Need help with a surfboard loft

[karolisd]

Hi Fusion community,

I need some help with my surfboard design. I sketched some cross sections of a surfboard and then lofted those sections to create a solid body. I used a single point as the last loft section (nose) of the board. Here is the screenshot:

In Fusion it looked almost perfect, but when I cut this board with a CNC, i noticed the nose is very thin and sharp and has a slight corner on the deck. 

I want the nose thicker and more rounded. To address this issue, I thought I would create a small profile and use it as the last loft section instead of a single point. After that I should be able to use fillet to round it if needed. Sounds easy, right? Well......

Now my board has some strange corners on the bottom. It seems that the shape of those corners depends on the shape of the nose sketch, but no matter how I draw the nose, I can't get rid of the bottom corners. 

OK, so next thing I tried to do is go back to "loft to point" approach, but round the profile line around the point. Unfortunately, no go. Fusion complains about non-smooth neighbourhood of a point:

I would appreciate any ideas how to thicken the nose of the board.

[karolisd]

Yes, I don't think .25mm fillet would be an issue. It is foam after all 🙂 Foam is soft, consists of bubbles and is never accurate to .25mm anyway.  In the end the sharp rail is formed using some excess epoxy during lamination process. I am a little bit more concerned that I can't do a big radius fillet on the center/front of the board, but I can try to overcome this just by adjusting the cross section shape maybe.

[karolisd]

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@karolisd wrote:

Here is one: Rails can not be tangent to profiles!

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This problem can be (somewhat) fixed by creating 2 lofts instead of one. I have no idea why two lofts A=>B and B=>C work, while one loft A=>B=>C does not. Also no idea if the resulting shape is the same or not. So far it looks smooth. The error is thrown only when both rails are selected. If any one rail is selected, there are no errors, but the shape isn't exactly optimal either 🙂

[karolisd]

I went back to the working version, redid all the changes one by one and probably found the problem with the loft:

I added a spline control point to pull the curve down a bit and make the corner more rounded. Apparently the loft feature doesn't like it, so I will have to figure out another way to handle the corner.

[karolisd]

OK, so the new surface based workflow with less sections is not as fantastic as I thought it would be. I'm trying to get the shape right for about 12 hours now and not getting anywhere close. Not even on the same planet yet. The main problem below:

The sharp corners at the bottom of section analysis is where the loft always wants to go. This behavior differs a bit depending on whether Tangent or Connected mode is selected for the rail, but in both cases the loft always wants to go inwards. I have no sharp corners in any of my sections. They look similar to this:

But the loft is always pulled inside for some reason.

I guess there are 2 ways to solve this: add more sections or add another rail guide. Adding more sections doesn't make sense, as the whole idea behind this workflow was to reduce the number of sections and have more freedom designing the board and also have a smoother surface of the board. It would also not solve the problem entirely, the loft would still get pulled inwards between the sections, but it would be less visible with smaller gaps.

In my previous designs I had the same issue, it just wasn't as obvious and I couldn't tell why the front side of the board is always so thin no matter what I do.

So maybe I need to add another rail guide. The question is where and how. I could probably add another rail on the widest point of the board the way I did in my previous designs, but it would be very close to the current rail and I'm not sure how much it would help. I'm very close to giving up on this idea altogether.

[TrippyLighting]

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@karolisd wrote:

Adding more sections doesn't make sense, as the whole idea behind this workflow was to reduce the number of sections and have more freedom designing the board and also have a smoother surface of the board.

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You can add more sections, for example at the rear of the board to control the surface flow. Just don't go crazy adding too many loft profiles. Us the Zebra Stripe inspection tool to check the surface.

[TrippyLighting]

A more tricky thing to do with surfacing is the transition from sharp into full round.

You still owe me a screenshot that explains where along the board you want start the transition from sharp to round.

[karolisd]

Well, THAT part (sending the screenshot) is easy!

Red: sharp

Green: transition (say 5mm radius)

Blue: as round/smooth as possible

This is the general rule for all surfboards. Depending on the model it may move a little bit to the front or back, but the principle is the same.

[karolisd]

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@TrippyLighting wrote:

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You can add more sections, for example at the rear of the board to control the surface flow. Just don't go crazy adding too many loft profiles. Us the Zebra Stripe inspection tool to check the surface.

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From this answer I'm getting an impression that trying to add another rail is not the way to go 🙂

Whenever I tried to add more sections manually (without actually measuring the board), it resulted in horrible bumps on the surface. I came up with an idea that I can create an intersection sketch, use that as a base, create a new curve on top of the intersection curve, then delete the intersection curve and move the sketch back in the timeline and use it for creating the loft. Maybe that will take care of the bumps.

