin

Post by quick61 »

westcoastguy wrote:
woodbuddha wrote:
trailingEdge1.png
trailingEdge1.png (3.16 KiB) Viewed 2221 times
I managed to do a typical raked fin. This was a little harder. I had to loft it in two sections to get the curves right.

TK
@woodbuddha:

I am trying to accomplish almost exactly the same thing (but for a hydrofoil, not exactly a fin), but as I am new to FreeCAD, I am struggling with how to do it. May I ask you please to explain the steps you took to create the raked fin model?

I am guessing it is something like:
* create cross sections by importing wing profile .dat file
* loft along a path (several paths) using the cross sections

Some of the problems I am seeing are:
I am trying to use an imported wing profile .dat file, but when I try to convert it to Bspline it gets deformed at the trailing edge.
How can both the shape of the leading edge and trailing edge be controlled in the loft process?

P.S. I have a 3D printer so if you have models that would need printing I might be able to help.

Thanks
BSplines from OCE have a funny way to deforming when closed. There are several ways to work with this. The direct way would be to edit the BSpline and move / add points to get a cleaner shape. The other would be to edit the .dat file and add more points at the beginning and end as .dat airfoils start and end at the trailing edge. editing the .dat files can of course be done manually with a text editor, or you can use a program like XFLR5 to edit the airfoil graphicly.

Yes, Lofting, Sweep, or maybe even ShapeBuilder can be used to get a desired shape.

Edit - here is a simple example using an ag36 airfoil. The first pic is what the trailing edge looks like when it is imported. Notice the deform that happens when a BSpline is closed. In this case, I only needed to move one point a little to get my trailing edge into a more reasonable shape. While this is an easy example and i have had to do more work on other airfoils, the basics are the same.
trailingEdge1.png
trailingEdge1.png (3.16 KiB) Viewed 2221 times
trailingEdge2.png
trailingEdge2.png (2.62 KiB) Viewed 2221 times
Mark

Mark
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woodbuddha
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Re: Designing a Surfboard Fin

Post by woodbuddha »

@westcoastguy

I was having issues with the trailing edges of the bsplines as well and being the lazy knuckle dragging chimp that I am, I decided to stick with d-wires, so I never really resolved the trailing edge issue myself. But good to see the experts on this forum leading the charge.

Designing the dolphin style fins is a bit tricky. There are two ways I do it.

1. Just using FreeCAD (and Inkscape)

1. I use Inkscape to design the outline as an SVG and then import that into FreeCAD.
2. I scale the outline to the fin depth that I want.
3. I then pick a point on the fin base that corresponds to the furtherest (is that a word) point of the fin tip and draw a number of lines from this point to past the leading edge of the fin. Think of dividing a pie into pieces using lines from the pie centre. Where each of these lines intersects the leading and trailing edge of the fin, I use the measure utility to determine the length of the foil over that line. The line is just used for measuring purposes. I import the foil using the macro with the measurement and position it over the line between the leading and training edges over the line. The reason I use this method is so that the thickness of the fin tapers gradually to the tip without any thick spots.
4. I repeat this for each line.
5. Loft the foils.
6. Add the fin tabs.

I have been using D-wires and machining the fins on my CNC. The surface finish is good.

2. Use Finfoil to design the fin and import that STL into FreeCAD to add the fin tabs and scale.

Hope this makes sense. If it doesn't drop me a PM on woodbuddha1@gmail.com

WB
woodbuddha
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Re: Designing a Surfboard Fin

Post by woodbuddha »

Finally managed to get some real live fins made. What started as an idea and designed in FreeCAD is now a real thing.

Field testing has been positive.

Here's the link to the blog post for anyone interested.

http://thewoodbuddha.blogspot.com.au/20 ... -fins.html

WB
Fin Mould CNC.JPG
Fin Mould CNC.JPG (73.02 KiB) Viewed 2190 times
Fin Mould Split.JPG
Fin Mould Split.JPG (72.73 KiB) Viewed 2190 times
Fins in Board.jpeg
Fins in Board.jpeg (57.83 KiB) Viewed 2190 times
triplus
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Re: Designing a Surfboard Fin

Post by triplus »

Nice.
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quick61
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Re: Designing a Surfboard Fin

Post by quick61 »

Hi WB, well done and very nice writeup on the blog. It's great to see your project make it to the real world. While not quite yet, but soon you should be able to do you CAM paths in FreeCAD as well with the addition of the Path module now merged with master.

Mark
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woodbuddha
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Re: Designing a Surfboard Fin

Post by woodbuddha »

Thanks for all you help Mark. Couldn't have done it without you and the other experts on this forum. It's one of the best forums around.

Can't wait to see the Toolpath generation feature when it hits the ground.

WB
chrisb
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Re: Designing a Surfboard Fin

Post by chrisb »

@woodbuddha:
I am not quite sure, if I understood it right, which format did you use to transfer to your CAM software? And may I ask what software you use for CAM and CNC? And BTW, the fins look good, but I'd like to see the FreeCAD model of the cat as well ;)
Chris
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woodbuddha
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Re: Designing a Surfboard Fin

Post by woodbuddha »

@chrisb:
See responses below.

I am not quite sure, if I understood it right, which format did you use to transfer to your CAM software? STL.

And may I ask what software you use for CAM? DeskProto

and CNC? UCCNC. It's like Mach3 but cheaper, nicer GUI and supports a USB interface (UC100).

CAD model of the cat is going to be tricky as his agent is one heck of a negotiator and he doesn't come cheap. Plus he's a bit of a prima donna.

WB
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