[TrippyLighting]

If you have an actual board, I'd get it 3D scanned!

Does not even need to be high resolution. Just enough to get the general shape correct.

[karolisd]

I had this idea about 3d scan months even before I started to build the CNC to cut the board. But if I scan it, I will have something like a mesh, right? So I can't edit it. In the end I want a 3d model. So the scan would basically work as a reference, but I would need to do the same modelling? 

[karolisd]

I started with the board by measuring the contours like this:

That's why my model was based on these section sketches. Unfortunately these are a bit more difficult to take accurately around the nose of the board because of the curved faces everywhere and the thin profile.

I will make some calls and ask around for a 3d scan, but in general I need to learn how to tell Fusion to give me the shape that I want. I know what I need to modify, just don't know how to get there.

[karolisd]

Apparently the same issue that is happening with the upper loft is also happening with the bottom loft.

@TrippyLighting this is a screenshot of all the concave curves from your last uploaded example without any changes:

They are all pointed downwards or straight sideways. So one would expect that the bottom surface lofted through those lines would have a similar concave shape. For some reason it doesn't work that way:

Interesting stuff.

[davebYYPCU]

Correct, output from scanning is a Mesh file, Fusion can then extract mesh section sketches for reference to create the planar profile / rail articles.

Your last picture must be very close to the nose, the c/line sketch (given thickness and position) - the outside rail does not - can not stay “low” in that region if the outside rail is converging to a nose curve.

I complain about the Loft shrink wrap effect once in 12 months or so, only you and I notice it.

More Rails helps but that is catch 22.  Doesn’t happen with Tsplines.

Might help.....

[TrippyLighting]

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@karolisd wrote:

I changed this to a single profile curve that is swept along a rail.

Now the surface has a constant concave shape without that strange bulge.

Also, I would use a scan and possible mesh section sketches only as a visual reference.

[karolisd]

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@davebYYPCU wrote:

 Doesn’t happen with Tsplines.

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Interesting. I tried using Tsplines for the bottom loft, and the result goes from this

to this

depending on how many faces I select to generate for the loft. Apparently there is no way to select the tangent rail in Form environment. The top example is 8x1 faces and the bottom one is 8x8.

[karolisd]

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@TrippyLighting wrote:

I changed this to a single profile curve that is swept along a rail.

Now the surface has a constant concave shape without that strange bulge.

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Thank you for your continued effort to find a solution. Unfortunately this example doesn't have the possibility to transition between different concave profiles. Here are the most popular transitions:

That's only a fraction of possibilities, but you get the idea.

[karolisd]

Something about the "better curvature" aspect of using surfaces vs intersection curve.

After considering all of the previously mentioned problems, I decided that I probably won't be able to finish this model without adding more sections. So I woke up in the morning and cheerfully started adding an additional section somewhere around the nose. How difficult can this be? Create an intersection sketch, fix the shape a little bit and use the new shape for the loft, right?

Nope.

Here is why:

The problem is that I have 3 fixed points in this sketch that I can not move. The point on the right is the interesting one. Basically the loft shrinking problem affects not only the top surface, but also the location of the side edge/rail. There is no way I can fix this section to have the correct shape without moving the point on the right side.

For comparison, I added another point, which I get by creating an intersection curve of board bottom profile and outline. It seems that in my case the intersection curve works much better. Using that point I can fix the shape of the section and use it as loft profile.

So my plan for today is as follows: drop the bottom surface loft,  go back to intersection curve and create the bottom surface after all the section sketches are done. 

[TrippyLighting]

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@karolisd wrote:

So my plan for today is as follows: drop the bottom surface loft,  go back to intersection curve and create the bottom surface after all the section sketches are done. 

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Post the model when you are done.

[karolisd]

I just realized that the intersection curve isn't accurate either, as it doesn't take the concave shape into account. It probably works as if the bottom was flat. No other ideas ATM, besides going back to the rigid sketch model.

[TrippyLighting]

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@karolisd wrote:

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@davebYYPCU wrote:

 Doesn’t happen with Tsplines.

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Interesting. I tried using Tsplines for the bottom loft, and the result goes from this

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That does not make any sense whatsoever. You would model the whole thing in T-Spines, not just one surface.

I would suggest you stay away from T-Splines until you have the surface approach down. Then you can move to T-Splines.